A manganese-based cathode material with discrete anchoring of carbon quantum dots and its preparation method

Abstract

This invention provides a manganese-based cathode material with discrete anchoring modification of carbon quantum dots and its preparation method. Using manganese-based cathode particles as a matrix, carbon quantum dots are anchored to Mn atoms on the surface of the manganese-based cathode particles. 3+ Ions form chemical coordination bonds, selectively anchoring Mn on the surface of the manganese-based cathode particles. 3+ At the active sites, carbon quantum dots are distributed discretely and discontinuously on the surface of manganese-based cathode particles. This invention breaks with the conventional mindset that coatings exist in a continuous or semi-continuous, dense manner, by selectively anchoring Mn. 3+ The innovative design of active sites and self-limiting discrete anchoring achieves selective passivation of unstable points in manganese-based cathode particles, inhibits disproportionation reactions, suppresses manganese dissolution from the source, and fundamentally solves the problems of interfacial side reactions and impedance increase caused by excessive coating.

Description

Technical Field

[0001] This invention relates to the field of chemical surface modification technology for lithium-ion battery cathode materials, specifically to a method for modifying the surface of manganese-based cathode materials with carbon quantum dots and Mn. 3+ Structures and their preparation methods that achieve selective, self-limiting discrete anchoring by forming chemical coordination bonds at active sites. Background Technology

[0002] Manganese-based cathode materials are important candidates for power batteries due to their abundant resources, low cost, high voltage platform, and safety and environmental friendliness. However, they suffer from severe capacity decay under high temperature and high voltage cycling, resulting in the loss of active material and damage to the crystal structure.

[0003] Surface coating is a common strategy to address this issue. While traditional carbon coating can improve conductivity, a uniform and complete coating layer can hinder lithium-ion transport and increase interfacial impedance. Oxide coatings (such as Al2O3), although stable, have poor conductivity and similarly lead to increased polarization. These methods attempt to isolate the electrolyte with physical barriers, but at the expense of kinetic performance.

[0004] Carbon quantum dots, as a novel nanomaterial, have been used in recent years for the modification of electrode materials. However, current technologies mainly focus on forming continuous or semi-continuous carbon quantum dot coatings, or constructing dense coatings by combining them with other matrix materials. This aims to utilize the good conductivity of carbon quantum dots while providing a physical barrier to isolate the electrolyte and side reactions. However, carbon quantum dots have weak intrinsic conductivity, and their abundant oxygen-containing functional groups, when distributed continuously or semi-continuously, can interconnect, forming a network of reactive side reactions that can actually exacerbate electrolyte decomposition.

[0005] Therefore, there is an urgent need for a new method that can efficiently suppress the dissolution of manganese in manganese-based cathode materials from the source without sacrificing lithium-ion and electron transport.

[0006] Therefore, this application is submitted. Summary of the Invention

[0007] Existing research generally considers continuous or semi-continuous coating as an important means to isolate cathode material particles from the electrolyte and reduce cycle degradation. While the establishment of continuous or semi-continuous coating layers reduces Li-ion degradation through physical barrier, this approach is not universally accepted. +The insertion / extraction channels, while sacrificing some capacity and kinetic performance, are still acceptable compared to their isolating effect in suppressing electrolyte side reactions. To minimize the impact of physical barriers from the coating layer, the common practice is to reduce the coating thickness as much as possible, making it ultrathin, uniform, and dense, thereby reducing the cycling or rate losses caused by the coating layer to a controllable level. It can be said that the establishment of continuous or semi-continuous coating layers is an inherent approach in cathode material surface modification technology. As a novel carbon material, existing research on carbon quantum dots has followed the same development approach, namely, preparing them as continuous or semi-continuous coating layers or dispersing them as a component within continuous or semi-continuous composite coating layer structures.

[0008] Through extensive research and understanding of the mechanism of cyclic degradation of manganese-based cathode materials in electrolytes, the inventors discovered that the cyclic degradation of manganese-based cathode materials mainly stems from the coupling of three factors: Mn dissolution, SEI side reactions, and structural degradation. Among these, Mn dissolution primarily involves Mn... 3+ Ions undergo disproportionation reaction (2 Mn) 3+ → Mn 4+ + Mn 2+ ), Mn 2+ Migrating to the negative electrode for reduction deposition, it consumes active Mn, catalyzes electrolyte decomposition, and destroys the negative electrode SEI; the main SEI side reaction is the formation of HF from F in fluorine-containing materials such as lithium salts, the formation of MnF2 / F-containing layer on the material surface through etching and accelerating Mn dissolution, while Li is released. + Oxygen escapes from the surface and ·O radicals attack the carbonate solvent, thereby producing gases (CO2, C2H4) and generating a thick-resistance SEI; structural degradation includes Li + / Mn 3+ Ion deintercalation / dissolution leads to octahedral distortion, which in turn generates lattice strain and microcracks, exposing new surfaces and exacerbating the aforementioned side reactions. Based on the above mechanisms, it can be seen that in manganese-based cathode materials, Mn... 3+ As a crucial structural site, it is a key node in breaking the chain of side effects. The construction of the coating layer holds promise for breaking the conventional understanding of continuous and dense structures, especially if it can act on exposed Mn. 3+ At key sites, the coating layer can be distributed discretely and discontinuously on the surface of the manganese-based cathode particles, while uncoated areas will not cause damage to Li. + The transmission obstruction will not cause a loss of capacity or dynamic performance.

[0009] The successful implementation of the aforementioned groundbreaking approach still faces numerous challenges. Through extensive research and experimentation, the inventors have obtained the following solution:

[0010] A carbon quantum dot discretely anchored manganese-based cathode material includes manganese-based cathode particles as a matrix, wherein the carbon quantum dots are anchored to the Mn atoms on the surface of the manganese-based cathode particles.3+ Ions form chemical coordination bonds, selectively anchoring Mn on the surface of the manganese-based cathode particles. 3+ On the active site, carbon quantum dots are distributed in a discrete and discontinuous manner on the surface of manganese-based cathode particles, with an average particle size of 0.5~15 nm.

[0011] The preparation method of the above-mentioned carbon quantum dot discrete anchoring modified manganese-based cathode material includes the following steps:

[0012] Carbon dot raw materials are dispersed in a polar liquid medium and homogenized until the average particle size of the carbon dot raw materials is 0.5~15nm to obtain a dispersion. Then, the dispersion is mixed with manganese-based cathode particles to obtain a mixture. The concentration of carbon dot raw materials in the mixture is adjusted to 1~3 mg / mL and the concentration of manganese-based cathode particles is 30~100 mg / mL. The mixture is stirred for 0.5~12h, the solid phase product is separated, washed, and dried at <100℃ to obtain the desired product.

[0013] The carbon dot raw material comprises particles with an ordered stacked structure of graphene or graphene-like aromatic sheets. These particles undergo homogenization and crushing to achieve the target particle size, and are then modified with oxygen- or nitrogen-containing functional groups in a liquid medium through a particle size refinement process, becoming particles that can chemically coordinate with Mn. 3+ Connected carbon quantum dots.

[0014] The inventors discovered in their research that carbon quantum dots and the Mn on the surface of manganese-based cathode particles... 3+ Selective connectivity is influenced by many factors.

[0015] First, there's the size effect of the bonding sites; the surface Mn of the manganese-based cathode particles... 3+ The coordination site spacing is generally between 0.3 and 3 nm, which determines that only small molecules with sufficiently small size can enter the nano-pits, grain boundaries, and slight agglomeration gaps on the particle surface to form stable selective coordination contacts. Single-point anchoring requires carbon quantum dots to form monodentate / bidentate internal spherical complexes with single or bimetallic sites. At the same time, bridging multiple metal sites can easily lead to localized film formation, thus deviating from the selectivity of single-point anchoring. Therefore, by using oxygen-containing / nitrogen-containing functional groups with Mn 3+ The size effect of active site linkage needs to be limited relative to Mn. 3+ Within a limited size multiple of the coordination site spacing, the average particle size of this invention is limited to 0.5~15 nm. This is based on the above considerations. If the size is too large, it is difficult to enter the micropores or tends to be film-forming with multi-point anchoring. If the size is too small, carbon quantum dots will easily lose the advantages of ordered stacking structure.

[0016] Besides the size effect, the competitive effect of carbon dot adsorption on the surface of manganese-based cathode particles is also closely related to the selective anchoring results at the microscopic level. At the microscopic scale, the adsorption of carbon dot materials on the surface of manganese-based cathode particles involves multiple competitive and synergistic interactions, including hydrogen bonding, electrostatic attraction, coordination, and van der Waals forces. Among these, hydrogen bonding and electrostatic attraction often exhibit synergy (for example, sometimes electrostatic attraction can hold -COO- - While being pulled toward the surface, adjacent -OH groups form hydrogen bonds with ≡M-OH groups (e.g., sometimes the surface interacts with -COO-OH groups). - Electrostatic repulsion (even though -OH groups can form hydrogen bonds, overall adsorption is suppressed); coordination is achieved between the carbon quantum dots and Mn in this invention. 3+ The main form of connection is through oxygen- or nitrogen-containing functional groups (-COOH, -OH, etc.) and Mn. 3+ An L→M coordination relationship is formed, dominating the local adsorption configuration; van der Waals forces, generally weak substrate attraction, play a modulating role in the aforementioned competitive-cooperative relationship. Therefore, this invention aims to achieve the desired adsorption configuration between carbon quantum dots and Mn. 3+ Selective discrete anchoring requires balancing the relationships between hydrogen bonds, electrostatic attraction, coordination, and van der Waals forces, suppressing non-specific adsorption (hydrogen bonds, electrostatics, van der Waals forces), and highlighting the dominant role of coordination. However, hydrogen bonds and electrostatic attraction cannot be completely eliminated; it is necessary to promote the interaction between oxygen-containing / nitrogen-containing functional groups and Mn to a certain extent first. 3+ Only through the close attraction between them can chemical coordination occur.

[0017] This invention further modulates the aforementioned multiple competitive and synergistic relationships, combining a polar liquid medium, significantly undersaturated low-concentration carbon dot raw materials (1~3 mg / mL) and manganese-based cathode particles (30~100 mg / mL), short-time adsorption control (0.5~12 h), and thorough washing and low-temperature drying. In this invention's system, the carbon dot raw materials were successfully deposited on the surface of manganese-based cathode particles with Mn. 3+ Selective anchoring at active sites. Specifically, the polar liquid medium, combined with concentration control, modulates the solvation degree of the carbon dot feedstock and the synergistic strength of hydrogen bonding and electrostatic adsorption, promoting the interaction between oxygen- and nitrogen-containing functional groups and Mn. 3+Metal sites are brought closer together and hydrogen bond spreading is controlled; the low concentration ratio of carbon dot raw materials and manganese-based cathode particles ensures that the carbon dot raw materials are far below the monolayer saturation concentration and can only occupy high-affinity metal coordination sites, while weakening multilayer stacking, lateral hydrogen bonding and multidentate coordination, thereby promoting the efficient binding of specific sites; short-time adsorption and thorough washing remove the limited other reversible / weakly bound physical adsorption and spreading films formed in a short time, remove uncoordinated molecules, and further improve the precision efficiency of specific coordination; finally, low-temperature drying (<100℃) limits the possibility of further prepolymerization and carbon film extension of carbon dot raw materials, removes solvent while stabilizing the carbon quantum dot structure, and also improves the surface stability of uncoordinated sites of manganese-based cathode particles.

[0018] Compared with existing technologies, this invention breaks away from the conventional mindset that coating layers exist in a continuous or semi-continuous, dense manner, by selectively anchoring Mn. 3+ The innovative design of active sites and self-limiting discrete anchoring selectively passivates unstable points in manganese-based cathode particles, suppresses disproportionation reactions, inhibits manganese dissolution at the source, and fundamentally solves the problems of interfacial side reactions and impedance increases caused by excessive coating. The preparation process is simple and mild, with a wide process window and good batch stability. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a comparison XRD pattern of Embodiment 1 and Comparative Example 1 of the present invention.

[0021] Figure 2 This is a TEM image of Embodiment 1 of the present invention.

[0022] Figure 3 This is a TEM image of Comparative Example 2 of the present invention.

[0023] Figure 4 The XPS Mn 2p spectra of Example 1 and Comparative Example 1 of this invention are compared.

[0024] Figure 5 This is a comparison chart of the cycling performance of Example 1 and Comparative Examples 1 and 2 of the present invention at 55°C and 1°C. Detailed Implementation

[0025] In this invention, "manganese-based cathode" refers to any active cathode material containing manganese. Generally, "manganese-based cathode material" and "manganese-based cathode particles" do not have any essential difference in the materials they refer to. When it is necessary to emphasize its existence as a raw material in the preparation process, or to emphasize its connection with carbon quantum dots or carbon dot raw materials as part of the overall manganese-based cathode material, the term "manganese-based cathode particles" is used.

[0026] In some examples, the manganese-based cathode is selected from one or more of doped or undoped spinel-type LiMn2O4, lithium-rich manganese-based layered oxides, lithium nickel manganese oxide, manganese-based phosphates, or manganese-containing layered oxides. The doped spinel-type LiMn2O4 is spinel-type LiMn2O4 modified by doping with one or more elements selected from Al, Mg, Ti, Co, Ni, Cr, Fe, Zr, La, Nb, and W. In this invention, the doped or undoped spinel-type LiMn2O4 has advantageous exposed surfaces (111) and (110), and the Mn octahedral arrangement on the (111) surface with shared vertices makes its Mn... 3+ The high site exposure density and the greater stability of the spinel structure with other contact surfaces of the electrolyte under discrete, discontinuous coating conditions make it the preferred choice for the system of this invention. Furthermore, undoped spinel-type LiMn2O4 is even more advantageous.

[0027] In some examples, further limiting the average particle size of carbon quantum dots to 0.5~5nm can bring better size effect advantages, specifically 0.5nm, 1nm, 1.5nm, 2nm, 2.5nm, 3nm, 3.5nm, 4nm, 4.5nm, and 5nm.

[0028] In some examples, carbon quantum dots interact with Mn on the surface of manganese-based cathode particles via oxygen- or nitrogen-containing functional groups. 3+ The ions form chemical coordination bonds. The oxygen-containing functional groups include at least one of carboxyl (-COOH), hydroxyl (-OH), and carbonyl (C=O), while the nitrogen-containing functional groups include at least one of amino (-NH2) and amide. The oxygen- and nitrogen-containing functional groups are usually intrinsically introduced onto the surface of the carbon dot raw materials through a polar liquid medium environment during the homogenization and crushing process.

[0029] In some examples, the concentration of carbon dot feedstock in the mixture was 1–2 mg / mL, and the concentration of manganese-based cathode particles was 50–80 mg / mL. The mixture was stirred for 3–8 h, and the solid-phase product was separated, washed, and dried at 20–80 °C to obtain the desired product. Optimized operating conditions are beneficial for further optimizing the multiple competing and synergistic effects of carbon dot feedstock adsorption on the surface of manganese-based cathode particles, thereby improving selective anchoring efficiency.

[0030] In some examples, the carbon dot raw materials include at least one of graphite oxide, graphene oxide, or graphene quantum dots. These carbon dot raw materials all possess a well-defined intrinsically ordered stacked structure, and homogeneous fragmentation ensures the integrity of the ordered stacked structure of the carbon quantum dots at their tiny size.

[0031] In some examples, selecting materials with an average flake diameter of 0.1~10 μm and a carbon-oxygen atomic ratio of 0.5~3.0 before homogenization of carbon dot raw materials is beneficial to improving the efficiency of homogenization.

[0032] In some examples, the particle size D50 of the manganese-based cathode particles is 0.3~100μm, preferably 0.5~50μm, and more preferably 1~30μm.

[0033] In some examples, the liquid phase medium and the washing solvent are each independently selected from one or more of water, a water / alcohol mixture, ethanol, isopropanol, ethylene glycol, N-methylpyrrolidone, and N,N-dimethylformamide; generally, the washing solvent is chosen in the same way as the liquid phase medium.

[0034] In some examples, the mixing process can be carried out at a temperature of 20~80°C to improve the efficiency of chemical coordination bonding at selective sites in the stirring reaction.

[0035] In some examples, the number of washes is not limited, but 1 to 5 washes are generally preferred. The termination of washing can be confirmed using auxiliary detection methods, such as stopping when no ultraviolet absorption signal of carbon quantum dots can be detected in the washing solution.

[0036] In some examples, the specific means of homogenization and fragmentation are not limited, and non-limiting means may include high-pressure homogenization (CDs-HP) and ultrasonic fragmentation (CDs-US). High-pressure homogenization is a preferred solution in the system of this invention because it has a more uniform fragmentation effect and a richer modification effect of oxygen-containing / nitrogen-containing functional groups.

[0037] The embodiments of this invention provide detailed preparation methods and technical steps, aiming to fully illustrate the specific implementation process of this invention. However, these detailed technical details represent only one specific way of implementing this invention and are not intended to limit the core content of this invention or its scope of protection. Those skilled in the art should understand that these embodiments are for illustrative purposes only and should not be considered as limiting the only or exclusive implementation of this invention.

[0038] I. Preparation of Carbon Dot Raw Material Dispersion

[0039] High-pressure homogenization (CDs-HP):

[0040] Weigh 5g of commercially available graphite oxide and disperse it in 500mL of deionized water. Pre-disperse the dispersion by sonication for 30 minutes. Transfer the solution to an ATS AH-1500 high-pressure homogenizer and cycle it 20 times at 120 MPa, with cooling in an ice-water bath throughout. Centrifuge the resulting dispersion (8000 rpm, 30 minutes) to remove large particles. Collect the supernatant to obtain a dispersion with a carbon dot content of 4.5 mg / mL and an average particle size of approximately 5 nm.

[0041] Ultrasonic fragmentation (CDs-US):

[0042] 3g of commercially available graphene oxide was weighed and dispersed in 300mL of deionized water. The mixture was then treated in an ice-water bath for 5 hours using a probe-type ultrasonic disruptor (Scientz JY92-IIN, 600 W, 20 kHz) (5 seconds on / off). After centrifugation, a dispersion of 3.8 mg / mL was obtained, with an average particle size of approximately 3 nm for the carbon dots.

[0043] II. Implementation Examples

[0044] Example 1

[0045] Take 40 mL of CDs-HP dispersion, add 110 mL of deionized water to dilute to 150 mL, then add 10 g of LiMn2O4 powder to achieve a carbon point raw material concentration of approximately 1.2 mg / mL and a manganese-based cathode particle concentration of approximately 66.7 mg / mL. Stir magnetically at 25 °C for 6 hours. Centrifuge, wash three times with deionized water, and vacuum dry at 80 °C for 12 hours.

[0046] Example 2

[0047] Take 50 mL of CDs-US dispersion, add 100 mL of deionized water to dilute to 150 mL, then add 10 g of LiMn2O4 powder to achieve a carbon dot raw material concentration of approximately 1.3 mg / mL and a manganese-based cathode particle concentration of approximately 66.7 mg / mL. Stir magnetically at 25°C for 8 hours. Other steps are the same as in Example 1.

[0048] Example 3

[0049] The mixture was magnetically stirred at 60°C for 6 hours. Other procedures were the same as in Example 1.

[0050] Example 4

[0051] Take 80 mL of CDs-HP dispersion and dilute it to 150 mL with 70 mL of deionized water to achieve a carbon dot raw material concentration of approximately 2.4 mg / mL and a manganese-based cathode particle concentration of approximately 66.7 mg / mL. Other steps are the same as in Example 1.

[0052] Example 5

[0053] Replace LiMn2O4 powder with aluminum-doped lithium manganese oxide Al-LiMn2O4 (LiAl 0.05 Mn 1.95 O4). Other aspects are the same as in Example 1.

[0054] Comparative Example 1

[0055] Pure commercial LiMn2O4 powder, without any processing.

[0056] Comparative Example 2

[0057] Take 120 mL of CDs-HP dispersion, add 30 mL of deionized water to dilute to 150 mL, then add 10 g of LiMn2O4 powder to achieve a carbon dot raw material concentration of approximately 3.6 mg / mL and a manganese-based cathode particle concentration of approximately 66.7 mg / mL. Other steps are the same as in Example 1.

[0058] Comparative Example 3

[0059] Take 10 mL of CDs-HP dispersion, add 140 mL of deionized water to dilute to 150 mL, then add 10 g of LiMn2O4 powder to achieve a carbon dot raw material concentration of approximately 0.3 mg / mL and a manganese-based cathode particle concentration of approximately 66.7 mg / mL. Other steps are the same as in Example 1.

[0060] Comparative Example 4

[0061] After the operation in Example 1, the product was not washed with deionized water, but directly dried at 80°C after centrifugation.

[0062] Comparative Example 5

[0063] Amorphous carbon nanoparticles (prepared by laser ablation of graphite target sputtering, without oxidation treatment), with an average particle size of 4 nm and almost no oxygen-containing functional groups on the surface (XPS O 4.5%), were used to replace carbon dots and dispersed in a liquid medium, and a mixture was prepared with LiMn2O4 powder. Other procedures were the same as in Example 1.

[0064] Comparative Example 6

[0065] The dispersion in Example 1 was replaced with a dispersion with a larger average particle size, and everything else was the same as in Example 1.

[0066] Specifically:

[0067] Weigh 5g of commercially available graphite oxide and disperse it in 500mL of deionized water. Pre-disperse the dispersion by sonication for 30 minutes. Transfer the dispersion to an ATS AH-1500 high-pressure homogenizer and cycle it 5 times at 30 MPa, with cooling in an ice-water bath throughout. Centrifuge the resulting dispersion (8000 rpm, 30 minutes) to remove large particles and collect the supernatant. The average particle size of the carbon dots is approximately 23.3 nm.

[0068] To verify the selective anchoring and coating effects of carbon quantum dots on manganese-based cathode particles of the present invention, Examples 1 and Comparative Examples 1 and 2 were used as examples to compare and demonstrate their preliminary differences in structural characterization and performance indicators, as shown in [the figures]. Figures 1-5 middle.

[0069] The products obtained from the above embodiments and comparative examples were used to prepare positive electrode sheets:

[0070] The prepared carbon quantum dot discrete anchored modified manganese-based cathode material, conductive agent (Super P), and binder (PVDF:NMP = 5%) were mixed in a mass ratio of 8:1:1 to form a slurry, which was then coated onto aluminum foil to a thickness of 50 μm, resulting in a wet electrode sheet. The wet electrode sheet was placed in a forced-air drying oven at 80 °C for 1 h, and then transferred to a vacuum oven at 120 °C for 8 h. After cooling to room temperature, it was cut into circular electrode sheets with a diameter of 12 mm for later use.

[0071] CR2032 button battery assembly:

[0072] First, the prepared positive electrode sheet is placed in a glove box. Then, the battery is assembled in the following order: negative electrode shell, electrode sheet, electrolyte (30 μL), separator (Celgard 2325), electrolyte (30 μL), lithium sheet (1 mm), gasket, spring sheet, and positive electrode shell. The battery is then sealed using a sealing machine and left to stand for about 5 hours before being tested and characterized.

[0073] The test characterization conditions are as follows:

[0074] Initial charge and discharge test at room temperature: Charge and discharge tests were conducted at 25 ℃, 0.1C rate, and 3.0~4.3 V voltage range. The test results are listed in Table 1.

[0075] High-temperature cycling test conditions: 300 charge-discharge cycles were performed at 55 ℃, 1C rate, and a voltage range of 3.0~4.3 V. The test results are listed in Table 2.

[0076] Rate testing conditions: Charge and discharge tests were conducted at 25 °C at rates of 0.1C, 0.5C, 1C, 2C, and 5C, and the results are listed in Table 3.

[0077] Electrochemical impedance spectroscopy: After 50 cycles at 1C, the results are listed in Table 4.

[0078] Mn solubility test: Each sample was assembled into a half cell, stored at 55℃ for 7 days, and then disassembled after 50 cycles of charge-discharge at 1C at 55℃. The electrolyte was taken and the Mn content was determined by ICP-OES. The results are listed in Table 5.

[0079] Table 1

[0080]

[0081] Table 2

[0082]

[0083] Table 3

[0084]

[0085] Table 4

[0086]

[0087] Table 5

[0088]

[0089] As shown in Figure 1, the XRD test results of Example 1 and Comparative Example 1 show that all the diffraction peaks of the two samples correspond to (111), (222), (311), (400), (331), (511), (440), (531), (533), and (622), respectively. They all correspond to the crystal planes of spinel-type lithium manganese oxide LiMn2O4. No impurity peaks appear, indicating that the carbon dot-coated lithium manganese oxide sample prepared by the present invention has high phase purity. After the carbon quantum dot discrete anchoring modification, no other impurity phases are introduced, and the intrinsic spinel crystal structure of lithium manganese oxide is not destroyed.

[0090] Meanwhile, the diffraction peaks of both samples exhibited sharp peak shapes, good symmetry, and narrow half-peak widths, indicating that both lithium manganese oxide materials, before and after carbon quantum dot discrete anchoring modification, possess excellent crystallinity and a complete crystal structure. Further comparison revealed that the characteristic peak positions of Example 1 and Comparative Example 1 were completely identical, with no significant shift. This proves that carbon quantum dots exist only in a selectively anchored coating form on the surface of lithium manganese oxide particles, without entering the internal crystal lattice of lithium manganese oxide, and without altering its intrinsic crystal structure and phase composition. This provides a structural basis for the material's excellent electrochemical stability.

[0091] To verify the selective and discontinuous discrete anchoring modification results of carbon quantum dots, this invention uses high-resolution transmission electron microscopy (HRTEM) to characterize the microstructure and interface structure of the samples, such as... Figure 2 As shown in the figure, discrete carbon quantum dots are anchored on the surface of LiMn2O4 particles without a continuous coating layer. Figure 4 The samples from Example 1 and Comparative Example 1 were further subjected to XPS Mn 2p analysis. 3 / 2 Analysis showed that the Mn 2p of the original pure phase LiMn2O4 in Comparative Example 1 was... 3 / 2 The binding energy is located at 642.1 eV (Mn 3+ ) and 643.8 eV (Mn 4+ In Example 1, after selective anchoring modification with carbon quantum dots, the two peaks shifted slightly towards the direction of higher binding energy by 0.3 eV and 0.4 eV, respectively, reaching 642.4 eV (Mn). 3+ ) and 644.2 eV (Mn 4+ ), while Mn 3+ / Mn 4+ The peak area ratio decreased from 0.52 (Comparative Example 1) to 0.46 (Example 1), indicating that the surface Mn 3+ The relative content decreases. The increase in binding energy reflects the decrease in electron cloud density around Mn atoms, proving that -COOH / -OH on carbon quantum dots coordinate with Mn ions, and that electrons of Mn are transferred to the ligands, thus making the electronic state of Mn more stable (Mn). 3+ (Passivated). This is direct spectroscopic evidence that the present invention inhibits the disproportionation reaction at the chemical level.

[0092] In comparison, Figure 3 The coating situation of the sample in Comparative Example 2 is shown as an example, and it can be seen that... Figure 3 A complete continuous carbon layer was formed. It can be seen that the mismatch between the high concentration of carbon point raw materials and the manganese-based cathode particles in the mixed solution disrupted the multiple competitive synergistic effects of hydrogen bonding, electrostatic attraction, coordination, and van der Waals forces in the preparation system of this invention, weakened the dominant role of coordination, and led to a decrease in the specificity of selective anchoring. At the same time, the high concentration promoted the tendency of film formation to be biased towards multi-point anchoring, resulting in the transformation of the discrete and discontinuous selective anchoring modification structure into a continuous carbon layer. Figure 5 This further demonstrates the advantages of Example 1 over Comparative Examples 1 and 2 in terms of high-temperature cycling, fully proving the advantages of the discrete, discontinuous selective anchoring modification structure of carbon quantum dots in this invention over continuous carbon layers in terms of performance improvement.

[0093] Table 1 shows the differences in first-cycle capacity and coulombic efficiency between the examples and comparative examples. The first-cycle capacity and coulombic efficiency of Examples 1-5 are essentially the same, indicating that the selective anchoring of carbon quantum dots did not significantly damage the main structure of LiMn2O4, nor did it introduce serious irreversible side reactions in the first cycle. However, the continuous coating in Comparative Example 2 led to a decrease in initial charge specific capacity, while the excessive carbon quantum dot residue from the lack of washing in Comparative Example 4 resulted in a decrease in coulombic efficiency.

[0094] Table 2 shows the differences in high-temperature cycling between the samples of the embodiments and comparative examples of the present invention. Examples 1 to 5 all showed good high-temperature stability, which was better than uncoated pure phase LiMn2O4 (Comparative Example 1) and excessive continuous coating (Comparative Example 2). Insufficient specific anchoring in Comparative Example 3, excessive carbon quantum dot residue in Comparative Example 4, and conventional continuous thick coating in Comparative Example 5 also led to more interfacial side reactions and poor high-temperature stability.

[0095] Table 2 further illustrates the performance differences between the examples. Example 4, compared to Examples 1-3, demonstrates that optimized operating conditions within the defined range (carbon dot raw material concentration 1-2 mg / mL, manganese-based cathode particle concentration 50-80 mg / mL) can better balance the multiple competing synergistic effects, thereby improving anchoring efficiency and high-temperature stability. Example 5, compared to Examples 1-3, shows that doping may lead to spinel structure instability and Mn content issues in the system of this invention. 3+ A reduction in the number of sites or decreased activity is detrimental to the performance of high-temperature cycling.

[0096] Table 3 shows similar performance differences at high rates. The comparative examples all exhibit varying degrees of high-rate loss. The good rate performance of Examples 1-5 verifies that the "discrete anchoring" structure does not hinder Li + Advantages of transmission. Meanwhile, Examples 1-3, compared to Examples 4-5, also demonstrate optimized operating conditions and better high-rate ion diffusion capability of undoped LiMn2O4. Furthermore, Comparative Example 6 further shows that size-effect mismatch makes it difficult for carbon quantum dots to fully penetrate the defects on the surface of manganese-based cathode particles and interact with Mn. 3+ To achieve precise selective alignment, a larger size may bridge multiple metal sites simultaneously, which can reduce the selectivity of single-point anchoring and ultimately make it difficult to achieve the expected improvement in rate performance.

[0097] Table 4 shows that the selective anchoring of carbon quantum dots does not affect the inherent resistance (Rs) of ion migration in the solution. However, the charge transfer resistance (Rct) caused by the electrochemical reaction at the electrode / electrolyte interface differs significantly. The selective anchoring of carbon quantum dots may stabilize the surface lattice through coordination with Mn sites, reducing the formation of surface remodeling layers (such as rock salt phases) during cycling, thereby maintaining a low charge transfer resistance. Although continuous carbon coating layers (Comparative Examples 2 and 5) and size effect mismatch (Comparative Example 6) can also conduct electricity, the dual-interface effect at the carbon / electrolyte interface and the carbon / LMO interface actually increases the total impedance.

[0098] The Mn solubility test in Table 5 further directly proves that carbon quantum dots are anchored to the Mn active sites on the surface through chemical coordination bonds, effectively inhibiting the disproportionation reaction and reducing Mn at the source. 2+ The formation and dissolution of Mn were observed. Comparative Example 3, with insufficient specific anchoring, and Comparative Example 6, with size effect mismatch, were almost ineffective in inhibiting Mn. In addition, although Comparative Example 2, which transitioned to continuous coating, showed some improvement in inhibition, the reduced specificity resulted in the continued dissolution of Mn, preventing sufficient chemical stabilization.

[0099] The above experiments of this invention fully demonstrate that carbon quantum dots interact with the Mn surface of manganese-based materials. 3+ Chemical coordination bonds are formed, enabling discrete and discontinuous anchoring of carbon quantum dots, thus stabilizing the surface Mn at a chemical level. 3+ This technology suppresses disproportionation and Mn dissolution while maintaining or even improving lithium-ion and electron transport performance. Compared with existing technologies, it achieves significant progress in cycle stability, rate performance, interfacial impedance, and Mn dissolution suppression.

[0100] The technical features of the embodiments described above can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make modifications, alterations, substitutions, and variations to the above embodiments within the scope of the present invention. Furthermore, without contradiction, those skilled in the art can combine and integrate different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

Claims

1. A manganese-based cathode material with discrete anchoring of carbon quantum dots, comprising manganese-based cathode particles as a matrix, wherein the carbon quantum dots are anchored to the Mn atoms on the surface of the manganese-based cathode particles. 3+ Ions form chemical coordination bonds, selectively anchoring Mn on the surface of the manganese-based cathode particles. 3+ On the active site, carbon quantum dots are distributed in a discrete and discontinuous manner on the surface of manganese-based cathode particles, with an average particle size of 0.5~15 nm.

2. The manganese-based cathode material with discrete anchoring modification of carbon quantum dots according to claim 1, characterized in that, The manganese-based cathode is selected from one or more of the following: doped or undoped spinel-type LiMn2O4, lithium-rich manganese layered oxide, lithium nickel manganese oxide, manganese-based phosphate, or manganese-containing layered oxide. The doped spinel-type LiMn2O4 is spinel-type LiMn2O4 modified by doping with one or more elements selected from Al, Mg, Ti, Co, Ni, Cr, Fe, Zr, La, Nb, and W.

3. The manganese-based cathode material with discrete anchoring modification of carbon quantum dots according to claim 1, characterized in that, The average particle size of carbon quantum dots is 0.5~5 nm; Preferably, carbon quantum dots interact with Mn on the surface of manganese-based cathode particles through oxygen-containing / nitrogen-containing functional groups. 3+ The ions form chemical coordination bonds, and the oxygen-containing functional groups include at least one of carboxyl (-COOH), hydroxyl (-OH), and carbonyl (C=O), while the nitrogen-containing functional groups include at least one of amino (-NH2) and amide.

4. A method for preparing the manganese-based cathode material with discrete anchoring modification of carbon quantum dots according to any one of claims 1-3, comprising the following steps: Carbon dot raw materials are dispersed in a polar liquid medium and homogenized until the average particle size of the carbon dot raw materials is 0.5~15 nm to obtain a dispersion. Then, the dispersion is mixed with manganese-based cathode particles to obtain a mixture. The concentration of carbon dot raw materials in the mixture is adjusted to 1~3 mg / mL and the concentration of manganese-based cathode particles is 30~100 mg / mL. The mixture is stirred for 0.5~12 h, the solid phase product is separated, washed, and dried at <100℃ to obtain the desired product.

5. The preparation method according to claim 4, characterized in that, The concentration of carbon dot raw material in the mixture is 1~2 mg / mL, and the concentration of manganese-based cathode particles is 50~80 mg / mL. The mixture is stirred for 3~8 h, the solid phase product is separated, washed, and dried at 20~80℃ to obtain the desired product.

6. The preparation method according to claim 4, characterized in that, The carbon dot raw material includes at least one of graphite oxide, graphene oxide, or graphene quantum dots. Preferably, the carbon point raw material selected before homogenization and crushing is a material with an average flake diameter of 0.1~10 μm and a carbon-oxygen atomic ratio of 0.5~3.

0. Preferably, the particle size D50 of the manganese-based cathode particles is 0.3~100μm, more preferably 0.5~50μm, and even more preferably 1~30μm.

7. The preparation method according to claim 4, characterized in that, The liquid phase medium and the washing solvent are each independently selected from one or more of the following: water, water / alcohol mixture, ethanol, isopropanol, ethylene glycol, N-methylpyrrolidone, and N,N-dimethylformamide.

8. The preparation method according to claim 4, characterized in that, The mixing process is carried out at a temperature of 20~80℃.

9. The preparation method according to claim 4, characterized in that, The washing process continues until no ultraviolet absorption signal from carbon quantum dots can be detected in the washing solution.

10. The preparation method according to claim 4, characterized in that, Homogenization processes include one of the following: high pressure homogenization (CDs-HP) and ultrasonic homogenization (CDs-US).

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