Manganese ion substituted mgconicuzn high-entropy oxides, methods of making and applications thereof

Abstract

This invention discloses manganese ion-substituted MgCoNiCuZn high-entropy oxides, their preparation methods, and applications, belonging to the field of metallic materials technology. It is a Mg... （1‑x） / 4 Co （1‑x） / 4 Ni x Cu （1‑x） / 4Zn （1‑x） / 4‑z Mn z O high-entropy oxides or Mg （1‑y） / 4 Co （1‑y） / 4Ni y Cu （1‑y） / 4 Zn （1‑y） / 4‑z Mn z The high-entropy oxides, with x and y values ​​of 0.15–0.35 and z values ​​of 0.02–0.08, are prepared by ball milling MgO, CoO, NiO, CuO, ZnO, and MnO powders in stoichiometric ratio, vacuum drying, thorough grinding, and then spreading the mixture evenly. The mixture is then placed in batches in a high-temperature tube furnace, slowly heated in an air atmosphere, held at that temperature, and then slowly cooled with the furnace. By gradually replacing Zn with Mn, the resulting high-entropy oxides exhibit excellent electrochemical performance.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials technology, specifically relating to manganese ion-substituted MgCoNiCuZn high-entropy oxides, their preparation methods, and applications. Background Technology

[0002] In 2015, Rost et al. successfully introduced the concept of high entropy into the field of inorganic nonmetallic materials. They synthesized a high-entropy oxide (MgO) with a single rock salt structure using equimolar ratios of MgO, CoO, NiO, CuO, and ZnO powders. 0.2 Co 0.2 Ni 0.2 Cu 0.2 Zn 0.2 This study revealed the crucial role of the "high entropy effect" in stabilizing crystal structures, thus defining "entropy-stable oxides" (ESOs). Rock salt-structured high-entropy oxide ceramics, due to their unique crystal structure advantages and significant "high entropy effect," show great promise in the field of electrochemical energy. These materials are composed of multiple cations randomly distributed within the rock salt lattice, which not only endows them with excellent compositional flexibility and structural stability but also allows for effective control of the material's electronic structure, thereby synergistically optimizing their electrochemical performance.

[0003] Traditional lithium-ion battery materials, such as graphite and lithium cobalt oxide, are prone to structural collapse and irreversible phase transitions during long-term charge-discharge cycles due to their single active component and relatively simple crystal structure, leading to rapid capacity decay. Simultaneously, their thermodynamic instability poses higher safety risks, typically exhibiting core disadvantages such as poor cycle stability, drastic volume changes, insufficient thermal stability, and limited performance characteristics. However, high-entropy ceramics, thanks to the four key effects, possess superior structural stability and ultra-long cycle life, while significantly improving thermal stability, effectively suppressing oxygen evolution, and enhancing battery safety.

[0004] Mehdi Kheradmandfard et al. developed an ultrafast, low-temperature, and green microwave-assisted synthesis method for preparing (Mg, Co, Ni, Cu, Zn)O high-entropy oxide nanoparticles. Using metal nitrates as precursors, the reaction was completed in just 3 minutes by microwave irradiation in an alkaline solution, followed by calcination at 950 °C to obtain the final product. Characterization techniques including XRD, HR-TEM, EDS-STEM, and XPS confirmed that the synthesized HEO nanoparticles possess a single rock salt structure, with uniform distribution of the five metal elements without significant agglomeration. The average particle size is 44 nm, with a distribution range of 20-70 nm. This method offers advantages such as extremely short reaction time, low temperature, high product purity, small particle size, and low cost. In electrochemical performance tests, HEO exhibited excellent lithium storage performance as a lithium-ion battery anode, achieving a reversible capacity of 400 mAh / g at a current density of 0.1 A / g, maintaining 250 mAh / g at a high rate of 5 A / g, and retaining over 98% capacity after 1000 cycles at 1 A / g, demonstrating good structural stability and cycle reversibility. Shijie Chen et al. regulated the high-entropy oxide (Co) structure of rock salt using a low-temperature post-treatment strategy. 0.2 Cu 0.2 Mg 0.2 Ni 0.2 Zn 0.2 The degree of lattice distortion of O was systematically studied to investigate its impact on the lithium storage performance of the material. The sample CCMNZ-10, which was post-annealed for 10 min, exhibited the most significant lattice distortion, with an oxygen vacancy concentration reaching 24.9%, and demonstrated a room-temperature electronic conductivity of 0.11 S / cm. -1 When used as a negative electrode in lithium-ion batteries, the CCMNZ-10 electrode exhibits excellent electrochemical performance: it retains a reversible capacity of 993 mAh / g after 150 cycles at a current density of 200 mA / g, a capacity retention of 66.3% at a high rate of 3000 mA / g, and a capacity of 771 mAh / g after 400 cycles at 1000 mA / g.

[0005] Rock-salt-type high-entropy oxide ceramics can also be used as supercapacitor materials. Compared with traditional supercapacitor materials, high-entropy ceramics integrate multiple transition metals, introducing abundant redox pairs with different potentials, which synergistically contribute a high Faraday pseudocapacitance, thus achieving a higher specific capacitance. Simultaneously, the inherent mixed-conductivity electronic pathways of high-entropy ceramics facilitate rapid charge transport, allowing them to maintain high capacitance even at high current densities. Ji Pengchao et al. studied the simplified synthesis and supercapacitor performance of high-entropy oxides (HEO) with a medium molar ratio in the (Mg, Co, Ni, Cu, Zn)O system. They successfully prepared (Mg, Co, Ni, Cu, Zn)O with a rock-salt structure using a polyacrylamide gelation method combined with calcination. 0.2 Co0.2 Ni 0.2 Cu 0.2 Zn 0.2 HEO nanoparticles were synthesized, and their structural characteristics and electrochemical behavior were systematically analyzed. The study found that the formation temperature of HEO is significantly affected by the molar ratio (A / M) of acrylamide to metal ions. When the A / M ratio is increased to 120:1, a single-phase rock salt structure can be formed at 900℃, and the nanoparticles are spherical with a particle size distribution of 40-65 nm. In terms of electrochemical performance, the HEO nanoparticles exhibit a high specific capacitance of 402 F / g at a current density of 1 A / g, and maintain a capacity retention of 62% at 20 A / g, demonstrating excellent rate performance. After 2000 cycles, the capacity retention is 61%, showing good cycling stability.

[0006] Rock-salt type high-entropy oxide ceramics can also be used as electrocatalytic materials. Kyung-Hwan Kim and Yun-Hyuk Choi systematically studied five-membered high-entropy oxides (Mg). 0.2 Fe 0.2 Co 0.2 Ni 0.2 Cu 0.2 The effects of different cations in O2 on its electrocatalytic oxygen evolution reaction (OER) performance were investigated. HEO and five quaternary medium-entropy oxides (MEOs) for removing Mg, Fe, Co, Ni, or Cu were synthesized via a hydrothermal method followed by calcination at 1000℃. All samples exhibited uniform morphology, equimolar composition, and a single rock salt structure. Electrochemical tests showed that MEO (w / o Cu) possessed the best OER performance, with the highest overpotential η. 10 The voltage is 454 mV, and the Tafel slope is 60 mV. -1 The charge transfer resistance is 4.3 Ω, and the double-layer capacitance is 87.0 μF·cm⁻¹. -2 And its performance only slightly degrades after 1000 cycles. Summary of the Invention

[0007] The main objective of this invention is to provide manganese ion-substituted MgCoNiCuZn high-entropy oxides. Based on rock-salt type (Mg, Co, Ni, Cu, Zn)O high-entropy oxides, Mn element is used to gradually replace Zn element in the system to obtain non-equimolar ratio (Mg, Co, Ni, Cu, Zn, Mn)O high-entropy oxides, namely manganese ion-substituted MgCoNiCuZn high-entropy oxides, which have excellent electrochemical performance.

[0008] Another objective of this invention is to provide a method for preparing the manganese ion-substituted MgCoNiCuZn high-entropy oxide, which is obtained by gradually replacing Zn ions with Mn ions, using a non-equimolar ratio mixing method combined with a high-temperature solid-state method, and optimizing the process by adjusting the calcination temperature, holding time, and other factors.

[0009] Another object of the present invention is to provide the application of the manganese ion-substituted MgCoNiCuZn high-entropy oxide in the preparation of supercapacitors and electrodes.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] In a first aspect, the present invention provides a manganese ion-substituted MgCoNiCuZn high-entropy oxide, wherein Mg is （1-x） / 4Co （1-x） / 4 Ni x Cu （1-x） / 4 Zn （1-x） / 4-z Mn z O high-entropy oxides or Mg （1-y） / 4 Co （1-y） / 4 Ni y Cu （1-y） / 4 Zn （1-y） / 4- z Mn z O high-entropy oxides, where x ranges from 0.15 to 0.35, y ranges from 0.15 to 0.35, and z ranges from 0.02 to 0.08.

[0012] Preferably, the manganese ion-substituted MgCoNiCuZn high-entropy oxide is Mg 0.1625 Co 0.1625 Ni 0.35 Cu 0.1625 Zn 0.1625-z Mn z O high-entropy oxide, where the value of z ranges from 0.02 to 0.08.

[0013] A second aspect of the present invention provides a method for preparing the manganese ion-substituted MgCoNiCuZn high-entropy oxide, comprising the following steps:

[0014] (1) MgO, CoO, NiO, CuO, ZnO and MnO powders were mixed in a planetary ball mill according to the stoichiometric ratio. Anhydrous ethanol was added to the mixed powder as the grinding medium. After ball milling and mixing, the mixture was vacuum dried to obtain the mixed material.

[0015] (2) The mixture is placed in an agate mortar and ground thoroughly. The ground material is spread evenly in an alumina crucible and placed in a high-temperature tube furnace in batches. The temperature is slowly raised to 1000-1200℃ in an air atmosphere, kept at the temperature for 10-14h, and then slowly lowered to 400-600℃. The material is then cooled to room temperature with the furnace to obtain the final product.

[0016] Preferably, in step (1), the ball milling speed is 410 r / min, the ball milling time is 4 h, and the vacuum drying time is 12 h.

[0017] Preferably, in step (2), the high-temperature tubular furnace is first heated to 1100°C at a heating rate of 5°C / min in an air atmosphere, then kept at that temperature for 12 hours, and then cooled to 500°C at a rate of 2°C / min, and then cooled to room temperature along with the furnace.

[0018] A third aspect of the present invention provides the application of the manganese ion-substituted MgCoNiCuZn high-entropy oxide in the preparation of supercapacitors and electrodes.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] (1) Based on the rock salt type (Mg, Co, Ni, Cu, Zn)O high entropy oxide, the Zn element in the system is gradually replaced by Mn element to obtain non-equimolar ratio (Mg, Co, Ni, Cu, Zn, Mn)O high entropy oxide, namely MgCoNiCuZn high entropy oxide substituted by manganese ions, which has excellent electrochemical performance.

[0021] (2) This invention prepares a series of non-equimolar (Mg, Co, Ni, Cu, Zn, Mn)O high-entropy oxides synthesized under different preparation processes by adjusting the preparation process, such as sintering temperature and holding time, thereby obtaining the optimal preparation process of the system, which is easy to mass-produce. Attached Figure Description

[0022] Figure 1 The following are XRD patterns and lattice constant comparison diagrams of the synthesized high-entropy oxide samples in the examples: (a) XRD patterns of the synthesized samples after Mn substitution of Zn at different ratios; (b) Trend diagram of lattice constant changes of the samples obtained by Jade refinement.

[0023] Figure 2 The images show high-resolution Co 2P and Mn 2P spectra of the high-entropy oxide samples synthesized under different Mn substitution ratios in the examples.

[0024] Figure 3 The following are SEM-EDS images of high-entropy oxide samples synthesized after different proportions of Mn substitution for Zn in the examples: (a) SEM images of high-entropy oxide samples synthesized after different proportions of Mn substitution for Zn; (b) EDS image of the sample synthesized with a substitution ratio of 2%; (c) EDS image of the sample synthesized with a substitution ratio of 4%; (d) EDS image of the sample synthesized with a substitution ratio of 6%; (e) EDS image of the sample synthesized with a substitution ratio of 8%.

[0025] Figure 4The image shows the CV diagrams of high-entropy oxide samples synthesized after different proportions of Mn substituting Zn in the examples.

[0026] Figure 5 The CV diagrams for sample Mn6 at different scan rates are shown in the examples.

[0027] Figure 6 The image shows the GCD diagrams of high-entropy oxide samples synthesized after different proportions of Mn substituting Zn in the examples.

[0028] Figure 7 The following are the GCD diagrams and rate performance diagrams of sample Mn6 in the examples: (a) GCD diagrams of sample Mn6 at different current densities; (b) Comparison of rate performance between sample Mn6 and sample Ni35.

[0029] Figure 8 The electrochemical impedance spectroscopy (EIS) spectra of high-entropy oxide samples with different Mn substitution amounts are shown in the examples. The EIS spectra of all Mn-substituted samples consist of two parts: a semi-circular arc in the high-frequency region and a slanted line in the mid-to-low-frequency region, which correspond to the charge transfer impedance (Rct) and ion diffusion impedance (Rw) of the electrode process, respectively.

[0030] Figure 9 The XRD patterns of the (Mg, Co, Ni, Cu, Zn, Mn)O high-entropy oxide synthesized by partially substituting Zn with Mn in the examples are shown at different sintering temperatures.

[0031] Figure 10 The high-resolution spectra of Co 2P and Mn 2P in the Mn6 samples generated at different sintering temperatures are shown in the examples.

[0032] Figure 11 The following are SEM-EDS images of Mn6 samples generated at different sintering temperatures in the examples: (a) SEM images of Mn6 samples generated at different sintering temperatures; (b) EDS image of the sample synthesized at a sintering temperature of 900℃; (c) EDS image of the sample synthesized at a sintering temperature of 1000℃; (d) EDS image of the sample synthesized at a sintering temperature of 1100℃; (e) EDS image of the sample synthesized at a sintering temperature of 1200℃.

[0033] Figure 12 The CV curves of Mn6 measured at different sintering temperatures and a scan rate of 10 mV / s are shown in the examples.

[0034] Figure 13 The image shows the CV curves of Mn6 after sintering at 1000℃ at different scan rates in the example.

[0035] Figure 14 The GCD diagrams of Mn6 samples generated at different sintering temperatures are shown in the examples.

[0036] Figure 15 The following are GCD diagrams and rate performance diagrams of Mn6 synthesized at 1000℃ in the examples: (a) GCD diagrams of Mn6 synthesized at 1000℃ at different current densities; (b) Comparison of rate performance of Mn6 synthesized at 1000℃ and Mn6 synthesized at 1100℃.

[0037] Figure 16 The electrochemical impedance spectroscopy of Mn6 samples at different sintering temperatures is shown in the examples.

[0038] Figure 17 The XRD patterns of the Mn6 samples in the examples are obtained after being treated at 1000℃ for different holding times.

[0039] Figure 18 The high-resolution spectra of Co 2P and Mn 2P in the Mn6 samples generated at different holding times in the examples are shown.

[0040] Figure 19 The images shown are SEM images and corresponding EDS elemental distribution maps of Mn6 components after being treated at 1000℃ for different holding times in the examples. SEM-EDS images of Mn6 samples generated at different holding times are shown in the following figures: (a) SEM images of Mn6 samples generated at different holding times; (b) EDS image of the sample synthesized at a holding time of 11h; (c) EDS image of the sample synthesized at a holding time of 12h; (d) EDS image of the sample synthesized at a holding time of 13h; and (e) EDS image of the sample synthesized at a holding time of 14h.

[0041] Figure 20 The CV curves of the Mn6 sample in the examples after being treated at 1000℃ for different holding times are shown.

[0042] Figure 21 The CV curves of the Mn6 sample at different scan rates are shown in the examples.

[0043] Figure 22 The GCD diagrams of Mn6 samples generated at different holding times are shown in the examples.

[0044] Figure 23 The following are the GCD diagrams and rate performance diagrams of Mn6 synthesized after 13 hours of heat preservation in the examples: (a) GCD diagrams of Mn6 synthesized after 13 hours of heat preservation at different current densities; (b) Comparison of rate performance between Mn6 synthesized after 13 hours of heat preservation and Mn6 synthesized after 12 hours of heat preservation.

[0045] Figure 24 The image shows the EIS spectrum of Mn6 synthesized after 13 hours of heat preservation in the example. Detailed Implementation

[0046] To more fully understand and demonstrate the technical solutions, objectives, and advantages of the present invention, the technical effects produced by the present invention will be further described in detail and completely below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. It should be noted that other embodiments obtained by those skilled in the art without departing from the concept of the present invention are all within the protection scope of the present invention.

[0047] The following examples provide manganese ion-substituted MgCoNiCuZn high-entropy oxides, which are Mg （1-x） / 4 Co （1-x） / 4Ni x Cu （1-x） / 4 Zn （1-x） / 4-z Mn z O high-entropy oxides or Mg （1-y） / 4 Co （1-y） / 4 Ni y Cu （1-y） / 4 Zn （1-y） / 4-z Mn z O high-entropy oxides, where x ranges from 0.15 to 0.35, y ranges from 0.15 to 0.35, and z ranges from 0.02 to 0.08.

[0048] In some embodiments, the manganese ion-substituted MgCoNiCuZn high-entropy oxide is Mg 0.1625 Co 0.1625 Ni 0.35 Cu 0.1625 Zn 0.1625-z Mn z O high-entropy oxide, where the value of z ranges from 0.02 to 0.08.

[0049] The following examples provide a method for preparing manganese ion-substituted MgCoNiCuZn high-entropy oxides, including the following steps:

[0050] (1) MgO, CoO, NiO, CuO, ZnO and MnO powders were mixed in a planetary ball mill according to the stoichiometric ratio. Anhydrous ethanol was added to the mixed powder as the grinding medium. After ball milling, the mixture was vacuum dried. The ball milling speed was 410 r / min, the ball milling time was 4 h, and the vacuum drying time was 12 h to obtain the mixed material.

[0051] (2) The mixture is placed in an agate mortar and ground thoroughly. The ground material is spread evenly in an alumina crucible and placed in a high-temperature tube furnace in batches. It is first heated to 1100 ℃ at a heating rate of 5 ℃ / min in an air atmosphere, then kept at the temperature for 12 h, and then cooled to 500 ℃ at a rate of 2 ℃ / min and cooled to room temperature with the furnace to obtain the final product.

[0052] Example 1

[0053] 1.1 Experimental Materials

[0054] The experimental drugs are shown in Table 1.

[0055] Table 1: Experimental Samples

[0056]

[0057] 1.2 Preparation of high-entropy oxide powders of MgCoNiCuZn with non-equimolar ratio manganese ion substitution

[0058] Mg （1-x） / 4 Co （1-x） / 4 Ni x Cu （1-x） / 4 Zn （1-x） / 4-z Mn z O high-entropy oxides or Mg （1-y） / 4 Co （1-y） / 4Ni y Cu （1-y） / 4 Zn （1-y） / 4-z Mn z The high-entropy oxide powders were all prepared by non-equimolar mixing combined with a high-temperature solid-state method. The specific process is as follows: MgO, CoO, NiO, CuO, ZnO, and MnO were mixed in a planetary ball mill with stoichiometric ratios of x=0.15, 0.2, 0.25, 0.35 or y=0.15, 0.2, 0.25, 0.35 and z=0.02, 0.04, 0.06, 0.08. Anhydrous ethanol was added as the grinding medium. The ball milling speed was 410 r / min, and the mixture was ball-milled for 4 h. After mixing, the mixture was placed in a vacuum drying oven and dried for 12 h. After drying, the material was thoroughly ground in an agate mortar. The ground material was then spread evenly in an alumina crucible and placed in batches in a high-temperature tube furnace. The furnace was heated to 1100℃ in air at a heating rate of 5℃ / min and held for 12 hours. Finally, the temperature was lowered to 500℃ at a rate of 2℃ / min and cooled to room temperature with the furnace to obtain manganese ion-substituted MgCoNiCuZn high-entropy oxide powder. Samples with Mn contents z of 0.02, 0.04, 0.06, and 0.08 were named Mn2, Mn4, Mn6, and Mn8, respectively. 0.2 Co 0.2 Ni 0.2 Cu 0.2 Zn 0.2 The sample containing O was named HEOs.

[0059] 1.3 Preparation of Electrode Sheets

[0060] High entropy oxide powder (HEOs) was used as the active material and mixed with acetylene black and polyvinylidene fluoride (PDVF) at a mass ratio of 8:1:1, with acetylene black acting as a conductive agent and PDVF as a binder. N-methylpyrrolidone was added as a solvent, and the mixture was thoroughly ground in an agate mortar. The mixture was then applied to nickel foam (1 cm × 1 cm). After drying at 60°C for 12 h in a vacuum drying oven, the dried nickel foam coated with the active material was pressed at 2 MPa for 1 min using a tablet press to obtain the working electrode. The mass loading of the active material on the nickel foam was approximately 1-2 mg / cm³. 2 .

[0061] 1.4 Structure of (MgCoNiCuZn)O high-entropy oxide composites with Mn ion substitution

[0062] Figure 1 (a) shows the XRD patterns of high-entropy oxide samples synthesized by gradually substituting Zn with Mn. As can be seen from the figure, the (Mg, Co, Ni, Cu, Zn, Mn)O high-entropy oxides synthesized under different Mn substitutions all exhibit typical high-entropy rock salt structures, corresponding to diffraction peaks on the (111), (200), (220), (311), and (222) crystal planes. Compared with the unsubstituted HEO group, the introduction of Mn significantly enhances the diffraction peak intensity, indicating that Mn promotes the improvement of the crystal structure to a certain extent. However, with further increases in Mn substitution, the diffraction peak intensity of the high-entropy rock salt structure gradually decreases, and the peak shape slightly broadens, indicating that excessive Mn introduction leads to increased lattice distortion. Furthermore, calculations using the Jade software show that with the gradual increase in Mn substitution, the lattice constant a decreases from the initial 4.1845 Å to 4.0258 Å, with a decreasing trend as shown in the figure. Figure 1 As shown in (b), this change is consistent with the fact that the radius of Mn²⁺ ions is smaller than that of Zn²⁺, further confirming that Mn has successfully entered the crystal lattice and caused lattice contraction. In the XRD pattern, in addition to the five diffraction peaks of the high-entropy rock salt structure, a MnCo₂O₄ diffraction peak also appeared, indicating that when the Mn substitution amount is 0.02 mol, Mn has entered the high-entropy rock salt structure, and some Mn is not completely dissolved in the main phase, but forms a spinel-structured second phase with Co. With the increase of Mn substitution amount, the peak intensity of the MnCo₂O₄ diffraction peak increases.

[0063] Figure 2 High-resolution spectra of Co₂P and Mn₂P in high-entropy oxide samples synthesized with different Mn substitution ratios are shown. Figure 2 In the high-resolution Co 2p spectrum shown, Co values ​​at 780.45 eV and 795.06 eV can be observed. 2+Characteristic peaks, and Co at 779.05 eV. 3+ The characteristic peaks indicate that Co maintains a mixed oxidation state of +2 and +3 in the sample. It is noteworthy that as the Mn substitution amount increases, Co... 3+ The relative content of Mn and Co showed a continuously increasing trend, reaching a peak in the Mn8 sample. This phenomenon confirms a significant charge compensation effect between Mn and Co: the introduction of Mn promotes the oxidation of Co, forming more highly reactive Co. 3+ The site, and this synergistic regulation of valence state, jointly contributes to the improvement of the material's pseudocapacitive properties. However, the Mn8 sample Co 3+ The proportion may be too high. Combined with XRD analysis, the results show that in the coarse MnCo2O4 impurity phase of the Mn8 sample, Co mainly exists as Co. 3+ The presence of this form can lead to an imbalance in valence distribution, which may reduce the reversibility of the reaction at the Co site, thereby affecting the electrochemical performance of the sample.

[0064] like Figure 2 As shown, in the high-resolution spectrum of Mn 2p, the binding energy peak at 639.75 is attributed to Mn. 2+ The binding energy peak at 640.95 eV is attributed to Mn. 3+ The binding energy peak at 642.35 eV corresponds to Mn. 4+ This indicates that Mn exists in the sample in a mixed valence state of +2, +3, and +4. Quantitative analysis of the peak area revealed that the valence state distribution of Mn exhibits a regular evolution with increasing Mn substitution: at low substitution levels, Mn... 2+ It is the dominant valence state; in the Mn6 sample, Co 2+ / Co 3+ The optimal equilibrium of mixed valence states constitutes the main body of electrochemical activity; however, when the substitution amount further increases to Mn8, Mn... 4+ The relative content of Mn increased significantly. This evolution indicates that the introduction of excess Mn forces the system to generate more thermodynamically stable Mn. 4+ To maintain charge balance, while Mn 4+ The pseudocapacitive activity is typically lower than that of Mn. 3+ This directly led to the degradation of the electrochemical performance of the Mn8 sample.

[0065] Figure 3 (a) SEM images of high-entropy oxide samples with different Mn substitution amounts. Combined with... Figure 3 (b)-(e) EDS elemental distribution analysis clearly shows the significant influence of Mn substitution on the microstructure of the material.

[0066] With increasing Mn substitution, the microstructure of the materials exhibits a systematic evolution trend. The Mn2 sample displays a morphology where spherical and irregular blocky particles coexist, with a wide particle size distribution and low interparticle aggregation. This structure facilitates electrolyte permeation, but the large particle size distribution may lead to uneven distribution of active sites. In the Mn4 sample, the particle morphology tends to be uniform, mainly consisting of irregular blocks with obvious interparticle gaps, resulting in optimal dispersibility. This morphological characteristic indicates that appropriate Mn substitution optimizes particle growth kinetics, providing a more uniform reaction interface for electrochemical reactions. The Mn6 sample exhibits the most ideal microstructure, with particles mostly being irregular polyhedra, a relatively uniform particle size distribution, and moderate contact and connection between particles. This structure, while ensuring sufficient active specific surface area, establishes a good electronic conduction network, laying the structural foundation for its excellent electrochemical performance.

[0067] However, when the substitution amount increased to Mn8, the microstructure deteriorated significantly, with severe particle agglomeration occurring, and a large number of particles adhering to each other to form "cluster-like" agglomerates. This structural degradation is directly related to the increased content of MnCo2O4 impurity phase observed in XRD analysis. The precipitation of excessive impurity phase at the grain boundaries disrupts the normal grain growth process, leading to abnormal particle agglomeration.

[0068] By combining XRD and SEM analysis, Mn was found to be at low substitution levels. 2+ For Zn 2+ The lattice shrinkage effect caused by substitution is dominant, which refines the particle morphology; while at high substitution levels, the phase separation effect becomes the dominant factor, and the precipitation of MnCo2O4 impurity phase interferes with the normal growth of the main phase, leading to particle coarsening and agglomeration.

[0069] EDS elemental distribution analysis further confirmed that all elements maintained a highly uniform distribution in the Mn2 to Mn6 samples, while local enrichment regions of Mn and Co elements could be observed in the Mn8 sample, which is consistent with the inference of second phase precipitation.

[0070] 1.5 Electrochemical Analysis of (Mg, Co, Ni, Cu, Zn)O High-Entropy Oxide Composites with Mn Ion Substitution

[0071] Figure 4The CV curves of high-entropy oxide samples with different Mn substitution amounts were obtained at a scan rate of 10 mV / s. All samples exhibited a pair of symmetrical redox peaks due to the Faradic redox reaction within the potential range of 0.2–0.5 V, confirming the pseudocapacitive behavior of the synthesized high-entropy ceramic materials. With increasing Mn substitution amount, the response current and the area enclosed by the CV curve first increased and then decreased. The Mn6 sample exhibited the largest response current and the largest integrated area of ​​the CV curve, indicating its superior electrochemical activity.

[0072] When the Mn substitution amount is low, for example, Mn2, Mn 2+ Successfully dissolved in the rock salt phase, its own Mn 2+ The redox activity of Mn³⁺ contributes additional pseudocapacitance to the system, while the redox activity of Mn... 3+ The Jahn-Teller effect was induced, enhancing the lattice polarizability, thereby optimizing ion diffusion kinetics and improving the electronic conductivity of the material, thus improving electrochemical performance. However, when the substitution amount was further increased to Mn8, the performance decline can be attributed to two factors: first, XRD results showed a significant MnCo2O4 impurity phase in Mn8, the presence of which led to a reduction in the number of active sites in the main phase; second, the excessive introduction of Mn exacerbated lattice distortion, hindering the rapid transport of electrons and ions, thus resulting in a degradation of electrochemical performance.

[0073] To further investigate the charge storage mechanism and reaction kinetics of the optimal-performing Mn6 sample, CV curves were tested at different scan rates. The results are as follows: Figure 5 As shown, it can be observed that as the scan rate increases from 10 mV / s to 100 mV / s, the peak currents of both the redox peaks significantly increase. Simultaneously, the oxidation peak potential shifts positively, and the reduction peak potential shifts negatively, leading to an increase in the peak potential difference ΔEp. This is a typical phenomenon caused by polarization effects, indicating that under high-speed scanning, the electrode reaction kinetics are limited by the ion diffusion rate.

[0074] Furthermore, quantitative analysis of the peak current and scan rate revealed a strong linear relationship, demonstrating that the charge storage process of the Mn6 sample is primarily driven by surface-controlled pseudocapacitive behavior. This mechanism implies rapid charge transport and excellent rate performance. Simultaneously, the CV curves maintained similar stable shapes at different scan rates without significant distortion, indicating that the Mn6 electrode exhibits excellent structural stability and electrochemical reversibility in continuous redox reactions.

[0075] Figure 6The graphs show the galvanostatic charge-discharge (GCD) curves of high-entropy oxide samples with different Mn substitution amounts measured at a current density of 1 A / g. All samples exhibit a clear and gentle charge-discharge plateau in the potential range of 0.3–0.51 V. This nonlinear characteristic corresponds closely to the redox peaks observed in the CV test, further confirming the charge storage mechanism dominated by pseudocapacitive behavior. Comparison of the discharge times of different samples reveals that the Mn6 sample has the longest discharge time, indicating that it possesses the highest specific capacity. This result is entirely consistent with the conclusion that Mn6 exhibits the largest current response in the CV test.

[0076] This trend of specific capacity first increasing and then decreasing with Mn content is the result of the synergistic effect of crystal structure characteristics and electrochemical activity. As shown by XRD analysis, appropriate Mn substitution can successfully dissolve in the high-entropy rock salt main phase, and its own Mn content... 2+ and Mn 3+ The redox couple contributes additional Faradic capacity to the system. Meanwhile, Mn... 2+ Replace larger Zn 2+ The lattice contraction caused by this process optimizes the ion diffusion path, thereby improving the utilization rate of active sites. When the Mn substitution amount gradually increases to 0.06 mol, the entropy value of the overall high-entropy rock salt structure increases. The high mixing entropy makes the rock salt structure more stable, improving the electrode's stability during charge and discharge. Furthermore, XRD patterns show that as the Mn substitution ratio increases, the diffraction peak intensity of the second phase MnCo2O4 also increases. At this point, (Mg... 0.1625 Co 0.1625 Ni 0.35 Cu 0.1625 Zn 0.1625-X Mn X O and MnCo2O4 form a composite electrode material, which combines (Mg) 0.1625 Co 0.1625 Ni 0.35 Cu 0.1625 Zn 0.1625-X Mn X The advantages of single electrodes of O and MnCo2O4 enable the composite electrode to possess both good structural stability and high discharge capacity. However, when the Mn content is too high, such as in Mn8, excessive precipitation of the MnCo2O4 second phase not only reduces the number of effective active sites in the main phase, but its potentially poor conductivity or incompatible reaction kinetics can also lead to an overall capacity decay. The Mn6 sample achieves the optimal balance between the integrity of the crystal structure and the number of electrochemical active sites, thus exhibiting the best electrochemical performance.

[0077] To further evaluate the practical application potential of the Mn6 sample, its GCD curves at different current densities were tested, such as... Figure 7 As shown in (a), even at a high current density of 4 A / g, the GCD curve of Mn6 maintains good symmetry and a clear voltage plateau, indicating its excellent electrochemical reversibility and rapid ion transport capability. Calculations based on the GCD curve show that at a current density of 1 A / g, the specific capacitance of sample Mn6 reaches 512.9 F / g, and when the current density is further increased to 4 A / g, the specific capacitance of sample Mn6 still reaches 437.3 F / g.

[0078] The Mn6 sample exhibits superior capacitance retention at high current densities; at a current density of 4 A / g, the capacitance retention of Mn6 reaches 85.3%, which is superior to the 77.1% of Ni35. Figure 7 As shown in (b), the excellent rate performance of the Mn6 sample is clearly visible, mainly attributed to the unique advantages brought about by the introduction of Mn: on the one hand, moderate lattice distortion and shrinkage facilitate rapid ion diffusion; on the other hand, the presence of multivalent Mn ions provides richer reaction pathways and faster reaction kinetics. These factors work together to enable the Mn6 electrode to maintain its electrochemical performance more effectively when facing high current surges, exhibiting superior rate performance.

[0079] like Figure 8 As shown, fitting analysis of the spectra revealed that with increasing Mn substitution, the solution resistance (Rs) and charge transfer impedance (Rct) of the series of samples initially decreased and then increased. Among them, the Mn6 sample exhibited the smallest Rs and Rct values. The smaller Rs value indicates superior intrinsic electronic conductivity of the electrode material itself and its interface with the electrolyte; while the smaller Rct value signifies that the Mn6 electrode significantly reduces the interfacial impedance of the high-entropy oxide electrode, exhibiting the fastest charge transport kinetics and the lowest reaction energy barrier in the Faraday redox reaction. The decreased Rct and Rs values ​​in the Mn8 sample are closely related to the MnCo2O4 second phase. The formation of excessive impurities disrupts the homogeneity of the main phase structure, introducing additional scattering centers at grain boundaries, hindering rapid charge transport, and thus increasing the interfacial impedance.

[0080] In summary, the EIS test results are in complete agreement with the conclusions of CV and GCD tests that Mn6 exhibits the highest specific capacity and optimal rate performance, providing strong evidence for its excellent electrochemical performance from the perspective of electrode reaction kinetics.

[0081] in conclusion:

[0082] A series of (Mg) elements were successfully prepared by stepwise substitution of Zn with Mn through a non-equimolar mixing method combined with a high-temperature solid-state process. 0.1625 Co 0.1625 Ni 0.35 Cu 0.1625 Zn 0.1625-x Mn x O high-entropy oxides were identified, and the following conclusions were drawn:

[0083] (1) A high-entropy oxide with a rock salt structure as the main phase was successfully synthesized in air by a combination of non-equimolar mixing and high-temperature solid-state method. The introduction of an appropriate amount of Mn can solidify in the main lattice, and due to the Mn 2+ Radius smaller than Zn 2+ This leads to a decrease in the lattice constant. However, when the substitution amount is too high, such as in sample Mn6, it will cause excessive precipitation of the second phase MnCo2O4, resulting in a weakening and broadening of the diffraction peak intensity of the main phase.

[0084] (2) Among all Mn-substituted samples, Mn6 exhibited the best overall electrochemical performance. It had the highest specific capacitance at a current density of 1 A / g, reaching 527.5 F / g. At the same time, this sample showed excellent rate performance at high current densities, with a capacitance retention rate as high as 90.7%.

[0085] (3) Synthetic (Mg) 0.1625 Co 0.1625 Ni 0.35 Cu 0.1625 Zn 0.1625-x Mn x The high-entropy oxide of O exhibits the best electrochemical performance, which can be attributed to the following synergistic effect: First, an appropriate amount of Mn solid solution introduces Mn. 2+ and Mn 3+ The multivalent redox couple contributes additional Faraday pseudocapacitance; secondly, Mn 3+ The Jahn-Teller effect enhances lattice polarizability and optimizes ion diffusion kinetics; furthermore, lattice contraction shortens ion migration paths and improves reaction kinetics; in addition, the high mixing entropy effect ensures the structural stability of the material during electrochemical cycling. The composite structure formed by the second phase MnCo2O4 and the main phase also combines the advantages of both electrode materials.

[0086] Example 2

[0087] In high-temperature solid-state reaction methods, sintering temperature and holding time are key factors determining the crystallinity, grain size, and even elemental distribution of the product. These microstructural characteristics directly dominate the ion conduction kinetics and electrochemical activity of the material. During the high-temperature solid-state reaction process, the sintering temperature directly affects the atomic diffusion ability and reaction driving force. Too low a temperature may lead to incomplete reaction, leaving amorphous or intermediate phase residues; while too high a temperature can easily cause abnormal grain growth, elemental segregation, or even the volatilization of some components, destroying the structural uniformity and stability of the material.

[0088] With Mg 0.1625 Co 0.1625 Ni 0.35 Cu 0.1625 Zn 0.1025 Mn 0.06 Based on high-entropy oxides, firstly, by fixing the holding time, the effects of different sintering temperatures on the material structure and electrochemical performance were systematically studied; secondly, the effects of different holding times were further explored at the optimal sintering temperature. Characterization techniques such as XRD, SEM / EDS, and XPS were used to analyze phase evolution and microstructure. Combined with cyclic voltammetry, electrochemical impedance spectroscopy, and constant current charge-discharge tests, the effects of different preparation processes on (Mg) were systematically investigated. 0.1625 Co 0.1625 Ni 0.35 Cu 0.1625 Zn 0.1025 Mn 0.06 The influence of high-entropy ceramic structure and electrochemical performance.

[0089] 2.1 Structural and electrochemical analysis of (Mg, Co, Ni, Cu, Zn, Mn)O high-entropy oxide composites at different sintering temperatures

[0090] Figure 9 The XRD patterns of (Mg, Co, Ni, Cu, Zn, Mn)O high-entropy oxides synthesized by partially substituting Zn with Mn at different sintering temperatures are shown. As can be seen from the figures, all samples exhibit a typical high-entropy rock salt structure within the sintering temperature range of 900℃ to 1200℃, accompanied by diffraction peaks of the MnCo2O4 impurity phase. This indicates that the material possesses good phase stability over a wide temperature range at this composition.

[0091] As the sintering temperature increased from 900℃ to 1200℃, the diffraction peak intensities of both the main phase rock salt structure and the second phase MnCo2O4 exhibited a non-monotonic change, first increasing and then decreasing. At 1000℃, the sample showed the strongest diffraction peak intensity and the sharpest peak shape, indicating that 1000℃ is the optimal temperature for achieving high crystallinity and synergistic coexistence of the two phases. At this temperature, the rock salt phase grains are fully developed, providing a stable main framework. When the sintering temperature continued to increase from 1000℃ to 1100℃ and 1200℃, the diffraction peak intensities of both phases decreased synchronously. This was not due to a decrease in crystallinity, but rather because thermodynamic equilibrium at high temperatures drove element rearrangement, with some MnCo2O4 phase dissolving and its constituent elements re-dissolving into the main rock salt phase. While this process may have increased the solid solubility of the main phase, it also simultaneously disrupted the highly active two-phase interface structure formed at 1000℃.

[0092] from Figure 10 The high-resolution 2p spectrum of Co shows that Co element always maintains the Co... 2+ and Co 3+ The mixed valence states of Co. It is worth noting that Co... 3+ and Co 2+ The ratio of Mn to Mn changes with temperature 3+ They exhibit a highly similar trend, both reaching their maximum value at 1000℃. At this optimal temperature of 1000℃, both simultaneously maximize the active trivalent state, providing the material with the most abundant redox couples. However, at 1200℃, Co... 3+ The decrease in the proportion is due to the partial Co at high temperatures. 3+ This is related to the reduction to maintain the overall charge balance of the system. Furthermore, the high-resolution Mn 2p spectra at all temperatures can be decomposed into three characteristic peaks, corresponding to Mn... 2+ Mn 3+ and Mn 4+ As the sintering temperature increased from 900℃ to 1200℃, the valence state distribution of Mn showed a clear and regular change. In the sample sintered at 1000℃, the valence state distribution of Mn... 3+ The relative content of Mn reaches its peak. This is partly because the temperature provides sufficient energy to drive the Mn content. 2+ Oxidized to Mn 3+ On the other hand, the stable rock salt-spinel multiphase structure formed at this optimal temperature is Mn 3+ The stable existence of Mn provides an ideal local crystal field environment. However, when the temperature is further increased to 1100-1200℃, Mn... 3+ The content actually decreased, while Mn 4+ The content increased significantly. This indicates that excessively high sintering temperatures drive Mn to transform into higher valence states, partially reactivating Mn. 3+Mn, which typically has low electrochemical activity 4+ The replacement directly led to the degradation of the capacitance performance of the high-temperature sample.

[0093] Figure 11 The figures show SEM images and corresponding EDS elemental distribution maps of the Mn6 composition at different sintering temperatures. As the sintering temperature increases from 900℃ to 1200℃, the microstructure of the material undergoes a complete evolution from "loose and porous" to "dense and integrated." At 900℃, the sample exhibits the most loose microstructure, composed of numerous fine primary particles with abundant inter-particle voids. While this structure provides the largest specific surface area and abundant ion transport channels, the poor inter-particle contact hinders rapid electron conduction, resulting in insufficient intrinsic conductivity. When the temperature rises to 1000℃, the material forms the most ideal microstructure. The particle size is moderately increased, and the morphology is more regular, maintaining sufficient porosity while establishing good contact and connection between particles. This unique structure achieves the optimal balance between specific surface area and conductivity: moderate porosity ensures sufficient electrolyte wetting and rapid ion transport, while good particle connectivity constructs an efficient electron conduction network.

[0094] At 1100℃, the densification of the material further improved, and the particle size became more uniform. However, the decrease in porosity began to hinder ion transport. When the temperature reached 1200℃, the sample exhibited obvious over-sintering characteristics, with particles fusing to form a dense blocky structure, leaving only a few isolated pores. This structure significantly reduced the specific surface area, substantially lengthened the ion transport path, and severely limited the depth and rate of the electrochemical reaction.

[0095] EDS elemental distribution analysis revealed that all elements maintained a highly uniform distribution within the temperature range of 900℃ to 1100℃, with no significant elemental segregation. This indicates that atomic diffusion was sufficient within this temperature range, resulting in a perfect solid solution structure. However, in the 1200℃ sample, a slight decrease in the signal intensity of Cu and Zn elements was observed. This may be due to the slight volatilization of volatile elements at high temperatures, leading to minor changes in the surface chemical composition.

[0096] Figure 12 The CV curves of Mn6 were measured at different sintering temperatures and a scan rate of 10 mV / s. All samples exhibited a pair of distinct redox peaks in the potential range of 0.2–0.5 V, confirming that the material retains its pseudocapacitive properties based on the redox reaction of transition metal ions at different sintering temperatures. Among them, the Mn6 sample sintered at 1000 °C showed the largest CV curve integral area and the highest response current, indicating that it possesses the best electrochemical capacity and activity.

[0097] Based on the microstructure evolution trend observed in the XRD patterns, the sample sintered at 1000℃ formed an ideal multiphase structure characterized by the coexistence of a highly crystalline rock salt main phase and a suitable amount of MnCo2O4 second phase. This structure offers two advantages: firstly, the well-developed rock salt phase provides a stable crystal framework and abundant intrinsic active sites; secondly, the uniformly distributed nano-MnCo2O4 second phase not only contributes to the capacity itself but may also have a synergistic effect with the main phase interface, optimizing electron transport and ion diffusion pathways. However, when the temperature increases to 1100℃ and 1200℃, the decrease in CV response current can be attributed to the partial dissolution of the second phase due to excessively high temperatures, as well as possible elemental volatilization and an increase in lattice defects. These factors collectively weaken the number of effective active sites and reaction kinetics of the electrode material.

[0098] Similarly, charge storage kinetics were studied on samples sintered at 1000℃. The samples were subjected to CV tests at different scan rates ranging from 10 to 100 mV / s. Figure 13 As shown, with the scan rate increasing from 10 mV / s to 100 mV / s, the current response of the redox peak significantly increased, while the peak position underwent a systematic shift. Furthermore, a good linear relationship was observed between the peak current and the scan rate, indicating that the energy storage process of this electrode is mainly controlled by surface capacitance behavior. This charge storage mechanism ensures that the material can achieve a rapid current response, thus endowing it with excellent rate performance. Even at a high scan rate of 100 mV / s, the CV curve shape maintained good stability, fully demonstrating the excellent structural stability and electrochemical reversibility of the Mn6-1000℃ electrode.

[0099] Figure 14 The GCD curves of Mn6 components measured at a current density of 1 A / g at different sintering temperatures are presented. All samples exhibit a clear charge-discharge plateau in the potential range of 0.3–0.5 V, which corresponds to the redox peaks observed in the CV test, confirming the pseudocapacitive properties of the materials. Among them, sample Mn6-1000 exhibits the longest discharge time and a specific capacitance of 527.5 F / g, significantly better than samples under other temperature conditions.

[0100] XRD analysis revealed that 1000℃ achieved the optimal match between the crystallinity of the rock salt main phase and the distribution of the second phase: the fully developed main phase provided a stable electron conduction framework, while the appropriately distributed MnCo2O4 nanoparticles enhanced reactivity through interfacial effects. Notably, SEM and EDS characterization showed that the material at this temperature exhibited the most uniform elemental distribution and optimal pore structure. This unique microstructure ensured both sufficient exposure of active sites and the construction of efficient channels for ion transport. In contrast, the 900℃ sample suffered from insufficient intrinsic conductivity due to incomplete crystallization, while samples at 1100℃ and above showed a significant reduction in effective reaction area due to excessive grain growth and elemental segregation.

[0101] To assess its potential for practical application, such as Figure 15 (a) The GCD behavior of Mn6-1000℃ at different current densities was tested. Even at a high current density of 4 A / g, its charge-discharge curves maintained high symmetry, and the plateau characteristics were clearly discernible. Calculations showed that the specific capacitance of this sample was as high as 527.5 F / g at a current density of 1 A / g, and 478.2 F / g when the current density was increased to 4 A / g. In addition, the sample achieved a capacity retention rate of 90.7% at a current density of 4 A / g, demonstrating excellent rate performance. This excellent performance stability is attributed to the synergistic effect of the multi-scale structure: at the microscale, XPS analysis confirmed the optimal Mn³⁺ / Mn 4 The ⁺ ratio effectively improves the intrinsic conductivity of the material; at the mesoscale, the uniform grain distribution and the interconnected porous structure together construct an efficient charge transport network.

[0102] like Figure 15 As shown in (b), the rate performance comparison chart clearly demonstrates that the capacity retention of Mn6-1000℃ at high current densities increased by 5.4 percentage points. This improvement is mainly attributed to the material's unique interface engineering: through a precisely controlled sintering process, uniformly distributed nanoscale second phases were constructed within the rock salt matrix. These interface regions not only provide additional active sites but also promote rapid charge transfer through local electronic structure modulation. This cross-scale structural optimization enables the material to maintain high specific capacity while also possessing excellent kinetic properties.

[0103] Figure 16Electrochemical impedance spectroscopy (EIS) spectra of Mn6 samples at different sintering temperatures are shown. All samples exhibit typical high-frequency semicircular arcs and mid-to-low-frequency oblique lines, corresponding to the charge transfer impedance (Rct) and ion diffusion impedance (Rw) at the electrode interface, respectively. Equivalent circuit fitting revealed that as the sintering temperature increased from 900℃ to 1200℃, both the solution resistance (Rs) and charge transfer impedance (Rct) of the electrode system initially decreased and then increased. The sample sintered at 1000℃ exhibited the lowest Rs and Rct values, indicating that the material possesses optimal charge transport performance under this condition. Combined with XRD results, sintering at 1000℃ promoted the formation of a fully crystalline rock salt main phase and a uniformly distributed nanoscale second phase. This ideal structural configuration effectively reduced grain boundary scattering effects, creating a continuous pathway for electron transport and minimizing electron scattering losses during transport, thus providing a crucial guarantee for obtaining excellent rate performance.

[0104] When the sintering temperature rises to 1100-1200℃, although the crystallinity of the main phase further increases, the values ​​of Rs and Rct actually increase. This is mainly due to two structural changes: firstly, XRD shows that the re-dissolution of the second phase leads to a reduction in the active interface, weakening the interfacial charge transfer efficiency; secondly, SEM observes excessive grain growth and pore structure degradation, hindering electrolyte permeation and ion transport. These structural changes together lead to an increase in electrode interfacial impedance and a decrease in reaction kinetics performance.

[0105] In summary, EIS analysis confirms from the perspective of electrode process kinetics that 1000℃ is the optimized sintering condition for achieving the best electrochemical performance of Mn6 composition. Its lowest interfacial impedance and fastest ion diffusion capability, along with the high specific capacity and excellent rate performance shown in CV and GCD tests, perfectly corroborate each other, jointly establishing the application potential of this composition material.

[0106] 1.2 Structural and electrochemical analysis of (Mg, Co, Ni, Cu, Zn, Mn)O high-entropy oxide composite materials under different heat preservation times

[0107] Figure 17 The XRD patterns of Mn6 samples after being treated at 1000℃ for different holding times are shown in the figure. As can be seen from the figure, within the holding time range of 11 to 14 h, all samples maintain a stable high-entropy rock salt main phase, accompanied by characteristic diffraction peaks of MnCo2O4, indicating that the change in holding time did not cause a fundamental change in the phase composition.

[0108] As the holding time increased, the crystallographic characteristics of the material exhibited a regular change. When the holding time reached 13 hours, the sample showed the best crystallization characteristics: the intensity of each characteristic diffraction peak of the rock salt phase reached its maximum value, and the peak shape was the sharpest, while the full width at half maximum (FWHM) narrowed significantly. This indicates that the grain development was most complete under this holding condition, and the crystal structure tended to be perfect. In addition, the diffraction peaks of the MnCo2O4 second phase also showed suitable intensity and morphology under this condition, indicating that a good structural match was achieved between the main phase and the second phase. In contrast, the diffraction peak intensity of the sample with a shorter holding time was relatively weaker, and the peak shape was slightly broadened. This may be due to insufficient atomic migration and incomplete crystal growth caused by insufficient holding time. When the holding time was extended to 14 hours, although the diffraction peak intensity remained at a high level, the intensity of each diffraction peak was weaker than that of the sample held for 13 hours. This is because excessive holding time leads to an increase in lattice defects and slight volatilization of elements, thus destroying the integrity of the crystal.

[0109] from Figure 18 The high-resolution Co 2p spectrum reveals that Co 2+ and Co 3+ The relative content of [agent] changes synchronously with the heat preservation time. In the 13h sample, Co [agent]... 3+ The proportion is relatively high, and Co 3+ and Co 2+ The ratio reaches its optimal equilibrium point, Mn 3+ The changing trend was also highly consistent with it, further confirming the synergistic effect of charge compensation between Mn and Co. This synchronicity in valence state evolution indicates that the 13-hour holding time precisely brought the system to the most favorable thermodynamic equilibrium state, achieving the optimal configuration of the valence states of the two key active elements. In the 14-hour sample, Co... 3+ The decrease in content may be related to local structural reconstruction induced by prolonged high-temperature treatment. The high-resolution Mn 2p spectra of all samples contained Mn. 2+ Mn 3+ and Mn 4+ Three characteristic components. As the holding time increased from 11 h to 14 h, the valence state distribution of Mn exhibited a non-monotonic change, first optimizing and then deteriorating. In the 13 h sample, Mn... 3+ The relative content of Mn reaches its maximum value while maintaining an appropriate level. 2+ and Mn 4+ The proportion. This optimal valence distribution indicates that 13h is the ideal time window for achieving valence equilibrium in Mn: sufficient atomic diffusion time allows Mn to achieve valence equilibrium. 2+ Fully converted into highly active Mn 3+ At the same time, it avoids excessive oxidation that generates too much Mn. 4+ When the heat preservation time is shortened to 11-12 hours, Mn 3+The content is low due to insufficient atomic migration; however, when the heat treatment time is extended to 14 hours, the excessively long heat treatment actually promotes the growth of some Mn. 3+ Further oxidation to Mn 4+ This leads to a decrease in the quality of active sites.

[0110] Figure 19 The images show SEM images and corresponding EDS elemental distribution maps of the Mn6 component after different holding times at 1000℃. As the holding time increased from 11 h to 14 h, the microstructure of the material changed significantly. In the 11 h sample, the particle size was large and unevenly distributed, with obvious agglomeration and voids. This structure led to uneven distribution of active sites and discontinuous electron conduction pathways. At 12 h, the material structure was initially optimized, with smaller and more uniform particle size and reduced agglomeration. This structural improvement provided a more uniform reaction interface and better ion transport channels for electrochemical reactions. In the 13 h sample, the material exhibited the most ideal microstructure: significantly refined and densely distributed particles with almost no agglomeration and a substantial reduction in voids. This structure, formed by the dense packing of numerous fine particles, has the largest specific surface area, providing abundant electrochemical active sites. Secondly, good interparticle contact ensures efficient electron conduction. Finally, the excellent pore structure promotes rapid electrolyte wetting and ion transport. However, when the holding time was extended to 14 hours, the material exhibited significant structural degradation, with particles agglomerating into large aggregates, leaving only voids between the aggregates. This structural transformation severely reduced the effective specific surface area, hindered ion transport, and directly led to a decline in electrochemical performance.

[0111] EDS elemental distribution analysis revealed that the uniform elemental distribution in the 13-hour sample complemented the optimal microstructure. From the perspective of crystal growth kinetics, the holding time influences the final microstructure of the material by controlling the degree of atomic diffusion and grain boundary migration. The 13-hour holding time precisely achieved the optimal balance between these two key processes.

[0112] Figure 20 The CV curves of Mn6 samples after different holding times at 1000℃ are shown. It can be clearly observed that as the holding time increases from 11 h to 13 h, the area enclosed by the CV curve and the current response of the redox peak significantly increase. The 13-h sample exhibits the largest integrated area and the highest peak current, indicating that it possesses the best pseudocapacitance and electrochemical activity. However, when the holding time is further extended to 14 h, both the current response and the curve area show a significant decrease.

[0113] The evolution trend of this performance closely matches the structural changes revealed by XRD. When the holding time is insufficient, atomic migration is inadequate, leading to incomplete crystal development and low crystallinity, which limits the number of active sites and intrinsic conductivity. A holding time of 13 hours is the key node for achieving crystal structure integrity and optimal distribution of the active phase. The highly crystalline rock salt main phase provides a stable conductive framework, while the uniformly distributed nano-MnCo2O4 second phase contributes abundant active interfaces, jointly promoting efficient redox reactions. However, when the holding time is too long, the performance degrades. This is mainly due to two aspects of structural degradation: first, the weakening of diffraction peaks in XRD suggests that the concentration of lattice defects increases due to excessive heat treatment, destroying the long-range order of the crystal; second, the trace volatilization of elements such as Cu and Zn and the coarsening of the MnCo2O4 phase lead to a reduction in active interfaces and obstruction of ion transport paths, thereby reducing the number of effective reaction sites and charge transfer kinetics.

[0114] Figure 21 The CV curves of Mn6 after 13 hours of heat treatment at different scan rates are shown. With increasing scan rate, the redox peak current significantly increases, and the peak position shift is small, indicating excellent reaction reversibility. Quantitative analysis revealed a good linear relationship between the peak current and the scan rate, confirming that its energy storage process is mainly controlled by rapid surface capacitance behavior. This kinetic advantage is attributed to the ideal microstructure formed during the 13-hour heat treatment.

[0115] Figure 22 The GCD curves of Mn6 components sintered at 1000℃ for different holding times are shown. In-depth analysis of these curves reveals that the holding time significantly affects the electrochemical performance of the material. The sample held for 13 hours exhibits the best overall performance, and its charge-discharge curve shows the flattest and most symmetrical voltage plateau in the 0.3-0.5V potential range. This indicates that the material achieves optimal charge storage capacity and reaction reversibility under these conditions.

[0116] Analysis of the material's microstructure revealed a systematic increase in discharge capacity as the holding time increased from 11 hours to 13 hours, primarily attributed to the continuous refinement of the crystal structure. XRD analysis showed that the 13-hour holding time enabled the material to reach an ideal balance between crystallinity and phase distribution: the rock salt main phase fully developed, forming a complete crystal framework and providing an efficient pathway for electron transport; simultaneously, the MnCo2O4 second phase was embedded at the grain boundaries of the main phase with optimal size and spatial distribution, constructing abundant active interfaces. This meticulously designed multiphase structure not only ensured a stable electron conduction network but also provided ample active sites for redox reactions, thereby significantly enhancing the overall electrochemical performance of the material.

[0117] Therefore, the short holding time results in incomplete crystal development due to insufficient atomic migration, leading to numerous grain boundaries and structural defects within the sample. While these defects increase the specific surface area to some extent, they also act as obstacles to charge transport, reducing the intrinsic conductivity of the material and consequently affecting its capacitance characteristics. Notably, this structural imperfection also exacerbates polarization during charging and discharging.

[0118] When the holding time is extended to 14 hours, the material properties show a significant decline, a phenomenon that closely matches the decreasing trend of diffraction peak intensity observed in XRD. Excessive holding time can also lead to the selective volatilization of volatile elements such as Cu and Zn, as well as the local segregation of elements such as Mn and Co, resulting in non-uniformity of the material's chemical composition and thus affecting its electrochemical stability.

[0119] Finally, GCD tests were also performed on Mn6-13h at different current densities, such as... Figure 23 As shown in (a), this sample exhibits excellent rate performance; even under high rate conditions of 1-4 A / g, its GCD curve maintains good symmetry and a clear voltage plateau characteristic. Quantitative calculations show that the specific capacitance of this sample is further improved at a current density of 1 A / g, reaching 582.5 F / g. Even when the current density increases to 4 A / g, its specific capacitance still reaches 555.9 F / g. Calculations show that the capacitance retention rate of this sample at a current density of 4 A / g is as high as 95.4%. Figure 23 As shown in (b), this superior performance significantly outperforms any other control group sample. This outstanding rate capability is primarily due to the rich interface formed between the main and second phases during the 13-hour heat treatment. Simultaneously, the synergistic effect of the Jahn-Teller effect between Mn and Co enables ultrafast ion transport. This provides numerous rapid pathways for ion migration, allowing ions and electrons to simultaneously and rapidly reach all active interfaces during high-rate charge and discharge, ensuring the full and rapid progress of redox reactions.

[0120] Figure 24 Electrochemical impedance spectroscopy (EIS) spectra of Mn6 fractions after different holding times at 1000℃ are presented. Equivalent circuit fitting analysis revealed a regular influence of holding time on the kinetic parameters of the electrode process. The sample held for 13 h exhibited the lowest charge transfer impedance (Rct) and the lowest solution resistance (Rs), indicating that the material possesses the best charge transport performance under these conditions.

[0121] As the holding time increased from 11 h to 13 h, the Rct and Rs values ​​of the electrode system showed a systematic decreasing trend. This is because the high orderliness of the rock salt main phase significantly improved the intrinsic conductivity of the material, while the uniformly distributed MnCo2O4 second phase formed abundant active interfaces with the main phase. These structural features together promoted the rapid transfer of interfacial charges, significantly reducing the energy barrier of the electrode reaction.

[0122] Of particular note is the fact that the 13-hour sample exhibited the lowest Warburg impedance in the low-to-mid-frequency region, indicating optimal bulk ion diffusion capability. This characteristic is consistent with the ideal channel structure observed by SEM and the uniform elemental distribution shown by EDS. The appropriate holding time enabled the material to form continuous, interconnected ion transport channels.

[0123] When the holding time was extended to 14 hours, although the crystallinity of the main phase remained at a high level, the Rct value showed a significant rebound. This indicates that the microstructural changes caused by excessive holding time have begun to have a negative impact on charge transport. Specifically, the excessively long holding time disrupts the integrity of the crystal and increases the scattering centers for electron transport; secondly, local segregation of elements and coarsening of the second phase reduce the efficiency of the active interface. These factors together lead to an increase in the electrode interface impedance.

[0124] By analyzing the effects of different sintering temperatures and holding times on (Mg) 0.1625 Co 0.1625 The influence of Ni0.35, Cu0.1625, Zn0.1025, Mn0.06)O high-entropy oxide materials on their structure and electrochemical performance was investigated, leading to the following conclusions:

[0125] (1) Within the range of 900-1200℃, the material always maintains the stable coexistence of the rock salt main phase and the MnCo2O4 second phase. Among them, the sample sintered at 1000℃ shows the best multiphase structure, with complete crystallization of the main phase and uniform distribution of the second phase, forming an ideal highly active interface structure. Excessive temperature will lead to the re-dissolution of the second phase and the volatilization of elements, which will destroy the optimized interface structure.

[0126] (2) Studies at different sintering temperatures revealed that electrochemical tests showed that the sample sintered at 1000℃ exhibited the best overall performance. This is attributed to the unique microstructure formed at this temperature: a complete crystal framework ensures rapid electron conduction, a uniformly distributed nano-second phase provides abundant active interfaces, and a suitable pore structure creates efficient channels for ion transport. Its specific capacitance at a current density of 1 A / g can reach 527.5 F / g, and its capacity retention reaches 90.7% at a high current density of 4 A / g.

[0127] (3) Studies on different holding times revealed that 13 hours is the key parameter for achieving the best material performance. Under this condition, the material achieves the optimal balance between crystallinity and defect concentration: the rock salt main phase is fully developed, providing a stable framework, and the MnCo2O4 second phase constructs an efficient charge transport network with the most suitable size and distribution. Too short a holding time leads to incomplete crystallization, while too long a holding time will induce lattice defect proliferation and elemental segregation. Its specific capacitance at a current density of 1 A / g can reach 582.5 F / g, and the capacity retention rate reaches 95.4% at a high current density of 4 A / g.

[0128] (4) Through systematic process optimization, it was determined that sintering at 1000℃ combined with 13h heat preservation is the optimal preparation process for the high-entropy oxide of this system. The sample obtained under this condition showed the best comprehensive performance in terms of specific capacity, rate performance and cycle stability, demonstrating broad application prospects.

[0129] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-entropy oxide of MgCoNiCuZn substituted with manganese ions, characterized in that, It is Mg （1-x） / 4 Co （1-x） / 4 Ni x Cu （1-x） / 4Zn （1-x） / 4-z Mn z O high-entropy oxides or Mg （1-y） / 4 Co （1-y） / 4 Ni y Cu （1-y） / 4 Zn （1-y） / 4-z Mn z For high-entropy oxides, the values ​​of x range from 0.15 to 0.35, y range from 0.15 to 0.35, and z range from 0.02 to 0.

08.

2. The manganese ion-substituted MgCoNiCuZn high-entropy oxide according to claim 1, characterized in that, The manganese ion-substituted MgCoNiCuZn high-entropy oxide is Mg 0.1625 Co 0.1625 Ni 0.35 Cu 0.1625 Zn 0.1625-z Mn z O high-entropy oxides, with z ranging from 0.02 to 0.

08.

3. The method for preparing manganese ion-substituted MgCoNiCuZn high-entropy oxides according to claim 1 or 2, characterized in that, Includes the following steps: (1) MgO, CoO, NiO, CuO, ZnO and MnO powders were mixed in a planetary ball mill according to the stoichiometric ratio. Anhydrous ethanol was added to the mixed powder as the grinding medium. After ball milling and mixing, the mixture was vacuum dried to obtain the mixed material. (2) The mixture is placed in an agate mortar and ground thoroughly. The ground material is spread evenly in an alumina crucible and placed in a high-temperature tube furnace in batches. The temperature is slowly raised to 1000-1200℃ in an air atmosphere, kept at the temperature for 10-14h, and then slowly lowered to 400-600℃. The material is then cooled to room temperature with the furnace to obtain the final product.

4. The method for preparing manganese ion-substituted MgCoNiCuZn high-entropy oxides according to claim 3, characterized in that, In step (1), the ball milling speed is 410 r / min, the ball milling time is 4 h, and the vacuum drying time is 12 h.

5. The method for preparing manganese ion-substituted MgCoNiCuZn high-entropy oxides according to claim 3, characterized in that, In step (2), the high-temperature tubular furnace is first heated to 1100°C at a heating rate of 5°C / min in an air atmosphere, then kept at that temperature for 12 hours, and then cooled to 500°C at a rate of 2°C / min, and then cooled to room temperature along with the furnace.

6. The application of the manganese ion-substituted MgCoNiCuZn high-entropy oxide as described in claim 1 or 2 in the preparation of supercapacitors and electrodes.

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