Lithium-rich manganese-based positive electrode material modified by sodium vanadium oxide and preparation method of lithium-rich manganese-based positive electrode material
By constructing a Na4V2O7 heterostructure interface layer and engineering oxygen vacancy defects on the surface of lithium-rich manganese-based cathode materials, the problems of low first-cycle coulombic efficiency, rapid capacity decay, insufficient rate performance, and severe voltage decay in existing technologies have been solved, achieving a comprehensive improvement in high specific capacity, high first-cycle efficiency, long cycle life, and high rate performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-21
- Publication Date
- 2026-04-10
AI Technical Summary
Existing lithium-rich manganese-based cathode materials suffer from problems such as low first-cycle coulombic efficiency, rapid cycle capacity decay, insufficient rate performance, and severe voltage decay. Existing modification strategies are insufficient to achieve a comprehensive improvement in high specific capacity, high first-cycle efficiency, long cycle life, high rate performance, and low voltage decay.
By constructing a Na4V2O7 heterostructure interface layer and engineering surface oxygen vacancy defects on the surface of lithium-rich manganese-based cathode material, a three-dimensional lithium-ion transport channel is formed, which inhibits the irreversibility of oxygen ion redox reaction and stabilizes the material structure by inducing oxygen vacancy generation through Li+/Na+ exchange.
It significantly improves the first-cycle coulomb efficiency, cycle stability, rate performance and voltage decay. The first-cycle coulomb efficiency is improved by 24.2%, the capacity retention rate after 100 cycles at 1C is improved to 95.6%, the specific capacity at 5C rate is improved by 40.6%, the voltage decay rate is reduced by 52.3%, and the initial discharge specific capacity is improved by 26.4%.
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Figure CN121839656A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium-ion battery cathode materials technology, and in particular to a lithium-rich manganese-based cathode material modified with sodium vanadium oxide and its preparation method. Background Technology
[0002] With the rapid development of the new energy industry, lithium-ion batteries, as core energy storage devices, have seen their energy density, cycle life, and rate performance become key factors restricting industrial upgrading. Lithium-rich manganese-based cathode materials (LMO) possess energy densities exceeding 250 mAh·g⁻¹. -1 The theoretical specific capacity (the specific capacity of traditional ternary materials is usually below 200 mAh·g) -1 With its advantages of low cost, it is considered a core candidate material for next-generation high-energy-density lithium-ion batteries. Its high capacity is essentially due to the reversible redox reaction of oxygen ions (O₂O₃O₄O₅). 2- →O2 n- ), breaking through the traditional transition metal ion (such as Ni) 2+ / Ni 3+ / Ni 4+ Co 3+ / Co 4+ Redox capacity limitations.
[0003] However, existing lithium-rich manganese-based cathode materials have the following technical problems in practical applications:
[0004] (1) Low first-cycle coulombic efficiency: During the first charge, the lattice oxygen on the surface of the material is easily irreversibly oxidized and escapes in the form of O2. At the same time, the electrolyte decomposes, resulting in a large number of lithium ions being "consumed". The first-cycle coulombic efficiency is usually less than 70%, which seriously affects the energy output of the battery.
[0005] (2) Rapid capacity decay during long-term charge and discharge: During long-term charge and discharge, the oxygen framework structure collapses due to the escape of lattice oxygen, and the material crystal structure transforms from layered to spinel phase or even rock salt phase, resulting in continuous capacity decay. After 100 cycles at 1C, the capacity retention rate is usually less than 76%.
[0006] (3) Insufficient rate performance: The lithium-ion diffusion coefficient in the layered structure of lithium-rich manganese-based materials is low (approximately 10). -14 -10 -12 cm 2 Furthermore, traditional surface modifications (such as Al2O3 coating) further increase lithium-ion transport resistance, resulting in a discharge specific capacity typically below 110 mAh·g at high rates (such as 5C). -1 This cannot meet the requirements of high-power scenarios;
[0007] (4) Severe voltage decay: During charging and discharging, transition metal ions (especially Mn) 3+ It is prone to dissolution and migration from the transition metal layer to the adjacent lithium layer. The irreversible structural changes cause the charge and discharge plateau to continuously decline, and the voltage decay rate is usually higher than 6 mV / cycle, which greatly reduces the actual operating voltage and energy density of the battery.
[0008] To address the above problems, existing technologies have proposed several modification strategies:
[0009] Element doping: The crystal structure is stabilized by introducing heterogeneous ions such as Al, Mg, and Ti, but the doped ions will occupy lithium ion sites, resulting in a sacrifice in specific capacity (usually reduced by 10%-15%).
[0010] Traditional surface coating: Inorganic materials such as Al2O3, TiO2, and Li3PO4 are used for coating, which can suppress interfacial side reactions, but the coating layer has no lithium-ion transport capability, which will deteriorate the rate performance.
[0011] Oxygen vacancy engineering: Introducing oxygen vacancies through high-temperature reduction, surface acid treatment, etc., can reduce the oxidation activity of oxygen ions. However, individual oxygen vacancies are easy to disappear in the cycle and have insufficient stability.
[0012] Multi-component interface modification: such as the "oxygen vacancy-assisted bifunctional surface coating" strategy proposed by Jiang Qinting et al. (2024) of Xi'an University of Technology. This strategy generates Li3PO4 coating and oxygen vacancies through the decomposition of NH4H2PO4. Although it improves cycle stability, it does not reveal the specific mechanism of oxygen vacancies on the reversibility of oxygen redox reaction and structural transformation, and fails to provide an effective lithium-ion transport channel. The lithium-ion transport efficiency of Li3PO4 coating is low, and the improvement of rate performance and long-term cycle stability is limited.
[0013] In summary, existing modification strategies struggle to simultaneously achieve the combined requirements of "high specific capacity, high first-cycle efficiency, long cycle life, high rate performance, and low voltage decay." The core reason lies in the lack of a synergistic system encompassing "efficient lithium-ion transport channels, stable interface structure, and reversible oxygen redox." Therefore, developing a modification method that can simultaneously optimize these properties is of great significance for promoting the industrial application of lithium-rich manganese-based materials. Summary of the Invention
[0014] To overcome the shortcomings of existing technologies, this invention provides a sodium vanadium oxide-modified lithium-rich manganese-based cathode material and its preparation method. Through a synergistic modification strategy of constructing a Na4V2O7 heterointerface layer and engineering surface oxygen vacancy defects, the oxygen redox reversibility and material structural transformation reversibility of LMO are improved. The Na4V2O7 heterointerface is Li... +Diffusion provides a VO4 tetrahedral three-dimensional ion transport network, constructing a more stable cathode-electrolyte interface and suppressing side reactions during cycling. Simultaneously, using Na4V2O7 as a conversion agent achieves Li… + / Na + Exchange induces the generation of surface oxygen vacancies. The additional oxygen vacancies reduce the redox activity of oxygen ions during the first charge and discharge process, inhibit the irreversible escape of lattice oxygen, and improve the reversibility of oxygen ion redox reactions and the stability of the oxygen framework structure.
[0015] The technical solution adopted by this invention to solve its technical problem is:
[0016] The present invention first provides a lithium-rich manganese-based cathode material modified with sodium vanadium oxide, comprising a lithium-rich manganese-based matrix and a Na4V2O7 heterostructure interface layer coated on the surface of the matrix; the Na4V2O7 has a VO4 tetrahedral structure, forming a three-dimensional lithium-ion transport channel; the surface of the matrix is rich in oxygen vacancies.
[0017] Preferably, the lithium-rich manganese matrix is Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2.
[0018] This invention also provides a method for preparing a lithium-rich manganese-based cathode material modified with sodium vanadium oxide, comprising the following steps:
[0019] Synthesis of S1 lithium-rich manganese-based matrix;
[0020] Surface modification treatment of S2 lithium-rich manganese-based substrate includes:
[0021] S2.1 A certain amount of Na4V2O7 is dispersed in 10-20 ml of anhydrous ethanol to form a dispersion;
[0022] S2.2 Add a certain amount of lithium-rich manganese-based matrix powder to the dispersion and stir at 450-550 rpm / min for 1.5-2.5 h at room temperature to make the lithium-rich manganese-based matrix powder and Na4V2O7 evenly mixed to obtain a mixed system.
[0023] S2.2 The mixture is transferred to an oil bath at 75-85℃ and stirred at 250-350 rpm / min to evaporate and remove the solvent. Then it is transferred to a vacuum drying oven at 105-115℃ and dried for 1-3 hours to obtain the mixed powder.
[0024] S2.3 Grind the mixed powder for 25-35 min, place it in a tube furnace under argon inert atmosphere protection, anneal at 450-550℃ for 1.5-2.5 h, and after cooling, obtain the sodium vanadium oxide modified lithium-rich manganese-based cathode material.
[0025] Preferably, in step S1, the lithium-rich manganese-based matrix Li is synthesized using the sol-gel method. 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2.
[0026] Preferably, step S1 is specifically operated as follows: lithium acetate dihydrate, manganese acetate tetrahydrate, nickel acetate tetrahydrate, and cobalt acetate tetrahydrate are dissolved in deionized water in a molar ratio of 1.2:0.54:0.13:0.13, and ultrasonically stirred to obtain a mixed solution; a certain amount of citric acid is added, and the mixture is stirred in an oil bath at 80-100℃, and then heated to 100-120℃ to evaporate water and form a gel; the gel is vacuum dried at 170-190℃ for 8-12 h, ground, and then pre-calcined at 450-550℃ for 4-6 h and calcined at 850-950℃ for 10-14 h, and naturally cooled to obtain lithium-rich manganese-based matrix powder, denoted as P-LMO.
[0027] Preferably, the molar ratio of citric acid to total metal cations is 2:1.
[0028] Preferably, the mass fraction of Na4V2O7 in the dispersion of step S2.1 is 1~2%.
[0029] Preferably, step S2.1 further includes the step of ultrasonically treating the dispersion at an ultrasonic frequency of 38-42 kHz for 20-40 min.
[0030] Preferably, in step S2.2, the mass ratio of lithium-rich manganese-based matrix powder to Na4V2O7 is 100:1.0-2.0.
[0031] The present invention also provides a lithium-ion battery, wherein the positive electrode is a lithium-rich manganese-based positive electrode material modified with the aforementioned sodium vanadium oxide.
[0032] The core innovation of this invention lies in the synergistic effect of the "Na4V2O7 heterogeneous interface" and the "oxygen vacancy", the specific mechanism of which is as follows:
[0033] 1. The role of oxygen vacancies:
[0034] 1.1 Reducing the oxidation activity of oxygen ions: Oxygen vacancies act as electron traps, capturing the valence electrons of oxygen ions and inhibiting the oxidation of oxygen ions. 2- Towards Excessive oxidation reduces irreversible escape of lattice oxygen;
[0035] 1.2 Stable oxygen framework structure: Oxygen vacancies can alleviate the volume expansion of the lattice during charging and discharging, and prevent the collapse of the layered structure;
[0036] 1.3 Inhibition of the Jahn-Teller effect: Oxygen vacancy-induced bulk Mn 3+ To Mn 4+ Transformation (Mn) 3+ It can easily induce Jahn-Teller distortion, leading to structural distortion, and reduce Mn. 3+ content.
[0037] 2. The role of the Na4V2O7 heterointerface:
[0038] 2.1 Constructing a three-dimensional lithium-ion channel: The gap size of the VO4 tetrahedron matches the radius of the lithium ion, providing an additional fast transport path for lithium ions and improving rate performance;
[0039] 2.2 Stabilizing the positive electrode-electrolyte interface: The Na4V2O7 layer can block PF6 in the electrolyte. - Corrosive species such as HF come into contact with the matrix, inhibiting the dissolution of transition metal ions;
[0040] 2.3 Anchoring oxygen vacancies: V in Na4V2O7 5+ It can form stable VOV bonds with oxygen vacancies, preventing oxygen vacancies from being reconstructed during cycling and improving stability.
[0041] 3. Synergistic effect: Oxygen vacancies inhibit the escape of lattice oxygen, providing a stable substrate for the heterostructure interface layer; the heterostructure interface layer provides a channel for lithium-ion transport and anchors oxygen vacancies, forming a virtuous cycle of "stable structure-efficient transport", which simultaneously optimizes multiple electrochemical properties of the material.
[0042] Compared with the prior art, the present invention has the following positive technical effects:
[0043] 1. The first-cycle coulombic efficiency was significantly improved: from 67.8% (unmodified P-LMO) to 84.2% (N-LMO-1.5wt%), an increase of 24.2%. This is because oxygen vacancies inhibit the escape of lattice oxygen and reduce lithium-ion loss.
[0044] 2. Significantly improved cycling stability: After 100 cycles at 1C, the capacity retention rate increased from 75.4% to 95.6%, which is much higher than existing technologies (such as 88.7% for Li3PO4 coating), thanks to the suppression of structural phase transition by the heterogeneous interface and oxygen vacancies;
[0045] 3. Breakthrough in rate performance: 5C rate discharge specific capacity increased from 105.8 mAh・g -1 Increased to 148.7 mAh・g-1 The efficiency of lithium-ion transport is improved by 40.6%; the VO4 tetrahedral three-dimensional channel significantly improves lithium-ion transport efficiency.
[0046] 4. Effective mitigation of voltage decay: The decay rate was reduced from 6.50mV / cycle to 3.10mV / cycle, a reduction of 52.3%, the dissolution of transition metal ions was inhibited, and the irreversible structural degradation was slowed down;
[0047] 5. Significantly improved initial discharge specific capacity: from 261.2 mAh·g -1 Increased to 287.6mAh·g -1 ;
[0048] 6. Simple and controllable preparation process: The sol-gel method and wet chemical method are adopted, which do not require special equipment (such as plasma generators and high-pressure reactors). The reaction conditions are mild (annealing temperature ≤550℃), which is suitable for industrial mass production.
[0049] 7. The lithium-ion diffusion coefficient is significantly improved, and the interfacial charge transfer resistance is reduced.
[0050] In summary, this invention effectively suppresses side reactions and improves the reversibility of oxygen oxidation-reduction and structural stability through the synergistic effect of the Na4V2O7 heterostructure and oxygen vacancies. Attached Figure Description
[0051] Figure 1 It is a topological chemical ion exchange (Li + / Na + The mechanism of induced surface oxygen vacancy generation;
[0052] Figure 2 A schematic diagram showing the structure of Na4V2O7 and its formation of a multi-component heterogeneous interface by binding with oxygen vacancies on the LMO surface;
[0053] Figure 3 These are SEM images of P-LMO and samples modified at various ratios, where Figures a, b, c, and d are SEM images of P-LMO, N-LMO-1.0wt%, N-LMO-1.5wt%, and N-LMO-2.0wt% samples at the 100 nm scale, respectively.
[0054] Figure 4 XPS spectra of the O 1s orbitals for P-LMO and N-LMO-1.5 wt% samples;
[0055] Figure 5 EPR test results for P-LMO and N-LMO-1.5 wt% samples;
[0056] Figure 6The first charge-discharge curves of P-LMO and its modified samples at various ratios are shown at 0.1 C.
[0057] Figure 7 Voltage decay curves of P-LMO and its modified samples at various ratios after 100 cycles at 1 C;
[0058] Figure 8 The rate performance graphs are for P-LMO and the modified samples at various ratios.
[0059] Figure 9 The graph shows the 100-cycle cycle of P-LMO and the modified samples at various ratios at 1 C. Detailed Implementation
[0060] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
[0061] Example 1
[0062] Example 1 of this invention provides a lithium-rich manganese-based cathode material modified with sodium vanadium oxide, comprising lithium-rich manganese-based matrix particles Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2 and a heterogeneous interface layer coating the surface of the matrix particles; the heterogeneous interface layer contains a Na4V2O7 phase crystal layer, the Na4V2O7 phase has a VO4 tetrahedral structure, forming a three-dimensional lithium-ion transport channel; the surface of the matrix particles is rich in oxygen vacancies. This invention constructs a multi-component heterogeneous interface structure on the surface of lithium-rich manganese-based cathode material particles, consisting of a Na4V2O7 heterogeneous interface layer and an oxygen-vacancy-rich matrix surface layer, with the oxygen vacancy concentration on the matrix surface layer significantly higher than that in the bulk phase of the material.
[0063] Reference Figure 1 and Figure 2 The preferred embodiment of the present invention also provides a method for preparing a lithium-rich manganese-based cathode material modified with sodium vanadium oxide. The advantage of this method is that the raw materials are mixed uniformly and the product particle size can be controlled, which can avoid the component segregation caused by the traditional solid-state method. The method includes the following steps:
[0064] Synthesis of S1 lithium-rich manganese-based matrix, namely, synthesis of lithium-rich manganese-based matrix Li using sol-gel method. 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2, the specific operation is as follows:
[0065] Lithium acetate dihydrate, manganese acetate tetrahydrate, nickel acetate tetrahydrate, and cobalt acetate tetrahydrate were dissolved in deionized water in a molar ratio of 1.2:0.54:0.13:0.13 and ultrasonically stirred to obtain a mixed solution.
[0066] Adding a certain amount of citric acid (the molar ratio of citric acid to total metal cations is 2:1) allows the carboxyl group (-COOH) of citric acid to form a stable chelate with the metal ions, ensuring that the metal ions are evenly distributed during subsequent calcination.
[0067] The mixture is stirred in an oil bath at 80-100℃, and then heated to 100-120℃ to evaporate the water and form a gel. The gel is then vacuum dried at 170-190℃ for 8-12 h, ground, and then pre-calcined at 450-550℃ for 4-6 h and calcined at 850-950℃ for 10-14 h. After natural cooling, lithium-rich manganese-based matrix powder is obtained.
[0068] Surface modification treatment of S2 lithium-rich manganese-based substrate includes:
[0069] S2.1 A certain amount of Na4V2O7 is dispersed in 10-20 ml of anhydrous ethanol to form a dispersion, wherein the mass fraction of Na4V2O7 in the dispersion is 1-2%; the dispersion is ultrasonically treated at an ultrasonic frequency of 38-42 kHz for 20-40 min.
[0070] S2.2 A certain amount of lithium-rich manganese-based matrix powder was added to the dispersion (the mass ratio of lithium-rich manganese-based matrix powder to Na4V2O7 was 100:1.0-2.0), and stirred at 450-550 rpm / min for 1.5-2.5 h at room temperature to make the lithium-rich manganese-based matrix powder and Na4V2O7 evenly mixed (Na4V2O7 was ultrasonically dispersed in ethanol to form nano-sized particles, and then adsorbed onto the P-LMO surface by van der Waals forces to ensure the uniformity of subsequent coating), and a mixed system was obtained;
[0071] S2.2 The mixture is transferred to an oil bath at 75-85℃ and stirred at 250-350 rpm / min to evaporate and remove the solvent. Then it is transferred to a vacuum drying oven at 105-115℃ and dried for 1-3 hours to obtain the mixed powder.
[0072] S2.3 Grind the mixed powder for 25-35 min, place it in a tube furnace under an argon inert atmosphere, and anneal at 450-550℃ for 1.5-2.5 h to coat the LMO surface with Na4V2O7, and to induce partial decomposition of Na4V2O7 to initiate Li + / Na + Topological chemical ion exchange is used to induce the generation of oxygen vacancies in situ, and after cooling, the lithium-rich manganese-based cathode material modified with sodium vanadium oxide is obtained.
[0073] Topological chemical ion exchange (Li + / Na + The mechanism of induced surface oxygen vacancy generation is as follows: Figure 1As shown, P2 type sodium manganese oxide undergoes ion exchange, Na + By Li + Substitution occurs, forming O2-type lithium manganese oxide (O2-LMO). During this process, the MnO2 layer slips, leading to structural rearrangement and the formation of a metastable O2 phase. O2-LMO undergoes thermal decomposition during heating (>400°C), accompanied by the release of oxygen. The released O2 originates from the oxidation of lattice oxygen, i.e.:
[0074] (Oxygen vacancy).
[0075] Figure 2 This invention illustrates the structure of Na4V2O7 and its formation of a multi-component heterogeneous interface on an LMO surface through binding with oxygen vacancies. The invention utilizes a simple wet chemical method to construct Na4V2O7 on an LMO surface, followed by a subsequent annealing modification process to obtain a Na4V2O7-modified lithium-rich manganese-based cathode material. Specifically, the preparation method described in this invention provides the following preferred embodiments:
[0076] Example 2
[0077] This embodiment 2 provides a lithium-rich manganese-based cathode material Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2 was synthesized using the sol-gel method, the specific steps of which are as follows:
[0078] Lithium acetate dihydrate, manganese acetate tetrahydrate, nickel acetate tetrahydrate, and cobalt acetate tetrahydrate were dissolved in deionized water in a molar ratio of 1.2:0.54:0.13:0.13 and ultrasonically stirred to obtain a mixed solution. A certain amount of citric acid (the molar ratio of citric acid to total metal cations was 2:1) was added. The mixture was stirred in an oil bath at 90°C, and then heated to 110°C to evaporate the water and form a gel. The gel was vacuum dried at 180°C for 10 h, ground, and then pre-calcined at 500°C for 5 h and calcined at 900°C for 12 h. After natural cooling, a lithium-rich manganese-based matrix powder was obtained, denoted as P-LMO.
[0079] Example 3
[0080] This embodiment 3 provides a method for preparing a lithium-rich manganese-based cathode material modified with sodium vanadium oxide, including a lithium-rich manganese-based matrix Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 The surface modification treatment with O2 is performed as follows:
[0081] S2.1 A certain amount of Na4V2O7 was dispersed in 15 ml of anhydrous ethanol to form a dispersion, the mass fraction of Na4V2O7 in the dispersion was 1%; the dispersion was ultrasonically treated at a frequency of 40 kHz for 30 min.
[0082] S2.2 A certain amount of lithium-rich manganese-based matrix powder was added to the dispersion (the mass ratio of lithium-rich manganese-based matrix powder to Na4V2O7 was 100:1.0), and stirred at 500 rpm / min for 2 hours at room temperature to make the lithium-rich manganese-based matrix powder and Na4V2O7 evenly mixed to obtain a mixed system.
[0083] S2.2 The mixture was transferred to an 80°C oil bath and stirred at 300 rpm / min to evaporate and remove the solvent. Then it was transferred to a 110°C vacuum drying oven and dried for 2 hours to obtain the mixed powder.
[0084] S2.3 The mixed powder was ground for 30 min and placed in a tube furnace under an argon inert atmosphere for annealing at 500 °C for 2 h, so that Na4V2O7 coated the LMO surface, and the partial decomposition of Na4V2O7 initiated Li + / Na + Topological chemical ion exchange is used to induce the generation of oxygen vacancies in situ. After cooling, the lithium-rich manganese-based cathode material modified with sodium vanadium oxide is obtained, denoted as N-LMO-1wt%.
[0085] Example 4
[0086] Example 4 provides a method for preparing a lithium-rich manganese-based cathode material modified with sodium vanadium oxide, including a lithium-rich manganese-based matrix Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 The surface modification treatment with O2 is performed as follows:
[0087] S2.1 A certain amount of Na4V2O7 was dispersed in 15 ml of anhydrous ethanol to form a dispersion, the mass fraction of Na4V2O7 in the dispersion was 1.5%; the dispersion was ultrasonically treated at a frequency of 40 kHz for 30 min.
[0088] S2.2 A certain amount of lithium-rich manganese-based matrix powder was added to the dispersion (the mass ratio of lithium-rich manganese-based matrix powder to Na4V2O7 was 100:1.5), and stirred at 500 rpm / min for 2 hours at room temperature to make the lithium-rich manganese-based matrix powder and Na4V2O7 evenly mixed to obtain a mixed system.
[0089] S2.2 The mixture was transferred to an 80°C oil bath and stirred at 300 rpm / min to evaporate and remove the solvent. Then it was transferred to a 110°C vacuum drying oven and dried for 2 hours to obtain the mixed powder.
[0090] S2.3 The mixed powder was ground for 30 min and placed in a tube furnace under an argon inert atmosphere for annealing at 500 °C for 2 h, so that Na4V2O7 coated the LMO surface, and the partial decomposition of Na4V2O7 initiated Li + / Na + Topological chemical ion exchange is used to induce the generation of oxygen vacancies in situ. After cooling, the lithium-rich manganese-based cathode material modified with sodium vanadium oxide is obtained, denoted as N-LMO-1.5wt%.
[0091] Example 5
[0092] Example 5 provides a method for preparing a lithium-rich manganese-based cathode material modified with sodium vanadium oxide, including a lithium-rich manganese-based matrix Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 The surface modification treatment with O2 is performed as follows:
[0093] S2.1 A certain amount of Na4V2O7 was dispersed in 15 ml of anhydrous ethanol to form a dispersion, the mass fraction of Na4V2O7 in the dispersion was 2%; the dispersion was ultrasonically treated at a frequency of 40 kHz for 30 min.
[0094] S2.2 A certain amount of lithium-rich manganese-based matrix powder was added to the dispersion (the mass ratio of lithium-rich manganese-based matrix powder to Na4V2O7 was 100:2), and stirred at 500 rpm / min for 2 hours at room temperature to make the lithium-rich manganese-based matrix powder and Na4V2O7 evenly mixed to obtain a mixed system.
[0095] S2.2 The mixture was transferred to an 80°C oil bath and stirred at 300 rpm / min to evaporate and remove the solvent. Then it was transferred to a 110°C vacuum drying oven and dried for 2 hours to obtain the mixed powder.
[0096] S2.3 The mixed powder was ground for 30 min and placed in a tube furnace under an argon inert atmosphere for annealing at 500 °C for 2 h, so that Na4V2O7 coated the LMO surface, and the partial decomposition of Na4V2O7 initiated Li + / Na + Topological chemical ion exchange is used to induce the generation of oxygen vacancies in situ. After cooling, the lithium-rich manganese-based cathode material modified with sodium vanadium oxide is obtained, denoted as N-LMO-2wt%.
[0097] Figure 3a, b, c, and d are SEM images of P-LMO, N-LMO-1.0wt%, N-LMO-1.5wt%, and N-LMO-2.0wt% samples at the 100nm scale, respectively. As can be seen from the figures, all samples are in the form of nanoparticles, indicating that the overall morphology of the sample surface did not change significantly before and after the modification treatment. This shows that the Na4V2O7 modification and annealing treatment did not destroy the microstructure of the matrix material, but only formed a thin heterogeneous layer on the surface, thus avoiding capacity loss caused by structural damage.
[0098] Figure 4 The figures show the O1s orbital spectra of P-LMO and N-LMO-1.5wt% samples, with peaks at 532.1 eV, 531.0 eV, and 529.1 eV corresponding to carbonate species, oxygen vacancies, and lattice oxygen in the samples, respectively. As shown in the figure, the oxygen vacancy content in the modified N-LMO-1.5wt% sample increased from 21.1% to 37.4% compared to P-LMO (based on the change in the area of the O1s orbital oxygen vacancy peak), indicating that additional oxygen vacancies were introduced into the N-LMO-1.5wt% sample after Na4V2O7 modification according to this invention. Simultaneously, the peak intensity of carbonate species at 532.1 eV in the N-LMO-1.5wt% sample significantly decreased, indicating that the heterojunction layer suppressed the reaction between the electrolyte and the material surface, reducing the formation of interfacial impurities.
[0099] Depend on Figure 5 The electron paramagnetic resonance (EPR) spectra show that, at a g-factor of 2.004, the paramagnetic symmetry signal of the N-LMO-1.5wt% sample is significantly higher than that of the P-LMO sample. This result demonstrates that more oxygen vacancies were generated in the N-LMO-1.5wt% sample. Oxygen vacancies, acting as electron acceptors, can modulate the electronic structure of the material surface, reduce the oxidative activity of oxygen ions, and thus inhibit the escape of lattice oxygen.
[0100] Figure 6 The first charge-discharge curves for all samples (P-LMO, N-LMO-1wt%, N-LMO-1.5wt%, N-LMO-2wt%) are shown. The first-cycle discharge specific capacity for each sample is 261.2 mAh g. -1 273.6 mAh g -1 287.6 mAh g -1 280.4 mAh g -1The first-cycle coulombic efficiencies were 67.8%, 83.4%, 84.2%, and 85.9%, respectively. This indicates that the samples modified according to this invention exhibit significantly improved discharge specific capacity and first-cycle coulombic efficiency, demonstrating better electrochemical reversibility. This is mainly attributed to the introduction of additional oxygen vacancies on the material surface, which, through reduction coupling, reduces oxygen activity during the initial charging process, inhibits the release of lattice oxygen, and improves the reversibility of oxygen ion redox.
[0101] Figure 7 The figure shows the voltage decay curves of P-LMO and N-LMO-1.5wt% samples. As can be seen from the figure, the voltage decay of the modified N-LMO-1.5wt% sample decreased from 6.50 mV / cycle to 3.10 mV / cycle, effectively mitigating voltage decay during cycling. This is mainly because the modified sample introduces additional oxygen vacancies, inducing charge transfer of transition metal ions in the bulk phase and inhibiting the dissolution of transition metal ions during charge and discharge, thereby suppressing voltage decay.
[0102] Figure 8 The graphs show the rate performance of each sample (P-LMO, N-LMO-1wt%, N-LMO-1.5wt%, N-LMO-2wt%) at different current densities. Compared to P-LMO, the discharge specific capacity of each modified sample increased to varying degrees at different rates, especially the N-LMO-1.5wt% sample, which had a first-cycle discharge specific capacity of 266.5 mAh g at 0.2 C. -1 The first discharge specific capacity at 5C is 148.7 mAh g. -1 P-LMO exhibits a discharge specific capacity of 245.6 mAh g⁻¹ at 0.2 C. -1 The discharge specific capacity at 5C is only 105.8 mAh g. -1 The modified sample showed a significant improvement in rate performance, and the difference in rate performance became more pronounced with increasing magnification. This is mainly due to the VO4 tetrahedral structure in the introduced Na4V2O7 heterointerface providing additional Li... + Diffusion channels improve Li + This improves transmission efficiency, thereby enhancing rate performance.
[0103] Figure 9The charts show the 100 charge-discharge cycle diagrams for all samples (P-LMO, N-LMO-1wt%, N-LMO-1.5wt%, and N-LMO-2wt%) at 1 C rate. After 200 cycles, the N-LMO-1.5wt% sample exhibited the highest capacity retention of 95.6%, and the cycle stability of N-LMO-1.0wt% (92.3%) and N-LMO-2.0wt% (79.8%) was significantly improved compared to P-LMO (75.4%). This is mainly due to the formation of a stable cathode-electrolyte interface after the introduction of the Na4V2O7 heterointerface on the LMO surface, which suppresses the occurrence of undesirable interfacial side reactions. Simultaneously, the introduced oxygen vacancies reduce oxygen activity during charge and discharge, thereby inhibiting irreversible lattice oxygen escape during charge and discharge. Furthermore, the oxygen vacancies induce charge transfer of transition metal ions in the bulk phase, reducing the Mn content in the bulk phase. 3+ The content of [specific ingredient] inhibited the structural distortion caused by the Jahn-Teller effect, and the synergistic effect of the three factors improved the cyclic stability of LMO.
[0104] The present invention also provides the following preferred embodiments:
[0105] Example 6
[0106] This embodiment 6 provides a method for preparing a lithium-rich manganese-based cathode material modified with sodium vanadium oxide, including a surface modification treatment step of the lithium-rich manganese-based substrate, specifically as follows:
[0107] S2.1 A certain amount of Na4V2O7 was dispersed in 10 ml of anhydrous ethanol to form a dispersion, the mass fraction of Na4V2O7 in the dispersion was 1.2%; the dispersion was ultrasonically treated at a frequency of 38 kHz for 20 min.
[0108] S2.2 A certain amount of lithium-rich manganese-based matrix powder was added to the dispersion (the mass ratio of lithium-rich manganese-based matrix powder to Na4V2O7 was 100:1.2), and stirred at 450 rpm / min for 1.5 h at room temperature to make the lithium-rich manganese-based matrix powder and Na4V2O7 evenly mixed to obtain a mixed system.
[0109] S2.2 The mixture was transferred to a 75°C oil bath and stirred at 250 rpm / min to evaporate and remove the solvent. Then it was transferred to a 105°C vacuum drying oven and dried for 3 hours to obtain the mixed powder.
[0110] S2.3 The mixed powder was ground for 25 min and placed in a tube furnace under an argon inert atmosphere for annealing at 450 °C for 2.5 h, so that Na4V2O7 coated the LMO surface, and the partial decomposition of Na4V2O7 initiated the Li + / Na+ Topological chemical ion exchange is used to induce the generation of oxygen vacancies in situ, and after cooling, the lithium-rich manganese-based cathode material modified with sodium vanadium oxide is obtained.
[0111] Example 7
[0112] This embodiment 7 provides a method for preparing a lithium-rich manganese-based cathode material modified with sodium vanadium oxide, including a surface modification treatment step of the lithium-rich manganese-based substrate, specifically as follows:
[0113] S2.1 A certain amount of Na4V2O7 was dispersed in 20 ml of anhydrous ethanol to form a dispersion, the mass fraction of Na4V2O7 in the dispersion was 1.8%; the dispersion was ultrasonically treated at a frequency of 42 kHz for 40 min.
[0114] S2.2 A certain amount of lithium-rich manganese-based matrix powder was added to the dispersion (the mass ratio of lithium-rich manganese-based matrix powder to Na4V2O7 was 100:1.8), and stirred at 550 rpm / min for 2.5 h at room temperature to make the lithium-rich manganese-based matrix powder and Na4V2O7 evenly mixed to obtain a mixed system.
[0115] S2.2 The mixture was transferred to an 85°C oil bath and stirred at 350 rpm / min to evaporate and remove the solvent. Then it was transferred to a 115°C vacuum drying oven and dried for 1 hour to obtain the mixed powder.
[0116] S2.3 The mixed powder was ground for 35 min and placed in a tube furnace under an argon inert atmosphere. Annealing was carried out at 550 °C for 1.5 h, allowing Na₄V₂O₇ to coat the LMO surface, and partial decomposition of Na₄V₂O₇ to initiate Li₂. + / Na + Topological chemical ion exchange is used to induce the generation of oxygen vacancies in situ, and after cooling, the lithium-rich manganese-based cathode material modified with sodium vanadium oxide is obtained.
[0117] Example 8
[0118] This embodiment 8 provides a lithium-ion battery, the positive electrode of which uses a lithium-rich manganese-based positive electrode material modified with sodium vanadium oxide as described in any of the embodiments 1, 3-7.
[0119] The above description is only a preferred embodiment of the present invention. It should be understood that the above description of the embodiments is only for the purpose of helping to understand the method and core idea of the present invention, and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, etc. made within the idea and principle of the present invention should be included within the scope of protection of the present invention.
Claims
1. A lithium-rich manganese-based cathode material modified with sodium vanadium oxide, comprising a lithium-rich manganese-based matrix and a Na4V2O7 heterostructure interface layer coated on the surface of the matrix; wherein the Na4V2O7 has a VO4 tetrahedral structure, forming a three-dimensional lithium-ion transport channel; and the surface of the matrix is rich in oxygen vacancies.
2. The lithium-rich manganese-based cathode material modified with sodium vanadium oxide according to claim 1, characterized in that: The lithium-rich manganese matrix is Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2.
3. A method for preparing a lithium-rich manganese-based cathode material modified with sodium vanadium oxide, characterized in that, Includes the following steps: Synthesis of S1 lithium-rich manganese-based matrix; Surface modification treatment of S2 lithium-rich manganese-based substrate includes: S2.1 A certain amount of Na4V2O7 is dispersed in 10-20 ml of anhydrous ethanol to form a dispersion; S2.2 Add a certain amount of lithium-rich manganese-based matrix powder to the dispersion and stir at 450-550 rpm / min for 1.5-2.5 h at room temperature to make the lithium-rich manganese-based matrix powder and Na4V2O7 evenly mixed to obtain a mixed system. S2.2 The mixture is transferred to an oil bath at 75-85℃ and stirred at 250-350 rpm / min to evaporate and remove the solvent. Then it is transferred to a vacuum drying oven at 105-115℃ and dried for 1-3 hours to obtain the mixed powder. S2.3 Grind the mixed powder for 25-35 min, place it in a tube furnace under argon inert atmosphere protection, anneal at 450-550℃ for 1.5-2.5 h, and after cooling, obtain the sodium vanadium oxide modified lithium-rich manganese-based cathode material.
4. The method for preparing a sodium vanadium oxide-modified lithium-rich manganese-based cathode material according to claim 3, characterized in that: In step S1, lithium-rich manganese-based matrix Li is synthesized using the sol-gel method. 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2.
5. The method for preparing a sodium vanadium oxide-modified lithium-rich manganese-based cathode material according to claim 4, characterized in that, The specific operation of step S1 is as follows: Lithium acetate dihydrate, manganese acetate tetrahydrate, nickel acetate tetrahydrate, and cobalt acetate tetrahydrate are dissolved in deionized water in a molar ratio of 1.2:0.54:0.13:0.13 and ultrasonically stirred to obtain a mixed solution; a certain amount of citric acid is added and stirred in an oil bath at 80-100℃, and then the temperature is raised to 100-120℃ to evaporate the water and form a gel; the gel is vacuum dried at 170-190℃ for 8-12 h, ground, and then pre-calcined at 450-550℃ for 4-6 h and calcined at 850-950℃ for 10-14 h. After natural cooling, lithium-rich manganese-based matrix powder is obtained, denoted as P-LMO.
6. The method for preparing a sodium vanadium oxide-modified lithium-rich manganese-based cathode material according to claim 5, characterized in that: The molar ratio of citric acid to total metal cations is 2:
1.
7. The method for preparing a sodium vanadium oxide-modified lithium-rich manganese-based cathode material according to claim 3, characterized in that: The mass fraction of Na4V2O in the dispersion of step S2.1 is 1~2%.
8. The method for preparing a sodium vanadium oxide-modified lithium-rich manganese-based cathode material according to claim 3, characterized in that: Step S2.1 also includes the step of sonicating the dispersion at an ultrasonic frequency of 38-42 kHz for 20-40 min.
9. The method for preparing a sodium vanadium oxide-modified lithium-rich manganese-based cathode material according to claim 3, characterized in that: In step S2.2, the mass ratio of lithium-rich manganese-based matrix powder to Na4V2O is 100:1.0-2.
0.
10. A lithium-ion battery, characterized in that, Its positive electrode uses a lithium-rich manganese-based positive electrode material modified with sodium vanadium oxide as described in any one of claims 1-9.