A surface high-efficiency modified layered lithium-rich manganese oxide and a preparation method and application thereof

Abstract

The application discloses a surface high-efficiency modified layered lithium-rich manganese oxide positive electrode material, which comprises a layered lithium-rich manganese oxide base material, a spinel heterostructure phase uniformly coated on the surface of the layered lithium-rich manganese oxide base material, and a coating layer uniformly coated on the surface of the spinel heterostructure phase; the coating layer is selected from a B2O3 / Li2B4O7 two-phase coating layer or a B2O3 single-phase coating layer; and the surface of the surface high-efficiency modified layered lithium-rich manganese oxide positive electrode material is also rich in oxygen vacancies. The material disclosed by the application has high electronic conductivity and ionic conductivity. In the charge-discharge cycle process of a battery, the release of oxygen is small, the dissolution of transition metals in an electrolyte is small, the material maintains high crystal structure stability in the cycle process, and a lithium ion battery assembled by using a positive electrode sheet prepared from the material has high initial coulomb efficiency, excellent cycle performance and rate performance, and high voltage retention rate in the cycle process.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and particularly relates to a surface highly modified layered lithium-rich manganese oxide, a preparation method thereof, and an application thereof. Background Art

[0002] Lithium ion batteries have occupied a dominant position in electrochemical energy storage devices due to advantages such as high energy density, low self-discharge, long cycle life, and environmental friendliness, and are widely used in the fields of smart phones, computers, power batteries, and energy storage batteries. In the past decade, lithium ion batteries have experienced rapid commercialization and scale development. Especially in the field of new energy vehicles, the huge market demand has promoted the vigorous development of power batteries. The development prospect of new energy vehicles is huge, but it also puts forward higher requirements for endurance and safety. At present, the energy density of the current lithium ion battery technology cannot reach what people expect, and the safety performance is an issue that must be solved to further increase the market share of automobiles. Therefore, developing lithium ion batteries and battery materials with high energy density, good safety and stability, and low cost is the focus of academia and industry.

[0003] As a key component of lithium ion batteries, the cathode material plays a crucial role in battery performance and energy density. Traditional commercial cathodes, such as LiCoO2, LiFePO4, and ternary materials, have gradually approached the capacity limit after continuous modification, but are still limited to a specific specific capacity. -1 , -1 , -1 ,

[0004] ,

[0003] , The huge advantage of layered lithium-rich manganese oxide cathode materials in terms of capacity has attracted extensive attention from researchers. Layered lithium-rich manganese oxide cathode materials have a high specific capacity (>280 mAh g -1 ) and mass energy density (>1000 Wh kg -1 ), and are very commercially potential cathode materials. The basic composition of typical layered lithium-rich manganese oxide cathode materials is xLi2MnO3·(1-x)LiMO2 (0<x<1), where M is a mixture of transition metals (TMs) such as Co, Mn, Ni, etc. However, there are also some key problems in lithium-rich manganese oxide cathode materials that limit their commercial applications, including low initial Coulomb efficiency, attenuation of capacity and voltage during cycling, which prevent them from exerting the advantage of high energy density. Due to the low electronic conductivity of Li2MnO3, lithium-rich manganese oxide cathode materials also have poor rate performance. In addition , due to the scarcity and high price of Co resources, cobalt-free lithium-rich manganese oxide cathodes can further reduce costs. The capacity and rate performance of cobalt-free lithium-rich manganese oxide cathode materials are slightly lower than those of traditional Co-containing lithium-rich manganese oxide cathode materials. How to solve these problems is the focus of the commercialization of cobalt-free lithium-rich manganese oxide cathode materials.

[0004] The primary reason for the low initial coulombic efficiency of lithium-rich manganese oxide cathode materials is the irreversible release of oxygen from Li₂MnO₃ during the initial charging process, resulting in the formation of LiMnO₂ and Li₂O phases. Furthermore, irreversible oxygen evolution continues during cycling, particularly during high-potential delithiation. In addition, during cycling, transition metals (TMs) dissolve in the electrolyte, and TM ions undergo lattice relocation, leading to a rearrangement of the lithium-rich manganese crystal structure. Consequently, the layered structure of the lithium-rich manganese oxide partially transforms into a low-crystallinity, defect-rich spinel structure, causing capacity and voltage decay during cycling.

[0005] Currently, the main methods to improve the electrochemical performance of lithium-rich manganese oxide cathode materials include: 1. Optimizing the composition and structure or constructing a concentration gradient to suppress oxygen release and phase transition; 2. Coating the surface of lithium-rich manganese oxide materials, such as coating with Al2O3, ZnO, and AlPO4, to suppress oxygen release and transition metal dissolution; 3. Ion doping to occupy the lattice sites of Li / TM / O to stabilize the structure and suppress phase transition; 4. Adding electrolyte additives to suppress adverse reactions of the electrolyte on the cathode surface.

[0006] However, current modification methods are insufficient to comprehensively improve their electrochemical performance, and the performance of layered lithium-rich manganese oxide cathode materials has not yet reached commercial levels. Developing simple and efficient methods to comprehensively enhance the electrochemical performance of lithium-rich manganese oxide cathode materials is crucial for realizing the commercial application of high-capacity lithium-rich manganese oxide materials. Summary of the Invention

[0007] To address the aforementioned problems in existing technologies, this invention discloses a surface-modified layered lithium-rich manganese oxide cathode material with high electronic and ionic conductivity. During battery charge-discharge cycles, oxygen release is minimal and transition metal dissolution in the electrolyte is low, maintaining high crystal structure stability during cycling. Lithium-ion batteries assembled from cathode sheets prepared using this surface-modified layered lithium-rich manganese oxide cathode material exhibit high initial coulombic efficiency, excellent cycle performance and rate capability, and high voltage retention during cycling.

[0008] The specific technical solution is as follows:

[0009] A surface-modified layered lithium-rich manganese oxide cathode material includes a layered lithium-rich manganese oxide substrate, a spinel heterostructure phase uniformly coated on the surface of the layered lithium-rich manganese oxide substrate, and a coating layer uniformly coated on the surface of the spinel heterostructure phase.

[0010] The coating layer is selected from B2O3 / Li2B4O7 dual-phase coating layer or B2O3 single-phase coating layer;

[0011] The surface of the surface-modified layered lithium-rich manganese oxide cathode material is rich in oxygen vacancies.

[0012] This invention also discloses a method for preparing the surface-modified layered lithium-rich manganese oxide cathode material, comprising:

[0013] The layered lithium-rich manganese oxide substrate was uniformly mixed with ammonium pentaborate, and then subjected to pyrolysis reduction treatment to obtain the surface-modified layered lithium-rich manganese oxide cathode material.

[0014] The mass ratio of layered lithium-rich manganese oxide substrate to ammonium pentaborate is 100:(3-20);

[0015] The temperature of the pyrolysis reduction treatment is 300–500℃.

[0016] The preparation method disclosed in this invention uses a layered lithium-rich manganese oxide substrate as raw material and performs thermal reduction treatment on its surface with ammonium pentaborate (NH4B5O8). During the heating process, NH4B5O8 reacts with the surface of the layered lithium-rich manganese oxide material to generate B2O3 or a two-phase complex of B2O3 and Li2B4O7 in situ, which coats the surface of the layered lithium-rich manganese oxide substrate. During the heating reaction, NH3 is released. NH3 has reducing properties, which causes the formation of a spinel phase with high crystallinity and few defects on the surface of the layered lithium-rich manganese oxide substrate, and greatly increases the concentration of oxygen vacancies on the surface of the lithium-rich manganese oxide substrate, correspondingly reducing the concentration of lattice oxygen. Since the decomposed NH3 is in the gas phase, it can flow well between the cathode material particles. Compared with the solid-phase interface reduction reaction, the gas phase interface reaction can react more fully with the surface of the lithium-rich manganese oxide, and the generated spinel heterostructure interface layer and the surface layer have a more uniform oxygen vacancy concentration.

[0017] In this invention, the layered lithium-rich manganese oxide substrate is selected from conventional lithium-rich manganese oxides, which can be synthesized by ourselves or obtained from commercial products. Its general structural formula is xLi2MnO3-(1-x)LiMO2, where M is selected from one or more of Ni, Mn, Co, Cr, Fe, and Al, and 0≤x≤1.

[0018] The layered lithium-rich manganese oxide substrate has a particle size of 100 nm to 10 μm.

[0019] Preferably, the layered lithium-rich manganese oxide substrate is selected from inexpensive cobalt-free lithium-rich manganese oxide cathode materials.

[0020] Experiments revealed that, in this preparation method, by controlling the mass ratio of the layered lithium-rich manganese oxide substrate to ammonium pentaborate, the content of the spinel heterostructure phase, the content of the coating layer (i.e., the thickness of the coating layer), and the content of oxygen vacancies can be controlled. Furthermore, it can be controlled whether the outermost layer of the final product is a B2O3 / Li2B4O7 biphase coating layer or a B2O3 single-phase coating layer. In addition, by controlling the mass ratio of the raw materials and the pyrolysis reduction treatment temperature, the molar ratio of B2O3 to Li2B4O7 in the prepared B2O3 / Li2B4O7 biphase coating layer can be adjusted.

[0021] In the surface-modified layered lithium-rich manganese oxide cathode material prepared by the above process, the content of spinel heterostructure phase is 1-8 wt%.

[0022] The thickness of the coating layer is 0.5–8.0 nm;

[0023] The concentration of oxygen vacancies is 45–85 mol%.

[0024] In the product prepared by this invention, oxygen exists in two forms: oxygen vacancies and lattice oxygen. When the total content is 100 mol%, the concentration of lattice oxygen is 15-55 mol% when the concentration of oxygen vacancies is 45-85 mol%.

[0025] Preferred:

[0026] The mass ratio of layered lithium-rich manganese oxide substrate to ammonium pentaborate is 100:(3-15);

[0027] The pyrolysis reduction treatment is carried out at a temperature of 300–400°C for a time of 0.5–2.0 h.

[0028] Further preferred, the mass ratio of layered lithium-rich manganese oxide substrate to ammonium pentaborate is 100:

[0029] (5-15); more preferably 100:(5-10); most preferably 100:5.

[0030] Further preferably, the temperature of the pyrolysis reduction treatment is 350°C.

[0031] By controlling the above parameters, the content of spinel heterostructure phase, coating layer, oxygen vacancy content, and composition and content of coating layer in the final product can be further regulated. With the continuous optimization of the above process parameters, the electrochemical performance of the final product is continuously improved.

[0032] The mixing is performed using common mixing methods in the art, such as ball milling, mechanical stirring, or magnetic stirring.

[0033] The surface-modified layered lithium-rich manganese oxide cathode material prepared by this invention features a highly crystalline, low-defect spinel phase coated on the surface of the layered lithium-rich manganese oxide matrix particles, which provides excellent three-dimensional lithium-ion diffusion channels and significantly improves the high-rate performance of the lithium-rich manganese oxide-based cathode material. Furthermore, the highly crystalline, low-defect spinel phase exhibits greater structural stability during charge and discharge compared to the layered oxide phase. Its transition metal has low solubility in the electrolyte, and its coating of the layered lithium-rich manganese oxide matrix particles avoids direct contact between the particles and the electrode solution. It also inhibits oxygen release and transition metal dissolution during cycling, improving the structural stability of the layered lithium-rich manganese oxide matrix material during cycling. This significantly slows down the transformation of the lithium-rich manganese oxide from a layered structure to a highly defective spinel structure caused by oxygen evolution, transition metal dissolution, and the rearrangement of transition metal atoms during cyclic lithium insertion / extraction, thereby greatly improving the material's cycling stability and mitigating voltage decay during cycling. The synergistic effect of the coating layer and spinel heterostructure phase in the surface-modified layered lithium-rich manganese oxide cathode material prepared by this invention significantly suppresses oxygen release during the first cycle and reduces oxygen evolution during cycling, improving anion redox reversibility. This, in turn, significantly improves the initial coulombic efficiency, discharge specific capacity, and cycle performance of the material. The high oxygen vacancy concentration on the surface of the surface-modified layered lithium-rich manganese oxide cathode material prepared by this invention increases the electronic conductivity and enhances the activity of the Li₂MnO₃ component, which is beneficial for improving the material's capacity and rate performance.

[0034] Preferred:

[0035] In the prepared surface-modified layered lithium-rich manganese oxide cathode material, the content of spinel heterostructure phase is 2.0–6.5 wt%.

[0036] The thickness of the coating layer is 1.0–5.0 nm;

[0037] The concentration of the oxygen vacancy is 50–80 mol%.

[0038] Further optimization:

[0039] In the prepared surface-modified layered lithium-rich manganese oxide cathode material, the content of spinel heterostructure phase is 4.0–6.1 wt%.

[0040] The thickness of the coating layer is 2.0–4.0 nm.

[0041] Further optimization:

[0042] In the prepared surface-modified layered lithium-rich manganese oxide cathode material, the coating layer is selected from the B2O3 / Li2B4O7 dual-phase coating layer;

[0043] The molar ratio of B2O3 to Li2B4O7 is 1:(0.5~5.0).

[0044] More preferably, the molar ratio of B2O3 to Li2B4O7 is 1:(1.0 to 4.0); even more preferably, it is 1:(1.0 to 2.5).

[0045] Experiments have shown that, compared to coating with a single B2O3, the two-phase coating of B2O3 / Li2B4O7 is more conducive to the overall improvement of the electrochemical performance of the material. This may be because the two-phase B2O3 / Li2B4O7 coating combines the high ionic conductivity of Li2B4O7 with the better ability of B2O3 to prevent side reactions at the electrolyte interface and the dissolution of transition metals.

[0046] Further experiments revealed that when the molar ratio of Li2B4O7 in the B2O3 / Li2B4O7 biphase coating was too high, the electrochemical performance of the biphase coating was not superior to that of the single-phase coating. Therefore, only when the molar ratio of B2O3 / Li2B4O7 is maintained can the synergistic effect of B2O3 and Li2B4O7 be fully utilized.

[0047] The present invention also discloses the application of the surface-modified layered lithium-rich manganese oxide cathode material in lithium-ion batteries. After preparing cathode sheets with the surface-modified layered lithium-rich manganese oxide cathode material, lithium-ion batteries are assembled. These batteries have high coulombic efficiency, excellent cycle stability, and high rate performance.

[0048] Compared with the prior art, the present invention has the following advantages:

[0049] This invention discloses a surface-modified lithium-rich manganese oxide cathode material with a coating structure, consisting of a layered lithium-rich manganese oxide substrate, a spinel heterostructure phase, and a coating layer from the inside out. The coating layer is selected from a B2O3 / Li2B4O7 dual-phase coating layer or a B2O3 single-phase coating layer. The surface of the cathode material is also rich in oxygen vacancies. By applying a double-layer coating of the layered lithium-rich manganese oxide substrate with a spinel heterostructure phase and a coating layer of a specific composition, and by introducing more oxygen vacancies onto its surface, the synergistic effect of these factors significantly suppresses oxygen release and transition metal dissolution during cycling, improving the structural stability of the layered lithium-rich manganese oxide substrate during cycling. This significantly slows down the transformation of the lithium-rich manganese oxide from a layered structure to a high-defect spinel structure caused by oxygen evolution, transition metal dissolution, and rearrangement of transition metal atoms during lithium insertion / extraction cycling. Therefore, it greatly improves the material's cycle stability and rate performance, and slows down voltage decay during cycling.

[0050] The preparation method disclosed in this invention uses layered lithium-rich manganese oxide substrate and NH4B5O8 as raw materials. After pyrolysis, spinel heterostructure phase, coating layer and more oxygen vacancies are generated in situ. Since the decomposed NH3 is gaseous, it can flow well between the cathode material particles. Compared with solid-phase interface reduction reaction, gas-phase interface reaction can react more fully with the surface of lithium-rich manganese oxide. The oxygen vacancy concentration of the generated spinel heterostructure interface layer and surface layer is more uniform. This preparation method is simple, controllable and suitable for industrial production.

[0051] A lithium-ion battery is assembled using a cathode sheet prepared from the surface-modified lithium-rich manganese oxide cathode material prepared in this invention. This cathode sheet exhibits high coulombic efficiency, excellent cycle stability, and high rate performance. Attached Figure Description

[0052] Figure 1 Transmission electron microscope (TEM) image (a), high-resolution transmission electron microscope (HRTEM) image (b), and XPS energy dispersive spectroscopy (EDS) image (c) of the surface-modified lithium-rich manganese oxide cathode material prepared in Example 1;

[0053] Figure 2 XPS spectra of B1S(a) and O1S(b) of the surface-modified lithium-rich manganese oxide cathode material prepared in Example 1;

[0054] Figure 3 The refined X-ray diffraction (XRD) pattern of the surface-modified lithium-rich manganese oxide cathode material prepared in Example 1;

[0055] Figure 4The battery assembled using the surface-modified lithium-rich manganese oxide cathode material prepared in Example 1 has the following characteristics: first charge-discharge curve at 0.1C (a), cycle performance curve at 0.1C current density (b), rate performance curve at different current densities (c), cycle curve at 1C current density (d), and voltage decay curve at 1C cycle (e).

[0056] Figure 5 HRTEM (a) and EDS line scan analysis (b-c) of the cathode sheet prepared by the surface-modified lithium-rich manganese oxide cathode material prepared in Example 1 after cycling;

[0057] Figure 6 XPS spectra of B1S(a) and O1S(b) of the surface-modified lithium-rich manganese oxide cathode material prepared in Example 2;

[0058] Figure 7 The battery assembled using the surface-modified lithium-rich manganese oxide cathode material prepared in Example 2 has the following parameters: first charge-discharge curve at 0.1C (a), cycle performance curve at 0.1C current density (b), rate performance curve at different current densities (c), cycle curve at 1C current density (d), and voltage decay curve at 1C cycle (e).

[0059] Figure 8 XPS spectra of B1S(a) and O1S(b) of the surface-modified lithium-rich manganese oxide cathode material prepared in Example 3;

[0060] Figure 9 The battery assembled using the surface-modified lithium-rich manganese oxide cathode material prepared in Example 3 has the following characteristics: first charge-discharge curve at 0.1C (a), cycle performance curve at 0.1C current density (b), rate performance curve at different current densities (c), cycle curve at 1C current density (d), and voltage decay curve at 1C cycle (e).

[0061] Figure 10 The battery assembled using the surface-modified lithium-rich manganese oxide cathode material prepared in Example 4 has the following characteristics: first charge-discharge curve at 0.1C (a), cycle performance curve at 0.1C current density (b), rate performance curve at different current densities (c), cycle curve at 1C current density (d), and voltage decay curve at 1C cycle (e).

[0062] Figure 11The battery assembled using the surface-modified lithium-rich manganese oxide cathode material prepared in Example 5 has the following parameters: first charge-discharge curve at 0.1C (a), cycle performance curve at 0.1C current density (b), rate performance curve at different current densities (c), cycle curve at 1C current density (d), and voltage decay curve at 1C cycle (e).

[0063] Figure 12 XPS spectrum of lithium-rich manganese oxide cathode material prepared in Comparative Example 1;

[0064] Figure 13 TEM (a) and HRTEM (b) images of the lithium-rich manganese oxide cathode material prepared in Comparative Example 1;

[0065] Figure 14 The battery assembled from the lithium-rich manganese oxide cathode material prepared in Comparative Example 1 has the following characteristics: first charge-discharge curve at 0.1C (a), cycle performance curve at 0.1C current density (b), rate performance curve at different current densities (c), cycle curve at 1C current density (d), and voltage decay curve at 1C cycle (e).

[0066] Figure 15 HRTEM (a) and EDS line scan analysis (b-c) of the cathode sheet prepared with the lithium-rich manganese oxide cathode material prepared in Comparative Example 1 after cycling. Detailed Implementation

[0067] The specific implementation methods of the present invention will be further described below with reference to examples. It should be noted that the specific implementation methods described herein are only for illustration and explanation of the present invention and are not intended to limit the scope of protection of the present invention.

[0068] Example 1

[0069] (1) A lithium-rich manganese oxide cathode material was prepared by conventional spray drying combined with high-temperature heat treatment. Specifically, Li, Ni, and Mn acetate raw materials were added to deionized water in a molar ratio of 1.24:0.2:0.6, and mechanical stirring was used to form 0.15 mol L... -1 The solution contained an excess of 4 mol% lithium acetate dihydrate to compensate for lithium loss during subsequent calcination; then 0.3 mol L was added. -1 Citric acid monohydrate was used as a complexing agent to prevent the hydrolysis of the metal salt. The thoroughly stirred solution was then pumped into a spray dryer via a peristaltic pump, where it underwent spray pyrolysis to obtain the precursor material. The inlet and outlet temperatures of the spray dryer were set to 200℃ and 100℃, respectively. The spray-obtained precursor material was loaded into an alumina crucible and heat-treated in an air atmosphere at 1000℃ for 20 minutes in a chamber furnace to obtain a cobalt-free lithium-rich manganese cathode material with the composition Li.1.2 Mn 0.6 Ni 0.2 O2, with a particle size of 100–300 nm;

[0070] (2) The lithium-rich manganese cathode material prepared in step (1) is mixed with 10 wt% ammonium pentaborate by ball milling. The ball milling speed is 400 rpm and the time is 1 h. The weight ratio of ball to material is 50:1. The mixture is heat-treated at 350°C for 1 h in a tube furnace with argon gas. After natural cooling, the surface-modified lithium-rich manganese oxide cathode material is obtained.

[0071] Figure 1 TEM images (a) and high-resolution TEM images (b) of the surface-modified lithium-rich manganese oxide cathode material prepared in this embodiment, and Fourier transform diagrams of regions I and II in (b). Analysis of the lattice fringe spacing and Fourier transform reveals that the bulk matrix is ​​a layered lithium-rich manganese oxide phase, with a 3-5 nm thick spinel structure formed on the surface of the layered lithium-rich manganese oxide matrix, and a 2-3 nm thick coating layer formed on the surface of the spinel phase. Energy dispersive spectroscopy (EDS) analysis was performed on the surface-modified lithium-rich manganese oxide cathode material prepared in this embodiment. Figure 1 (c) It was found that in addition to Ni, O and Mn elements in lithium-rich manganese materials, B element was also uniformly distributed on the particle surface, indicating that there is a B-containing phase in the surface layer.

[0072] Figure 2 The XPS analysis results of the surface-modified lithium-rich manganese oxide cathode material prepared in this embodiment show that the peaks at 192.1 eV and 192.7 eV in the B1s spectrum (Figure (a)) correspond to Li2B4O7 and B2O3, respectively, indicating the presence of a two-phase coating layer on the lithium-rich manganese surface. The calculated contents of Li2B4O7 and B2O3 are 60 mol% and 40 mol%, respectively. Analysis of the O1s spectrum (Figure (b)) shows an oxygen vacancy concentration of 76 mol% (corresponding to a lattice oxygen concentration of 24 mol%). Compared with Comparative Example 1 (initial Li... 1.2 Mn 0.6 Ni 0.2 Compared to O2), its oxygen vacancy concentration is 42 mol%. Figure 12 In this embodiment, the surface-modified lithium-rich manganese oxide cathode material exhibits a significantly increased surface oxygen vacancy concentration. This increased oxygen vacancy concentration helps suppress oxygen release and enhances the material's electronic and ionic conductivity.

[0073] Refined image by X-ray diffraction (XRD) Figure 3 Analysis showed that the surface-modified lithium-rich manganese oxide cathode material prepared in this embodiment contained 4.3 wt% spinel phase.

[0074] Performance testing:

[0075] The surface-modified lithium-rich manganese oxide cathode material prepared in this embodiment was mixed with Super P conductive agent (20 wt% of the cathode material by weight) and a 1 wt% sodium carboxymethyl cellulose (CMC) aqueous solution binder (5 wt% of the total weight of the cathode material and Super P conductive agent). The mixture was then coated onto an aluminum foil current collector, vacuum dried at 80°C, and pressed at 10 MPa to obtain the cathode sheet. A 2025 coin cell was used, with lithium metal sheets as the reference and counter electrodes, and a Celgard-2400 separator. Assembly was performed in a glove box. The electrolyte was LiPF6 (1 mol / L) / EC+DEC+EMC (volume ratio 1:1:1). The test voltage window was 2.0–4.8 V, and the electrochemical performance of the battery was tested using a constant current charge-discharge method.

[0076] Figure 4 The electrochemical performance of the battery assembled in this embodiment is shown in Figure (a), which shows the first charge-discharge curve of the battery at 0.1C. The first coulombic efficiency reached 90.0%, and the first reversible capacity was 275 mAh g. -1 (b) The figure shows the cycling performance curve of the battery at a current density of 0.1C. The capacity initially decreases, then slowly increases and remains stable. The slow increase in capacity is due to the activation of the Li2MnO3 component, which gradually increases the capacity provided. After 100 cycles, the battery still has 271 mAh g⁻¹. -1 The specific capacity is as high as 98.5%. (c) The figure shows the battery from 0.1C to 20C (1C = 200mA g). -1 Rate performance curves at current densities. It exhibits high capacity (166, 144, and 117 mAh g⁻¹) at current densities of 5C, 10C, and 20C, respectively. -1 The discharge specific capacity. (d) The figure shows the cycling curve of the battery at a 1C current density, with an initial reversible capacity of 209 mAh g. -1 It can still maintain 194mAh g after 300 cycles. -1 The capacity retention rate is 92.8%. (e) The figure shows the voltage decay curve of the battery under 1C cycle. The median voltage of the first discharge in Example 1 is 3.57V. After 300 cycles, the median voltage of the electrode is still maintained at 3.26V, with a voltage retention rate as high as 91.3%.

[0077] The electrochemical performance data of the assembled battery in this embodiment are listed in Table 1 below, and the capacity data at different rates are listed in Table 2 below.

[0078] Figure 5The images show the HRTEM morphology ((a)) and EDS line scan analysis results ((b) and (c)) of the cathode sheet prepared using the surface-modified lithium-rich manganese oxide cathode material of this embodiment after 300 cycles at 1C. The thickness of the spinel structure layer remained almost unchanged after cycling, and the internal lattice fringes of the particles were clear, indicating good crystallinity. EDS line scan analysis confirmed that the surface-modified lithium-rich manganese oxide cathode material prepared in this embodiment had a surface elemental loss layer thickness of only 20 nm after 300 cycles at 1C, compared to the 60 nm thickness of the surface elemental loss layer in Comparative Example 1. Figure 15 The reduction in (c) is significant. This demonstrates that the surface-modified lithium-rich manganese oxide cathode material prepared in this embodiment exhibits excellent structural stability during cycling, significantly suppressing the transformation of the material from a layered to a spinel structure and the dissolution of transition metal elements in the electrolyte during cycling.

[0079] Example 2

[0080] The preparation method is basically the same as in Example 1, except that the mass of ammonium pentaborate added in step (2) is 3 wt% of the mass of the lithium-rich manganese cathode material.

[0081] TEM characterization revealed that a 2-3 nm thick spinel structure was formed on the surface of the layered lithium-rich manganese oxide matrix, and a 1-2 nm thick coating layer was formed on the surface of the spinel phase.

[0082] Figure 6 The XPS test results for the surface-modified lithium-rich manganese oxide cathode material prepared in this embodiment are shown. In the B1s spectrum (Figure (a), the peaks at 192.1 eV and 192.7 eV correspond to Li2B4O7 and B2O3, respectively, and their contents are calculated to be 79 mol% and 21 mol%, respectively. Analysis of the O1s spectrum (Figure (b)) shows that the oxygen vacancy concentration is 51 mol%, and the corresponding lattice oxygen concentration is 49 mol%. Further X-ray diffraction (XRD) analysis reveals that the surface-modified lithium-rich manganese oxide cathode material prepared in this embodiment contains 2.1 wt% spinel phase.

[0083] The test battery was prepared and its electrochemical performance was tested using the same method as in Example 1.

[0084] Figure 7 (a) shows the first charge-discharge curve of the battery assembled in this embodiment at a current density of 0.1C, with an initial discharge capacity of 266 mAh g. -1 The initial coulombic efficiency was 80.2%. After 100 cycles at a current density of 0.1C, the capacity remained at 239 mAh g⁻¹. -1 The capacity retention rate was 89.8%. Figure 7(b)). It exhibits high current densities of 155, 133, and 109 mAh g at 5C, 10C, and 20C, respectively. -1 Discharge specific capacity ( Figure 7 (c)). At a current density of 1C, its initial discharge capacity is 200 mAh g. -1 After 300 cycles, the capacity still remains at 170mAh g. -1 The capacity retention rate reached 85.0%. Figure 7 (d)). After 300 cycles at 1C, the median voltage remained at 3.20V, a retention rate of 88.9%. Figure 7 (e)).

[0085] The electrochemical performance data of the assembled battery in this embodiment are listed in Table 1 below, and the capacity data at different rates are listed in Table 2 below.

[0086] Compared to Example 1, under the condition of less ammonium pentaborate addition, the Li2B4O7 content on the surface of the lithium-rich manganese oxide material is relatively increased, while the B2O3 phase content is relatively decreased. Moreover, the total content of Li2B4O7 and B2O3 phases is also relatively low, and the spinel phase content is low. This results in insufficient coating thickness, which cannot effectively facilitate the dissolution of transition metals in the electrolyte during cycling. Furthermore, the relatively low oxygen vacancy concentration is not conducive to improving the electronic conductivity of the material and preventing oxygen leakage. In addition, the low spinel phase content cannot provide sufficient lithium-ion diffusion channels. Therefore, overall, it is not conducive to fully improving the electrochemical performance of the material.

[0087] Example 3

[0088] The preparation method is basically the same as in Example 1, except that the mass of ammonium pentaborate added in step (2) is 15 wt% of the mass of the lithium-rich manganese cathode material.

[0089] TEM characterization revealed that a spinel structure with a thickness of 4–6 nm was formed on the surface of the layered lithium-rich manganese oxide matrix, and a coating layer with a thickness of 3–4 nm was formed on the surface of the spinel phase.

[0090] Figure 8 XPS tests on the surface-modified lithium-rich manganese oxide cathode material prepared in this embodiment showed a peak at 192.7 eV in the B1s spectrum (Figure (a)), originating from B2O3, with no Li2B4O7 detected. Meanwhile, the oxygen vacancy concentration on the material surface, calculated from the O1s spectrum (Figure (b)), was 80 mol%, corresponding to a lattice oxygen concentration of 20 mol%. The spinel phase content, calculated through XRD refinement, was 6.1 wt%.

[0091] As can be seen, compared with Example 1, under the condition of relatively high ammonium pentaborate addition, only B2O3 was generated on the surface of the lithium-rich manganese oxide matrix material. This may be due to the higher ammonium pentaborate addition, which creates a more reducing environment. Li2B4O7 is less stable than B2O3, thus generating the more stable B2O3. Furthermore, the introduction of more reducing substances leads to a higher oxygen vacancy content and spinel phase formation on the material surface.

[0092] The test battery was prepared using the same method as in Example 1, and its electrochemical performance was tested.

[0093] Figure 9 (a) shows the first charge-discharge curve of the battery assembled with the positive electrode material in this embodiment at a current density of 0.1C, with an initial discharge capacity of 268 mAh g. -1 The initial coulombic efficiency was 88.2%. After 100 cycles at a current density of 0.1C, the capacity remained at 247 mAh g⁻¹. -1 Capacity retention rate 92.2% Figure 9 (b)). It exhibits current densities of 158, 137, and 114 mAh g at 5C, 10C, and 20C, respectively. -1 Discharge specific capacity ( Figure 9 (c) The material exhibits high rate performance. At a current density of 1C, its initial discharge capacity is 209 mAh g⁻¹. -1 After 300 cycles, the capacity still remains at 174 mAh g. -1 The capacity retention rate was 83.3%. Figure 9 (d) exhibits high initial Coulomb effect, high capacity, and excellent charge-discharge cycle stability. After 300 cycles at 1C, the median voltage remains at 3.24V, with a retention rate of 90.7%. Figure 9 (e)) The voltage decay is small during the cycle.

[0094] The electrochemical performance data of the assembled battery in this embodiment are listed in Table 1 below, and the capacity data at different rates are listed in Table 2 below.

[0095] Compared to the Li₂B₄O₇ / B₂O₃ dual-phase coating prepared in Example 1, this example uses a single B₂O₃ coating. Although the B₂O₃ coating exhibits good stability in the electrolyte and strong resistance to transition metal dissolution, and the lithium-rich manganese oxide matrix material contains a high concentration of oxygen vacancies and a relatively high content of spinel phase generated by pyrolysis, theoretically, while the high oxygen vacancy concentration and spinel phase reduce capacity to some extent, the high oxygen vacancy concentration can improve the material's electronic conductivity and reduce irreversible oxygen evolution during cycling. The spinel phase can improve the material's ionic conductivity and, to some extent, reduce the dissolution of transition metals in the electrolyte during cycling of the layered lithium-rich manganese matrix material. Increasing the content of both can improve the material's cycling performance and reaction kinetics, thus improving its rate performance. However, compared to Example 1, the capacity of the material prepared in this example is relatively low, and its cycling performance is still relatively poor. Furthermore, the capacity of the material at current densities of 5C, 10C, and 20C is also lower than that of Example 1. This demonstrates that under the two-phase coating of Li2B4O7 and B2O3 in Example 1, compared to a single B2O3 coating, the high ionic conductivity of Li2B4O7 and the corresponding content of B2O3 (40 mol%) can effectively prevent the dissolution of transition metal elements during cycling, which is more conducive to maintaining the structural stability of the layered lithium-rich manganese cathode material during cycling, resulting in high rate performance and excellent cycling performance.

[0096] Example 4

[0097] The preparation method is basically the same as in Example 1, except that in step (2), the ball-milled mixture is heat-treated at 300°C for 2 hours.

[0098] XPS analysis revealed that the surface coating consisted of a dual-phase structure of Li₂B₄O₇ and B₂O₃, with relative contents of 57 mol% and 43 mol%, respectively. The oxygen vacancy concentration was 71 mol% (corresponding to a lattice oxygen concentration of 29 mol%). Further XRD analysis showed that the surface-modified lithium-rich manganese oxide cathode material prepared in this embodiment contained 4.2 wt% spinel phase.

[0099] The test battery was prepared and the electrochemical performance of the material was tested using the same method as in Example 1.

[0100] The battery assembled in this embodiment has an initial discharge capacity of 270 mAh g at a current density of 0.1C. -1 The initial coulomb efficiency was 85.8% ( Figure 10 (a)). At a current density of 0.1C, the capacity remained at 258 mAh g after 100 cycles. -1 The capacity retention rate was 95.5%. Figure 10(b)). The rate performance of the cathode in this example was also improved, achieving high values ​​of 161, 142, and 115 mAh g at current densities of 5C, 10C, and 20C, respectively. -1 Discharge specific capacity ( Figure 10 (c)). At a current density of 1C, its initial discharge capacity is 205 mAh g. -1 After 300 cycles, the capacity still remains at 189mAh g. -1 The capacity retention rate reached 92.2% ( Figure 10 (d) demonstrates good charge-discharge cycle stability. In this example, the voltage decay of the positive electrode during cycling is also suppressed; after 300 cycles at 1C, the median voltage remains at 3.16V, with a retention rate of 88.3%. Figure 10 (e)).

[0101] The electrochemical performance data of the assembled battery in this embodiment are listed in Table 1 below, and the capacity data at different rates are listed in Table 2 below.

[0102] Example 5

[0103] The preparation method is basically the same as in Example 1, except that in step (2), the ball-milled mixture is heat-treated at 400°C for 0.5 h.

[0104] XPS analysis revealed that the surface coating consisted of a dual-phase structure of Li₂B₄O₇ and B₂O₃, with relative contents of 63 mol% and 57 mol%, respectively. The oxygen vacancy concentration was 79 mol% (corresponding to a lattice oxygen concentration of 21 mol%). Further XRD analysis showed that the surface-modified lithium-rich manganese oxide cathode material prepared in this embodiment contained 5.1 wt% spinel phase.

[0105] The test battery was prepared and the electrochemical performance of the material was tested using the same method as in Example 1.

[0106] The battery assembled in this embodiment has an initial discharge capacity of 272 mAh g at a current density of 0.1C. -1 The initial coulomb efficiency was 87.3% ( Figure 11 (a)). At a current density of 0.1C, the capacity remained at 260 mAh g after 100 cycles. -1 The capacity retention rate reached 95.6%. Figure 11 (b)). The current densities at 5C, 10C, and 20C are 161, 141, and 114 mAh g, respectively. -1 ( Figure 11 (c)). At a current density of 1C, its initial discharge capacity is 209 mAh g. -1 After 300 cycles, the capacity still remains at 190mAh g.-1 The capacity retention rate reached 90.9% ( Figure 11 (d) demonstrates high charge-discharge cycle stability. After 300 cycles at 1C, the median voltage remains at 3.17V, with a retention rate of 88.0%. Figure 11 (e)).

[0107] The electrochemical performance data of the assembled battery in this embodiment are listed in Table 1 below, and the capacity data at different rates are listed in Table 2 below.

[0108] Comparative Example 1

[0109] Step (1) is exactly the same as in Example 1, and lithium-rich manganese oxide cathode material Li is prepared. 1.2 Mn 0.6 Ni 0.2 O2.

[0110] XPS analysis showed that the oxygen vacancy concentration in the lithium-rich manganese oxide cathode material prepared in this comparative example was 42 mol%. Figure 12 XRD refinement did not reveal any spinel phase in the material.

[0111] Figure 13 The TEM image (a) and high-resolution TEM morphology image (b) of the lithium-rich manganese oxide cathode material prepared in this comparative example, and the Fourier transform diagram of region I in (b) show that there is no coating layer on the particle surface and the material has a layered structure.

[0112] The test battery was assembled and its electrochemical performance was tested using the same method as in Example 1.

[0113] Figure 14 (a) shows the charge-discharge curve of the battery assembled in this embodiment at 0.1C, with a discharge specific capacity of 250 mAh g. -1 The initial coulombic efficiency at 0.1C is 72%. The discharge specific capacity after 100 cycles is 185 mAh g. -1 The capacity retention rate was 74.0%. Figure 14 (b)); the capacities at 5C, 10C, and 20C are 143, 104, and 81 mAh g, respectively. -1 Specific capacity ( Figure 14 (c)); The discharge specific capacity at 1C is 195 mAh g. -1 After 300 cycles, the discharge specific capacity is 146 mAh g. -1 The capacity retention rate was 74.8%. Figure 14 (d)); After 300 cycles, the median discharge voltage was 2.94V, with a retention rate of 83.3%. Figure 14 (e)), the median discharge voltage drops significantly.

[0114] The electrochemical performance data of the comparative assembled battery are listed in Table 1 below, and the capacity data at different rates are listed in Table 2 below.

[0115] Figure 15 The image shows the HRTEM (a) and EDS line scans (b-c) of the cathode sheet prepared using the lithium-rich manganese oxide cathode material for this comparative example after 300 cycles at 1C. Although the internal region still retains a layered structure, the lattice fringes are unclear, the crystallinity is significantly reduced, and oxygen release and transition metal dissolution are severe during cycling. EDS analysis shows that the elemental loss layer depth of the cathode material prepared in this comparative example reaches 60 nm after 300 cycles at 1C, which is much greater than the 20 nm of Example 1.

[0116] The cycling performance of the above embodiments and comparative examples is listed in Table 1. The capacity performance at different rates is listed in Table 2.

[0117] Table 1

[0118]

[0119] Table 2

[0120]

[0121]

[0122] In summary, this invention utilizes ammonium pentaborate to modify the surface of lithium-rich manganese oxide cathode materials, providing an effective method to improve the overall electrochemical performance of these materials. The amount of ammonium pentaborate added affects the thickness and composition of the coating layer, the concentration of surface oxygen vacancies, and the content of the spinel phase, thus having varying impacts on performance. Therefore, the amount of ammonium pentaborate added needs to be carefully controlled. Following the above embodiments, this invention can be effectively implemented.

[0123] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. The specific examples used above to illustrate the present invention are only for the purpose of helping to understand the present invention and are not intended to limit the present invention. Those skilled in the art to which this invention pertains can make several simple deductions, modifications, substitutions, or combinations based on the concept of the present invention. These deductions, modifications, substitutions, or combinations also fall within the scope of the claims of the present invention.

Claims

1. A method for preparing a surface-modified layered lithium-rich manganese oxide cathode material, characterized in that, include: The layered lithium-rich manganese oxide substrate was uniformly mixed with ammonium pentaborate, and then subjected to pyrolysis reduction treatment to obtain the surface-modified layered lithium-rich manganese oxide cathode material. The layered lithium-rich manganese oxide substrate is selected from cobalt-free lithium-rich manganese oxide cathode materials; The mass ratio of layered lithium-rich manganese oxide substrate to ammonium pentaborate is 100:(5~15). The temperature of the pyrolysis reduction treatment is 300~500℃; The prepared surface-modified layered lithium-rich manganese oxide cathode material includes a layered lithium-rich manganese oxide substrate, a spinel heterostructure phase uniformly coated on the surface of the layered lithium-rich manganese oxide substrate, and a coating layer uniformly coated on the surface of the spinel heterostructure phase; the coating layer is selected from a B2O3 / Li2B4O7 dual-phase coating layer. The molar ratio of B2O3 to Li2B4O7 is 1:(1.0~2.5). The content of the spinel heterostructure phase is 4.0~6.1 wt%; the surface of the surface-modified layered lithium-rich manganese oxide cathode material is rich in oxygen vacancies, and the concentration of oxygen vacancies is 50~80 mol.

2. The method for preparing the surface-modified layered lithium-rich manganese oxide cathode material according to claim 1, characterized in that: The general structural formula of the layered lithium-rich manganese oxide substrate is as follows: x Li2MnO3-(1- x LiMO2, where M is selected from one or more of Ni, Mn, Cr, Fe, and Al, and 0 ≤ x ≤1; The layered lithium-rich manganese oxide substrate has a particle size of 100 nm to 10 µm.

3. The method for preparing the surface-modified layered lithium-rich manganese oxide cathode material according to claim 1, characterized in that: The thickness of the coating layer is 0.5~8.0 nm.

4. The method for preparing the surface-modified layered lithium-rich manganese oxide cathode material according to claim 3, characterized in that: The thickness of the coating layer is 1.0~5.0 nm.

5. The method for preparing the surface-modified layered lithium-rich manganese oxide cathode material according to claim 4, characterized in that: The thickness of the coating layer is 2.0~4.0 nm.

6. The method for preparing the surface-modified layered lithium-rich manganese oxide cathode material according to claim 1, characterized in that: The temperature of the pyrolysis reduction treatment is 300~400℃.

7. The application of a surface-modified layered lithium-rich manganese oxide cathode material prepared according to any one of claims 1 to 6 in lithium-ion batteries.

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