A surface cation-disordered modified lithium-rich manganese-based positive electrode material, a preparation method thereof and a lithium battery

Abstract

The application relates to the technical field of lithium battery materials, and discloses a surface cation-disordered modified lithium-rich manganese-based positive electrode material, a preparation method thereof and a lithium battery. A lithium-rich manganese-based positive electrode material is mixed with an exogenous transition metal compound with a full empty or half empty state at a d electron track, and secondary annealing treatment is carried out at 600 DEG C to 850 DEG C, so that a co-lattice growth layer with a cation-disordered structure is formed on the surface of the lithium-rich manganese-based positive electrode material. The disorderly distributed cations simultaneously affect the oxygen arrangement in the crystal structure, and further construct a surface-distributed delocalized oxygen structure. Therefore, the cation-disordered modified lithium-rich manganese-based positive electrode material exhibits excellent reversibility and kinetics of anion redox reaction, and the surface layer constructed can significantly inhibit the electrode / electrolyte interface side reaction; the prepared modified positive electrode can realize comprehensive improvement of high capacity and long cycle. The method has the advantages of simple process, low cost and obvious effect.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials technology, specifically to a surface cation disorder-modified lithium-rich manganese-based cathode material, its preparation method, and a lithium battery thereof. Background Technology

[0002] Lithium-ion batteries, due to their high energy density and long cycle life, have been widely used in electric vehicles, energy storage grids, and portable electronic products. However, the increasing demand for these batteries places higher requirements on their energy density, primarily limited by the cathode materials used. Existing commercial cathode materials, such as high-nickel ternary, lithium cobalt oxide, and lithium iron phosphate, have reached their capacity limits, making it impossible to achieve significant capacity breakthroughs within existing systems. Meanwhile, lithium-rich manganese-based cathodes (with the general molecular formula Li...)... 1.2 TM 0.8 O2 or xLi2MnO3·(1-x)LiTMO2 (TM = Mn, Ni, Co, etc.) stand out due to their ability to simultaneously utilize cation and anion redox reactions, providing extremely high discharge capacity. However, the poor reversibility of anion redox reactions can trigger irreversible oxygen oxidation, leading to OO dimerization and ultimately lattice oxygen loss. This process not only accelerates the migration and structural rearrangement of transition metals but also exacerbates side reactions with the electrolyte, causing continuous degradation and irreversible evolution of the electrode / electrolyte interface. Therefore, improving the reversibility of the anion redox reaction and stabilizing the electrode surface structure are key to improving the performance of lithium-rich manganese-based cathodes.

[0003] Chinese patent CN114784234A discloses a modification method for lithium-rich manganese-based cathodes through metal salt solution quenching and secondary annealing. This method achieves the synergistic construction of the surface coating layer caused by metal ion doping and fast ions rich in oxygen vacancies, thus optimizing the material's cycling stability and other properties. However, quenching conditions such as cooling rate are difficult to control, and the brine quenching process requires subsequent treatment of metal ions and organic solvents in the waste metal solution, which is not conducive to large-scale production. Chinese patent CN119481005A discloses a surface-modified lithium-rich manganese-based cathode material with multiple anion and cation modifications, which significantly improves the material's cycling stability and thermal stability under high temperature and high voltage conditions. However, the coating layer that cannot co-grow with the lithium-rich manganese-based cathode material is prone to uneven distribution, forming discontinuous island-like coating layers that are easily detached during electrochemical cycling. Furthermore, the introduction of various electrochemically inert elements can lead to a decrease in the material's specific capacity. Chinese patent CN103500824A discloses a lithium-rich manganese-based cathode with F and S anion surface post-treatment, which optimizes the material properties to some extent. However, obvious impurity phases appear in its X-ray diffraction, resulting in a lower specific capacity.

[0004] Current mainstream surface structure enhancement methods typically involve creating a protective surface layer by introducing epitaxial coatings or secondary phases with high Young's modulus. Epitaxial coatings can often construct fast ion transport channels or form HF isolation layers to strengthen the surface structure, while rigid substrates suppress lattice distortion by increasing lattice tolerance. However, these exogenous coatings often suffer from poor lattice matching and weak interfacial compatibility with the host material, increasing the risk of stress accumulation and coating delamination during long-term cycling. Given these challenges, there is an urgent need for intrinsic crystal structure engineering to simultaneously promote reversible redox reactions and enhance the electrode / electrolyte interface. Summary of the Invention

[0005] The primary objective of this invention is to provide a novel lithium-rich manganese-based cathode material. By forming a surface structure with a cation-disordered eutectic lattice growth on the surface of the lithium-rich manganese-based cathode, an oxygen structure with delocalized surface oxygen distribution is constructed. Therefore, the cation-disordered modified lithium-rich manganese-based cathode material exhibits excellent reversibility and kinetics of anionic redox reactions, while the constructed surface layer can significantly suppress side reactions at the electrode / electrolyte interface.

[0006] Another object of the present invention is to provide a method for preparing the above-mentioned material, which is simple, environmentally friendly and easy to scale up.

[0007] Another object of the present invention is to provide a lithium battery comprising the above-mentioned cathode material, which has high specific capacity and excellent cycle performance.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing a lithium-rich manganese-based cathode material with disordered surface cation modification, comprising the following steps:

[0010] S1. A precursor mixture is obtained by mixing lithium-rich manganese-based cathode material with an exogenous transition metal compound in which the d electron orbitals are in a fully or partially empty state.

[0011] S2. The precursor mixture is subjected to a secondary annealing treatment at 600℃~850℃ in an oxygen-containing atmosphere to form a eutectic lattice growth layer with a cation disordered structure on the surface of the lithium-rich manganese-based cathode material.

[0012] This process induces exogenous metal ions to enter the surface lattice of the material, rather than forming cation doping and surface coating modification in the traditional sense. It introduces supersaturated exogenous special d-electron structure cations into the gaps of the layered crystal structure to produce a disordered structure. This surface cation disordered structure coexists with the bulk lattice structure.

[0013] Furthermore, the lithium-rich manganese-based cathode material has a composition of Li 1.2 TM0.8 O2 or xLiTMO2·(1-x)Li2MnO3, where TM is one or more of Mn, Co, and Ni, and x ranges from 0 to 1.

[0014] Furthermore, the metal element in the exogenous transition metal compound is selected from at least one of Sc, Ti, V, Y, Zr, Nb, Mo, La, Hf, Ta, W, and Fe.

[0015] Furthermore, exogenous transition metals participate in the reaction in stable ionic form with their d-electron orbitals either fully or partially empty, including Sc. 3+ Ti 4+ V 5+ Y 3+ Zr 4+ 、Nb 5+ Mo 6+ La 3+ Hf 4+ Ta 5+ W 6+ Fe 3+ At least one of them.

[0016] Furthermore, based on the amount of transition metal elements, the mixing ratio of the transition metal content in the lithium-rich manganese-based cathode material to the content of the exogenous transition metal is (0.8:0.001) to (0.8:0.05).

[0017] Furthermore, the secondary annealing process takes 2 to 15 hours and the heating rate is 1 to 10 °C / min.

[0018] Furthermore, the exogenous metal compound is selected from at least one of oxides, carbonates, acetates, sulfates, and nitrates.

[0019] Secondly, the present invention provides a surface-modified lithium-rich manganese-based cathode material with cation-disordered structure, prepared by the aforementioned method, comprising: a lithium-rich manganese-based cathode material substrate; and a cation-disordered structural layer formed on the surface of the substrate; wherein the cation-disordered structural layer contains at least one doping element selected from Sc, Ti, V, Y, Zr, Nb, Mo, La, Hf, Ta, W, and Fe, and the cation-disordered structural layer and the substrate are in a eutectic lattice growth relationship. The thickness of the cation-disordered structural layer is 1–10 nm.

[0020] Thirdly, the present invention provides a lithium battery, including a positive electrode, wherein the positive electrode comprises a surface cation disorder modified lithium-rich manganese-based positive electrode material.

[0021] The technical solution provided by this invention has the following advantages compared with the prior art:

[0022] 1. The surface cation disordered structure prepared in this invention utilizes the original surface crystal structure of the cathode material, introducing supersaturated exogenous special d-electron structure cations into the interstitial spaces of the layered crystal structure to generate a disordered structure. This surface cation disordered structure coexists with the bulk lattice structure, which is fundamentally different from traditional cation doping and surface coating modification.

[0023] 2. The surface cation disordered lithium-rich manganese-based cathode material prepared by this invention can significantly improve the reversibility and kinetics of the anionic redox reaction of lithium-rich manganese-based cathode material, and the prepared modified cathode can achieve high discharge specific capacity and excellent cycle stability.

[0024] 3. The preparation method of this invention has low raw material costs, only requires raw material mixing and material calcination, and has a high degree of compatibility with existing production lines, making it suitable for large-scale industrial production. Attached Figure Description

[0025] Figure 1 The X-ray diffraction patterns are those of the unmodified lithium-rich manganese-based cathode material, the FeTi-induced surface cation disorder-modified lithium-rich manganese-based cathode material, the Fe-induced surface cation disorder-modified lithium-rich manganese-based cathode material, and the Ti-induced surface cation disorder-modified lithium-rich manganese-based cathode material obtained in Comparative Example 1 and Examples 1-3.

[0026] Figure 2 The images show scanning transmission electron microscopy (STEM) images of the unmodified lithium-rich manganese-based cathode material obtained in Comparative Example 1 and Example 1, and the FeTi-induced surface cation disorder-modified lithium-rich manganese-based cathode material.

[0027] Figure 3 The X-ray diffraction patterns are those of the unmodified lithium-rich manganese-based cathode materials and the Al-modified lithium-rich manganese-based cathode materials obtained in Comparative Examples 1 and 2.

[0028] Figure 4 This is an elemental distribution diagram of the lithium-rich manganese-based cathode material modified by low-temperature treatment of FeTi element in Comparative Example 3.

[0029] Figure 5 The X-ray diffraction patterns are those of the FeTi-induced surface cation disorder-modified lithium-rich manganese-based cathode material and the high-concentration FeTi-modified lithium-rich manganese-based cathode material obtained in Example 1 and Comparative Example 4.

[0030] Figure 6 Cycle performance of coin cells prepared from the materials obtained in Comparative Examples 1-4 and Examples 1-3.

[0031] Figure 7 Average voltage diagrams of coin cells prepared from the materials obtained in Comparative Examples 1-4 and Examples 1-3. Detailed Implementation

[0032] The present invention will now be described in detail with reference to the accompanying drawings, specific embodiments and comparative examples. The following embodiments and comparative examples are only some embodiments of this application and not all embodiments. The scope of protection of the present invention is not limited to the following embodiments and comparative examples.

[0033] Comparative Example 1

[0034] Preparation method of unmodified lithium-rich manganese-based cathode material, using Li 1.2 Mn 0.54 Co 0.13 Ni 0.13 Taking the classic O2-rich lithium-manganese-based cathode as an example, the steps are as follows:

[0035] Mn 4 / 6 Co 1 / 6 Ni 1 / 6 The CO3-rich lithium manganese-based cathode precursor and the lithium source were thoroughly mixed at a TM:Li molar ratio of 0.8:1.2. The mixture was heated to 500 °C at a heating rate of 3 °C / min in air and held for 6 h. Then, the mixture was heated to 850 °C at a heating rate of 3 °C / min and held for 12 h. After natural cooling to room temperature, the unmodified lithium-rich manganese-based cathode material (denoted as LRM) was obtained.

[0036] Example 1

[0037] The unmodified lithium-rich manganese-based cathode material Li obtained in Comparative Example 1 1.2 Mn 0.54 Co 0.13 Ni 0.13 O2 and exogenous transition metal compounds Fe2O3 and TiO2 were thoroughly mixed in a molar ratio of unmodified lithium-rich manganese-based cathode material:Fe:Ti=1:0.01:0.01. The mixture was then heated to 800 °C in air at a heating rate of 3 °C / min for a second annealing treatment for 12 h. After natural cooling to room temperature, FeTi-induced surface cation disordered modified lithium-rich manganese-based cathode material was obtained (denoted as FeTi-LRM).

[0038] Example 2

[0039] The steps are the same as in Example 1, except that the exogenous transition metal compound is replaced with Fe2O3, and the mixing molar ratio is unmodified lithium-rich manganese-based cathode material:Fe=1:0.02, to obtain Fe-induced surface cation disorder modified lithium-rich manganese-based cathode material (denoted as Fe-LRM).

[0040] Example 3

[0041] The steps are the same as in Example 1, except that the exogenous transition metal compound is replaced with TiO2, and the mixing molar ratio is unmodified lithium-rich manganese-based cathode material:Ti=1:0.02, to obtain Ti-induced surface cation disorder modified lithium-rich manganese-based cathode material (denoted as Ti-LRM).

[0042] Comparative Example 2

[0043] The unmodified lithium-rich manganese-based cathode material Li obtained in Comparative Example 1 1.2 Mn 0.54 Co 0.13 Ni 0.13 O2 and Al2O3 were thoroughly mixed in a molar ratio of unmodified lithium-rich manganese-based cathode material:Al = 1:0.02. The mixture was then subjected to a second annealing treatment at 800 °C for 12 h in air at a heating rate of 3 °C / min. After natural cooling to room temperature, Al-modified lithium-rich manganese-based cathode material (denoted as Al-LRM) was obtained.

[0044] Comparative Example 3

[0045] The unmodified Li obtained from Comparative Example 1 1.2 Mn 0.54 Co 0.13 Ni 0.13 O2 cathode material was thoroughly mixed with Fe2O3 and TiO2 at a molar ratio of unmodified cathode material:Fe:Ti = 1:0.01:0.01. The mixture was then subjected to a second annealing treatment in air at a heating rate of 3 °C / min to 500 °C for 12 h. After natural cooling to room temperature, a low-temperature FeTi-modified lithium-rich manganese-based cathode material (denoted as low-temperature FeTi-LRM) was obtained.

[0046] Comparative Example 4

[0047] The unmodified lithium-rich manganese-based cathode material obtained in Comparative Example 1, Li 1.2 Mn 0.54 Co 0.13 Ni 0.13 O2, Fe2O3, and TiO2 are thoroughly mixed at a molar ratio of unmodified cathode material:Fe:Ti = 1:0.03:0.03 (at this point, the molar ratio of the bulk transition metals Mn, Co, and Ni in the cathode material to the exogenous transition metals Fe and Ti is 0.8:0.06). The mixture is then subjected to a second annealing treatment at 800 °C for 12 h in air at a heating rate of 3 °C / min. After natural cooling to room temperature, a lithium-rich manganese-based cathode material modified with high concentration FeTi is obtained (denoted as high-concentration FeTi-LRM).

[0048] Electrochemical performance testing

[0049] The materials obtained in the examples and comparative examples were mixed with a conductive agent (such as Super P) and a binder (such as polyvinylidene fluoride) in a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone was added to form a slurry, which was then coated onto aluminum foil. After drying, the slurry was cut to serve as the positive electrode. A lithium metal negative electrode was matched in a glove box. The electrolyte used was the commercial electrolyte LB012 (specifically, a formulation of 1.15 M LiPF6 dissolved in ethylene carbonate, dimethyl carbonate, and methyl ethyl ester in a volume ratio of 1:1:1). Coin cells were assembled and their electrochemical performance was tested. The battery testing conditions were: three cycles of activation at 25 mA / g, followed by a cycle test at 125 mA / g.

[0050] Figure 1 The X-ray diffraction patterns of the unmodified lithium-rich manganese-based cathode material, the Fe-induced surface cation disorder-modified lithium-rich manganese-based cathode material, the Ti-induced surface cation disorder-modified lithium-rich manganese-based cathode material, and the FeTi-induced surface cation disorder-modified lithium-rich manganese-based cathode material obtained in Comparative Example 1 and Examples 1-3 are shown. The phase of the modified material did not change significantly, indicating that the secondary annealing did not introduce impurity phases and cause phase segregation. The elements of the secondary annealing entered the material lattice, and the X-ray diffraction peaks did not shift at all. The cell parameters of the modified material did not change significantly.

[0051] Figure 2 The images are scanning transmission electron microscope images of the unmodified lithium-rich manganese-based cathode material and the surface cation-disordered modified cathode material obtained in Comparative Example 1 and Example 1. The modified lithium-rich manganese-based cathode material shows obvious cation disorder distribution on the surface, while the interior still maintains a good ordered layered structure, indicating that the secondary annealing induces exogenous elements to enter the material surface lattice to form a cation disordered surface structure.

[0052] Figure 3 The X-ray diffraction patterns of the unmodified lithium-rich manganese-based cathode materials and the Al-modified lithium-rich manganese-based cathode materials obtained in Comparative Examples 1 and 2 are shown. Al does not have the special chemical property of a stable ionic form with d electron orbitals in a fully or partially empty state. After secondary annealing, its X-ray diffraction peaks shifted significantly, indicating that it entered the crystal lattice in the form of elemental doping. This shows a significant structural difference from the surface cation disorder modified cathode material in Example 1, indicating that Al cannot form a special surface cation disorder modified structure.

[0053] Figure 4The elemental distribution diagram of the lithium-rich manganese-based cathode material modified by FeTi element under low temperature treatment in Comparative Example 3 shows that the elemental distribution of Fe and Ti elements under annealing treatment at lower temperatures shows obvious local segregation. This indicates that Fe and Ti compounds cannot completely react with the material to form a homogeneous phase at lower temperatures, resulting in excessively high local concentrations of FeTi elements in the material, which cannot completely form the special surface cation disorder modification structure.

[0054] Figure 5 The X-ray diffraction patterns of the FeTi-induced surface cation disorder-modified lithium-rich manganese-based cathode material and the high-concentration FeTi-modified lithium-rich manganese-based cathode material obtained in Example 1 and Comparative Example 4 are shown. After secondary annealing, high concentrations of Fe and Ti elements were introduced, and obvious impurity phases appeared in the cathode material. This indicates that the introduction of excessively high concentrations of exogenous transition metal elements cannot completely enter the crystal lattice through the annealing process, and the cathode material changes from a pure phase material to a material containing impurity phases.

[0055] Figure 6 To compare the cycle performance of coin cells prepared from unmodified lithium-rich manganese-based cathode materials, Al-modified cathode materials, low-temperature treated FeTi-modified cathode materials, high-concentration FeTi-modified cathode materials, surface FeTi cation-disordered modified cathode materials, surface Fe cation-disordered modified cathode materials, and surface Ti cation-disordered modified cathode materials obtained in Examples 1-4 and 1-3, constant current charge-discharge tests were conducted at a current density of 125 mA / g. It can be seen that the performance of surface FeTi cation-disordered modified cathode materials, surface Fe cation-disordered modified cathode materials, and surface Ti cation-disordered modified cathode materials is improved due to the disordered cation structure, exhibiting cycle capacity retention rates of 90%, 87.8%, and 88.7%, respectively. The unmodified lithium-rich manganese-based cathode material exhibits the worst performance, with a cycle capacity retention rate of 75.8%. Al-modified cathode materials cannot achieve a disordered cation structure design, and their performance improvement effect is limited. Both low-temperature FeTi element-modified cathodes and high-concentration FeTi element-modified cathodes exhibit poor initial discharge specific capacity due to elemental or phase segregation.

[0056] Figure 7The average voltage evolution of coin cells prepared from unmodified lithium-rich manganese-based cathode materials, Al-modified cathode materials, low-temperature treated FeTi-modified cathode materials, high-concentration FeTi-modified cathode materials, surface FeTi cation disorder modified cathode materials, surface Fe cation disorder modified cathode materials, and surface Ti cation disorder modified cathode materials obtained in Comparative Examples 1-4 and Examples 1-3 was measured under constant current charge-discharge tests at a current density of 125 mA / g. The voltage decay of the cation disorder modified cathode materials was suppressed to varying degrees. Among them, the voltage decay of the surface FeTi cation disorder modified cathode material in Example 1 was only 1.10 mV / cycle.

[0057] In summary, the embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a surface cationically disordered modified lithium-rich manganese-based positive electrode material, characterized in that, The method comprises the following steps: S1. mixing a lithium-rich manganese-based positive electrode material with an exogenous transition metal compound having a full empty or half empty state at the d electron orbit, to obtain a precursor mixture; S2. performing secondary annealing treatment on the precursor mixture in an oxygen-containing atmosphere at 600-850 DEG C, to form a eutaxitic growth layer having a cation disordered structure on the surface of the lithium-rich manganese-based positive electrode material.

2. The production method according to claim 1, characterized by, The lithium-rich manganese-based positive electrode material has a composition of Li 1.2 TM 0.8 O2 or xLiTM02·(1-x)Li2Mn03, wherein TM is one or more of Mn, Co, Ni, and x ranges from 0 to 1.

3. The preparation method according to claim 1, characterized in that, The metal element in the exogenous transition metal compound is selected from at least one of Sc, Ti, V, Y, Zr, Nb, Mo, La, Hf, Ta, W and Fe.

4. The production method according to claim 3, characterized by, The exogenous transition metal participates in the reaction in the form of a stable ion with a full or half-empty d electron shell, including at least one of Sc 3+ , Ti 4+ , V 5+ , Y 3+ , Zr 4+ , Nb 5+ , Mo 6+ , La 3+ , Hf 4+ , Ta 5+ , W 6+ , Fe 3+ .

5. The preparation method according to claim 1, characterized in that, The mixing ratio of the transition metal content in the lithium-rich manganese-based positive electrode material body to the exogenous transition metal content is (0.8:0.001)-(0.8:0.05) in terms of the amount of substance of the transition metal element.

6. The method of claim 1, wherein, The processing time of the secondary annealing is 2-15 h, and the heating rate is 1-10 DEG C / min.

7. The preparation method according to claim 1, characterized in that, The exogenous transition metal compound is selected from at least one of oxides, carbonates, acetates, sulfates and nitrates.

8. A surface cationically disordered modified lithium-rich manganese-based positive electrode material, characterized in that, The positive electrode material is prepared by the method of any one of claims 1-7, and comprises a lithium-rich manganese-based positive electrode material body and a cation disordered structure layer formed on the surface of the body, wherein the cation disordered structure layer contains at least one doping element selected from Sc, Ti, V, Y, Zr, Nb, Mo, La, Hf, Ta, W and Fe, and the cation disordered structure layer and the body are in a eutaxitic growth relationship.

9. The surface cation-disordered modified lithium-rich manganese-based positive electrode material of claim 8, wherein, The thickness of the cation disordered structure layer is 1-10 nm.

10. A lithium battery comprising a positive electrode, characterized in that, The positive electrode contains the surface cation disordered modified lithium-rich manganese-based positive electrode material of any one of claims 8-9.

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