A lattice interlocking type lithium-rich manganese-based positive electrode material, a preparation method and application thereof

Abstract

This invention provides a lattice-interlocked lithium-rich manganese-based cathode material, its preparation method, and its application, relating to the field of battery cathode material preparation technology. By introducing a certain amount of sodium ions during the synthesis process, highly stacked stacking faults are induced in a high-temperature chamber, further inducing the growth and fusion of surface defects to form a lattice-interlocked twin structure. This requires only one high-temperature sintering and one water washing process, improving the TM migration barrier and oxygen diffusion barrier, interrupting phase transition diffusion, solving the problem of cyclic instability in lithium-rich material structures, reducing stress and strain in layered materials during charge and discharge, greatly eliminating lattice stress, suppressing expansion and crystal plane slip during charge and discharge, and improving interface stability.

Description

Technical Field

[0001] This invention relates to the field of battery cathode material preparation technology, and in particular to a lattice-interlocked lithium-rich manganese-based cathode material, its preparation method, and its application. Background Technology

[0002] Layered lithium-rich cathode materials have attracted significant market attention and popularity in recent years due to their advantages such as high specific capacity, high thermal stability, and low cost. Developing manganese-rich high-energy-density cathode materials can not only meet the industry's urgent needs for high specific energy and high safety, but also reduce nickel and cobalt resource consumption, promoting the healthy and sustainable development of the industry. However, layered lithium-rich materials suffer from rapid structural phase transitions and degradation during cycling, as well as oxygen loss caused by the generation, diffusion, and condensation of oxygen vacancies. Furthermore, the large anisotropic lattice stress generated in layered oxide materials during charge-discharge cycling leads to volume expansion and harmful crystal facet slip, further reducing the stability of the material structure. These degradations are closely related to oxygen loss, but the inherent limitations of the traditional oxygen framework, constrained by the cubic lattice arrangement of oxygen, have prevented the resolution of the intrinsic problems of lithium-rich materials.

[0003] Because the traditional cubic oxygen framework of layered oxides facilitates transition metal migration, structural phase transitions, and diffusion, the cubic oxygen structure is unstable in the delithiation state, and even phase transitions are thermodynamically permissible. Layered-spinel-rock salt phase transitions are readily observed in lithium-rich materials. From a crystallographic perspective, the layered-spinel phase transition is extremely easy. This is because both spinel and layered structures possess the same close-packed oxygen structure and ABCABC stacking sequence, meaning they have the same oxygen framework. The only difference lies in the arrangement of lithium and transition metals in the gaps between the oxygen framework. The layered-spinel phase transition requires and necessitates the same oxygen framework, namely a cubic close-packed (ccP) oxygen structure. Lithium-rich crystal structures are two-dimensional layered structures, with alternating lithium and transition metal layers. Phase transition diffusion is directional, and the generation, diffusion, and migration of oxygen vacancies are also directional, perpendicular to the direction of change. <003> Therefore, by controlling the geometry of the oxygen framework to form lattice interlocks, the formation of a cubic close-packed (CCP) oxygen structure can be prevented, thus disrupting the order of the oxygen framework and preventing transition metal migration, phase transition diffusion, and oxygen vacancy diffusion and condensation, thereby improving the stability of the oxygen framework structure. For example, Chinese patent CN117038953A discloses a micron-scale monodisperse lithium-rich manganese-based cathode material with a layered structure and a local oxygen atom packing pattern of ABCACB. It has twin interfaces that improve rate performance, but the phase interface angle is about 150°, close to 180°, which still has limited effect on improving stress and strain.

[0004] Therefore, the design and synthesis disrupted the long-range structure of the original transition metal layer, forming a lattice-interlocked crystal configuration. This improved the TM migration barrier and oxygen diffusion barrier, interrupted phase transition diffusion, and solved problems such as the structural instability and stress-strain issues of lithium-rich materials. However, an effective method for preparing cathode materials with lattice-interlocked characteristics is still lacking and requires further development. Summary of the Invention

[0005] To address the above problems, this invention improves the stress-strain and cycle stability of layered materials during charge-discharge processes by preparing lithium-rich manganese-based cathode materials with a lattice-interlocked crystal structure.

[0006] One of the objectives of this invention is to provide a lattice-interlocked lithium-rich manganese-based cathode material.

[0007] The second objective of this invention is to provide a method for preparing the lattice-interlocked lithium-rich manganese-based cathode material.

[0008] A third objective of this invention is to provide an application of this lattice-interlocked lithium-rich manganese-based cathode material.

[0009] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0010] In a first aspect, the present invention provides a lattice-interlocked lithium-rich manganese-based cathode material, wherein the molecular formula of the lithium-rich manganese-based cathode material is xLi2MnO3·(1-x)LiMO2, wherein M is one or more elements selected from Mn, Ni, Mg, La and W, and 0≤x≤0.6 (x, for example, 0.1, 0.2, 0.3, 0.4, 0.5);

[0011] The lithium-rich manganese-based cathode material has at least two sets of crystal lattices with different orientations, which are grown together in different directions to form a crystal structure with interlocked lattices. The interaction angle θ of the crystal lattices is 15° < θ < 90°.

[0012] The material of this invention has a lattice-interlocked crystal structure, having two or more sets of lattices ( Figure 1 The diagram shows two sets of crystal lattices, i.e., twin or multiple structures, which are nested together at a certain angle to form an interlocking structure. The interlocking interaction angle θ is 15° < θ < 90°. θ represents the angle (acute angle) formed between crystal lattices in different directions.

[0013] In some embodiments, the (018) / (110) layered indicator peak of the lithium-rich manganese-based cathode material in XRD shows broadening and splitting into one or more shoulder peaks. This indicates a lattice-interlocked twin (mirror-symmetric) crystal structure with an interlocked twin interface. The interface structure has three-dimensional lithium-ion conduction capability, allowing lithium ions to be rapidly transported along the twin interface.

[0014] Figure 2 A schematic diagram is shown comparing the layered structure of a conventional lithium-rich material with the interlocked crystal structure of this invention. The interlocked lattice stress is much lower than that of the conventional layered structure. Figure 2 As shown in the middle right figure, due to the different lengths of each layer, the center of mass of the force also differs. Because the transition metal layers gradually decrease in size, F1>F2>F…>F… n Then the interlocking cumulative stress can be expressed as: F tw =F1 + F2 + ... + F n-1 Furthermore, the stress centers are not on the same straight line, greatly dispersing the stress distribution. In this case, the stress can be considered to be distributed on a single plane, whereas conventional lattice stress is highly concentrated on a single straight line. In twinned structures, the stress points are dispersed, not on the same straight line, and are much smaller than conventional stress. In addition, the lattice stress in another direction forms a certain angle with the twinned structure, and their resultant force is directed towards the twin grain boundary, forming an angle with the c-axis. This significantly reduces stress concentration.

[0015] Secondly, the present invention provides a method for preparing a lattice-interlocked lithium-rich manganese-based cathode material, comprising the following steps:

[0016] A cobalt-free manganese-rich hydroxide precursor, lithium salt, and sodium salt are mixed in stoichiometric ratio and sintered. The mixture is then naturally cooled to room temperature, washed with water, and dried to obtain a lithium-rich manganese-based cathode material. The mass of the sodium salt is more than 20% of the mass of the lithium salt.

[0017] The cobalt-free manganese-rich hydroxide precursor has the molecular formula Mn. z M 1-z (OH)2, M is one or more selected from Ni, Mg, La and W, where z>0.5;

[0018] The lithium salt is selected from one or more of lithium carbonate, lithium acetate and lithium hydroxide;

[0019] The sodium salt is selected from one or more of sodium carbonate, sodium bicarbonate, sodium nitrate, and sodium acetate.

[0020] In some embodiments, the sintering heating rate is 2-10℃ / min, the sintering temperature is 750-950℃, and the holding time is 6-20h.

[0021] In some implementations, the drying temperature is 100-300°C.

[0022] In one specific embodiment, the preparation of lithium-rich manganese-based cathode material includes the following steps:

[0023] Prepare Mn according to stoichiometric ratio 0.75 Ni 0.25 (OH)2, Mn 0.65 Ni0.35 (OH)2 and Mn 0.70 Ni 0.30 (OH)2 and other precursors are weighed together with lithium salt Li2CO3 and sodium carbonate accounting for more than 20% of the lithium salt. They are mixed evenly in a high-speed mixer. Sintering process: The temperature is increased at 5℃ / min and held at 880℃ for 15h. Then it is naturally cooled to room temperature. The residual sodium is then washed away with deionized water and dried at 200℃ for 5h to obtain lithium-rich manganese-based cathode material.

[0024] Thirdly, the present invention provides an application of the above-mentioned lattice-interlocked lithium-rich manganese-based cathode material in the preparation of lithium-ion batteries.

[0025] Beneficial effects:

[0026] This invention provides a lattice-interlocked lithium-rich manganese-based cathode material. By introducing a specific amount of sodium ions into a cobalt-free manganese-rich precursor and lithium carbonate during sintering, a highly large-scale stacking fault is induced under high-temperature conditions, which in turn induces the growth and fusion of surface defects, forming a lattice-interlocked twin structure. It only requires one high-temperature sintering and one water washing process, without the need for additional ion exchange. This improves the TM (transition metal) migration barrier and oxygen diffusion barrier, interrupts phase transition diffusion, solves the problem of cyclic instability of lithium-rich material structure, reduces the lattice stress and strain of layered materials during charging and discharging, greatly eliminates lattice stress, reduces lattice stress during charging and discharging to suppress expansion and crystal plane slip, and increases the proportion of stable crystal plane (003) (twin planes end with (003) crystal planes, so the proportion of (003) surface in twin structure is naturally high), which is more conducive to improving interface stability.

[0027] The lithium-rich manganese-based cathode material of this invention significantly improves electrochemical performance, such as initial efficiency and cycle stability at room temperature and high temperature. For example, the initial efficiency of the material is increased to over 85%, and the high-temperature cycle stability of the lithium-rich manganese-based cathode material is improved, with the capacity retention rate after 300 cycles at 4.8V-45℃ increasing to over 80.0%.

[0028] The present invention has been described in detail above; however, the above embodiments are merely illustrative in nature and are not intended to limit the invention. Furthermore, this document is not limited to the foregoing prior art or the invention itself, or to any theory described in the following embodiments. Attached Figure Description

[0029] Figure 1 This is a simulation diagram of the interlocked lattice structure (dots represent twin grain boundary atoms);

[0030] Figure 2 The diagram shows a lattice interlocked structure, where (a) is the crystal structure of a traditional lithium-rich material and (b) is the lattice interlocked crystal structure of the present invention.

[0031] Figure 3 The phase structures of Comparative Example 1 and Example 1 are shown;

[0032] Figure 4 The images are TEM images of the crystal structures of Comparative Example 1 and Example 1, where the left image is the conventional crystal structure of Comparative Example 1 and the right image is the lattice-interlocked crystal structure of Example 1.

[0033] Figure 5 First charge-discharge curves of Comparative Example 1 and Examples 1-4;

[0034] Figure 6 High-temperature cycling stability of Examples 1-4;

[0035] Figure 7 The images show TEM images of the crystal structures of Comparative Example 1 and Example 1 after cycling.

[0036] Figure 8 This is a TEM image of the crystal structure for Comparative Example 2. Detailed Implementation

[0037] The present invention will be further described below with reference to the embodiments. It should be noted that the following embodiments are provided for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention.

[0038] Unless otherwise specified, the raw materials, reagents, and methods used in the embodiments are all conventional raw materials, reagents, and methods in the art.

[0039] Electrochemical performance testing: Evaluation was conducted using a coin cell in a Blue Battery testing system. The charge / discharge current was set at 1C = 200 mAh / g, and the voltage window was 2.0-4.8V. High-temperature cycling was performed in a biochemical incubator at a temperature of 45℃.

[0040] Characterization of the interlocked lattice structure: performed using transmission electron microscopy.

[0041] Comparative Example 1

[0042] Preparation of lithium-rich manganese-based cathode materials:

[0043] Weigh the precursor Mn according to stoichiometry. 0.75 Ni 0.25 (OH)₂ and lithium salt Li₂CO₃ were mixed uniformly using a high-speed mixer and then sintered: the temperature was increased at 5℃ / min and held at 880℃ for 15 hours, followed by natural cooling to room temperature to obtain lithium-rich manganese-based cathode material Li. 1.09 (Mn 0.75 Ni 0.25 ) 0.91 O2.

[0044] Comparative Example 2

[0045] Preparation of lithium-rich manganese-based cathode materials:

[0046] Weigh the precursor Mn according to stoichiometry. 0.67 Ni 0.165 Co 0.165 (OH)₂ and lithium salt Li₂CO₃ were mixed uniformly using a high-speed mixer and then sintered: the temperature was increased at 5℃ / min and held at 880℃ for 15 hours, followed by natural cooling to room temperature to obtain lithium-rich manganese-based cathode material Li. 1.2 (Mn 0.67 Ni 0.165 Co 0.165 ) 0.8 O2. Crystal structure as follows Figure 8 As shown, traditional layered cobalt-rich lithium materials have a highly ordered orientation, with lithium layers and transition metal layers stacked alternately, but do not form an interlocking lattice structure.

[0047] Example 1

[0048] Take 6g of manganese-rich precursor Mn 0.75 Ni 0.25 (OH)₂, 2.952 g of lithium carbonate, and 0.6 g of sodium carbonate were mixed evenly using a mixer. The mixture was heated to 880°C at a rate of 5°C / min and held at that temperature for 15 hours. It was then allowed to cool naturally to room temperature. Residual sodium was washed away with deionized water, and the mixture was dried at 200°C for 5 hours to obtain the lattice-interlocked twinned lithium-rich material Li. 1.1 (Mn 0.75 Ni 0.25 ) 0.9 O2.

[0049] The phase structure and degree of interlocking of the sample are determined by XRD, such as... Figure 3 As shown, the lithium-rich material in Comparative Example 1 has a typical composite layered structure of R-3m and C2 / m phases. However, the intensity ratio of the modified (003) / (104) peak increases from 1.375 to 1.429, indicating that the layered structure is strengthened. It is also worth noting that the layered indicator peak (018) / (110) peak has broadened and split. These additional peaks correspond to the special structure at the twin interface, indicating that twin phases may be formed.

[0050] The lattice interlocking structure was further determined using HR-TEM, such as... Figure 4 As shown in the middle left figure, traditional layered lithium-rich materials exhibit highly ordered orientation, with lithium layers and transition metal layers stacked alternately, all in accordance with... <001> The direction is perpendicular. In this type of structure, the lattice stress is anisotropic during charging and discharging, along... <001> The direction exhibits the greatest stress and the most intense expansion and contraction. For example... Figure 4 As shown in the middle right figure, the sample structure of Example 1 is different from the traditional layered structure. It has two sets of lattices with different orientations, which grow together at a certain angle, with an interaction angle of about 60°.

[0051] The electrochemical performance of lithium-rich materials with this structure will be greatly improved:

[0052] First Coulomb efficiency, such as Figure 5 Compared with Table 1, the initial efficiency of Comparative Example 1 was significantly improved from 76.5% to 85.6%. The first-week specific capacity increased from 242 mAh g / L of Comparative Example 1. -1 Increased to 256.6mAh g -1 .

[0053] Cyclic performance, such as Figure 6 As shown, the initial 1C discharge capacity of the Comparative Example 1 sample was 194 mAh g. -1 After 300 cycles, it decreased to 79.4 mAh g. -1 The capacity retention rate was only 40.9%; while the 1C discharge capacity of the lithium-rich material with lattice interlocking increased to 216.9 mAh g. -1 After 300 full cycles, there is still 200.5 mAh g. -1 The capacity retention rate is as high as 92.4%. These results indicate that lattice-locked structures exhibit excellent electrochemical performance, especially high-temperature cycling stability.

[0054] Furthermore, lithium-rich materials with interlocked lattices exhibit very stable structures even after cycling. For example... Figure 7 As shown, in Comparative Example 1, after cycling, the crystal structure transformed from layered to spinel, and even to rock salt phase, as obtained by Fourier transform. Meanwhile, the crystal structure with interlocked lattice exhibited clear layered lattice fringes, indicating that it maintained its structural stability during long cycles.

[0055] Example 2

[0056] Take 6.0g of manganese-rich precursor Mn 0.75 Ni 0.25 (OH)2, increase the lithium carbonate content to 3.32g and sodium carbonate to 1g, mix evenly using a mixer, heat at 880℃ for 15h at a heating rate of 5℃ / min, then allow to cool naturally to room temperature. Wash away residual sodium with deionized water, and dry at 200℃ for 5h to obtain the lattice-interlocked twinned lithium-rich material Li. 1.13 (Mn 0.75 Ni 0.25 ) 0.87 O2.

[0057] The electrochemical performance is shown in Table 1.

[0058] Example 3

[0059] Take 6g of manganese-rich precursor Mn 0.75 Ni 0.25 (OH)₂, 3.36 g of lithium carbonate, and 1 g of sodium carbonate were mixed evenly using a mixer. The mixture was heated to 880°C at a rate of 5°C / min and held at that temperature for 15 hours. It was then allowed to cool naturally to room temperature. Residual sodium was washed away with deionized water, and the mixture was dried at 200°C for 5 hours to obtain the lattice-interlocked twinned lithium-rich material Li. 1.16 (Mn 0.75 Ni 0.25 ) 0.84 O2.

[0060] The electrochemical performance is shown in Table 1.

[0061] Example 4

[0062] Take 6g of manganese-rich precursor Mn 0.65 Ni 0.35 The synthesis of lithium-rich material Li-1, consisting of (OH)2, 3g of lithium carbonate, and 0.65g of sodium carbonate, follows the same procedure as above. 1.09 (Mn 0.65 Ni 0.35 ) 0.91 O2.

[0063] The electrochemical performance is shown in Table 1.

[0064] Example 5

[0065] Take 6g of manganese-rich precursor Mn 0.6 Ni 0.4 The synthesis of lithium-rich material Li-1, consisting of (OH)2, 3g of lithium carbonate, and 0.65g of sodium carbonate, follows the same procedure as above. 1.09 (Mn 0.6 Ni 0.4 ) 0.91 O2.

[0066] The electrochemical performance is shown in Table 1.

[0067] Example 6

[0068] Take 6g of manganese-rich precursor Mn 0.7 Ni 0.3 The synthesis of lithium-rich material Li-1, consisting of (OH)2, 3g of lithium carbonate, and 0.65g of sodium carbonate, follows the same procedure as above. 1.09 (Mn 0.7 Ni 0.3 ) 0.91 O2.

[0069] The electrochemical performance is shown in Table 1.

[0070] Example 7

[0071] Take 6g of manganese-rich precursor Mn 0.7 Ni 0.3 The synthesis of lithium-rich material Li-1, consisting of (OH)2, 3g of lithium carbonate, and 1g of sodium carbonate, follows the same procedure as above. 1.09 (Mn 0.7 Ni 0.3 ) 0.91 O2.

[0072] The electrochemical performance is shown in Table 1. With increasing sodium carbonate content, the specific capacity increased to 268.8 mAh / g, but the cycle performance decreased to 81.7%.

[0073] Example 8

[0074] Take 6g of manganese-rich precursor Mn 0.7 Ni 0.3 The synthesis of lithium-rich material Li-1, a lattice-interlocked twinned lithium material, can be obtained by combining (OH)2, 3.32 g of lithium carbonate, and 3 g of sodium carbonate, following the same procedure as above. 1.15 (Mn 0.7 Ni 0.3 ) 0.85 O2.

[0075] The electrochemical performance is shown in Table 1.

[0076] Table 1 Electrochemical performance

[0077]

[0078] The above embodiments are merely illustrative of the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and substance defined by the claims of the present invention; and such modifications or substitutions are still within the scope defined by the claims of the present invention.

Claims

1. A lattice-interlocked lithium-rich manganese-based cathode material, characterized in that, The molecular formula of the lithium-rich manganese-based cathode material is xLi2MnO3·(1-x)LiMO2, where M is one or more elements selected from Mn, Ni, Mg, La and W, and 0≤x≤0.6; The lithium-rich manganese-based cathode material has at least two sets of crystal lattices with different orientations, which are grown together in different directions to form a crystal structure with interlocked lattices. The interaction angle θ of the crystal lattices is 15° < θ < 90°. The (018) / (110) layered indicator peak of the lithium-rich manganese-based cathode material XRD is broadened and split into one or more shoulder peaks; The preparation method of the lattice-interlocked lithium-rich manganese-based cathode material includes the following steps: A cobalt-free manganese-rich hydroxide precursor, lithium salt, and sodium salt are mixed in a stoichiometric ratio and then sintered. The mixture is then naturally cooled to room temperature, washed with water, and dried to obtain a lithium-rich manganese-based cathode material. The mass of the sodium salt is more than 20% of the mass of the lithium salt. The molecular formula of the cobalt-free manganese-rich hydroxide precursor is Mn z M 1-z (OH)2, where M is one or more of Mn, Ni, Mg, La and W, and z>0.

5.

2. The lithium-rich manganese-based cathode material according to claim 1, characterized in that, The lithium salt is selected from one or more of lithium carbonate, lithium acetate, and lithium hydroxide.

3. The lithium-rich manganese-based cathode material according to claim 1, characterized in that, The sodium salt is selected from one or more of sodium carbonate, sodium bicarbonate, sodium nitrate, and sodium acetate.

4. The lithium-rich manganese-based cathode material according to claim 1, characterized in that, The sintering heating rate is 2-10℃ / min, the sintering temperature is 750-950℃, and the holding time is 6-20h.

5. The lithium-rich manganese-based cathode material according to claim 1, characterized in that, The drying temperature is 100-300℃.

6. The application of the lithium-rich manganese-based cathode material according to any one of claims 1-5 in the preparation of lithium-ion batteries.

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