Lattice interlocking type lithium-rich manganese-based positive electrode material as well as preparation method and application thereof

Abstract

The invention provides a lattice interlocking type lithium-rich manganese-based positive electrode material as well as a preparation method and application thereof, and relates to the technical field of preparation of battery positive electrode materials. A certain amount of sodium ions are introduced in the synthesis process, formation of highly stacked faults is induced in a high-temperature box, then surface defect growth and fusion are induced, a lattice interlocking twin crystal structure is formed, only one-time high-temperature sintering and one-time washing processes are needed, a TM migration energy barrier and an oxygen diffusion energy barrier are improved, phase change diffusion is interrupted, and the preparation method is simple and convenient to operate. The problem of structural circulation instability of the lithium-rich material is solved, the stress strain of the layered material in the charging and discharging process is reduced, the lattice stress is greatly eliminated, the lattice stress in the charging and discharging process is reduced, the expansion and crystal face slippage are inhibited, and the interface stability is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of cathode materials for batteries, and particularly relates to a lithium-rich manganese-based cathode material with lattice interlocking, and a preparation method and application thereof. Background Art

[0002] Layered lithium-rich cathode materials have the advantages of high specific capacity, high thermal stability, and low price, and have attracted much attention and pursuit in the market in recent years. Developing high specific energy lithium-rich manganese-based cathode materials can not only meet the urgent needs of the industry for high specific energy and high safety, but also reduce the consumption of nickel and cobalt resources and promote the healthy and sustainable development of the industry. However, layered lithium-rich materials are subject to rapid structural phase transformation and degradation during cycling, the generation, diffusion, and aggregation of oxygen vacancies resulting in oxygen loss, etc., and large anisotropic lattice stresses are generated during the charge and discharge cycling process of layered oxide materials, leading to volume expansion, and harmful crystal plane slip further reduces the structural stability of the materials. These attenuations are closely related to oxygen loss, but have long been limited by the stacking arrangement of the oxygen cubic lattice and cannot break through the inherent limitations of the traditional oxygen skeleton, resulting in the failure to solve the intrinsic problems of lithium-rich materials.

[0003] Due to the traditional oxygen cubic skeleton of layered oxides being conducive to the migration of transition metals, the generation and diffusion of structural phase transformation, the oxygen cubic structure is unstable in the delithiated state, and even the occurrence of phase transformation is thermodynamically allowed. In lithium-rich materials, layered-spinel-rocksalt structure phase transformation is prone to occur. From a crystallographic perspective, the layered-spinel phase transformation is extremely easy. Because both the spinel structure and the layered structure have the same oxygen close-packed structure and the ABCABC stacking sequence, that is, they have the same oxygen skeleton, and the only difference lies in the arrangement of lithium and transition metals in the oxygen skeleton gaps. The layered-spinel phase transformation requires and has the same oxygen skeleton, which is an oxygen cubic close stacking (ccp) structure. The lithium-rich crystal structure is a two-dimensional layered structure, formed by alternating stacking of lithium layers and transition metal layers. And the phase transformation diffusion is directional, and the generation, diffusion, and migration of oxygen vacancies are also directional, perpendicular to <003>. Therefore, by regulating the geometric structure of the oxygen skeleton to form lattice interlocking to prevent the formation of oxygen cubic close packing (ccp) structure, break the order of the oxygen skeleton, and then prevent the migration of transition metals, phase transformation diffusion, and oxygen vacancy diffusion and aggregation, and improve the stability of the oxygen framework structure. For example, Chinese Patent CN117038953A discloses a micron-sized monodisperse lithium-rich manganese-based cathode material, which is a layered structure, and the local oxygen atom stacking mode is ABCACB, with twin interfaces improving the rate performance, but the phase interface angle is about greater than 150°, close to 180 °C, and the effect on improving stress and strain is still limited.

[0004] Therefore, the design and synthesis break the long-range structure of the original transition metal layer, form a crystal configuration with lattice interlocking, increase the TM migration barrier and oxygen diffusion barrier, interrupt the phase change diffusion, and solve the problems of structural cycling instability, stress and strain of lithium-rich materials. However, there is still a lack of an effective method for preparing cathode materials with lattice interlocking characteristics, which needs to be further developed. Summary of the Invention

[0005] In view of the above problems, the present invention improves the stress-strain and cyclic stability of the structure of layered materials during charge and discharge by preparing a lithium-rich manganese-based cathode material with a lattice interlocking crystal configuration.

[0006] One of the purposes of the present invention is to provide a lithium-rich manganese-based cathode material with a lattice interlocking type.

[0007] Another purpose of the present invention is to provide a preparation method for the lithium-rich manganese-based cathode material with a lattice interlocking type.

[0008] A third purpose of the present invention is to provide an application of the lithium-rich manganese-based cathode material with a lattice interlocking type.

[0009] In order to achieve the above purposes of the present invention, the following technical solutions are specifically adopted:

[0010] In the first aspect, the present invention provides a lithium-rich manganese-based cathode material with a lattice interlocking type. 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 (x is, 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 lattices with different orientations, which grow together interactively in different directions to form a crystal structure with lattice interlocking. The interaction angle θ of the lattices is 15° < θ < 90°.

[0012] The material of the present invention has a crystal structure with lattice interlocking, and has two or more sets of lattices ( Figure 1 two sets of lattices are shown), that is, a twin (twinning) or multiple birth structure, which grow together nested at a certain angle to form an interlocking structure. The interaction angle θ of the interlocking is 15° < θ < 90°. θ represents the included angle (acute angle) formed between lattices in different directions.

[0013] In some embodiments, the (018) / (110) layered indication peaks of the XRD of the lithium-rich manganese-based cathode material are broadened and split into one or more shoulder peaks. This indicates that it has a twin (mirror symmetry) crystal structure with lattice interlocking, there is an interlocking twin interface, and the interface structure has three-dimensional lithium-ion conduction ability, and lithium ions can be rapidly transported along the twin interface.

[0014] Figure 2 The schematic diagrams of the layered structure of traditional lithium-rich materials and the interlocked crystal structure of the present invention are shown. The interlocked lattice stress is much smaller than that of the traditional layered structure. As Figure 2 shown in the right figure in [reference], since the length of each layer is different, the centroid of the force is also different. Due to the gradual decrease of the transition metal layer, F1 > F2 > F... > F n , then the cumulative interlocked stress can be expressed as: F tw = F1 + F2 +... + F n-1 . Moreover, the centroids of the stress are not on the same straight line, which greatly disperses the stress distribution. At this time, it can be considered that the stress is distributed on a plane, while the conventional lattice stress is highly concentrated on the same straight line. The stress points of the twin crystal structure are dispersed, not on the same straight line, and are much smaller than the conventional stress. In addition, the lattice stress in the other direction forms a certain angle with it, and the resultant force direction of them is the direction of the twin crystal boundary, forming an angle with the c-axis. This greatly reduces the stress concentration.

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

[0016] Mix a cobalt-free rich-manganese hydroxide precursor, a lithium salt, and a sodium salt according to a stoichiometric ratio, then sinter them, naturally cool to room temperature, and then perform water washing and drying to obtain the lithium-rich manganese-based cathode material; the mass of the sodium salt is more than 20% of the mass of the lithium salt.

[0017] Among them, the formula of the cobalt-free rich-manganese hydroxide precursor is 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 one or more selected from lithium carbonate, lithium acetate, and lithium hydroxide;

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

[0020] In some embodiments, the heating rate of sintering is 2 - 10 °C / min, the sintering temperature is 750 - 950 °C, and the heat preservation time is 6 - 20 h.

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

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

[0023] Prepare Mn 0.75 Ni 0.25 (OH)2, Mn 0.65 Ni0.35 (OH)2 and Mn 0.70 Ni 0.30 Precursors such as (OH)2, weigh out the precursors and lithium salt Li2CO3, and sodium carbonate accounting for more than 20% of the lithium salt, and mix them evenly together with a high-speed mixer. Sintering process: heat at a rate of 5 °C / min, hold at 880 °C for 15 h, then cool naturally to room temperature, then wash the residual sodium with deionized water, and dry at 200 °C for 5 h to obtain the 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] The present invention provides a lattice-interlocked lithium-rich manganese-based cathode material. By introducing a specific amount of sodium ions during the sintering process of the cobalt-free manganese-rich precursor and lithium carbonate, a highly large-scale stacking fault is induced to form under high-temperature conditions, and then the growth and fusion of plane defects are induced to form a lattice-interlocked twin structure. Only one high-temperature sintering and one water-washing process are required, and no additional ion-exchange method is needed. It improves the migration energy barrier of TM (transition metal) and the oxygen diffusion energy barrier, interrupts the phase-transition diffusion, solves the problem of structural cyclic instability of lithium-rich materials, reduces the lattice stress and strain of layered materials during charge and discharge, greatly eliminates the lattice stress, reduces the lattice stress during charge and discharge to inhibit expansion and crystal plane slip, and moreover, increases the proportion of the stable crystal plane (003) (the twin plane ends with the (003) crystal plane, so the proportion of the (003) surface in the twin structure is naturally high), which is more conducive to improving the interface stability.

[0027] The lithium-rich manganese-based cathode material of the present invention greatly improves the electrochemical performance, such as the initial efficiency and the cycle stability at room temperature and high temperature. For example: the initial efficiency of the material is increased to more than 85%, the high-temperature cycle stability of the lithium-rich manganese-based cathode material is improved, and the capacity retention rate after 300 cycles at 4.8 V - 45 °C is increased to more than 80.0%.

[0028] The present invention has been described in detail above, but the above embodiments are essentially illustrative and are not intended to limit the present invention. In addition, the present invention is not limited by any theory described in the foregoing prior art, invention content or the following examples. Description of the drawings

[0029] Figure 1 It is a simulation diagram of the lattice-interlocked structure (the dots represent the atoms at the twin grain boundaries);

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

[0031] Figure 3 For the phase structures of Comparative Example 1 and Example 1;

[0032] Figure 4 For the TEM images of the crystal structures of Comparative Example 1 and Example 1, where the left figure is the traditional crystal structure of Comparative Example 1 and the right figure is the lattice interlocked crystal structure of Example 1;

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

[0034] Figure 6 For the high-temperature cycle stability of Examples 1-4;

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

[0036] Figure 8 For the TEM image of the crystal structure of Comparative Example 2. Detailed implementation manners

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

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

[0039] Electrochemical performance test: Evaluation was carried out using coin cells. The test was performed on a Blue-Energy battery test system with a charge-discharge current set at 1C = 200 mAh / g and a voltage window of 2.0 - 4.8 V. High-temperature cycling was tested in a biochemical incubator with the temperature set at 45 °C.

[0040] Lattice interlocked structure characterization: Conducted using a transmission electron microscope.

[0041] Comparative Example 1

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

[0043] Weigh the precursors Mn 0.75 Ni 0.25 (OH)2 and the lithium salt Li2CO3 according to stoichiometry, and mix them evenly using a high-speed mixer for the sintering process: With a heating rate of 5 °C / min, hold at 880 °C for 15 h, and then naturally cool to room temperature to obtain the 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 material:

[0046] Weigh the precursor Mn 0.67 Ni 0.165 Co 0.165 (OH)2 and lithium salt Li2CO3 according to stoichiometry, mix them evenly with a high-speed mixer and carry out the sintering process: heat at a rate of 5 °C / min to 880 °C, hold for 15 h, and then cool naturally to room temperature to obtain the lithium-rich manganese-based cathode material Li 1.2 (Mn 0.67 Ni 0.165 Co 0.165 ) 0.8 O2. The crystal structure is as Figure 8 shown. The traditional layered cobalt-containing lithium-rich material has a highly ordered orientation, with lithium layers and transition metal layers alternatingly stacked, and no interlocked lattice structure is formed.

[0047] Example 1

[0048] Take 6 g 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, mix them evenly with a mixer, heat at a rate of 5 °C / min to 880 °C, hold for 15 h, then cool naturally to room temperature, and then wash the residual sodium with deionized water and dry at 200 °C for 5 h to obtain the lattice-interlocked twin lithium-rich material Li 1.1 (Mn 0.75 Ni 0.25 ) 0.9 O2.

[0049] The phase structure and the degree of interlocked structure of the sample are determined by XRD, as Figure 3 shown. The structure of the lithium-rich material in Comparative Example 1 is a composite layered structure material of typical R-3m and C2 / m phases. However, the intensity ratio of the (003) / (104) peaks after modification increases from 1.375 to 1.429, indicating that the layered structure is strengthened. Additionally, it is worth noting that the (018) / (110) peaks, which are the layered indicator peaks, show broadening and splitting. These additional peaks correspond to the special structure at the twin grain boundary, indicating the possible formation of twin phases.

[0050] The lattice interlocked structure is further determined by HR-TEM, as Figure 4 shown in the left figure in it. The traditional layered lithium-rich material has a highly ordered orientation, with lithium layers and transition metal layers alternatingly stacked, both perpendicular to the <001> direction. This type of structure has lattice stress anisotropy during charge and discharge, with the maximum stress and severe expansion and contraction along the <001> direction. AsFigure 4 As shown in the right middle 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, and the interaction angle is about 60°.

[0051] The electrochemical performance of the lithium-rich material with such a structure will be greatly improved:

[0052] The initial Coulombic efficiency, as Figure 5 and Table 1, significantly increases the initial efficiency of Comparative Example 1 from 76.5% to 85.6%. The specific capacity in the first week increases from 242 mAh g -1 of Comparative Example 1 to 256.6 mAh g -1 .

[0053] The cycling performance, as Figure 6 shown, the initial discharge capacity of the sample in Comparative Example 1 at 1C is 194 mAh g -1 , and it drops to 79.4 mAh g -1 after 300 cycles, and the capacity retention rate is only 40.9%; while the 1C discharge capacity of the lithium-rich material with lattice interlocking increases to 216.9 mAh g -1 , and there is still 200.5 mAh g -1 after 300 full cycles, and the capacity retention rate is as high as 92.4%. The above results show that the lattice interlocking has excellent electrochemical performance, especially high-temperature cycling stability.

[0054] In addition, the structure of the lithium-rich material with lattice interlocking is also very stable after cycling. As Figure 7 shown, after cycling, the crystal structure of Comparative Example 1 obtained by Fourier transform changes from layered to spinel, and even to rock salt phase. While the crystal structure with lattice interlocking shows clear layered lattice stripes, indicating that its structure stability is maintained during long cycling.

[0055] Example 2

[0056] Take 6.0 g of the manganese-rich precursor Mn 0.75 Ni 0.25 (OH)2, increase the lithium carbonate content to 3.32 g and sodium carbonate 1 g, mix them evenly with a mixer, heat at a rate of 5 °C / min, keep the temperature at 880 °C for 15 h, then naturally cool to room temperature, and then wash the residual sodium with deionized water and dry at 200 °C for 5 h to obtain the lattice interlocking twin 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 6 g of the manganese-rich precursor Mn 0.75 Ni 0.25 (OH)2, 3.36 g of lithium carbonate and 1 g of sodium carbonate, mix them evenly with a mixer, heat at a rate of 5 °C / min, hold at 880 °C for 15 h, then cool naturally to room temperature, and then wash the residual sodium with deionized water and dry at 200 °C for 5 h to obtain the lattice-interlocked twin 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 6 g of the manganese-rich precursor Mn 0.65 Ni 0.35 (OH)2, 3 g of lithium carbonate and 0.65 g of sodium carbonate, the synthesis process is the same as above, and the lattice-interlocked twin lithium-rich material Li 1.09 (Mn 0.65 Ni 0.35 ) 0.91 O2 can be obtained.

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

[0064] Example 5

[0065] Take 6 g of the manganese-rich precursor Mn 0.6 Ni 0.4 (OH)2, 3 g of lithium carbonate and 0.65 g of sodium carbonate, the synthesis process is the same as above, and the lattice-interlocked twin lithium-rich material Li 1.09 (Mn 0.6 Ni 0.4 ) 0.91 O2 can be obtained.

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

[0067] Example 6

[0068] Take 6 g of the manganese-rich precursor Mn 0.7 Ni 0.3 (OH)2, 3 g of lithium carbonate and 0.65 g of sodium carbonate, the synthesis process is the same as above, and the lattice-interlocked twin lithium-rich material Li 1.09 (Mn 0.7 Ni 0.3 ) 0.91 O2 can be obtained.

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

[0070] Example 7

[0071] Take 6 g of the manganese-rich precursor Mn 0.7 Ni 0.3 (OH)2, 3 g of lithium carbonate and 1 g of sodium carbonate. The synthesis process is the same as above, and the lattice-interlocked twin lithium-rich material Li 1.09 (Mn 0.7 Ni 0.3 ) 0.91 O2 can be obtained.

[0072] The electrochemical performance is shown in Table 1. When the content of sodium carbonate increases, the specific capacity increases to 268.8 mAh / g, but the cycling performance decreases, being 81.7%.

[0073] Example 8

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

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

[0076] Table 1 Electrochemical Performance

[0077]

[0078] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: within the scope of the spirit and essence defined by the claims of the present invention, the technical solutions described in the foregoing embodiments can be modified, or some or all of the technical features can be equivalently replaced; and these modifications or replacements are still within the scope defined by the claims of the present invention.

Claims

1. A lattice interlocking lithium-rich manganese-based positive electrode material, characterized in that: The molecular formula of the lithium-rich manganese-based positive electrode 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; The lithium-rich manganese-based positive electrode material has at least two sets of lattices with different orientations, which grow together in different directions to form a crystal structure with interlocking lattices, and the interaction angle θ of the lattices is 15°<θ<90°.

2. The lithium-rich manganese-based positive electrode material according to claim 1, characterized in that: The (018) / (110) layered indicator peak of the XRD pattern of the lithium-rich manganese-based positive electrode material is broadened and split into one or more shoulder peaks.

3. A method for preparing the lithium-rich manganese-based positive electrode material according to claim 1 or 2, characterized in that: The following steps are involved: A cobalt-free manganese-rich hydroxide precursor, a lithium salt and a sodium salt are mixed in a stoichiometric ratio and then sintered, naturally cooled to room temperature, and then washed and dried to obtain a lithium-rich manganese-based positive electrode material; the mass of the sodium salt is more than 20% of the mass of the lithium salt.

4. The preparation method according to claim 3, characterized in that: The molecular formula of the cobalt-free manganese-rich hydroxide precursor is Mn z M 1-z (OH)2, wherein M is one or more selected from Mn, Ni, Mg, La and W, and z>0.

5.

5. The preparation method according to claim 3, characterized in that: The lithium salt is one or more selected from lithium carbonate, lithium acetate and lithium hydroxide.

6. The preparation method according to claim 3, characterized in that: The sodium salt is one or more selected from sodium carbonate, sodium bicarbonate, sodium nitrate and sodium acetate.

7. The preparation method according to claim 3, characterized in that: The sintering heating rate is 2-10°C / min, the sintering temperature is 750-950°C, and the holding time is 6-20h.

8. The preparation method according to claim 3, characterized in that: The drying temperature is 100-300℃.

9. Use of the lithium-rich manganese-based positive electrode material according to claim 1 or 2 or the lithium-rich manganese-based positive electrode material prepared by the preparation method according to any one of claims 3 to 8 in the preparation of lithium-ion batteries.

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