A lithium-rich manganese-based cathode material with an ultra-large crystal plane spacing, its preparation method and application

Abstract

The present invention provides a lithium-rich manganese-based cathode material with an ultra-large crystal plane spacing, a preparation method thereof, and an application thereof, relating to the technical field of the preparation of battery cathode materials. By adding an excessive amount of sodium in one step during the synthesis process, an ultra-large crystal plane spacing is induced to form, and a superlattice ordered structure is used to stabilize the structure of the ultra-large crystal plane spacing. During the thermal post-treatment, a dense structure layer is in-situ induced to form on the surface of the material. The arrangement mode of the crystal plane spacing of the bulk lithium layer is an ordered superlattice structure, and the surface layer is a dense atomic layer and a structure with a small crystal plane spacing. This superlattice structure not only improves the lithium-ion transport kinetics of the bulk structure, but also the dense surface layer improves the stability of the surface structure, enabling the material to have excellent high-rate and long-cycle performance, and solving the problem of poor post-cycle performance of lithium-rich manganese-based cathode materials with high rate and high capacity.

Description

Technical Field

[0001] The present invention relates to the technical field of preparing cathode materials for batteries, and particularly to a lithium-rich manganese-based cathode material with an ultra-large crystal plane spacing, a preparation method thereof, and an application thereof. Background Art

[0002] Lithium-rich manganese-based cathode materials have advantages such as high specific capacity and low price. However, their low initial efficiency, poor cycling performance, and poor rate performance have hindered their large-scale application. In particular, the problem of poor rate performance has hindered their application in new energy vehicles because current power batteries usually require 3C fast charging and ultra-fast charging >4C capabilities. Due to the redox activity of anionic oxygen and manganese activity involved after the activation of Li2MnO3 in lithium-rich manganese, its kinetic performance is poor, resulting in low rate performance. Strategies to improve the rate usually include coating conductive and electro-lithium-ion substances, doping, and nanosizing to shorten the transmission path to enhance kinetics. Expanding the lithium layer spacing is one of the important directions to improve the lithium-ion diffusion kinetics, but the conventional doping of large atoms such as Na / K in the lithium layer is very limited in expanding the lithium layer spacing. For example, Chinese Patent CN104218235B discloses a double-doped lithium-rich solid solution cathode composite material, a preparation method thereof, a lithium-ion battery cathode sheet, and a lithium-ion battery, doping one or a combination of Na and K to increase the surface conductivity of the lithium-rich solid solution cathode material and the cycling stability during charge and discharge. Another example is that Chinese Patent CN107215900B discloses that W doping causes an increase in the layer spacing, which is beneficial to the rate performance, but W still has problems such as difficult doping and high cost.

[0003] Therefore, it is necessary to design and synthesize a larger lithium layer spacing to improve the lithium-ion transmission kinetics in the lithium layer, thereby enhancing its rate performance and ensuring its cycling stability, and solving the problems of poor rate performance and poor large-rate cycling of the lithium-rich material structure. Summary of the Invention

[0004] In view of the above problems, the present invention prepares a lithium-rich manganese-based cathode material with an ultra-large crystal plane spacing and a dense surface layer, which not only improves the lithium-ion kinetics of the bulk structure but also improves the stability of the surface structure.

[0005] One of the purposes of the present invention is to provide a lithium-rich manganese-based cathode material with an ultra-large crystal plane spacing.

[0006] Another purpose of the present invention is to provide a preparation method of the lithium-rich manganese-based cathode material with an ultra-large crystal plane spacing.

[0007] A third purpose of the present invention is to provide an application of the lithium-rich manganese-based cathode material with an ultra-large crystal plane spacing.

[0008] In order to achieve the above purposes of the present invention, the following technical solutions are specifically adopted:

[0009] In a first aspect, the present invention provides a lithium-rich manganese-based cathode material with an ultra-large interplanar spacing. 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, Al, Co, Cr, Fe, Ti, Mo, Ru, V, Nb, Zr, and Sn, and 0.2 < x ≤ 0.6;

[0010] The bulk phase of the lithium-rich manganese-based cathode material has an ordered arrangement structure with an interplanar spacing of (003) > 5 Å, and the surface of the lithium-rich manganese-based cathode material has a dense structure with an interplanar spacing parallel to the (003) plane < 3 Å, forming a dense layer.

[0011] In some embodiments, the bulk phase of the lithium-rich manganese-based cathode material consists of three types of (003) interplanar spacing structures with different sizes: the first interplanar spacing d1 (003) 、the second interplanar spacing d2 (003) and the third interplanar spacing d3 (003) , where d1 (003) > 6 Å, 6 Å > d2 (003) > 5 Å, d3 (003) < 4 Å; in the <001> direction, the (003) interplanar spacing is sequentially arranged in an order of d3 (003) |d3 (003) 、d2 (003) |d1 (003) 、d3 (003) |d3 (003) 、d1 (003) |d2 (003) .

[0012] "|" means "and".

[0013] In some embodiments, the thickness of the dense layer is 3 - 15 nm.

[0014] In some embodiments, the dense layer is composed of a repeated arrangement of structures with interplanar spacings of 2.2 Å and 2.6 Å parallel to the (003) plane.

[0015] The bulk phase of the lithium-rich manganese-based cathode material of the present invention has an ordered arrangement with an ultra-large interplanar spacing > 5 Å, and the surface layer has a dense layer structure, which is a structure with a small interplanar spacing. The interplanar spacing of the lithium layer in the bulk phase consists of regularly sized interplanar spacings. The first type of interplanar spacing d (003) > 6 Å, the second type of interplanar spacing 6 Å > d (003) > 5 Å, the third type of interplanar spacing d (003)<3.0 Å. The arrangement of the lithium layer crystal plane spacing in the <001> direction is: "the third type|the third type" - "the second type|the first type" - "the third type|the third type" - "the first type|the second type" ordered superstructure, such as "2.2 Å|3.3 Å" - "5.3 Å|6.3 Å" - "3.3 Å|2.2 Å" - "6.3 Å|5.2 Å". The surface layer is a dense atomic layer with a small crystal plane spacing structure.

[0016] In a second aspect, the present invention provides a method for preparing the above-mentioned lithium-rich manganese-based cathode material with an ultra-large crystal plane spacing, comprising the following steps:

[0017] Mix a manganese-rich precursor, a lithium salt, and a sodium salt, then perform sodium sintering, followed by water washing and heat post-treatment to obtain the lithium-rich manganese-based cathode material, where the mass ratio of the lithium salt to the sodium salt is 100:20 - 100.

[0018] The manganese-rich precursor is a hydroxide precursor Mn z M 1-z (OH)₂, M is one or more selected from Ni, Mg, Al, Co, Cr, Fe, Ti, Mo, Ru, V, Nb, Zr, and Sn, where z > 0.5;

[0019] The lithium salt is one or more selected from lithium carbonate, lithium sulfate, nitrate, lithium acetate, and lithium hydroxide;

[0020] The manganese-rich precursor and the lithium salt are in a stoichiometric ratio.

[0021] The sodium salt is one or more selected from sodium carbonate, sodium bicarbonate, sodium nitrate, and sodium acetate.

[0022] In some embodiments, the heating rate of sodium sintering is 2 - 10 °C / min, the sintering temperature is 750 - 950 °C, and the holding time is 6 - 20 h.

[0023] In some embodiments, the temperature of the heat post-treatment is 100 - 400 °C, and the time of the heat post-treatment is 3 - 15 h.

[0024] In a third aspect, the present invention provides an application of the above-mentioned lithium-rich manganese-based cathode material with an ultra-large crystal plane spacing in the preparation of lithium-ion batteries.

[0025] Beneficial effects:

[0026] The present invention provides a lithium-rich manganese-based cathode material with an ultra-large crystal plane spacing, which is prepared by sodiumation and post-heat treatment. By adding a specific amount of sodium in one step during the synthesis, the formation of an ultra-large crystal plane spacing is induced, and a superlattice ordered structure is formed to stabilize the structure of the ultra-large crystal plane spacing. During the post-heat treatment, a dense structure layer is in-situ induced on the surface of the material. Among them, the arrangement of the lithium layer crystal plane spacing in the <001> direction of the bulk phase is an ordered superlattice structure, and this superlattice structure has the effect of stabilizing the ultra-large spacing. The surface layer is a dense atomic layer and a structure with a small crystal plane spacing. This superlattice structure not only improves the lithium-ion transport kinetics and the stability of the bulk phase structure of the material, but also the dense surface layer improves the stability of the surface structure and the electrode-interface stability.

[0027] The cathode material of the present invention not only improves the initial efficiency of the material, but also improves the lithium-ion transport kinetics, rate performance and cycle stability of the material, making the material have the characteristics of both high rate and excellent cycle performance.

[0028] The present invention has been described in detail above, but the above embodiments are essentially illustrative only 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 or the summary of the invention or the following examples. Brief Description of the Drawings

[0029] Figure 1 Schematic diagrams of the crystal plane spacing of the traditional layered lithium-rich material and the cathode material of the present invention, where (a) is the traditional layered lithium-rich material and (b) is the cathode material of the present invention;

[0030] Figure 2 Morphology diagrams of Comparative Example 1 and Example 1, where (a) is Comparative Example 1 and (b) is Example 1;

[0031] Figure 3 Phase structures of Comparative Example 1 and Example 1;

[0032] Figure 4 TEM diagram of the crystal structure and lithium layer crystal plane spacing of Comparative Example 1;

[0033] Figure 5 TEM diagram of the crystal structure of Example 1;

[0034] Figure 6 Lithium layer crystal plane spacing of Example 1, where (a) is the surface crystal plane spacing; (b) is the bulk phase crystal plane spacing;

[0035] Figure 7 First charge-discharge curves of Comparative Example 1 and Example 1;

[0036] Figure 8 Cycle stability of Comparative Example 1 and Example 1. Detailed implementation manners

[0037] The present invention will be further described below in conjunction with 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 required by the present invention.

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

[0039] Electrochemical performance test: Evaluation was carried out using a button cell. The test was performed on a Blue Electric battery test system with a charge-discharge current setting of 1C = 200 mAh / g and a voltage window of 2.0 - 4.8 V.

[0040] Measurement and method for crystal structure and crystal plane spacing characterization: A transmission electron microscope was used and carried out with Gatan Digital Micrograph software. Specifically, a straight line perpendicular to the (003) crystal plane was drawn using the wireframe tool, and then the frame width was set to 30 - 50. For crystal plane spacing measurement, the width between two peaks was measured to obtain the crystal plane spacing.

[0041] Preparation example: Preparation of precursor

[0042] According to the stoichiometric ratio, Mn 0.68 Ni 0.29 Co 0.03 (OH)2 was first synthesized by the hydroxide co-precipitation method and then mixed and sintered with lithium carbonate. The specific steps are as follows: Nickel sulfate, manganese sulfate, and cobalt sulfate solutions with a concentration of 2M were prepared according to the stoichiometric ratio, with ammonia water and sodium tripolyphosphate as complexing agents, and a sodium hydroxide solution with a concentration of 2M; the two liquids were pumped into the reaction kettle at an appropriate flow rate (flow), and stirred at a speed of 300 - 800 r / min. After reacting for 24 h, washing, filtering, and drying were carried out to obtain the high-manganese precursor. The other component precursors were prepared in the same way.

[0043] Comparative example 1

[0044] Material sintering: The precursors Mn 0.68 Ni 0.29 Co 0.03 (OH)2 and lithium salt Li2CO3 were weighed respectively according to the stoichiometry and mixed evenly with a high-speed mixer. Sintering process: The temperature was raised at a rate of 5 °C / min, held at 850 °C for 10 h, and then naturally cooled to room temperature to obtain the lithium-rich manganese-based cathode material Li 1.184 (Mn 0.68 Ni 0.29 Co 0.03 ) 0.816 O2.

[0045] Example 1

[0046] Take 12 g of the manganese-rich precursor Mn 0.68 Ni 0.29 Co 0.03 (OH)2, 7.08 g of lithium carbonate and 3 g of sodium carbonate, mix them evenly with a mixer, heat at a heating rate of 3 °C / min, keep the temperature at 850 °C for 15 h, then naturally cool to room temperature, and then wash the residual sodium with deionized water 3 - 5 times, and perform heat post-treatment at 300 °C for 5 h to obtain a lithium-rich manganese-based cathode material Li 1.184 (Mn 0.68 Ni 0.29 Co 0.03 ) 0.816 O2.

[0047] Characterize the morphology of the material by SEM, as Figure 2 shown, the appearance morphology of the lithium-rich material in Comparative Example 1 is also a lamellar near-spherical shape. After the sodiumation treatment in Example 1, the primary morphology of the material is still a lamellar structure, and the lamellar thickness of the primary particles is also thinner.

[0048] The phase structure of the sample is determined by XRD, as Figure 3 shown, the structure of the lithium-rich material in Comparative Example 1 is a typical R- 3 m and C 2 / m phase composite layered structure material, and the peak position of the (003) diffraction peak is 18.72°. After the sodiumation of the present invention, the peak position of the (003) diffraction peak of the material decreases to 18.63°. This shows the expansion of the (003) layer spacing.

[0049] Use HR-TEM to further determine the size of the crystal plane spacing, as Figure 4 shown, from the high-resolution and Fourier transform pictures of the traditional layered structure lithium-rich material, it is a typical layered material structure with a crystal plane spacing of 4.769 Å, which is a conventional crystal plane spacing. However, after the sodiumation treatment, the crystal plane spacing can increase and form a stable structure. As Figure 5 shown by the high-resolution and Fourier transform obtained, the bulk phase is a layered structure, and the surface has a reconstructed layer of 3 - 15 nm. From the analysis of the crystal plane spacing, as Figure 6As shown, the arrangement of the lithium layer crystal plane spacing in the <001> direction of the bulk phase is an ordered superlattice structure of “—(“small, small”-“large, extra-large”-“small, small”-“extra-large, large”)—” (— represents continuous, repeatable unit). Such as “0.22nm - 0.33nm”—“0.53nm - 0.63nm”—“0.33nm - 0.22nm”—“0.63nm - 0.52nm”, where the “extra-large” crystal plane spacing refers to the lithium layer spacing > 6 Å, and the “large” crystal plane spacing refers to the lithium layer spacing > 5 Å.

[0050] The electrochemical performance of the lithium-rich material with this structure has been greatly improved:

[0051] The initial Coulombic efficiency, as Figure 7 shown in Table 1 and Table 2, significantly increases the initial efficiency of Comparative Example 1 from 77.3% to 89.70%. The specific capacity in the first week increases from 232.2 mAh g -1 of Comparative Example 1 to 272 mAh g -1 .

[0052] The rate performance is shown in Table 1. The capacities of Comparative Example 1 at 0.33C, 0.5C, 1C, 3C, and 5C are 204.9, 200.1, 190.3, 168.1, and 154.2 mAh / g respectively; while the rate performance of Example 1 with an extra-large crystal plane spacing after sodiation is 258.6, 237.9, 246, 200.2, and 184.1 mAh / g respectively, and the rate capacity has been greatly improved.

[0053] The cycle performance is shown in Table 2. The initial discharge capacity of the sample in Comparative Example 1 at 1C is 185.9 mAh g -1 , and it drops to 155.1 mAh g -1 after 200 cycles, with a capacity retention rate of 83.4%; while for Example 1 of the lithium-rich material with an extra-large crystal plane and a dense surface structure, the 1C charge-discharge capacity increases to 220.1 mAh g -1 , and there is still 207.1 mAh g -1 after 200 cycles, with a capacity retention rate as high as 94.1%. It shows that the lithium-rich manganese-based cathode material obtained by this method has higher initial efficiency, more optimized rate performance, higher specific capacity, and better cycle stability.

[0054] Example 2

[0055] Take 12g of the manganese-rich precursor Mn 0.68 Ni 0.29 Co 0.03 (OH)2, 6.8g of lithium carbonate, and 1.5g of sodium carbonate. Other operations are the same as in Example 1 to obtain the new structure lithium-rich material Li 1.13(Mn 0.68 Ni 0.29 Co 0.03 ) 0.87 O2。

[0056] The 1 C discharge capacity of Example 2 was increased to 215.7 mAh / g -1 , and after 200 cycles it was 200.4 mAh / g -1 , and the capacity retention rate was as high as 92.9%.

[0057] Example 3

[0058] Take 12 g of the manganese-rich precursor Mn 0.63 Ni 0.37 (OH)2, 6.2 g of lithium carbonate and 2 g of sodium carbonate, and other operations were the same as in Example 1. The lithium-rich material Li 1.13 (Mn 0.63 Ni 0.37 ) 0.87 O2 was obtained.

[0059] The 1 C discharge capacity of Example 3 was increased to 214.9 mAh / g -1 , and after 200 cycles it was 196.2 mAh / g -1 , and the capacity retention rate was as high as 91.3%.

[0060] Example 4

[0061] Take 6 g of the manganese-rich precursor Mn 0.65 Ni 0.35 (OH)2, 3.2 g of lithium carbonate and 1 g of sodium carbonate; the post-heat treatment temperature was 350 °C and the treatment time was 3 h. Other operations were the same as in Example 1, and the lithium-rich material Li 1.13 (Mn 0.65 Ni 0.35 ) 0.87 O2 was obtained.

[0062] The 1 C discharge capacity of Example 4 was increased to 210.5 mAh / g -1 , and after 200 cycles it was 205.3 mAh / g -1 , and the capacity retention rate was as high as 97.53%.

[0063] Comparative Example 2

[0064] Take 12 g of the manganese-rich precursor Mn 0.68 Ni 0.29 Co 0.03 (OH)2, 7.08 g of lithium carbonate, and the sodium carbonate content was 1% (0.0708 g). Other operations were the same as in Example 1, and a lithium-rich material was obtained.

[0065] The 1 C discharge capacity of Comparative Example 2 was increased to 191.2 mAh g -1 , and the capacity was 160.8 mAh g after 200 cycles -1 , and the capacity retention rate was only 84%.

[0066] Table 1 Electrochemical performance

[0067]

[0068] Table 2 Cycle stability

[0069]

[0070] The above embodiments are only used to illustrate 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 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 may be modified, or some or all of the technical features may be equivalently replaced; and these modifications or replacements are still within the scope defined by the claims of the present invention.

Claims

1. A lithium-rich manganese-based positive electrode material with ultra-large interplanar spacing, 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 the group consisting of Mn, Ni, Mg, Al, Co, Cr, Fe, Ti, Mo, Ru, V, Nb, Zr and Sn, and 0.2<x≤0.6; The bulk phase of the lithium-rich manganese-based positive electrode material has an ordered arrangement structure with a (003) crystal plane spacing of >5Å, and the surface of the lithium-rich manganese-based positive electrode material has a dense structure with a crystal plane spacing of <3Å parallel to the (003) crystal plane, forming a dense layer.

2. The lithium-rich manganese-based positive electrode material according to claim 1, characterized in that: The bulk phase of the lithium-rich manganese-based positive electrode material is composed of three types of (003) crystal plane spacing structures of different sizes: the first crystal plane spacing d1 (003) , the second interplanar spacing d2 (003) and the third interplanar spacing d3 (003) , where d1 (003) >6Å, 6Å>d2 (003) >5Å, d3 (003) <4Å; <001> The spacing between the (003) crystal planes in the direction is d3 (003) |d3 (003) , d2 (003) |d1 (003) , d3 (003) |d3 (003) , d1 (003) |d2 (003) The orderly arrangement of .

3. The lithium-rich manganese-based positive electrode material according to claim 1, characterized in that: The thickness of the dense layer is 3-15 nm.

4. The lithium-rich manganese-based positive electrode material according to claim 1, characterized in that: The dense layer is composed of repeated structures with interplanar spacings of 2.2 Å and 2.6 Å parallel to the (003) crystal plane.

5. A method for preparing the lithium-rich manganese-based positive electrode material according to any one of claims 1 to 4, characterized in that: The following steps are involved: The manganese-rich precursor, lithium salt and sodium salt are mixed and sintered for sodiumization, and then washed with water and subjected to thermal post-treatment to obtain a lithium-rich manganese-based positive electrode material, wherein the mass ratio of the lithium salt to the sodium salt is 100:20-100.

6. The preparation method according to claim 5, characterized in that: The manganese-rich precursor is a hydroxide precursor Mn z M 1-z (OH)2, M is one or more selected from Ni, Mg, Al, Co, Cr, Fe, Ti, Mo, Ru, V, Nb, Zr and Sn, wherein z>0.

5.

7. The preparation method according to claim 5, characterized in that: The lithium salt is one or more selected from lithium carbonate, lithium sulfate, nitrate, lithium acetate and lithium hydroxide; The sodium salt is one or more selected from sodium carbonate, sodium bicarbonate, sodium nitrate and sodium acetate.

8. The preparation method according to claim 5, characterized in that: The heating rate of sintering sodium is 2-10℃ / min, the sintering temperature is 750-950℃, and the holding time is 6-20h.

9. The preparation method according to claim 5, characterized in that: The temperature of the thermal post-treatment is 100-400°C, and the time of the thermal post-treatment is 3-15h.

10. Use of the lithium-rich manganese-based positive electrode material according to any one of claims 1 to 4 or the lithium-rich manganese-based positive electrode material prepared by the preparation method according to any one of claims 5 to 9 in preparing a lithium-ion battery.

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