A layered cathode material with regulated interface phase structure, its preparation method and lithium-ion battery

Abstract

This invention discloses a layered cathode material with interface phase structure regulated, its preparation method, and a lithium-ion battery, belonging to the field of lithium-ion battery technology. The preparation method provided by this invention is as follows: a ternary cathode material precursor is mixed with lithium hydroxide and lithium amide to obtain an initial mixture; the ternary cathode material precursor is Ni. x Co y Mn 1‑x‑y (OH)₂, where 0.1≤x≤0.92, 0<y≤0.9; the initial mixture is sintered to obtain the desired product. This invention introduces lithium amino and lithium hydroxide as a mixed lithium source to construct a spinel structure in situ on the surface of a ternary cathode material. The surface spinel phase allows for rapid lithium-ion transport and improves surface stability. The "spinel-transition phase-layered" phase reduces charge transfer impedance and significantly alleviates anisotropic stress concentration caused by phase transition. The resulting layered cathode material exhibits excellent rate performance and cycle stability.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a layered cathode material with interface phase structure regulated, its preparation method, and a lithium-ion battery. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] With the rapid development of the new energy vehicle and energy storage technology industries, higher requirements have been placed on the energy density, cycle stability, and price of lithium-ion batteries. As the most critical material in lithium-ion batteries, the cathode material determines the battery's performance and cost. Ternary layered transition metal oxide cathode materials have higher specific capacity and are better able to meet the demand for high energy density, among which Li[Ni] 1-x-y Co x Mn y O2 (NCM) cathode materials have long been considered the most promising cathode materials due to their advantages such as low cost and high specific capacity.

[0004] Increasing the nickel content can significantly improve the discharge capacity of NCM ternary cathode materials. However, excessively high nickel content can reduce the cycle stability of the cathode material. In particular, high-nickel ternary layered cathode materials with a nickel content exceeding 80% can develop microcracks due to mechanical stress caused by anisotropic volume changes during cycling. This increases the contact area between the electrode active material and the electrolyte, leading to side reactions. Furthermore, the high oxidation state of Ni... 4+ Ni-O-like compounds will form on the surface of microcracks in the cathode material. Simultaneously, inherent defects in the high-nickel cathode material and a series of secondary degradations occurring during charge and discharge processes, such as Li... + / Ni 2+ Mixing, irreversible phase transitions, and dissolution of transition metals can lead to a significant decrease in the stability and rate performance of cathode materials during cycling.

[0005] To address the aforementioned issues, bulk doping and surface coating are currently common solutions. Bulk doping stabilizes the layered structure of the material by incorporating other elements, enhancing the thermal stability of the H3 phase at the microstructural level, thereby improving the material's long-term cycling and electrochemical performance under high current densities. Different dopants can play different roles in the material. However, the amount of dopant, the dopant element, and the type of dopant all significantly affect the performance of the cathode material. Surface coating involves coating the material's surface with a non-electrochemical or electrochemical material to stabilize the cathode-electrolyte interface, thereby reducing side reactions and improving the material's structural stability during cycling. However, it often suffers from insufficient adhesion to the cathode surface and easy detachment during long cycles. Furthermore, the coating thickness is difficult to control. While atomic layer deposition (ALD) can control the coating thickness, its high cost makes industrialization difficult. Therefore, a simple and effective method is needed. Summary of the Invention

[0006] In view of this, the present invention provides a layered cathode material with interface phase structure regulation, its preparation method and lithium-ion battery. A spinel structure is constructed in situ on the surface of the cathode material, which can facilitate the rapid transport of lithium ions and improve surface stability. At the same time, a "spinel-transition phase-layered" phase transition layer is formed between the surface spinel phase and the internal layered structure, thereby reducing charge transfer impedance and greatly alleviating the anisotropic stress concentration caused by phase transition.

[0007] In a first aspect, the present invention provides a method for preparing a layered cathode material with regulated interface phase structure, comprising the following steps:

[0008] A ternary cathode material precursor was mixed with lithium hydroxide and lithium amino groups to obtain an initial mixture; the ternary cathode material precursor was Ni. x Co y Mn 1-x-y (OH)2, where 0.1≤x≤0.92, 0<y≤0.9;

[0009] The initial mixture is sintered to obtain a layered cathode material with regulated interfacial phase structure.

[0010] Preferably, 0.8≤x≤0.9, 0<y≤0.1.

[0011] Preferably, in the initial mixture, the molar ratio of Li to the total molar ratio of Ni, Co and Mn is controlled to be (1 to 1.1):1.

[0012] Preferably, the mass ratio of lithium hydroxide to lithium aminohydride is (2-8):1.

[0013] Preferably, the lithium hydroxide is anhydrous lithium hydroxide or lithium hydroxide monohydrate.

[0014] Preferably, the sintering process specifically involves: heating to 300–600°C and holding for sintering for 3–10 hours; then heating to 650–850°C and holding for sintering for 12–24 hours.

[0015] Furthermore, the heating rate is 1–5 °C / min; after sintering, the furnace is cooled to room temperature.

[0016] Preferably, the sintering process is carried out in an oxygen atmosphere with an oxygen purity of 99.5% or higher.

[0017] Secondly, the present invention provides a layered cathode material with regulated interface phase structure, which is prepared by the above-described preparation method.

[0018] Thirdly, the present invention provides a lithium-ion battery comprising the layered cathode material with the interface phase structure regulated as described above.

[0019] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0020] This invention introduces lithium amino group and lithium hydroxide as a mixed lithium source, which undergoes a high-temperature solid-state lithiation reaction with an NCM ternary material precursor. Interface modification is performed to construct a spinel structure in situ on the surface of the ternary cathode material, while maintaining a layered internal structure. Under high-temperature solid-state conditions, lithium amino group (LiNH2) decomposes to produce NH3, releasing some Ni... 3+ Reduced to Ni 2+ The spinel phase structure is formed, and the surface spinel phase can facilitate the rapid transport of lithium ions and improve surface stability. At the same time, a "spinel-transition phase-layer" phase transition layer is formed between the surface spinel phase and the internal layered structure, thereby reducing charge transfer impedance and greatly alleviating the anisotropic stress concentration caused by phase transition. Based on the synergistic effect of the above functions, the layered cathode material with interface phase structure regulation prepared by the present invention exhibits excellent rate performance and cycle stability. Attached Figure Description

[0021] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation thereof. Obviously, those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0022] Figure 1 These are scanning electron microscope images of the surface of the layered cathode material prepared in Example 1 of this invention;

[0023] Figure 2This is a comparison chart of the cycle performance of the layered cathode material assembled batteries of Embodiment 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0024] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0025] This invention provides a method for preparing a layered cathode material with regulated interface phase structure, comprising the following steps:

[0026] A ternary cathode material precursor was mixed with lithium hydroxide and lithium amino groups to obtain an initial mixture; the ternary cathode material precursor was Ni. x Co y Mn 1-x-y (OH)2, where 0.1≤x≤0.92, 0<y≤0.9;

[0027] The initial mixture is sintered to obtain a layered cathode material with regulated interfacial phase structure.

[0028] This invention introduces lithium amide and lithium hydroxide as a mixed lithium source, which undergoes a high-temperature solid-state lithiation reaction with an NCM ternary material precursor. Interface modification is performed to construct a spinel structure in situ on the surface of the cathode material, while maintaining a layered internal structure. Lithium hydroxide, as the main lithium source, reacts with the precursor and lithium source in a solid-state reaction at a certain temperature to generate LiMO2 (M = Ni, Co, Mn). Sintering yields a fully crystalline layered LiMO2 structure. Under high-temperature solid-state conditions, lithium amide (LiNH2) decomposes to produce NH3, partially dissolving the Ni... 3+ Reduced to Ni 2+ The spinel phase structure is formed, and the surface spinel phase can facilitate the rapid transport of lithium ions and improve surface stability. At the same time, a "spinel-transition phase-layer" phase transition layer is formed between the surface spinel phase and the internal layered structure, thereby reducing charge transfer impedance and greatly alleviating the anisotropic stress concentration caused by phase transition. Based on the synergistic effect of the above functions, the layered cathode material with interface phase structure regulation prepared by the present invention exhibits excellent rate performance and cycle stability.

[0029] In this invention, in the ternary cathode material precursor, 0.8 ≤ x ≤ 0.9, 0 < y ≤ 0.1. While existing high-nickel-content ternary cathode materials possess high specific capacity, their cycle performance is often poor. The preparation method of this invention is particularly suitable for preparing high-nickel-content cathode materials, improving their rate performance and stability. Specifically, in the embodiments of this invention, Ni can be used. 0.9 Co 0.05 Mn0.05 Even with a nickel content of 90%, the assembled battery can still maintain a cycle retention rate of over 90% at 1C for 50 cycles, and may even reach over 95%.

[0030] This invention does not impose any special restrictions on the mixing method and equipment for mixing the ternary cathode material precursor with lithium hydroxide and lithium amide, as long as a uniform initial mixture can be obtained. This invention also does not impose any special restrictions on the source of the ternary cathode material; it can be obtained commercially or manufactured in-house.

[0031] In this invention, the initial mixture is controlled to have a molar ratio of Li to the total molar ratio of Ni, Co and Mn of (1 to 1.1):1, more preferably (1.01 to 1.05):1.

[0032] In this invention, the mass ratio of lithium hydroxide to lithium amide is (2-8):1, more preferably (3-7):1, and even more preferably (5-6):1. Batteries assembled from cathode materials prepared by adding lithium hydroxide alone exhibit poor cycle stability, low ionic conductivity, and low initial discharge specific capacity. Adding lithium amide alone not only increases costs but also generates a large amount of ammonia during decomposition, disrupting the original oxygen atmosphere and causing excessive reduction of the high-nickel cathode material, leading to a decrease in Ni... 2+ Increased concentration of lithium hydroxide exacerbates Li / Ni mixing, weakening material performance. When lithium hydroxide is used in combination with other lithium sources, both ionic conductivity and initial discharge specific capacity are low.

[0033] In this invention, the lithium hydroxide is anhydrous lithium hydroxide or lithium hydroxide monohydrate, and for cost considerations, lithium hydroxide monohydrate is preferred.

[0034] In this invention, the sintering process specifically comprises: heating to 300–600°C, more preferably 450–550°C; holding the temperature for sintering for 3–10 hours, more preferably 4–6 hours; then heating to 650–850°C, more preferably 700–800°C; and holding the temperature for sintering for 12–24 hours, more preferably 12–18 hours. Gradient sintering provides a way to remove the water of crystallization from lithium hydroxide, preventing the presence of excessive moisture during sintering from leading to high residual alkali levels.

[0035] Furthermore, the heating rate is 1–5 °C / min; after sintering, the furnace is cooled to room temperature.

[0036] In this invention, the sintering process is carried out in an oxygen atmosphere with an oxygen purity of 99.5% or higher.

[0037] The present invention also provides a layered cathode material with interface phase structure regulation, which is prepared by the above preparation method. The surface of the layered cathode material is a spinel structure, and the interior is still a layered structure. A "spinel-transition phase-layered" phase transition layer is formed between the surface spinel phase and the interior layered structure, thereby reducing charge transfer impedance and greatly alleviating anisotropic stress concentration caused by phase transition.

[0038] This invention provides a lithium-ion battery, comprising the layered positive electrode material with the interface phase structure regulated as described above. Other components of the lithium-ion battery, such as the negative electrode, electrolyte, and separator, can all be components commonly used by those skilled in the art for lithium-ion battery negative electrode, electrolyte, and separator; therefore, they will not be described in detail here.

[0039] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0040] Example 1

[0041] This embodiment provides a method for preparing layered cathode materials with interface phase structure controlled.

[0042] (1) Weigh out the hydroxide precursor Ni 0.9 Co 0.05 Mn 0.05 (OH)2 was mixed with lithium sources LiNH2 and LiOH·H2O, with the molar ratio Li / (Ni+Co+Mn) controlled at 1.03 and the weight ratio of LiOH·H2O to LiNH2 at 5:1. The mixture was homogeneous using a high-speed mixer at a speed of 500 r / min for 30 min to obtain a uniformly mixed mixture.

[0043] (2) The mixture is sintered at high temperature in an oxygen atmosphere using a box furnace. Specifically, the temperature is increased to 500°C at a heating rate of 3°C / min, sintered for 5 hours, then increased to 730°C and held for 15 hours. After sintering, the mixture is cooled to room temperature in the furnace to obtain a layered cathode material.

[0044] Figure 1 The images shown are scanning electron microscope (SEM) images of the layered cathode material prepared in this embodiment. It can be seen that the sintered cathode material has good sphericity, and the secondary spheres composed of primary particles have smooth surfaces and particle sizes of about 10 μm.

[0045] Example 2

[0046] This embodiment provides a method for preparing layered cathode materials with interface phase structure controlled.

[0047] (1) Weigh out the hydroxide precursor Ni 0.9 Co 0.05 Mn 0.05(OH)2 was mixed with lithium sources LiNH2 and LiOH·H2O, with the molar ratio Li / (Ni+Co+Mn) controlled at 1.03 and the weight ratio of LiOH·H2O to LiNH2 at 3:1. The mixture was homogeneous using a high-speed mixer at a speed of 500 r / min for 30 min to obtain a uniformly mixed mixture.

[0048] (2) The mixture is sintered at high temperature in an oxygen atmosphere using a box furnace. Specifically, the temperature is increased to 500°C at a heating rate of 3°C / min, sintered for 5 hours, then increased to 730°C and held for 15 hours. After sintering, the mixture is cooled to room temperature in the furnace to obtain a layered cathode material.

[0049] Example 3

[0050] This embodiment provides a method for preparing layered cathode materials with interface phase structure controlled.

[0051] (1) Weigh out the hydroxide precursor Ni 0.9 Co 0.05 Mn 0.05 (OH)2 was mixed with lithium sources LiNH2 and LiOH·H2O, with the molar ratio Li / (Ni+Co+Mn) controlled at 1.03 and the weight ratio of LiOH·H2O to LiNH2 at 7:1. The mixture was homogeneous using a high-speed mixer at a speed of 500 r / min for 30 min to obtain a uniformly mixed mixture.

[0052] (2) The mixture is sintered at high temperature in an oxygen atmosphere using a box furnace. Specifically, the temperature is increased to 500°C at a heating rate of 3°C / min, sintered for 5 hours, then increased to 730°C and held for 15 hours. After sintering, the mixture is cooled to room temperature in the furnace to obtain a layered cathode material.

[0053] Comparative Example 1

[0054] The difference between this comparative example and Example 1 is that the lithium source in this comparative example is only LiOH·H2O.

[0055] (1) Weigh out the hydroxide precursor Ni 0.9 Co 0.05 Mn 0.05 (OH)2 and lithium source LiOH·H2O were mixed evenly with a high-speed mixer at a speed of 500 r / min for 30 min, controlling the molar ratio Li / (Ni+Co+Mn) to be 1.03.

[0056] (2) The mixture is sintered at high temperature in an oxygen atmosphere using a box furnace. Specifically, the temperature is increased to 500°C at a heating rate of 3°C / min, sintered for 5 hours, then increased to 730°C and held for 15 hours. After sintering, the mixture is cooled to room temperature in the furnace to obtain a layered cathode material.

[0057] Comparative Example 2

[0058] The difference between this comparative example and Example 1 is that the lithium source in this comparative example is only LiNH2.

[0059] (1) Weigh out the hydroxide precursor Ni 0.9 Co 0.05 Mn 0.05 (OH)2 and lithium source LiNH2 were mixed evenly with a molar ratio of Li / (Ni+Co+Mn) of 1.03 using a high-speed mixer at a speed of 500 r / min for 30 min to obtain a uniformly mixed mixture.

[0060] (2) The mixture is sintered at high temperature in an oxygen atmosphere using a box furnace. Specifically, the temperature is increased to 500°C at a heating rate of 3°C / min, sintered for 5 hours, then increased to 730°C and held for 15 hours. After sintering, the mixture is cooled to room temperature in the furnace to obtain a layered cathode material.

[0061] Comparative Example 3

[0062] The difference between this comparative example and Example 1 is that the lithium source in this comparative example is LiNO3 and LiOH·H2O.

[0063] (1) Weigh out the hydroxide precursor Ni 0.9 Co 0.05 Mn 0.05 (OH)2 was mixed with lithium sources LiNO3 and LiOH·H2O, with the molar ratio Li / (Ni+Co+Mn) controlled at 1.03 and the weight ratio of LiNO3 to LiOH·H2O at 5:1. The mixture was homogeneous using a high-speed mixer at a speed of 500 r / min for 30 min to obtain a uniformly mixed mixture.

[0064] (2) The mixture is sintered at high temperature in an oxygen atmosphere using a box furnace. Specifically, the temperature is increased to 500°C at a heating rate of 3°C / min, sintered for 5 hours, then increased to 730°C and held for 15 hours. After sintering, the mixture is cooled to room temperature in the furnace to obtain a layered cathode material.

[0065] Test case

[0066] The layered cathode materials from the examples and comparative examples were used to assemble button cells, and their electrochemical performance was measured. The button cell assembly process is as follows: Layered cathode material, polyvinylidene fluoride (PVDF), and conductive carbon black were mixed in a mass ratio of 8:1:1 and dissolved in N-methylpyrrolidone (NMP) solvent to prepare a cathode slurry. The slurry was made free of particles. The slurry was then evenly coated onto aluminum foil using a coating machine to form an electrode sheet. The coated electrode sheet was placed in a vacuum drying oven at 120°C and vacuum dried for 12 hours. The electrode sheet was then removed and rolled on a roller press for later use. The electrode sheets were cut into 12mm diameter circular pieces using a cutting machine, dried in a vacuum drying oven at 60℃ for 12 hours, and then weighed using an electronic balance. Finally, the positive electrode sheet, lithium sheet, spring sheet, gasket, positive electrode shell, negative electrode shell, separator, and electrolyte were assembled into a CR2025 coin cell in an argon-filled glove box. The electrolyte was a 1M NaPF6 solution dissolved in a mixed solvent of EC (ethylene carbonate) and DMC (dimethyl carbonate) (by volume, EC:DMC = 1:1). The lithium metal sheet served as the counter electrode. The charge / discharge voltage range was 2.8-4.4V, the initial charge / discharge rate was 0.1C, and the nominal specific capacity was 1C = 200mAh / g. Cyclic performance was tested at a charge / discharge rate of 1C for 50 cycles, and the test results are shown in Table 1.

[0067] Table 1. Physicochemical properties of the layered cathode material assembled batteries in the examples and comparative examples.

[0068]

[0069]

[0070] Figure 2 Table 1 shows a comparison of the cycle performance of the batteries assembled with the layered cathode materials of Example 1 and Comparative Example 1. Figure 2 Comparing the test results, after introducing a mixed lithium source, due to the reduction effect of NH3 generated by the high-temperature solid-phase lithiation reaction, the Ni in the example... 2+ The significantly higher occupancy rate compared to the comparative example facilitates the formation of a spinel structure at the interface. Simultaneously, the ionic conductivity is several orders of magnitude higher, thanks to the fast ion transport capability of the spinel phase, which helps improve the material's rate performance. Furthermore, the capacity retention after 1C and 50 cycles is superior to the comparative example. This is mainly because the "spinel-transition phase-layered" phase gradient transition layer formed at the interface effectively releases the anisotropic stress concentration caused by the irreversible phase transition, avoiding the generation of microcracks and thus improving cycle life. Using a single LiNH2 as the lithium source not only makes the material preparation cost excessively high, but also generates a large amount of ammonia during decomposition, disrupting the original oxygen atmosphere and causing excessive reduction of the high-nickel cathode material, leading to Ni degradation. 2+ Increased concentration of Li / Ni leads to increased Li / Ni mixing and weakens material properties.

[0071] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a layered cathode material with interface phase structure regulated, characterized in that, Includes the following steps: A ternary cathode material precursor was mixed with lithium hydroxide and lithium amino groups to obtain an initial mixture; the ternary cathode material precursor was Ni. x Co y Mn 1-x-y (OH)2, wherein 0.8≤x≤0.92, 0<y≤0.1; the mass ratio of lithium hydroxide to lithium amino group is (2~8):1; The initial mixture is sintered to obtain a layered cathode material with regulated interfacial phase structure. The sintering process is as follows: heat up to 300~600℃ and hold for sintering for 3~10h; then heat up to 650~850℃ and hold for sintering for 12~24h.

2. The preparation method according to claim 1, characterized in that, In the initial mixture, the ratio of the molar amount of Li to the total molar amount of Ni, Co and Mn is controlled to be (1~1.1):

1.

3. The preparation method according to claim 1, characterized in that, The lithium hydroxide is anhydrous lithium hydroxide or lithium hydroxide monohydrate.

4. The preparation method according to claim 1, characterized in that, The heating rate is 1~5℃ / min; after sintering, the furnace is cooled to room temperature.

5. The preparation method according to claim 1, characterized in that, The sintering process is carried out in an oxygen atmosphere with an oxygen purity of over 99.5%.

6. A layered cathode material with interface phase structure regulated, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 5.

7. A lithium-ion battery, characterized in that, Including the layered cathode material with interface phase structure regulated as described in claim 6.

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