High-stability layered positive electrode material and preparation method and application thereof

Abstract

The invention discloses a high-stability layered positive electrode material and a preparation method and application thereof, the positive electrode material has the following triple structures: an internal pore structure, a bulk-phase stable phase and a surface coating, by introducing the lattice-matched stable phase, local stress concentration caused by anisotropic volume change in a cycle process is relieved, and the stability of the positive electrode material is improved. The initiation and expansion of microcracks are inhibited; a compact and stable protective layer is constructed on the surface of the particle, direct contact between an electrolyte and a high-activity surface is blocked, and interface side reaction and surface structure degradation are reduced; cooperative reinforcement of a bulk phase structure and a surface interface is realized, limitation of a single modification strategy is broken through, and an effective solution is provided for practical application of the high-voltage layered positive electrode. According to the design expectation, on the premise of keeping high specific capacity, the cycling stability and thermal safety of the material under a high-pressure condition are remarkably improved, and the development of a high-energy-density lithium / sodium ion battery technology is promoted.

Description

Technical Field

[0001] This invention relates to the field of lithium / sodium ion battery cathode material technology, and more specifically, to a highly stable layered cathode material, its preparation method, and its application. Background Technology

[0002] Currently, the rapid popularization of electric vehicles and the widespread application of large-scale energy storage systems have placed higher demands on battery energy density. Layered oxide cathode materials for lithium / sodium-ion batteries are considered ideal candidates for next-generation high-energy-density lithium-ion batteries due to their high theoretical specific capacity and low cost. However, these materials still face severe challenges in practical applications, especially under high-voltage conditions where they are prone to mechanical and chemical failures, leading to rapid capacity decay and decreased kinetic performance. On the one hand, there is mechanical failure, where localized stress concentration caused by anisotropic lattice changes during cycling is a significant cause of material failure. Studies show that lattice strain accumulates most significantly in the core region of secondary particles, where the primary grain orientation is highly random, making it more susceptible to microcrack nucleation. As cycling progresses, these microcracks gradually expand and connect, eventually forming macroscopic cracks extending from the particle interior to the surface. On the other hand, there is chemical failure, where interfacial side reactions between the electrode and electrolyte are another key failure mechanism. When charged to high voltage, ions on the material surface undergo reduction, accompanied by lattice oxygen precipitation to maintain charge balance. This process not only induces oxygen vacancies but also promotes the migration of transition metals to the original octahedral sites in the lithium layer, causing the surface structure to gradually transform from a layered phase to an electrochemically inert spinel or rock salt phase. This degradation mechanism severely restricts the practical application of layered cathode materials.

[0003] It should be noted that mechanical failure and chemical failure are not independent but rather mutually reinforcing. Crack formation exposes new active surfaces, exacerbating electrolyte decomposition and interfacial side reactions; while chemical processes such as oxygen release and transition metal dissolution weaken lattice stability, further promoting crack propagation. To address these issues, various modification strategies have been developed. Surface coatings (such as CeO2, ZrO2, MgO, AlF3-Al2O3) can effectively isolate electrolyte contact and improve interfacial stability, but they are insufficient to suppress lattice distortion in the bulk phase. Traditional bulk doping, while capable of controlling grain size and orientation and suppressing crack initiation to some extent, cannot effectively alleviate lattice strain accumulation during cycling, nor can it form a stable interfacial protective layer. Recent studies have shown that constructing a coherent second phase in a layered structure can effectively release lattice strain, while introducing controllable porous structures helps alleviate stress concentration, thereby inhibiting crack initiation. However, a single modification strategy often only addresses one aspect of the problem and has inherent limitations. Therefore, developing a simple, cost-effective, and integrated modification strategy that can combine multiple advantages has become a key path to promote the practical application of layered cathodes. Summary of the Invention

[0004] This invention aims to address the mechanical cracking caused by lattice strain accumulation in high-energy-density layered lithium / sodium-ion battery cathode materials under high-voltage operating conditions, as well as the chemical degradation caused by interfacial side reactions. By constructing a synergistic modification structure, it enhances interfacial stability while suppressing bulk lattice distortion, thereby synergistically improving the structural durability and electrochemical performance of the layered cathode material. Specifically, this invention focuses on the following technical paths: introducing a lattice-matched stable phase to alleviate local stress concentration caused by anisotropic volume changes during cycling, suppressing the initiation and propagation of microcracks; constructing a dense and stable protective layer on the particle surface to prevent direct contact between the electrolyte and the highly active surface, reducing interfacial side reactions and surface structure degradation; achieving synergistic strengthening of the bulk structure and surface interface, overcoming the limitations of single modification strategies, and providing an effective solution for the practical application of high-voltage layered cathodes. This design aims to significantly improve the cycling stability and thermal safety of the material under high-voltage conditions while maintaining high specific capacity, thus promoting the development of high-energy-density lithium / sodium-ion battery technology.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A highly stable layered cathode material, wherein the cathode material has the following triple structure: internal porous structure, bulk stable phase, and surface coating.

[0007] Preferably, the internal pore structure is a central pore formed inside the secondary particles.

[0008] Preferably, the internal pore structure is formed by the partial decomposition of one or more of Ln(NO3)3, Ln2(CO3)3, and Ln(CH3COO)3 in the precursor body to produce gas, and the pore size is 1-500 nanometers.

[0009] Preferably, the bulk stable phase is a perovskite-type stable phase coherently embedded in a layered lattice, with the general formula Ln₂TMO. 4+δ , where Ln represents lanthanide elements and TM represents transition metal elements.

[0010] Preferably, the general formula Ln2TMO 4+δ In the δ value, the amount of extra oxygen that the perovskite structure can accommodate is 0.25-0.30. The lanthanide element Ln is one or more of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. The transition metal element TM is one or more of Ni, Co, Mn, Nb, B, and Al.

[0011] Preferably, a lattice coherent coherent or semi-coherent interfacial bonding relationship exists between the perovskite-type stable phase and the layered host material. More preferably, the doping ratio of the lanthanide element is 0.1% to 5% relative to the total molar amount of the transition metal.

[0012] Preferably, the surface coating is a protective coating covering the particle surface and composed of the perovskite-type stable phase.

[0013] Preferably, the layered cathode material includes LiNi 1-x-y Co x Mn y O2 (0.6 ≤ 1 - x - y ≤ 1), x Li2MnO3 ·(1 - x) LiTMO2 (0 < x ≤ 1), O3-NaTMO2, P2-Na x TMO2(0 < x < 1), where TM is one of Mn, Fe, Ni, Cu, Ti, Mg.

[0014] The present application also provides a method for preparing the high-stability layered cathode material as described above. The precursor of the cathode material, a lithium source, a pore-forming agent, and a low-melting-point salt constituting the perovskite stable phase are mixed and sintered once in an oxygen-containing atmosphere to simultaneously achieve the crystallization of the cathode material, the generation of internal pores, the in-situ symbiosis of the bulk perovskite stable phase, and the formation of the surface coating.

[0015] In addition, the present application also provides the application of the high-stability layered cathode material as described above in a lithium-ion battery.

[0016] The present invention provides a high-stability layered cathode material with a "stress buffering - bulk pinning - surface protection" synergistic structure and a preparation method thereof. The core feature is that through a one-step sintering process, the construction of the internal pore structure of the secondary particles, the bulk coherent interface perovskite stable phase, and the surface perovskite protective coating is simultaneously achieved.

[0017] Specifically, the formation mechanism and implementation method of this synergistic structure are as follows: Construction of internal stress buffering pores: The central pore structure is realized by introducing a low-melting-point salt as a pore-forming agent into the precursor. During the sintering process, the low-melting-point salt decomposes deep into the material to generate gas, thereby in-situ forming central pores with a size of 1 - 500 nanometers in the core region of the secondary particles. This structure can effectively release the lattice stress generated during the charge and discharge process and inhibit the initiation and expansion of microcracks. Bulk lattice coherence and pinning strengthening: The general formula of the perovskite-type stable phase is Ln2TMO 4+δ , where Ln is a lanthanide element (such as La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc.), and TM is elements such as Ni, Co, Mn, Nb, B, Al. Due to this R-P type Ln2TMO4+δ The perovskite structure and layered structure are highly matched in lattice parameters, allowing them to be coherently embedded into the main layered lattice during high-temperature sintering. This coherently grown stable phase anchors the primary nanocrystals through a "pinning effect," significantly suppressing their anisotropic volume changes and enhancing the reversibility of the bulk structure. Formation of the surface protective coating: During sintering, some of the perovskite precursors that have not diffused into the interior form a perovskite protective coating in situ on the particle surface. This coating physically isolates the electrolyte from direct contact with the highly active cathode surface, effectively reducing interfacial side reactions and acting as an oxygen buffer layer to improve surface oxygen stability. The preferred preparation method is a one-step sintering method, with key process parameters including: Precursor: Can be single-crystal particles with a size of several micrometers, or polycrystalline secondary spherical particles with a size of tens of micrometers. Doping elements: The doping ratio of the lanthanide and other perovskite constituent elements is 0.1% to 5% (relative to the total molar amount of transition metals). Sintering temperature: Sintering is carried out once within a suitable temperature range in an oxygen or air atmosphere.

[0018] This solution ingeniously integrates three functions through a single process step, breaking through the limitations of traditional modification technologies that only address symptoms. The resulting positive effects are synergistic and significant: internal pores resolve mechanical stress issues, bulk pinning stabilizes the crystal structure, and surface coating protects against interfacial side reactions. Ultimately, while maintaining high specific capacity, the material exhibits excellent cycle life and structural integrity under harsh conditions such as high voltage (4.5V and above) and high temperature (45℃), providing a practical material solution for developing next-generation high-energy-density, high-safety lithium-ion batteries.

[0019] The beneficial effects of this invention are as follows:

[0020] 1. Significantly improved overall performance

[0021] It achieves a high reversible specific capacity of 215 mAh g⁻¹ at 0.1C rate; it exhibits excellent rate performance, maintaining 160 mAh g⁻¹ at a high rate of 5C; and after 200 cycles at a high cutoff voltage of 4.5V, it retains a capacity of up to 95.4%.

[0022] 2. Breakthroughs in Structural Design and Stability

[0023] A one-step process simultaneously achieves three functions: microstructure regulation, bulk phase stabilization, and surface protection. The central pore structure built inside the particles effectively inhibits crack initiation and achieves uniform stress distribution. The coherent embedding of the perovskite phase in the layered structure generates a pinning effect, significantly suppressing anisotropic volume changes. The surface perovskite coating has both protective and oxygen buffering functions, enhancing interfacial stability.

[0024] 3. Synergistic enhancement of electrochemical and thermal stability

[0025] The modified material possesses excellent mechanical, chemical, and thermal stability; the perovskite phase serves as both a carrier transport channel and participates in the lattice oxygen stabilization process; and the protective coating effectively suppresses side reactions between the electrode and the electrolyte, thereby improving cycle life.

[0026] 4. Technological and cost advantages

[0027] It adopts a simple and efficient one-step process, which has good scalability and economy; it achieves multiple functions through a single process, avoiding complex multi-step processing procedures.

[0028] This invention, through a comprehensive structural design from the inside out, significantly improves the cycle stability and safety performance of layered cathode materials under high-pressure conditions while maintaining high specific capacity, providing an effective technical path for developing high-performance, long-life advanced lithium-ion batteries. Attached Figure Description

[0029] Figure 1 The XRD pattern of the cathode material prepared for comparison.

[0030] Figure 2 The image shows the XRD pattern of the cathode material prepared in Example 1.

[0031] Figure 3 The first charge-discharge curves of the cathode materials prepared in Example 1 and the comparative example are shown.

[0032] Figure 4 The above are rate performance curves of the cathode materials prepared in Example 1 and the comparative example, respectively.

[0033] Figure 5 The cycling curves of the cathode materials prepared in Example 1 and the comparative example are shown below;

[0034] Figure 6 This is an electron probe image of the cathode material prepared in Example 1;

[0035] Figure 7 The image shows the elemental analysis diagrams of the cross-sections of the cathode material prepared in Example 1 and the comparative material.

[0036] Figure 8 This is a cross-sectional SEM image of the cathode material prepared in Example 1;

[0037] Figure 9 This is a cycle curve diagram of the cathode material in Example 2;

[0038] Figure 10 This is a cycle curve diagram of the cathode material in Example 3;

[0039] Figure 11 This is a cycle curve diagram of the cathode material in Example 4;

[0040] Figure 12 This is a cycle curve diagram of the positive electrode material in Example 5;

[0041] Figure 13 This is a cycle curve diagram of the cathode material in Example 6. Detailed Implementation

[0042] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Based on the embodiments in this application, other similar embodiments obtained by those skilled in the art without creative effort should all fall within the scope of protection of this application.

[0043] Example 1:

[0044] According to the precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)2:Nd(NO3)3·6H2O (Chinese medicine, analytical grade):LiOH·H2O (Chinese medicine, analytical grade) molar ratio 1:0.001:1.03. Weigh the raw materials, mix them evenly, and place them in a tube furnace. Incubate at 500℃ for 3 min. -1 The material was calcined at a heating rate of 5 h, then calcined in oxygen at 750 °C for 12 h, and then naturally cooled to room temperature to obtain a highly stable layered cathode material, LiNi. 0.8 Co 0.1 Mn 0.1 O2.

[0045] Example 2:

[0046] According to the precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)2:La(NO3)3·6H2O (Chinese medicine, analytical grade):LiOH·H2O (Chinese medicine, analytical grade) molar ratio 1:0.02:1.03. Weigh the materials, mix them evenly, and place them in a tube furnace. Incubate at 500℃ for 3 min. -1 The material was calcined at a heating rate of 5 h, then calcined in oxygen at 750 °C for 12 h, and then naturally cooled to room temperature to obtain a highly stable layered cathode material, LiNi. 0.8 Co 0.1 Mn 0.1 O2.

[0047] Example 3

[0048] According to the precursor Ni 0.9 Mn0.1 (OH)2:Nd2(CO3)3·6H2O (Chinese medicine, analytical grade):LiOH·H2O (Chinese medicine, analytical grade) molar ratio 1:0.025:1.03. Weigh the materials, mix them evenly, and place them in a tube furnace. Incubate at 500℃ for 3 min. -1 The material was calcined at a heating rate of 5 h, then calcined in oxygen at 750 °C for 12 h, and then naturally cooled to room temperature to obtain a highly stable layered cathode material, LiNi. 0.9 Mn 0.1 O2.

[0049] Example 4

[0050] According to the precursor Ni 0.9 Mn 0.05 Co 0.05 (OH)2:Ce(CH3COO)3·xH2O (Chinese medicine, analytical grade):LiOH·H2O (Chinese medicine, analytical grade) molar ratio 1:0.05:1.03. Weigh the materials, mix them evenly, and place them in a tube furnace. Incubate at 500℃ for 3 min. -1 The material was calcined at a heating rate of 5 h, then calcined in oxygen at 750 °C for 12 h, and then naturally cooled to room temperature to obtain a highly stable layered cathode material, LiNi. 0.9 Mn 0.05 Co 0.05 O2.

[0051] Example 5

[0052] According to the precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)2:Yb(CH3COO)3·4H2O (Chinese medicine, analytical grade):NaOH·H2O (Chinese medicine, analytical grade) molar ratio 1:0.03:0.02:1.03. Weigh the materials, mix them evenly, and place them in a tube furnace. Incubate at 650℃ for 3 min. -1 The material was calcined at a heating rate of 12 h and then naturally cooled to room temperature to obtain a highly stable layered cathode material, NaNi. 0.8 Co 0.1 Mn 0.1 O2.

[0053] Example 6

[0054] According to the precursor Ni 0.8 Co 0.1 Mn 0.1(OH)2:Ho(NO3)3·6H2O (Chinese medicine, analytical grade):NaOH·H2O (Chinese medicine, analytical grade) molar ratio 1:0.05:1.03. Weigh the materials, mix them evenly, and place them in a tube furnace. Incubate at 650℃ for 3 min. -1 The material was calcined at a heating rate of 12 h and then naturally cooled to room temperature to obtain a highly stable layered cathode material, NaNi. 0.8 Co 0.1 Mn 0.1 O2.

[0055] Comparative Example

[0056] According to the precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)2:LiOH·H2O (Chinese medicine, analytical grade) molar ratio 1:1.03. Weigh the materials, mix them evenly, and place them in a tube furnace. Incubate at 500℃ for 3 min. -1 The raw LiNi was calcined at a heating rate of 5 h, then calcined in oxygen at 750 °C for 12 h, and then naturally cooled to room temperature to obtain the original LiNi. 0.8 Co 0.1 Mn 0.1 O2.

[0057] The XRD results of the unmodified cathode material obtained in the comparative example are as follows: Figure 1 As shown in the figure (corresponding to process 1 in the figure), the characteristic peaks of the cathode material agree well with the standard PDF card, indicating a classic α-NaFeO2 layered structure. This demonstrates that the cathode material has good crystallinity and a well-developed layered structure. The XRD results of the modified cathode material prepared in Example 1 are as follows: Figure 2 As shown (corresponding to process 2 in the figure), a new perovskite peak appeared, indicating that the perovskite structure was successfully integrated into the bulk phase. The electrochemical performance of the modified cathode material obtained in Example 1 was tested. The test voltage range was 3–4.5 V, and the charge / discharge rate was 0.1 C. The test results are as follows: Figure 3-5 Example 1 corresponds to process 2 in the figure, and the control group corresponds to process 1 in the figure. Figure 3 It can be seen that the first-cycle charge-discharge specific capacity of the lithium-ion ternary layered oxide prepared in Example 1 is 215 mAh / g; the rate performance is as follows: Figure 4 As shown, its stability test results are as follows. Figure 5 ,Depend on Figure 5 It can be seen that the capacity retention rate is 92.5% after 100 cycles. The electrochemical performance is superior to most high-nickel cathode materials reported to date. In order to further explore the distribution of the new phase in the particles, we first used electron probe X-ray microscopy (EPMA) to observe the distribution of each element in the modified cathode material sample particles. Figure 6The results showed that Ni, Co, and Mn were uniformly distributed in the secondary particles, while Nd was enriched on the surface of the secondary particles. Figure 7 As shown, group (a) is the cathode material prepared in the comparative example, and the elemental analysis results of the cross-section show that there are no lanthanide elements inside; group (b) is the cathode material prepared in Example 1, and the elements Ni, Co, Mn and Nd are uniformly distributed in the cross-section. Figure 8 As shown, observing the cross-section of the secondary particles, we found that some small pores were distributed in the central region of the secondary particles of the cathode material prepared in Example 1, while this phenomenon was not found in the secondary particles of the initial material. Figure 9-13 As shown, the capacity retention of the cathode materials prepared in Examples 2 to 6 is >60% after 100 cycles.

[0058] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A highly stable layered cathode material, characterized in that, The cathode material has the following triple structure: internal porous structure, bulk stable phase, and surface coating.

2. The high-stability layered cathode material according to claim 1, characterized in that, The internal pore structure is a central pore formed inside the secondary particles.

3. The high-stability layered cathode material according to claim 2, characterized in that, The internal pore structure is formed by the partial decomposition of one or more of Ln(NO3)3, Ln2(CO3)3, and Ln(CH3COO)3 in the precursor body to produce gas, and the pore size is 1-500 nanometers.

4. The high-stability layered cathode material according to claim 1, characterized in that, The bulk stable phase is a perovskite-type stable phase coherently embedded in a layered lattice, with the general formula Ln2TMO. 4+δ , where Ln represents lanthanide elements and TM represents transition metal elements.

5. The high-stability layered cathode material according to claim 4, characterized in that, General formula Ln2TMO 4+δ In the δ value, the amount of extra oxygen that the perovskite structure can accommodate is 0.25-0.

30. The lanthanide element Ln is one or more of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. The transition metal element TM is one or more of Ni, Co, Mn, Nb, B, and Al.

6. The high-stability layered cathode material according to claim 4, characterized in that, The perovskite-type stable phase and the layered host material are bonded by a lattice-coherent coherent or semi-coherent interface. Preferably, the doping ratio of lanthanide elements is 0.1% to 5% relative to the total molar amount of transition metals.

7. The high-stability layered cathode material according to claim 1, characterized in that, The surface coating is a protective coating that covers the particle surface and consists of the perovskite-type stable phase.

8. The high-stability layered cathode material according to any one of claims 1-7, characterized in that, The layered cathode material includes LiNi 1-x-y Co x Mn y O2 (0.6 ≤ 1 - x - y ≤ 1), xLi2MnO3·(1 - x)LiTMO2 (0 < x ≤ 1), O3 - NaTMO2, P2 - Na x TMO2 (0 < x < 1), where TM is one of Mn, Fe, Ni, Cu, Ti, and Mg.

9. A method for preparing a highly stable layered cathode material as described in any one of claims 1-8, characterized in that, The precursor of the cathode material, the lithium source, the pore-forming agent, and the low-melting-point salt constituting the perovskite stable phase are mixed and sintered in an oxygen-containing atmosphere in one step, so as to simultaneously realize the crystallization of the cathode material, the generation of internal pores, the in-situ symbiosis of the bulk perovskite stable phase, and the formation of the surface coating.

10. The application of the highly stable layered cathode material as described in any one of claims 1-8 in lithium / sodium-ion batteries.

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