An in-situ reaction-generated sodium titanate-coated modified oxygen cathode material and its preparation method.

Abstract

This invention discloses an in-situ reaction-generated sodium titanate-coated modified oxygen cathode material and its preparation method, belonging to the field of battery cathode material technology. The preparation method includes: first, ball milling and mixing a nickel source, an iron source, a manganese source, and a sodium source, followed by high-temperature sintering at 800–1000℃ to obtain an O3 phase cathode material matrix; then, ball milling and mixing the obtained matrix material with a trace amount of titanium-containing compound, followed by a secondary sintering at a lower temperature of 500–600℃. The titanium-containing compound undergoes an in-situ solid-phase chemical reaction with residual sodium carbonate on the matrix surface to generate a sodium titanate coating layer chemically bonded to the matrix, primarily composed of the Na2TiO3 crystalline phase. This coating layer possesses both fast sodium ion conduction characteristics and the ability to chemically neutralize acidic substances in the electrolyte, significantly reducing interfacial impedance, improving rate performance, and effectively suppressing transition metal dissolution and interfacial side reactions, thereby endowing the material with excellent high-voltage cycle stability and long lifespan.

Description

Technical Field

[0001] This invention relates to the field of battery cathode material technology, and in particular to an in-situ reaction-generated sodium titanate-coated modified oxygen cathode material and its preparation method. Background Technology

[0002] Sodium-ion batteries are considered an important supplement to lithium-ion batteries in large-scale energy storage due to the abundance and low cost of sodium resources. Among many cathode materials, layered transition metal oxides (Na₂O₃) are... x Transition metals (TM, such as Mn, Ni, Fe, Cu, etc.) have attracted much attention due to their high specific capacity and relatively simple synthesis process. However, these materials, especially manganese-rich or high-capacity O3 phase materials, exhibit interfacial instability, particularly when in contact with electrolytes: the material surface can undergo side reactions with the electrolyte, especially under high voltages; furthermore, moisture and impurities in the electrolyte can induce degradation of the material surface structure. Transition metal ion dissolution, especially of Mn, is also a concern. 3+ The Jahn-Teller effect causes manganese ions to dissolve into the electrolyte, which not only damages the structure of the positive electrode material, but also causes the dissolved ions to migrate to the negative electrode, damaging the solid electrolyte interface film of the negative electrode.

[0003] To address the aforementioned issues, surface coating is one of the effective strategies for improving the stability of material interfaces. Existing technologies have reported the use of pre-fabricated nano-titanic acid to physically coat layered oxide cathode materials. This method involves ball milling nano-titanic acid onto the material surface, followed by high-temperature sintering to form a coating layer, which can reduce surface residual alkali and improve ion transport rates to some extent. However, this coating method mainly relies on physical mixing and mechanical adhesion, resulting in limited bonding strength between the coating layer and the substrate. Furthermore, its ability to chemically neutralize harmful acidic substances in the electrolyte during cycling is insufficient, making it difficult to achieve long-term, active protection of the material interface.

[0004] Therefore, developing a coating method that allows the coating layer to bond more firmly to the substrate and possesses both high ionic conductivity and active chemical protection is of great significance for improving the overall electrochemical performance of layered oxide cathode materials for sodium-ion batteries. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing an in-situ reaction-generated sodium titanate-coated modified oxygen cathode material, which can be used to prepare a sodium-ion battery cathode material with both high ionic conductivity and active interfacial chemical protection function.

[0006] The present invention also aims to provide an in-situ reaction-generated sodium titanate-coated modified oxygen cathode material to solve the problem that the physical coating modified oxygen cathode material in the prior art has poor bonding and insufficient performance improvement.

[0007] In a first aspect, the present invention provides a method for preparing an in-situ reacted sodium titanate-coated modified oxygen cathode material, comprising the following steps: S1. Weigh out nickel source, iron source, manganese source and sodium source according to the proportion, ball mill and mix, sinter at high temperature, and then pulverize and sieve to obtain O3 phase cathode material a:Na 1.01 Ni 0.33 Fe 0.33 Mn 0.33 O2; S2. After ball milling and mixing the O3 phase cathode material a and the titanium-containing compound, and sintering at medium temperature, the mixture is immediately cooled, pulverized, and sieved to obtain the coated O3 phase cathode material Na. 1.01 Ni 0.33 Fe 0.33 Mn 0.33 O2@T.

[0008] By adopting the above technical solution, this invention abandons the traditional approach of physical mixing and coating. Through stepwise sintering and precise temperature control, it achieves an in-situ solid-phase chemical reaction between the titanium-containing compound and the residual alkali on the surface of the cathode material. This reaction is carried out within a specific low temperature window, directly generating a uniform, dense, and chemically bonded sodium titanate coating layer on the substrate surface, fundamentally solving the problems of weak bonding and uneven distribution in physical coatings. Specifically, in step S1, nickel, iron, manganese, and sodium sources are mixed in proportion, and after ball milling and high-temperature sintering, a well-crystallized and uniformly composed O3-phase cathode material a(Na3) can be precisely synthesized. 1.01 Ni 0.33 Fe 0.33 Mn 0.33 O2), the small amount of sodium carbonate remaining on its surface provides the necessary sodium source for subsequent in-situ reactions, laying the foundation for the formation of the coating layer; step S2 directly generates a sodium titanate coating layer through the in-situ reaction of titanium-containing compounds with residual alkali on the surface of material a, avoiding the mechanical adhesion defects of physical coating, realizing the chemical bonding between the coating layer and the substrate, and greatly improving the bonding stability.

[0009] Preferably, in step S2, the sodium source is sodium carbonate.

[0010] Preferably, in step S2, the nickel source includes nickel oxide and nickel carbonate; the iron source includes iron oxide and iron hydroxide; and the manganese source includes manganese tetroxide and manganese dioxide.

[0011] Preferably, in step S2, the titanium-containing compound includes titanium tetrachloride and / or titanium dioxide.

[0012] Preferably, in step S2, the amount of titanium-containing compound added is 0.1% to 0.5% of the mass of O3 phase cathode material a.

[0013] Preferably, in step S1, the high-temperature sintering temperature is 800–1000°C, and the holding time is 10–15 h.

[0014] Preferably, in step S2, the temperature of the medium-temperature sintering is 500–600°C.

[0015] Preferably, the ball milling speed is 400-600 r / min and the time is 5-10 h.

[0016] Secondly, the present invention also provides an in-situ reaction-generated sodium titanate-coated modified layered oxygen cathode material, the cathode material having a core-shell structure, the core being a layered oxide and the outer shell being a sodium titanate coating layer.

[0017] Preferably, the sodium titanate coating layer is a Na2TiO3 crystalline phase.

[0018] The beneficial effects of this invention are: 1. In terms of the preparation method, this invention cleverly promotes an in-situ solid-phase chemical reaction between the added titanium-containing compound and the residual sodium carbonate inherent on the surface of the cathode material by precisely controlling the second sintering at a relatively low temperature range of 500-600℃, rather than a simple physical adhesion. This process directly grows a sodium titanate coating layer with Na2TiO3 as the main crystalline phase on the substrate surface. The coating layer is chemically bonded to the substrate, and the bonding strength is much higher than that of physical mechanical bonding. This ensures the structural integrity and stability of the coating layer during long-term charge-discharge cycles and avoids performance degradation caused by coating layer detachment.

[0019] 2. The Na₂TiO₃ coating layer generated in this invention is itself an excellent fast sodium ion conductor. It constructs a high-speed sodium ion transport channel on the surface of the cathode material particles, significantly reducing the migration energy barrier of sodium ions at the electrode-electrolyte interface, thereby greatly improving the rate performance of the material and enabling the battery to maintain a high capacity output even at high current densities. More importantly, this sodium titanate coating layer has unique chemical functions. Its alkaline properties can actively and chemically neutralize trace amounts of acidic substances generated during electrolyte decomposition during cycling, especially highly corrosive hydrofluoric acid. This effectively inhibits the erosion of the cathode material structure by HF and slows down the degradation of transition metal ions (especially Mn). 3+ This active interfacial chemical protection mechanism effectively mitigates material structural collapse and capacity decay caused by side reactions, significantly improving the material's cycling stability and lifespan under high voltage. Furthermore, while effectively forming a functional coating layer, this method also significantly reduces the residual alkali content on the material surface, improving the material's processing performance and compatibility with the electrolyte.

[0020] 3. This invention achieves the triple goals of enhancing interfacial bonding, accelerating ion transport, and providing active chemical protection through a mild and simple in-situ reaction coating strategy. The resulting cathode material exhibits superior comprehensive electrochemical performance, particularly in high-rate charge-discharge and long cycle life, and has significant practical application value. Attached Figure Description

[0021] Figure 1 This is a capacity retention diagram of Embodiment 1 and Comparative Example 1 of the present invention; Figure 2 This is a rate performance diagram of Embodiment 1 and Comparative Example 1 of the present invention; Figure 3 This is an electron microscope image of Embodiment 1 of the present invention. Detailed Implementation

[0022] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0023] A method for preparing an in-situ reaction-generated sodium titanate-coated modified oxygen cathode material includes the following steps: S1. Weigh out nickel source, iron source, manganese source and sodium source according to the proportion, ball mill and mix, sinter at high temperature, and then pulverize and sieve to obtain O3 phase cathode material a:Na 1.01 Ni 0.33 Fe 0.33 Mn 0.33 O2; S2. After ball milling and mixing the O3 phase cathode material a and the titanium-containing compound, and sintering at medium temperature, the mixture is immediately cooled, pulverized, and sieved to obtain the coated O3 phase cathode material Na. 1.01 Ni 0.33 Fe 0.33 Mn 0.33 O2@T.

[0024] By adopting the above technical solution, this invention abandons the traditional approach of physical mixing and coating. Through stepwise sintering and precise temperature control, it achieves an in-situ solid-phase chemical reaction between the titanium-containing compound and the residual alkali on the surface of the cathode material. This reaction is carried out within a specific low temperature window, directly generating a uniform, dense, and chemically bonded sodium titanate coating layer on the substrate surface, fundamentally solving the problems of weak bonding and uneven distribution in physical coatings. Specifically, in step S1, nickel, iron, manganese, and sodium sources are mixed in proportion, and after ball milling and high-temperature sintering, a well-crystallized and uniformly composed O3-phase cathode material a(Na3) can be precisely synthesized. 1.01 Ni 0.33 Fe 0.33 Mn 0.33O2), the small amount of sodium carbonate remaining on its surface provides the necessary sodium source for subsequent in-situ reactions, laying the foundation for the formation of the coating layer; step S2 directly generates a sodium titanate coating layer through the in-situ reaction of titanium-containing compounds with residual alkali on the surface of material a, avoiding the mechanical adhesion defects of physical coating, realizing the chemical bonding between the coating layer and the substrate, and greatly improving the bonding stability.

[0025] In some embodiments, in step S2, the sodium source is sodium carbonate. Sodium carbonate is chosen as the sodium source because its thermal decomposition temperature matches well with the primary sintering process, ensuring a stable supply of sodium elements to form the O3 phase structure. More importantly, after primary sintering, a small amount of unreacted sodium carbonate remains on the material surface. This provides a crucial sodium source and reactant for the in-situ reaction with titanium-containing compounds in subsequent steps, serving as a prerequisite for generating the target coating layer.

[0026] In some embodiments, in step S2, the nickel source includes nickel oxide and nickel carbonate; the iron source includes iron oxide and iron hydroxide; and the manganese source includes manganese tetroxide and manganese dioxide. These raw materials have the characteristics of high purity and moderate reactivity, which can avoid the introduction of impurity ions and ensure the formation of a pure O3 phase structure. At the same time, their reaction characteristics are compatible with the high-temperature sintering process, ensuring the crystal integrity of material a and the controllability of the surface residual alkali content.

[0027] In some embodiments, in step S2, the titanium-containing compound includes titanium tetrachloride and / or titanium dioxide; titanium tetrachloride has high activity and readily diffuses at lower temperatures, reacting with residual alkali on the surface; titanium dioxide is stable and has good process safety. Both can serve as effective titanium sources, reacting with surface Na2CO3 under set medium-temperature sintering conditions to generate the target product Na2TiO3, providing a flexible and reliable raw material selection for the formation of the coating layer.

[0028] In some embodiments, in step S2, the amount of titanium-containing compound added is 0.1% to 0.5% of the mass of the O3 phase cathode material a. This addition range is optimized to ensure the formation of a complete coating layer with appropriate thickness. If the addition amount is too low, the coating will be incomplete and the protective effect will be insufficient; if it is too high, the coating layer may be too thick, or even unnecessary bulk doping may occur, which will hinder ion transport and affect the bulk capacity of the material. This range achieves the best balance between surface modification effect and bulk performance.

[0029] In some embodiments, in step S1, the high-temperature sintering temperature is 800-1000°C and the holding time is 10-15 hours. This high-temperature and long-time sintering regime is the key to forming a cathode material with a regular layered structure and high crystallinity of O3 phase. Under this condition, the atoms of each element can fully diffuse and arrange, complete the lattice construction, and ensure that the material has high intrinsic specific capacity and structural stability.

[0030] In some embodiments, the temperature of the intermediate-temperature sintering in step S2 is 500–600°C. This temperature is much lower than the conventional crystallization sintering temperature after coating (typically >800°C), but it is precisely the optimal window for driving the titanium-containing compound to undergo a solid-state reaction with surface Na2CO3 to generate Na2TiO3. If the temperature is too low, the reaction cannot proceed; if it is too high, it may lead to over-sintering of the coating layer or unfavorable interdiffusion with the substrate, or even damage to the substrate structure. This intermediate-temperature sintering achieves a perfect balance between reaction occurrence and "structural preservation".

[0031] In some embodiments, the ball milling speed is 400–600 r / min, and the time is 5–10 h. These ball milling parameters ensure that the material after one sintering is fully pulverized to the required particle size, while simultaneously achieving atomic-level homogeneous mixing of the titanium-containing compound and the precursor material a. Sufficient mechanical force helps expose more surface reaction sites and creates conditions for close contact in subsequent in-situ chemical reactions, ensuring the uniformity and consistency of the coating layer.

[0032] An in-situ reaction-generated sodium titanate-coated modified layered oxygen cathode material is disclosed. The cathode material has a core-shell structure, with a layered oxide core and a sodium titanate coating layer on the outer shell.

[0033] In some embodiments, the sodium titanate coating layer is a Na2TiO3 crystalline phase.

[0034] By adopting the above technical solutions, Na2TiO3 has an orthorhombic crystal structure, which not only forms a stable chemical bond with the matrix, but also has excellent sodium ion conduction performance. At the same time, it has a strong adsorption and neutralization ability for HF in the electrolyte, realizing the dual functions of protection and ion transport.

[0035] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0036] Example

[0037] Example 1: A method for preparing an in-situ reaction-generated sodium titanate-coated modified oxygen cathode material, comprising the following steps: S1. Weigh 560g of nickel oxide, 480g of iron oxide, 450g of manganese tetroxide, and 960g of battery-grade sodium carbonate, add them to a ball mill jar, and ball mill at 400 rpm / min for 5 hours to mix. Then pour the mixture into a crucible and sinter it in an atmosphere furnace at 900℃ for 15 hours. After natural cooling, remove and pulverize to obtain the O3 phase cathode material a:Na. 1.01 Ni 0.33 Fe 0.33 Mn 0.33 O2; S2. Weigh 500g of O3 phase cathode material a and 1g of titanium tetrachloride, ball mill and mix them, then sinter at a medium temperature of 550℃. After natural cooling, pulverize and sieve to obtain the coated O3 phase cathode material Na. 1.01 Ni 0.33 Fe 0.33 Mn 0.33 O2@T.

[0038] Example 2, a method for preparing an in-situ reaction-generated sodium titanate-coated modified oxygen cathode material, comprising the following steps: S1. Weigh 560g of nickel oxide, 480g of iron oxide, 450g of manganese tetroxide, and 960g of battery-grade sodium carbonate, add them to a ball mill jar, and ball mill at 400 rpm / min for 5 hours to mix. Then pour the mixture into a crucible and sinter it in an atmosphere furnace at 900℃ for 15 hours. After natural cooling, remove and pulverize to obtain the O3 phase cathode material a:Na. 1.01 Ni 0.33 Fe 0.33 Mn 0.33 O2; S2. Weigh 500g of O3 phase cathode material a and 1g of titanium dioxide, ball mill and mix them, then sinter at a medium temperature of 550℃. After natural cooling, pulverize and sieve to obtain the coated O3 phase cathode material Na. 1.01 Ni 0.33 Fe 0.33 Mn 0.33 O2@T.

[0039] Example 3: A method for preparing an in-situ reaction-generated sodium titanate-coated modified oxygen cathode material, comprising the following steps: S1. Weigh 560g of nickel oxide, 480g of iron oxide, 450g of manganese tetroxide, and 960g of battery-grade sodium carbonate, add them to a ball mill jar, and ball mill at 400 rpm / min for 5 hours to mix. Then pour the mixture into a crucible and sinter it in an atmosphere furnace at 900℃ for 15 hours. After natural cooling, remove and pulverize to obtain the O3 phase cathode material a:Na. 1.01 Ni 0.33 Fe 0.33 Mn 0.33 O2; S2. Weigh 500g of O3 phase cathode material a and 0.7g of titanium tetrachloride, ball mill and mix them, then sinter at a medium temperature of 600℃. After natural cooling, pulverize and sieve to obtain the coated O3 phase cathode material Na. 1.01 Ni 0.33 Fe 0.33 Mn 0.33 O2@T.

[0040] Comparative Example

[0041] Comparative Example 1: A method for preparing an in-situ reaction-generated sodium titanate-coated modified oxygen cathode material, comprising the following steps: S1. Weigh 560g of nickel oxide, 480g of iron oxide, 450g of manganese tetroxide, and 960g of battery-grade sodium carbonate, add them to a ball mill jar, and ball mill at 400 rpm / min for 5 hours to mix. Then pour the mixture into a crucible and sinter it in an atmosphere furnace at 900℃ for 15 hours. After natural cooling, remove and pulverize to obtain the O3 phase cathode material a:Na. 1.01 Ni 0.33 Fe 0.33 Mn 0.33 O2.

[0042] Comparative Example 2, a method for preparing an in-situ reaction to generate sodium titanate-coated modified oxygen cathode material, differs from Example 1 only in that the amount of titanium tetrachloride added is 0.01% of the mass of O3 phase cathode material a.

[0043] Comparative Example 3, a method for preparing an in-situ reaction-generated sodium titanate-coated modified oxygen cathode material, differs from Example 1 only in that the amount of titanium tetrachloride added is 1% of the mass of the O3 phase cathode material a.

[0044] Comparative Example 4, a method for preparing an in-situ reaction-generated sodium titanate-coated modified oxygen cathode material, differs from Example 1 only in that the same amount of tetraethyl titanate is used instead of titanium tetrachloride.

[0045] Comparative Example 5, a method for preparing an in-situ reaction-generated sodium titanate-coated modified oxygen cathode material, differs from Example 1 only in that the sintering temperature in S2 is 800℃.

[0046] Performance testing: The positive electrode materials prepared in Examples 1-3 and Comparative Examples 1-5 were respectively mixed with SP, PVDF, and CNT in a ratio of 96:0.9:2:1.1 to form electrode sheets. These sheets were then used to fabricate pouch cells with hard carbon negative electrodes, and rate and cycle tests were performed. The results are as follows: Figure 1 , Figure 2 As shown in Table 1; Table 1 Performance test results

[0047] Test results show that in Examples 1-3, medium-temperature sintering at 500-600℃ successfully induced an in-situ reaction between the titanium-containing compound and residual alkali on the material surface, forming a chemically bonded Na2TiO3 coating layer. Compared with the comparative examples, this coating layer not only provides a high-speed sodium ion channel and has a significantly higher specific capacity than the uncoated Comparative Example 1, but its active chemical protection function also more effectively suppresses interfacial side reactions. The performance degradation of Comparative Examples 2-5 indicates that insufficient or excessive coating amount, mismatched titanium source, and excessively high sintering temperature all prevent the optimal in-situ reaction from being achieved, resulting in incomplete coating function or damage to the matrix, thus reducing the overall performance.

[0048] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A method for preparing an in-situ reaction-generated sodium titanate-coated modified oxygen cathode material, characterized in that, Includes the following steps: S1, the nickel source, iron source, manganese source and sodium source are weighed according to the proportion, ball-milled, mixed, high-temperature sintered, crushed and sieved to obtain the O3 phase positive electrode material a: Na 1.01 Ni 0.33 Fe 0.33 Mn 0.33 O2; S2. After ball milling and mixing the O3 phase cathode material a and the titanium-containing compound, and sintering at medium temperature, the mixture is immediately cooled, pulverized, and sieved to obtain the coated O3 phase cathode material Na. 1.01 Ni 0.33 Fe 0.33 Mn 0.33 O2@T.

2. The method for preparing an in-situ reaction-generated sodium titanate-coated modified oxygen cathode material according to claim 1, characterized in that, In step S1, the sodium source is sodium carbonate.

3. The method for preparing an in-situ reaction-generated sodium titanate-coated modified oxygen cathode material according to claim 1, characterized in that, In step S1, the nickel source includes nickel oxide and nickel carbonate; the iron source includes iron oxide and iron hydroxide; and the manganese source includes manganese tetroxide and manganese dioxide.

4. The method for preparing an in-situ reaction-generated sodium titanate-coated modified oxygen cathode material according to claim 1, characterized in that, In step S2, the titanium-containing compound includes titanium tetrachloride and / or titanium dioxide.

5. The method for preparing an in-situ reaction-generated sodium titanate-coated modified oxygen cathode material according to claim 1, characterized in that, In step S2, the amount of titanium-containing compound added is 0.1% to 0.5% of the mass of O3 phase cathode material a.

6. The method for preparing an in-situ reaction-generated sodium titanate-coated modified oxygen cathode material according to claim 1, characterized in that, In step S1, the high-temperature sintering temperature is 800-1000℃, and the holding time is 10-15h.

7. The method for preparing an in-situ reaction-generated sodium titanate-coated modified oxygen cathode material according to claim 1, characterized in that, In step S2, the temperature of the medium-temperature sintering is 500-600℃.

8. The method for preparing an in-situ reaction-generated sodium titanate-coated modified oxygen cathode material according to claim 1, characterized in that, The ball mill operates at a speed of 400–600 r / min for 5–10 h.

9. An in-situ reaction-generated sodium titanate-coated modified oxygen cathode material, prepared by the preparation method according to any one of claims 1-8, characterized in that, The cathode material has a core-shell structure, with a layered oxide core and a sodium titanate coating layer on the outer shell.

10. The in-situ reaction-generated sodium titanate-coated modified oxygen cathode material according to claim 9, characterized in that, The sodium titanate coating layer is of the Na2TiO3 crystalline phase.

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