A high specific capacity cathode material and a preparation method thereof

Abstract

The application discloses a high specific capacity positive electrode material and a preparation method thereof. 1‑x‑y Co x Mn y (OH)2, a first niobium precursor, a lithium precursor are mixed, corresponding ternary oxides, niobium oxides and lithium oxides are respectively generated at a first temperature, the oxides react at a second temperature, a second niobium precursor is added, and a niobium-doped ternary lithium positive electrode material is generated at a third temperature; x>0, y>0, x+y<1; the first temperature is less than the third temperature, and the third temperature is less than the second temperature; in step 2, the niobium-doped ternary lithium positive electrode material is mixed with CrO3 powder, the CrO3 powder is melted at a fourth temperature, the melted CrO3 powder is decomposed into Cr8O 21 , and the niobium-doped ternary lithium positive electrode material is coated, so that the high specific capacity positive electrode material is obtained; the fourth temperature is less than the fifth temperature. The application simultaneously improves the specific capacity, structural stability and interface stability of the material by doping the niobium oxide in the positive electrode material and coating the material surface with the chromium oxide.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and in particular to a high specific capacity cathode material and its preparation method. Background Technology

[0002] Lithium-ion batteries, with their high energy density, long cycle life, and excellent charge-discharge performance, have become core energy storage devices in the field of energy utilization and transformation. Especially in the aerospace equipment sector, lithium-ion batteries serve as the power heart, providing stable power support for spacecraft's on-orbit operation, attitude adjustment, and mission payloads. Their performance and reliability are crucial to the success or failure of aerospace missions. As aerospace equipment develops towards lightweight, long-endurance, and high-payload designs, more stringent requirements are being placed on the energy density of lithium-ion batteries. Higher specific energy not only reduces the volume and weight of the battery system but also extends the on-orbit operating time of the spacecraft, improving mission efficiency.

[0003] One of the core pathways to improving the specific energy of lithium-ion batteries is the development and adoption of electrode materials with high specific capacity. Among these, the specific capacity and structural stability of the cathode material play a decisive role in the overall battery performance. Currently, in practical applications of high-specific-capacity cathode materials, nickel-cobalt-manganese-lithium ternary materials (NCM) with a layered structure are the mainstream choice. The specific capacity of this type of material is positively correlated with the nickel (Ni) content: as the Ni content increases, the Ni content in the material increases. 2+ Ni 3+ The multivalent redox reaction can enable more lithium ions to be inserted and extracted, which significantly improves the specific capacity of the material, thus effectively meeting the high specific energy requirements of batteries.

[0004] However, the increase in nickel content leads to a significant decrease in the structural stability of nickel-cobalt-manganese-lithium ternary materials, which directly results in a shortened cycle life of high-nickel ternary materials. Furthermore, the risk of thermal runaway increases under high-voltage charging and discharging or high-temperature environments, making it difficult to meet the safety requirements of demanding application scenarios.

[0005] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art. Summary of the Invention

[0006] The purpose of this invention is to extend the cycle life of the battery by uniformly distributing Nb in the inner layer and enriching it in the outer layer of the cathode material, and by coating the surface of the cathode material with chromium oxide, thereby improving the specific capacity, structural stability and interface stability of the material.

[0007] To achieve the above objectives, the present invention provides a method for preparing a high specific capacity cathode material, the method comprising:

[0008] Step 1: Under an oxygen atmosphere, the hydroxide precursor Ni...1-x-y Co x Mn y (OH)2, a first niobium precursor and a lithium precursor are mixed, and corresponding ternary oxides, niobium oxides and lithium oxides are generated at a first temperature, respectively. At a second temperature, the ternary oxides, niobium oxides and lithium oxides react, and then a second niobium precursor is added. At a third temperature, niobium-doped ternary lithium cathode material is generated; wherein, x > 0, y > 0, x + y < 1; the first temperature < the third temperature < the second temperature.

[0009] Step 2: Under an oxygen atmosphere, the niobium-doped ternary lithium cathode material and CrO3 powder are mixed. The CrO3 powder is melted at a fourth temperature, and the molten CrO3 powder decomposes into Cr8O at a fifth temperature. 21 The niobium-doped ternary lithium cathode material is coated to obtain a high specific capacity cathode material; wherein the fourth temperature is less than the fifth temperature.

[0010] Optionally, the hydroxide precursor Ni 1-x-y Co x Mn y In (OH)₂, x≤0.1, y≤0.1; both the first and second niobium precursors are niobate H₅Nb₃O₂. 10 The lithium precursor is LiOH·H2O.

[0011] Optionally, the molar ratio of the hydroxide precursor, the first niobium precursor, the second niobium precursor, and the lithium precursor is 1:(0.005~0.02):(1.02~1.10); the molar ratio of the first niobium precursor and the second niobium precursor is (5~20):1.

[0012] Optionally, the molar ratio of the niobium-doped ternary lithium cathode material to the CrO3 powder is 1:(0.01~0.2).

[0013] Optionally, the first temperature is 400℃~450℃, and the holding time is 1h~5h; the second temperature is 720℃~850℃, and the holding time is 5h~20h; the third temperature is 475℃~525℃, and the holding time is 1h~8h; the fourth temperature is 190℃~200℃, and the holding time is 1h~5h; the fifth temperature is 260℃~270℃, and the holding time is 8h~20h.

[0014] Optionally, before step 1, the method further includes: co-precipitating nickel, cobalt, and manganese under alkaline conditions to obtain the hydroxide precursor Ni. 1-x-y Co x Mn y (OH)2.

[0015] Optionally, the CrO3 powder is in granular form with a particle size of 0.2 μm to 10 μm.

[0016] Optionally, the niobium-doped ternary lithium cathode material is spherical, and the spherical shape is formed by the aggregation of several nanoparticles.

[0017] Optionally, the nanoparticles are rod-shaped, with a length of 50 nm to 1 μm and a width of 5 nm to 20 nm; the spherical particles have a diameter of 8 μm to 15 μm.

[0018] The present invention also provides a high specific capacity cathode material obtained by the above preparation method, wherein the high specific capacity cathode material is a sheet-like Cr8O 21 A spherical structure formed by coating niobium-doped ternary lithium cathode material.

[0019] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:

[0020] 1) Doping ternary lithium cathode materials with niobate precursor niobate H5Nb3O 10 The generated niobium oxide, due to niobic acid H5Nb3O 10 With high reactivity, niobium can rapidly and uniformly distribute itself in the bulk phase of ternary lithium cathode materials and participate in the formation of crystal structures, thus forming niobium-doped ternary lithium cathode materials. 5+ After ions are introduced into the crystal structure (including transition metal ions), the high-energy Nb-O bonds (bond energy approximately 13.66 eV) formed with oxygen can replace some Ni-O bonds (bond energy approximately 9.21 eV), significantly enhancing the stability of the metal-oxygen framework. During charge-discharge cycling, the high-energy Nb-O bonds can effectively suppress the release of lattice oxygen, reduce the oxygen vacancy concentration, and thus mitigate the in-plane migration of transition metal ions and Jahn-Teller distortion. Furthermore, Nb... 5+ A larger ionic radius helps to extend the c-axis of single crystal particles, enhance lithium-ion diffusion kinetics, and at the same time, by forming stable chemically bonded phase boundaries, it stabilizes the crystal structure like a rivet, fundamentally suppressing phase transition inhomogeneity and strain mismatch, and improving the structural stability of the material in long-term cycling.

[0021] 2) Further, niobium-doped ternary lithium cathode material is mixed with CrO3 powder, and the CrO3 powder decomposes into flake-like Cr8O at high temperature. 21 And it completely coats the surface of the niobium-doped ternary lithium cathode material. On the one hand, Cr8O 21 The crystal structure of Cr8O contains a large number of interstitial sites (such as octahedral interstitials and tetrahedral interstitials) that can accommodate lithium ions. Lithium ions can be embedded in its crystal lattice. Therefore, Cr8O 21 It has strong lithium storage capacity, which can significantly improve the specific capacity of the material. On the other hand, Cr8O21 The low surface energy weakens the driving force of spontaneous reactions at the interface, thereby suppressing side reactions between the electrolyte and the material surface; simultaneously, Cr8O 21 It can combine with oxygen vacancies on the material surface, inhibit oxygen desorption, and form a coating layer on the material surface, which helps to inhibit the dissolution of transition metal ions, thereby improving the interfacial stability of the material.

[0022] 3) Furthermore, this invention fully utilizes temperature-controlled reaction kinetics. First, a first temperature (400℃~450℃) is used to achieve the complete decomposition of each precursor to generate the corresponding oxides. Then, a second temperature (720℃~850℃) is used to achieve uniform doping of Nb elements into the bulk phase of the cathode material and uniform distribution in the inner layer of the material. Next, a third temperature (475℃~525℃) is used to achieve enrichment and distribution of Nb elements in the outer layer of the material. The enrichment in the outer layer will reduce the average valence state of Ni (according to the principle of chemical valence equilibrium, the addition of high valence state Nb will cause the +3 valence Ni to shift to the +2 valence Ni to maintain the overall valence state unchanged), which is beneficial to reducing interfacial oxidation. The Nb elements in the inner and outer layers synergistically improve the structural stability of the material. Then, a fourth temperature (190℃~200℃) is used to achieve complete melting of CrO3 and uniform distribution in the pores of the material. Finally, a fifth temperature (260℃~270℃) is used to achieve the decomposition of CrO3 into Cr8O. 21 It completely coats the material surface, improving the material's specific capacity and interfacial stability.

[0023] This invention employs a combined modification technique, combining the internal structure of niobium-doped ternary lithium cathode material with chromium oxide coating on its surface, to synergistically improve the specific capacity, structural stability, and interface stability of ternary lithium cathode material, thereby extending the cycle life of the battery. Attached Figure Description

[0024] Figure 1 This is a flowchart of the preparation method of the high specific capacity cathode material of the present invention.

[0025] Figure 2 This is a schematic diagram of the high specific capacity cathode material of the present invention.

[0026] Figure 3 The image shows the XRD pattern of the niobium-doped ternary lithium cathode material of the present invention.

[0027] Figure 4 This is an EDS mapping diagram of the niobium-doped ternary lithium cathode material of the present invention.

[0028] Figure 5 The image shows the XPS Cr2p spectrum of the high specific capacity cathode material of this invention.

[0029] Figure 6 This is an EDS diagram of the cross-section of the high specific capacity cathode material of the present invention.

[0030] Figure 7 This is a SEM image of the high specific capacity cathode material of the present invention.

[0031] The attached diagram is labeled as follows: homogeneous layer 1, enrichment layer 2, and coating layer 3. Detailed Implementation

[0032] The following detailed description, in conjunction with the accompanying drawings and specific embodiments, provides a further detailed explanation of the high specific capacity cathode material and its preparation method proposed in this invention. The advantages and features of this invention will become clearer from the following description. It should be noted that the accompanying drawings are in a very simplified form and use non-precise proportions, used only to facilitate and clearly illustrate the embodiments of this invention. Please refer to the accompanying drawings to make the objectives, features, and advantages of this invention more apparent and understandable. It should be understood that the structures, proportions, sizes, etc., depicted in the accompanying drawings are only for illustrative purposes to aid those skilled in the art and are not intended to limit the implementation conditions of this invention. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to the size, without affecting the effects and objectives achieved by this invention, should still fall within the scope of the technical content disclosed in this invention.

[0033] In existing technologies, to improve the specific capacity of nickel-cobalt-manganese-lithium ternary cathode materials, the common approach is to increase the nickel content. However, increasing the nickel content to a certain level can lead to a significant decrease in the structural stability of the cathode material. The main reasons are: 1) As the nickel content increases, due to Ni... 2+ With Li + With similar ionic radii, Ni 2+ It is easier to migrate from the transition metal layer to the lithium layer and occupy Li. + The position forms Li + / Ni 2+ Mixed arrangement defects, for moving Li + Electrostatic repulsion occurs, hindering Li + 1) Normal migration and deintercalation. 2) The higher the nickel content, the easier it is for the cathode material to undergo an irreversible phase transition from the H2 phase to the H3 phase, increasing the degree of volume anisotropy and leading to material structure degradation and microcrack formation. 3) Ni 3+ It is easily reduced to Ni at high temperatures. 2+ This is accompanied by the release of oxygen, which may react with the electrolyte to release heat, creating a vicious cycle and triggering thermal runaway.

[0034] Based on this, the present invention improves existing nickel-cobalt-manganese-lithium ternary cathode materials to simultaneously enhance their structural stability, specific capacity, and interfacial stability. The technical concept is as follows: first, niobium oxide is doped into the cathode material. The high-energy Nb-O bonds formed after niobium doping effectively suppress the release of lattice oxygen, and Nb... 5+ A larger ionic radius helps to extend the c-axis of single-crystal particles, enhancing lithium-ion diffusion kinetics. Simultaneously, by forming stable chemically bonded phase boundaries, it fundamentally suppresses phase transition inhomogeneities and strain mismatch, thereby improving the structural stability of the material. Furthermore, the use of plate-like Cr8O... 21 Completely coating the surface of niobium-doped ternary lithium cathode material using Cr8O 21 Its strong lithium storage properties and low surface energy characteristics improve the specific capacity and interfacial stability of the material. For example... Figure 1 As shown, this invention provides a method for preparing a high specific capacity cathode material, the method comprising:

[0035] Step 1: Under an oxygen atmosphere, the hydroxide precursor Ni... 1-x-y Co x Mn y (OH)2, a first niobium precursor and a lithium precursor are mixed, and corresponding ternary oxides, niobium oxides and lithium oxides are generated at a first temperature. The ternary oxides, niobium oxides and lithium oxides react at a second temperature, and a second niobium precursor is added. Niobium-doped ternary lithium cathode material is generated at a third temperature. Wherein, x > 0, y > 0, x + y < 1; the first temperature < the third temperature < the second temperature.

[0036] Before step 1, the process further includes: under alkaline conditions, co-precipitating nickel, cobalt, and manganese to obtain the hydroxide precursor Ni. 1-x-y Co x Mn y (OH)₂. The specific steps are as follows: Prepare a mixed salt solution of nickel, cobalt, and manganese, a NaOH solution, and ammonia water of a certain concentration. Simultaneously add these solutions dropwise to a reaction vessel at a temperature of 40℃ to 60℃ at a rotation speed of 300 rpm to 800 rpm. Adjust the dropping rate of each solution to stabilize the pH of the system at 10-11. Continuously purge with nitrogen during the reaction to ensure complete reaction of the metal ions to form hydroxide precipitates. After the addition is complete, maintain the temperature and stirring, and continue aging with nitrogen for 2 to 12 hours to allow the precipitate particles to grow uniformly and stabilize their structure, forming a hydroxide precursor Ni with uniform particle size. 1-x-y Co x Mn y (OH)2, where 0 < x ≤ 0.1, 0 < y ≤ 0.1, and x + y < 1.

[0037] Ni hydroxide precursor1-x-y Co x Mn y After mixing (OH)2, the first niobium precursor, and the lithium precursor, the mixture is heated to a first temperature of 400℃~450℃ at a heating rate of 3℃ / min~10℃ / min under an oxygen atmosphere and held for 1h~5h. At this temperature, the three precursors generate corresponding ternary oxides, niobium oxides, and lithium oxides, respectively. Then, the mixture is heated to a second temperature of 720℃~850℃ at a heating rate of 1℃ / min~3℃ / min and held for 5h~20h. At the higher temperature, the generated oxides react with each other to form spherical particles, allowing Nb to be uniformly doped into the bulk phase of the material and evenly distributed in the inner layer of the material. After the reaction is complete, the mixture is allowed to cool naturally to room temperature. Then, a second niobium precursor is added, and the temperature is increased to a third temperature of 475℃~525℃ at a heating rate of 3℃ / min~10℃ / min, and held for 1h~8h. This allows the second niobium precursor to completely decompose and Nb to accumulate and distribute in the outer layer of the material, resulting in a niobium-doped ternary lithium cathode material with the molecular formula Li(Ni) 1-x-y Co x Mn y)1-z Nb z O2, where 0 < x ≤ 0.1, 0 < y ≤ 0.1, and 0.015 ≤ z ≤ 0.06. Outer layer enrichment lowers the average valence state of Ni, thereby reducing interfacial oxidation. The inner and outer layers of Nb synergistically improve the structural stability of the material. However, in niobium doping, excessively high Nb content can lead to electroactive Ni... 3+ More towards Ni 2+ Offset, on the contrary, reduces the discharge specific capacity of the material; if the Nb content is too low, the improvement in the stability of the material will not be significant; therefore, the Nb content needs to be controlled within an appropriate range.

[0038] During the second heating process, the temperature should not be too high and the holding time should not be too long; otherwise, the material is prone to agglomeration or even clumping. Ni 2+ It is easier to occupy Li + Location, Li + / Ni 2+ Mixed-row defects hinder Li +Normal migration and deintercalation make it difficult to release capacity during the charge and discharge process. Furthermore, the temperature should not be too low and the holding time should not be too short; otherwise, the material will struggle to form the desired morphology and crystal structure, resulting in insufficient crystallinity and impurities, thus reducing the material's capacity and stability. During the third heating process, the temperature should not be too high and the holding time should not be too long; otherwise, Nb will be difficult to accumulate and distribute in the outer layer. Conversely, the temperature should not be too low and the holding time should not be too short; otherwise, the second niobium precursor will not decompose completely. Throughout the reaction, oxygen plays two roles: 1) inhibiting the reduction of high-valence transition metal ions and maintaining the stable valence state of metal ions in the layered structure; 2) timely replenishing oxygen that may be lost from the lattice, reducing oxygen vacancies and structural defects, and ensuring the regularity of the layered structure.

[0039] In this embodiment, both the first niobium precursor and the second niobium precursor are niobate H5Nb3O. 10 Niobic acid H5Nb3O 10 With high reactivity, niobium can rapidly and uniformly distribute itself within the bulk phase of the ternary cathode material and participate in the formation of the crystal structure, thereby forming a niobium-doped ternary lithium cathode material. Furthermore, in this step, the lithium precursor reacts with the hydroxide precursor to form a nickel-cobalt-manganese-lithium ternary cathode material. In this embodiment, the lithium precursor is LiOH·H₂O.

[0040] In some embodiments, the molar ratio of hydroxide precursor, first niobium precursor, second niobium precursor, and lithium precursor is 1:(0.005~0.02):(1.02~1.10); the molar ratio of first niobium precursor to second niobium precursor is (5~20):1; and the molar ratio of the sum of the molar numbers of nickel, cobalt, and manganese to niobium is 1:(0.015~0.06). Controlling the molar ratio of each substance is beneficial for generating niobium-doped ternary lithium cathode materials with stable structure and fewer defects. Since the hydroxide precursor formed by co-precipitation is a spherical structure formed by the aggregation of several nanoparticles, the structure of the niobium-doped ternary lithium cathode material obtained after niobium doping to form the ternary lithium cathode material is still spherical, and the spheres are formed by the aggregation of several nanoparticles. Among them, the nanoparticles are rod-shaped, with a length of 50nm~1μm and a width of 5nm~20nm; the particle size of the spheres is 8μm~15μm.

[0041] Step 2: Under an oxygen atmosphere, the niobium-doped ternary lithium cathode material and CrO3 powder are mixed. The CrO3 powder is melted at a fourth temperature, and the molten CrO3 powder decomposes into Cr8O at a fifth temperature. 21 The niobium-doped ternary lithium cathode material is coated to obtain a high specific capacity cathode material; wherein the fourth temperature is less than the fifth temperature.

[0042] After mixing niobium-doped ternary lithium cathode material and CrO3 powder, the mixture is heated to a fourth temperature (190℃~200℃) at a rate of 0.5℃ / min~2℃ / min under an oxygen atmosphere and held for 1h~5h. At this temperature, the CrO3 powder fully melts and forms a molten state that is uniformly distributed in the pores of the niobium-doped ternary lithium cathode material. The temperature is then further increased to a fifth temperature (260℃~270℃) at a rate of 0.1℃ / min~1℃ / min and held for 8h~20h. At this point, the molten CrO3 powder decomposes, forming Cr8O3. 21 The reaction will completely coat the surface of the niobium-doped ternary lithium cathode material. After the reaction is complete, it is allowed to cool naturally to room temperature, ultimately yielding a high-specific-capacity cathode material with the molecular formula: m Cr8O 21 @Li(Ni 1-x-y Co x Mn y)1-z Nb z O2, where 0 < x ≤ 0.1, 0 < y ≤ 0.1, 0.015 ≤ z ≤ 0.06, and 0.00125 ≤ m ≤ 0.025. Throughout the reaction, the main role of oxygen is to inhibit the decomposition rate of CrO3 powder and simultaneously inhibit the decomposition of Cr8O. 21 Excessive decomposition results in byproducts such as Cr2O5 and Cr2O3.

[0043] In some embodiments, the molar ratio of niobium-doped ternary lithium cathode material to CrO3 powder is 1:(0.01~0.2). If the CrO3 content is too high, its high irreversibility will reduce the capacity reversibility of the material during long-term cycling; if the CrO3 content is too low, uniform coating of the material surface cannot be achieved. Within this content range, it is possible to ensure that the Cr8O formed by the decomposition of CrO3 powder is within acceptable limits. 21 The surface of the niobium-doped ternary lithium cathode material is completely coated without reducing its capacity reversibility. It is understood that this invention uses a direct mixing method between CrO3 powder and niobium-doped ternary lithium cathode material, utilizing the dispersibility of the niobium-doped ternary lithium cathode material and the melting characteristics of CrO3 powder to achieve a complete coating of the niobium-doped ternary lithium cathode material surface without reducing its capacity reversibility. 21 This provides reaction crystallization sites, thus forming a thin and continuous coating layer. If CrO3 is first heated and decomposed to form Cr8O... 21 If it is then combined with niobium-doped ternary lithium cathode material, the melting characteristics of CrO3 powder cannot be fully utilized to allow it to enter the material pores, thus failing to form a coating layer.

[0044] In this embodiment, the CrO3 powder is granular with a particle size of 0.2 μm to 10 μm. If the CrO3 particle size is too large, it will reduce the melting rate, causing CrO3 to accumulate more on the material surface and making it difficult to quickly penetrate the material pores; if the CrO3 particle size is too small, the powder particles are difficult to disperse uniformly, making uniform coating impossible. The Cr8O formed from the decomposition of CrO3 powder... 21 It appears as flakes. For example... Figure 2 As shown, the high specific capacity cathode material is sheet-like Cr8O. 21 A spherical structure formed by coating niobium-doped ternary lithium cathode material. Nb is uniformly distributed in the inner layer to form a uniform layer 1, and enriched in the outer layer to form an enriched layer 2. Cr8O... 21 A coating layer 3 is formed by completely covering the surface of the material.

[0045] The preparation method of the high specific capacity cathode material of the present invention is described in detail below with reference to the embodiments. All chemical reagents used in the following embodiments and comparative examples were purchased from Sinopharm Chemical Reagent Co., Ltd. Unless otherwise specified, the experimental methods used in the following embodiments and comparative examples were carried out under conventional or manufacturer-recommended conditions.

[0046] Example 1

[0047] S1: Ni hydroxide precursor 0.96 Co 0.02 Mn 0.02 Preparation of (OH)₂. A 2 mol / L mixed salt solution of nickel, cobalt, and manganese, a 2 mol / L NaOH solution, and a 2 mol / L ammonia solution were prepared. These solutions were simultaneously added dropwise to a reaction vessel at 50°C at a rotation speed of 500 rpm. The pH of the system was stabilized at 11 by adjusting the dropping rate of each solution. Nitrogen gas was continuously purged during the reaction to ensure complete reaction of the metal ions to form hydroxide precipitates. After the addition was complete, the temperature and stirring were maintained, and nitrogen gas was continued to purge for 5 hours to allow the precipitate particles to grow uniformly and stabilize their structure, forming a hydroxide precursor Ni with uniform particle size. 0.96 Co 0.02 Mn 0.02 (OH)2.

[0048] S2: Preparation of niobium-doped ternary lithium cathode material. Under an oxygen atmosphere, the obtained Ni hydroxide precursor... 0.96 Co 0.02 Mn 0.02 (OH)2 and H5Nb3O 10LiOH·H₂O was mixed in a molar ratio of 1:0.01:1.10. The mixture was first heated to 420℃ at a rate of 5℃ / min and held for 4 hours to generate the corresponding ternary oxide, niobium oxide, and lithium oxide. Then, the mixture was heated to 750℃ at a rate of 2℃ / min and held for 10 hours to allow the ternary oxide, niobium oxide, and lithium oxide to react. After the reaction was complete, the mixture was allowed to cool naturally to room temperature, and H₅Nb₃O₃ was added. 10 (For the first addition of H5Nb3O) 10 Niobium-doped ternary lithium cathode material was obtained by heating to 500℃ at a heating rate of 5℃ / min and holding for 3 h using 1 / 5 of the molar amount of niobium. The niobium-doped ternary lithium cathode material was characterized by XRD and EDS mapping, and the results are as follows: Figure 3 and Figure 4 As shown. From Figure 3 As can be seen, the niobium-doped ternary lithium cathode material has an R3m layered structure with no impurity phase generated, indicating that Nb has been successfully doped into the bulk phase of the material. Figure 4 As can be seen, Nb is uniformly distributed in the inner layer of the material and enriched in the outer layer. Since the outer layer of the material is more likely to come into contact with the electrolyte, leading to more side reactions, the enrichment of Nb in the outer layer will reduce the average valence state of Ni, which is beneficial to reducing interfacial oxidation. The distribution of Nb in the inner and outer layers synergistically improves the structural stability of the material.

[0049] S3: Preparation of high specific capacity cathode material. Under an oxygen atmosphere, the obtained niobium-doped ternary lithium cathode material and CrO3 powder (particle size 8 μm) were mixed at a molar ratio of 1:0.1. The mixture was first heated to 196℃ at a heating rate of 1℃ / min and held for 4 hours to fully melt the CrO3 powder. Then, the temperature was increased to 265℃ at a heating rate of 0.5℃ / min and held for 12 hours to decompose the molten CrO3 powder into Cr8O3. 21 The niobium-doped ternary lithium cathode material is then coated onto its surface. After the reaction is complete, the material is allowed to cool naturally to room temperature, ultimately yielding a high-specific-capacity cathode material.

[0050] The high-specific-capacity cathode material prepared in Example 1 was characterized by XPS Cr2p, and the results are as follows: Figure 5 As shown. Figure 5 The average valence state of Cr was calculated to be 5.246 using peak area, indicating that the substance obtained from the decomposition of CrO3 powder is Cr8O. 21 .

[0051] The cross-section of the high specific capacity cathode material prepared in Example 1 was characterized by EDS, and the results are as follows: Figure 6 As shown. From Figure 6 As can be seen, Cr is uniformly distributed on the surface of Ni, indicating that Cr8O 21Coating the surface of niobium-doped ternary lithium cathode material is beneficial to improving the specific capacity and interface stability of the material.

[0052] The high-specific-capacity cathode material prepared in Example 1 was characterized by SEM, and the results are as follows: Figure 7 As shown. From Figure 7 As can be seen, the high specific capacity cathode material is a spherical structure formed by the aggregation of several nanoparticles.

[0053] Example 2

[0054] Replace 1:0.01:1.10 in S2 with 1:0.017:1.10, and replace 750℃ with 800℃. All other conditions are the same as in Example 1.

[0055] Example 3

[0056] H5Nb3O added for the first time in S2 10 One-fifth of the molar number was replaced with H5Nb3O added for the first time. 10 Instead of heating to 500°C and holding for 3 hours, use 1 / 15 of the molar number of the sample, and heat to 475°C and hold for 5 hours. All other conditions are the same as in Example 1.

[0057] Example 4

[0058] Replace 1:0.1 with 1:0.2 in S3, and replace the particle size of 8μm with the particle size of 1μm. All other conditions are the same as in Example 1.

[0059] Example 5

[0060] In Example 1, the heating rate of 1℃ / min to 196℃ and holding for 4 hours in step S3 was replaced by the heating rate of 2℃ / min to 200℃ and holding for 2 hours, and the heating rate of 0.5℃ / min to 265℃ and holding for 12 hours was replaced by the heating rate of 0.3℃ / min to 260℃ and holding for 20 hours. All other conditions remained the same as in Example 1.

[0061] Comparative Example 1

[0062] Niobium-doped ternary lithium cathode material was prepared according to S1 and S2 in Example 1.

[0063] Comparative Example 2

[0064] Niobium-doped ternary lithium cathode material was prepared according to S1 and S2 in Example 1.

[0065] In S3, under an oxygen atmosphere, CrO3 powder (particle size 8 μm) is first heated to 196°C at a heating rate of 1°C / min and held at that temperature for 4 hours to fully melt the CrO3 powder. Then, the temperature is increased to 265°C at a heating rate of 0.5°C / min and held at that temperature for 12 hours to decompose the molten CrO3 powder into Cr8O. 21 Then Cr8O 21 The cathode material is then combined with niobium-doped ternary lithium cathode material, and after the reaction is complete, it is naturally cooled to room temperature to obtain the cathode material.

[0066] Comparative Example 3

[0067] H5Nb3O added for the first time in S2 10 One-fifth of the molar number was replaced with H5Nb3O added for the first time. 10 Instead of heating to 500°C and holding for 3 hours, use 1 / 15 of the molar number of the sample, and heat to 650°C and hold for 15 hours. All other conditions are the same as in Example 1.

[0068] Comparative Example 4

[0069] Niobium-doped ternary lithium cathode material was prepared according to S1 and S2 in Example 1.

[0070] In S3, under an oxygen atmosphere, the obtained niobium-doped ternary lithium cathode material and CrO3 powder (particle size of 8μm) were mixed in a molar ratio of 1:0.1, heated to 260℃ at a heating rate of 0.3℃ / min and held at that temperature for 20h. After the reaction was completed, the mixture was naturally cooled to room temperature to finally obtain the cathode material.

[0071] The cathode materials prepared in Examples 1-5 and Comparative Examples 1-4 were assembled into lithium batteries, and the discharge specific capacity and capacity retention rate after 200 cycles (1C) were tested. The results are shown in Table 1. As can be seen from the table, the discharge specific capacity and capacity retention rate after 200 cycles (1C) of the lithium batteries assembled with the cathode materials prepared in Examples 1-5 are higher than those in Comparative Examples 1-4, indicating that the cathode materials prepared using the method of this invention have higher discharge specific capacity and capacity retention rate.

[0072] Table 1. Comparison of discharge specific capacity and capacity retention rate after 200 cycles (1C) of different lithium batteries

[0073]

[0074] In summary, this invention improves existing nickel-cobalt-manganese-lithium ternary cathode materials by first doping the cathode material with niobate. The high-energy Nb-O bonds formed after niobate doping can effectively suppress the release of lattice oxygen, and Nb... 5+A larger ionic radius helps to extend the c-axis of single-crystal particles, enhancing lithium-ion diffusion kinetics. Simultaneously, by forming stable chemically bonded phase boundaries, it fundamentally suppresses phase transition inhomogeneities and strain mismatch, thereby improving the structural stability of the material. Furthermore, the use of plate-like Cr8O... 21 Completely coating the surface of niobium-doped ternary lithium cathode material using Cr8O 21 The strong lithium storage characteristics and low surface energy of the material enhance its specific capacity and interfacial stability. By employing a combined modification technique of niobium-doped ternary lithium cathode material internally and chromium oxide coating its surface, the specific capacity, structural stability, and interfacial stability of the ternary lithium cathode material are synergistically improved, thereby extending the cycle life of the battery.

[0075] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0076] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method for preparing a high specific capacity cathode material, characterized in that, The method includes: Step 1: Under an oxygen atmosphere, the hydroxide precursor Ni... 1-x-y Co x Mn y (OH)2, a first niobium precursor and a lithium precursor are mixed, and at a first temperature, corresponding ternary oxides, niobium oxides, and lithium oxides are generated respectively. At a second temperature, the ternary oxides, niobium oxides, and lithium oxides react, and then a second niobium precursor is added. At a third temperature, a niobium-doped ternary lithium cathode material is generated; wherein, x > 0, y > 0, x + y < 1; both the first niobium precursor and the second niobium precursor are niobate H5Nb3O 10 The molar ratio of the first niobium precursor to the second niobium precursor is (5~20):1; the first temperature is 400℃~450℃, the second temperature is 720℃~850℃, and the third temperature is 475℃~525℃; in the niobium-doped ternary lithium cathode material, niobium is uniformly distributed in the inner layer and enriched in the outer layer. Step 2: Under an oxygen atmosphere, the niobium-doped ternary lithium cathode material and CrO3 powder are mixed. The CrO3 powder is melted at a fourth temperature, and the molten CrO3 powder decomposes into Cr8O at a fifth temperature. 21 The niobium-doped ternary lithium cathode material is coated to obtain a high specific capacity cathode material; wherein, the fourth temperature is less than the fifth temperature; the fifth temperature is 260℃~270℃; the molar ratio of the niobium-doped ternary lithium cathode material and CrO3 powder is 1:(0.01~0.2).

2. The method for preparing the high specific capacity cathode material as described in claim 1, characterized in that, The hydroxide precursor Ni 1-x-y Co x Mn y In (OH)2, x≤0.1, y≤0.1; the lithium precursor is LiOH·H2O.

3. The method for preparing the high specific capacity cathode material as described in claim 1, characterized in that, The molar ratio of the hydroxide precursor, the first niobium precursor, the second niobium precursor, and the lithium precursor is 1:(0.005~0.02):(1.02~1.10).

4. The method for preparing the high specific capacity cathode material as described in claim 1, characterized in that, The temperature is maintained at the first temperature for 1 to 5 hours; at the second temperature for 5 to 20 hours; at the third temperature for 1 to 8 hours; at the fourth temperature of 190°C to 200°C for 1 to 5 hours; and at the fifth temperature for 8 to 20 hours.

5. The method for preparing the high specific capacity cathode material as described in claim 1, characterized in that, Before step 1, the process further includes: co-precipitating nickel, cobalt, and manganese under alkaline conditions to obtain the hydroxide precursor Ni. 1-x-y Co x Mn y (OH)2.

6. The method for preparing the high specific capacity cathode material as described in claim 1, characterized in that, The CrO3 powder is in granular form with a particle size of 0.2 μm to 10 μm.

7. The method for preparing the high specific capacity cathode material as described in claim 1, characterized in that, The niobium-doped ternary lithium cathode material is spherical, and the spherical shape is formed by the aggregation of several nanoparticles.

8. The method for preparing the high specific capacity cathode material as described in claim 7, characterized in that, The nanoparticles are rod-shaped, with a length of 50 nm to 1 μm and a width of 5 nm to 20 nm; the spherical particles have a diameter of 8 μm to 15 μm.

9. A high-specific-capacity cathode material obtained by the preparation method according to any one of claims 1-8, characterized in that, The high-capacity cathode material is sheet-like Cr8O. 21 A spherical structure formed by coating niobium-doped ternary lithium cathode material.

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