High-specific-capacity positive electrode material and preparation method thereof

Abstract

The invention discloses a high-specific-capacity positive electrode material and a preparation method thereof, and the method comprises the following steps: step 1, mixing a hydroxide precursor Ni1-x-yCoxMny (OH) 2, a first niobium precursor and a lithium precursor, respectively generating corresponding ternary oxide, niobium oxide and lithium oxide at a first temperature, and reacting the oxides at a second temperature, and adding a second niobium precursor, and generating the niobium-doped ternary lithium positive electrode material at a third temperature, x > 0, y > 0, and x + y < 1; the first temperature < the third temperature < the second temperature; 2, mixing the niobium-doped ternary lithium positive electrode material and CrO3 powder, melting the CrO3 powder at a fourth temperature, decomposing the CrO3 powder molten at a fifth temperature into Cr8O21, and coating the niobium-doped ternary lithium positive electrode material with the Cr8O21 to obtain a positive electrode material with high specific capacity; the fourth temperature is smaller than the fifth temperature. The niobium oxide is doped in the positive electrode material, and the surface of the material is coated with the chromium oxide, so that the specific capacity, the structural stability and the interface stability of the material are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium batteries, in particular to a high specific capacity cathode material and a preparation method thereof. BACKGROUND

[0002] Lithium ion batteries have become the core energy storage devices in the field of energy utilization and transformation due to their high energy density, long cycle life and excellent charge and discharge performance. In particular, in the field of aerospace equipment, lithium ion batteries, as the power heart, provide stable power support for the on-orbit operation, attitude adjustment and task load of spacecraft, and their performance reliability is related to the success or failure of the space mission. With the development of aerospace equipment towards lightweight, long endurance and high load, higher energy density of lithium ion batteries is required. Higher specific energy not only reduces the volume and weight proportion of the battery system, but also prolongs the on-orbit working time of the spacecraft and improves the task execution efficiency. One of the core paths to improve the specific energy of lithium ion batteries is to develop and use high specific capacity electrode materials. Among them, the specific capacity and structural stability of the cathode material play a decisive role in the overall performance of the battery. Currently, in the practical application of high specific capacity cathode materials, nickel-cobalt-manganese lithium ternary materials (NCM for short) with a layered structure are the mainstream choice. The specific capacity of this type of material is positively correlated with the content of nickel (Ni) element: as the content of Ni increases, the multi-valence redox reaction of Ni 2+ , Ni 3+ in the material can realize more lithium ion insertion and extraction, which significantly improves the specific capacity of the material, thus effectively meeting the demand for high specific energy of the battery. However, the increase of nickel content will lead to a significant decrease in the structural stability of nickel-cobalt-manganese lithium ternary materials, thus directly leading to a shortened cycle life of high-nickel ternary materials, and in high-voltage charging and discharging or high-temperature environments, the risk of thermal runaway of the material increases, and the safety cannot meet the requirements of severe application scenarios.

[0003] The statements herein merely provide background technology related to the present application, and do not necessarily constitute the prior art. SUMMARY

[0004] The purpose of the present application is to prolong the cycle life of the battery by uniformly distributing the Nb element in the inner layer of the cathode material and enriching the distribution in the outer layer, and coating the surface of the cathode material with chromium oxide, while improving the specific capacity, structural stability and interface stability of the material.

[0005] In order to achieve the above purpose, the present application provides a preparation method of a high specific capacity cathode material, which comprises: Step 1, under an oxygen atmosphere, a hydroxide precursor Ni 1-x-y Co x Mn ymixing a first niobium precursor, a lithium precursor, generating corresponding ternary oxides, niobium oxides, lithium oxides at a first temperature, respectively, reacting the ternary oxides, the niobium oxides, the lithium oxides at a second temperature, adding a second niobium precursor, and generating a niobium-doped ternary lithium cathode material at a third temperature; wherein x>0, y>0, x+y<1; the first temperature Step 2, mixing the niobium-doped ternary lithium cathode material and CrO3 powder in an oxygen atmosphere, melting the CrO3 powder at a fourth temperature, and decomposing the melted CrO3 powder into Cr8O 21 and coating the niobium-doped ternary lithium cathode material to obtain a high-capacity cathode material; wherein the fourth temperature

[0006] Optionally, the hydroxide precursor Ni 1-x-y Co x Mn y x≤0.1, y≤0.1 in the hydroxide precursor Ni 10 (OH)2; the first niobium precursor and the second niobium precursor are both H5Nb3O

[0007] 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.

[0008] Optionally, the molar ratio of the niobium-doped ternary lithium cathode material and the CrO3 powder is 1:(0.01-0.2).

[0009] Optionally, the first temperature is 400-450°C, and the holding time is 1-5h; the second temperature is 720-850°C, and the holding time is 5-20h; the third temperature is 475-525°C, and the holding time is 1-8h; the fourth temperature is 190-200°C, and the holding time is 1-5h; and the fifth temperature is 260-270°C, and the holding time is 8-20h.

[0010] Optionally, before Step 1, it further comprises: co-precipitating nickel, cobalt, and manganese under alkaline conditions to obtain the hydroxide precursor Ni 1-x-y Co x Mn y (OH)2.

[0011] Optionally, the CrO3 powder is in a granular form, and the particle size is 0.2-10μm.

[0012] Optionally, the niobium-doped ternary lithium cathode material is spherical, and the spherical shape is formed by agglomeration of a plurality of nanoparticles.

[0013] Optionally, the nanoparticles are rod-shaped, the length of the nanoparticles is 50 nm-1 μm, and the width of the nanoparticles is 5 nm-20 nm; and the particle size of the spherical shape is 8 μm-15 μm.

[0014] The application further provides a high-specific-capacity cathode material obtained by the preparation method, and the high-specific-capacity cathode material is a flaky Cr8O 21 The niobium-doped ternary lithium cathode material is coated to form a spherical structure.

[0015] Compared with the prior art, the technical scheme of the application has at least the following beneficial effects: 1) The niobium precursor H5Nb3O 10 The generated niobium oxide is doped into the ternary lithium cathode material, and the niobium element can be rapidly and uniformly distributed in the body phase of the ternary lithium cathode material and participate in the formation of the crystal structure, thereby forming the niobium-doped ternary lithium cathode material. 10 The high reactivity of the generated niobium oxide is doped into the ternary lithium cathode material, and the niobium element can be rapidly and uniformly distributed in the body phase of the ternary lithium cathode material and participate in the formation of the crystal structure, thereby forming the niobium-doped ternary lithium cathode material. 5+ After the Nb ion is introduced into the crystal structure (containing transition metal ions), the high bond energy Nb-O bond (bond energy of about 13.66 eV) formed by the Nb ion and oxygen can replace part of the Ni-O bond (bond energy of about 9.21 eV), thereby significantly enhancing the stability of the metal-oxygen skeleton. In the charging and discharging cycle process, the high bond energy Nb-O bond can effectively inhibit the release of lattice oxygen and reduce the oxygen vacancy concentration, thereby reducing the in-plane migration of transition metal ions and Jahn-Teller distortion. In addition, the Nb 5+ The large ionic radius helps to lengthen the c-axis of the single crystal particle, enhance the lithium ion diffusion dynamics, and at the same time, form a stable chemical bond phase boundary, like a rivet, to stabilize the crystal structure, thereby fundamentally inhibiting phase transformation unevenness and strain mismatch and improving the structural stability of the material in long-term cycling.

[0016] 2) Further, the niobium-doped ternary lithium cathode material is mixed with CrO3 powder, the CrO3 powder is decomposed into flaky Cr8O 21 at a high temperature, and the flaky Cr8O 21 completely coats the surface of the niobium-doped ternary lithium cathode material. On the one hand, the flaky Cr8O 21 has a large number of interstitial sites (such as octahedral interstitial sites, tetrahedral interstitial sites, etc.) that can accommodate lithium ions, and lithium ions can be embedded in the crystal lattice, so the flaky Cr8O 21 has a strong lithium storage capacity and can significantly improve the specific capacity of the material. On the other hand, the flaky Cr8O 21Can be combined with the oxygen vacancy of material surface, inhibit oxygen desorption, and form a layer of coating on the material surface, help to inhibit the transition metal ion elution, thereby improving the interface stability of the material.

[0017] 3) Further, the present application makes full use of temperature regulation reaction kinetics, first uses the first temperature (400℃~450℃) to realize each precursor decomposition to generate corresponding oxide; then uses the second temperature (720℃~850℃) to realize the uniform doping of Nb element into the positive electrode material body phase and uniform distribution in the material inner layer; then uses the third temperature (475℃~525℃) to realize the enrichment distribution of Nb element in the material outer layer, the outer layer enrichment will reduce the average valence of Ni (according to the chemical valence balance principle, the high valence Nb will make the +3 valence Ni shift to +2 valence Ni after adding to maintain the total valence unchanged), which is beneficial to reduce the interface oxidation, and the Nb elements in the inner and outer layers cooperatively improve the structural stability of the material; then uses the fourth temperature (190℃~200℃) to realize the full melting of CrO3 and uniform distribution in the material pores; finally, the fifth temperature (260℃~270℃) is used to realize the decomposition of CrO3 into Cr8O 21 And completely covers the material surface, improves the specific capacity and interface stability of the material.

[0018] The present application cooperatively improves the specific capacity, structural stability and interface stability of the ternary lithium positive electrode material by adopting the combined modification technology of niobium-doped ternary lithium positive electrode material inside and chromium oxide coated on the surface, thereby prolonging the cycle life of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The preparation method flow chart of the high specific capacity positive electrode material of the present application.

[0020] Figure 2 The structure schematic diagram of the high specific capacity positive electrode material of the present application.

[0021] Figure 3 The XRD diagram of the niobium-doped ternary lithium positive electrode material of the present application.

[0022] Figure 4 The EDS mapping diagram of the niobium-doped ternary lithium positive electrode material of the present application.

[0023] Figure 5 The XPS Cr2p spectrum diagram of the high specific capacity positive electrode material of the present application.

[0024] Figure 6 The EDS diagram of the cross section of the high specific capacity positive electrode material of the present application.

[0025] Figure 7 The SEM diagram of the high specific capacity positive electrode material of the present application.

[0026] The attached diagram is labeled as follows: homogeneous layer 1, enrichment layer 2, and coating layer 3. Detailed Implementation

[0027] 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.

[0028] 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.

[0029] 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: 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.

[0030] 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.

[0031] Ni hydroxide precursor 1-x-y Co x Mn yAfter 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.

[0032] 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.

[0033] In the embodiment, the first niobium precursor and the second niobium precursor are both H5Nb3O 10 H5Nb3O 10 has high reactivity, and the niobium element can be rapidly and uniformly distributed in the body phase of the ternary positive electrode material and participate in the formation of the crystal structure, thereby forming the niobium-doped ternary lithium positive electrode material. In addition, in this step, the lithium precursor reacts with the hydroxide precursor to form the nickel-cobalt-manganese lithium ternary positive electrode material. In the embodiment, the lithium precursor is LiOH·H2O.

[0034] In some embodiments, the molar ratio of the hydroxide precursor, the first niobium precursor and 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; and the molar ratio of the sum of the moles of nickel, cobalt, and manganese to the mole of niobium is 1:(0.015-0.06). Controlling the molar ratio of each substance is conducive to generating a niobium-doped ternary lithium positive electrode material with stable structure and fewer defects. Since the hydroxide precursor formed by co-precipitation is spherical and formed by agglomeration of a plurality of nanoparticles, after niobium doping to form the ternary lithium positive electrode material, the structure of the obtained niobium-doped ternary lithium positive electrode material is still spherical and formed by agglomeration of a plurality of nanoparticles. The nanoparticles are rod-shaped, and the length of the nanoparticles is 50 nm-1 μm and the width is 5 nm-20 nm; the particle size of the spherical shape is 8 μm-15 μm.

[0035] In step 2, the niobium-doped ternary lithium positive electrode material and CrO3 powder are mixed under an oxygen atmosphere, the CrO3 powder is melted at a fourth temperature, and the melted CrO3 powder is decomposed into Cr8O 21 at a fifth temperature, and the Cr8O

[0036] After the niobium-doped ternary lithium positive electrode material and the CrO3 powder are mixed, under an oxygen atmosphere, the temperature is first increased at a rate of 0.5°C / min-2°C / min to a fourth temperature of 190°C-200°C, and the temperature is maintained for 1 h-5 h. At this temperature, the CrO3 powder is fully melted, and the melted CrO3 powder is uniformly distributed in the pores of the niobium-doped ternary lithium positive electrode material. Then, the temperature is continuously increased at a rate of 0.1°C / min-1°C / min to a fifth temperature of 260°C-270°C, and the temperature is maintained for 8 h-20 h. At this time, the melted CrO3 powder is decomposed, and the decomposed Cr8O 21 completely coats the surface of the niobium-doped ternary lithium positive electrode material. After the reaction is completed, the temperature is naturally decreased to room temperature, and finally the high-capacity positive electrode material with the molecular formula m Cr8O21 Li(Ni 1-x-y Co x Mn y)1-z Nb z O2, wherein 0 < x ≤ 0.1, 0 < y ≤ 0.1, 0.015 ≤ z ≤ 0.06, 0.00125 ≤ m ≤ 0.025. Throughout the reaction, the main role of oxygen is to inhibit the decomposition rate of CrO3 powder, while inhibiting the excessive decomposition of Cr8O 21 into by-products such as Cr2O5 and Cr2O3.

[0037] In some embodiments, the molar ratio of the niobium-doped ternary lithium cathode material to the CrO3 powder is 1: (0.01-0.2). If the content of CrO3 is too high, the capacity reversibility of the material in the long-term cycle process will be reduced due to the high irreversibility of CrO3; if the content of CrO3 is too low, the uniform coating of the material surface cannot be achieved. Within this content range, the Cr8O 21 formed by the decomposition of CrO3 powder can completely coat the surface of the niobium-doped ternary lithium cathode material without reducing the capacity reversibility of the material. It can be understood that, by using the direct mixing method of CrO3 powder and the niobium-doped ternary lithium cathode material, the dispersion of the niobium-doped ternary lithium cathode material and the melting characteristics of the CrO3 powder are utilized to provide reaction crystallization sites for the Cr8O 21 , thereby forming a thin and continuous coating layer. If CrO3 is first heated and decomposed to form Cr8O 21 , and then compounded with the niobium-doped ternary lithium cathode material, the melting characteristics of the CrO3 powder cannot be fully utilized to make it enter the material pores, thereby failing to form a coating layer.

[0038] In this embodiment, the CrO3 powder is in a granular form, and the particle size is 0.2 μm-10 μm. If the particle size of CrO3 is too large, the melting speed will be reduced, and CrO3 will be more enriched on the surface of the material, making it difficult to quickly enter the material pores; if the particle size of CrO3 is too small, the powder particles will be difficult to uniformly disperse, and uniform coating cannot be achieved. The Cr8O 21 formed by the decomposition of CrO3 powder is in a sheet form. As shown in FIG. 1, the high-capacity cathode material is in a spherical structure coated with sheet-shaped Cr8O Figure 2 . 21 The Nb element is uniformly distributed in the inner layer of the material to form a uniform layer 1, is enriched and distributed in the outer layer of the material to form an enrichment layer 2, and the Cr8O 21 completely coats the surface of the material to form a coating layer 3.

[0039] The preparation method of the high specific capacity positive electrode material of the present application is described in detail below in combination with examples. The chemical reagents used in the following examples and comparative examples are all purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd. The experimental methods used in the following examples and comparative examples are all performed according to the conventional or manufacturer-recommended conditions, unless otherwise specified.

[0040] Example 1 S1: Preparation of hydroxide precursor Ni 0.96 Co 0.02 Mn 0.02 (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 water were prepared respectively. The above-mentioned mixed salt solution of nickel, cobalt and manganese, the NaOH solution and the ammonia water were synchronously added into a reaction kettle at 50°C under a rotation speed of 500 rpm, and the pH of the system was stabilized at 11 by adjusting the dropping speed of each solution. Nitrogen was continuously introduced during the reaction to ensure that the metal ions were fully reacted to form hydroxide precipitate. After the dropping was completed, the temperature and stirring were maintained, and nitrogen was continuously introduced for 5 h to make the precipitate particles grow uniformly and stably, thereby forming the hydroxide precursor Ni 0.96 Co 0.02 Mn 0.02 (OH)2.

[0041] S2: Preparation of niobium-doped ternary lithium positive electrode material. The obtained hydroxide precursor Ni 0.96 Co 0.02 Mn 0.02 (OH)2and H5Nb3O 10 , LiOH·H2O were mixed in a molar ratio of 1:0.01:1.10, and were first heated to 420°C at a heating rate of 5°C / min and maintained for 4 h to respectively form corresponding ternary oxides, niobium oxides and lithium oxides; then were heated to 750°C at a heating rate of 2°C / min and maintained for 10 h to make the ternary oxides, niobium oxides and lithium oxides react; after the reaction was completed, the system was naturally cooled to room temperature, and H5Nb3O 10 (the first added H5Nb3O 10 was 1 / 5 of the molar number), and were heated to 500°C at a heating rate of 5°C / min and maintained for 3 h to obtain the niobium-doped ternary lithium positive electrode material. The niobium-doped ternary lithium positive electrode material was characterized by XRD and EDS mapping, and the results are shown in Figure 3 and Figure 4 It can be seen from Figure 3 that the niobium-doped ternary lithium positive electrode material has an R3m layered structure and no impurity phase is generated, indicating that the Nb element is successfully doped into the material bulk phase. Figure 4As 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.

[0042] 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.

[0043] 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 .

[0044] 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 21 Coating the surface of niobium-doped ternary lithium cathode material is beneficial to improving the specific capacity and interface stability of the material.

[0045] 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.

[0046] Example 2 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.

[0047] Example 3 H5Nb3O added for the first time in S2 10 One-fifth of the molar number was replaced with H5Nb3O added for the first time. 101 / 15 of the mole number, and the temperature was raised to 500°C and kept for 3h instead of 475°C and kept for 5h. The rest of the conditions were the same as in Example 1.

[0048] Example 4 1:0.1 in S3 was replaced by 1:0.2, and the particle size of 8μm was replaced by the particle size of 1μm. The rest of the conditions were the same as in Example 1.

[0049] Example 5 The temperature was raised to 196°C and kept for 4h at the rate of 1°C / min in S3 instead of the temperature being raised to 200°C and kept for 2h at the rate of 2°C / min, and the temperature was raised to 265°C and kept for 12h at the rate of 0.5°C / min instead of the temperature being raised to 260°C and kept for 20h at the rate of 0.3°C / min. The rest of the conditions were the same as in Example 1.

[0050] Comparative Example 1 The niobium-doped ternary lithium cathode material was prepared according to S1 and S2 in Example 1.

[0051] Comparative Example 2 The niobium-doped ternary lithium cathode material was prepared according to S1 and S2 in Example 1.

[0052] In S3, the CrO3 powder (particle size of 8μm) was first raised to 196°C and kept for 4h at the rate of 1°C / min under the oxygen atmosphere to make the CrO3 powder melt completely, and then the temperature was raised to 265°C and kept for 12h at the rate of 0.5°C / min to decompose the melted CrO3 powder into Cr8O 21 Then, the Cr8O 21 was compounded with the niobium-doped ternary lithium cathode material, and after the reaction was completed, the temperature was naturally lowered to room temperature, and finally the cathode material was obtained.

[0053] Comparative Example 3 The H5Nb3O 10 was replaced by 1 / 5 of the mole number of the first added H5Nb3O 10 was replaced by 1 / 15 of the mole number, and the temperature was raised to 650°C and kept for 15h instead of 500°C and kept for 3h. The rest of the conditions were the same as in Example 1.

[0054] Comparative Example 4 The niobium-doped ternary lithium cathode material was prepared according to S1 and S2 in Example 1.

[0055] In S3, the obtained niobium-doped ternary lithium cathode material and CrO3 powder (particle size of 8 μm) are mixed in a molar ratio of 1:0.1, heated to 260°C at a heating rate of 0.3°C / min and kept for 20 h, and after the reaction is completed, the temperature is naturally lowered to room temperature, and finally the cathode material is obtained.

[0056] The cathode materials prepared in Examples 1-5 and Comparative Examples 1-4 are assembled into lithium batteries respectively, and the discharge specific capacity and 200 cycle (1C) capacity retention rate of the lithium batteries are tested, and the results are shown in Table 1. As can be seen from the table, the discharge specific capacity and 200 cycle (1C) capacity retention rate of the lithium batteries assembled by the cathode materials prepared in Examples 1-5 are higher than those of Comparative Examples 1-4, indicating that the cathode materials prepared by the method of the present application have higher discharge specific capacity and capacity retention rate.

[0057] Table 1 Comparison of discharge specific capacity and 200 cycle (1C) capacity retention rate of different lithium batteries

[0058] In summary, the present application improves the existing nickel-cobalt-manganese lithium ternary cathode material, first dopes niobium acid into the cathode material, the high bond energy Nb-O bond formed after niobium doping can effectively inhibit the release of lattice oxygen, and the Nb 5+ Large ionic radius helps to extend the c-axis of single crystal particles, enhance lithium ion diffusion dynamics, and at the same time, inhibit phase transformation unevenness and strain mismatch from the root, improve the structural stability of the material; then the sheet-shaped Cr8O 21 completely coats the surface of the niobium-doped ternary lithium cathode material, and the strong lithium storage property and low surface energy property of Cr8O 21 The combined modification technology of niobium-doped ternary lithium cathode material inside and chromium oxide coating on the surface of the ternary lithium cathode material is adopted, which synergistically improves the specific capacity, structural stability and interface stability of the ternary lithium cathode material, thereby prolonging the cycle life of the battery.

[0059] It should be noted that in this article, the terms "include", "contain" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or equipment. Without more limitation, the element defined by the statement "including a" does not exclude the presence of another identical element in the process, method, article or equipment including the element.

[0060] While the application has been described in detail and with reference to specific preferred embodiments thereof, it will be apparent to one skilled in the art that various modifications and alternatives can be employed without departing from the spirit and scope of the application. Accordingly, the scope of the application should be determined by the appended claims and their equivalents.

Claims

1. A method for preparing a high specific capacity cathode material, characterized by, The method comprises: Step 1, under oxygen atmosphere, mixing hydroxide precursor Ni 1-x-y Co x Mn y (OH)2, first niobium precursor, lithium precursor, respectively generating corresponding ternary oxides, niobium oxides, lithium oxides at a first temperature, the ternary oxides, niobium oxides, lithium oxides reacting at a second temperature, then adding a second niobium precursor, generating niobium-doped ternary lithium cathode material at a third temperature; wherein x>0, y>0, x+y<1; the first temperature < the third temperature < the second temperature; Step 2, mixing the niobium-doped ternary lithium cathode material and CrO3 powder under oxygen atmosphere, the CrO3 powder melts at a fourth temperature, the melted CrO3 powder decomposes into Cr8O 21 and coating the niobium-doped ternary lithium cathode material to obtain a high specific capacity cathode material; wherein the fourth temperature < the fifth temperature.

2. The method for preparing the high specific capacity cathode material as described in claim 1, characterized in that, said hydroxide precursor Ni 1-x-y Co x Mn y (OH)2, x≤0.1, y≤0.1; said first niobium precursor and second niobium precursor are both H5Nb3O 10 said lithium precursor is LiOH H2O.

3. The method of claim 1, wherein the high specific capacity cathode material is prepared by the steps of: 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. ​ 4. The method for preparing the high specific capacity cathode material as described in claim 1, characterized in that, The molar ratio of the niobium-doped ternary lithium positive electrode material and the CrO3 powder is 1:(0.01-0.2).

5. The method for preparing the high specific capacity cathode material as described in claim 1, characterized in that, The first temperature is 400-450 DEG C, and the holding time is 1-5 h; the second temperature is 720-850 DEG C, and the holding time is 5-20 h; the third temperature is 475-525 DEG C, and the holding time is 1-8 h; the fourth temperature is 190-200 DEG C, and the holding time is 1-5 h; and the fifth temperature is 260-270 DEG C, and the holding time is 8-20 h.

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

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

8. The method for preparing the high specific capacity cathode material as described in claim 1, characterized in that, The niobium-doped ternary lithium positive electrode material is in a spherical form, and the spherical form is formed by agglomeration of a plurality of nanoparticles.

9. The method for preparing the high specific capacity cathode material as described in claim 8, characterized in that, The nanoparticles are in a rod-like form, the length of the nanoparticles is 50-1,000 nm, and the width is 5-20 nm; and the particle size of the spherical form is 8-15 μm.

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

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