A modified lithium-rich manganese-based cathode material with a hollow microsphere structure and its preparation and application

Abstract

The present invention discloses a modified lithium-rich manganese-based cathode material with a hollow microsphere structure and its preparation and application. The lithium-rich manganese-based material has a hollow microsphere structure. The microsphere is formed by self-assembly of primary nanoparticles. The outer layer of the microsphere is a LiCeO2 coating layer with a thickness of 1 to 10 nm. The main part of the coating layer is a cerium-doped lithium-rich manganese-based material. The interior of the microsphere presents a hollow structure. The molecular formula of the lithium-rich manganese-based cathode material is Li 1+ a Mn b Ni c Co d Ce e O2, wherein 0.1≤a≤0.4, 0≤b≤0.8, 0≤c≤0.3, 0≤d≤0.3, 0.005≤e≤0.1, and a+b+c+d+e=1. The present invention provides a preparation method of the modified lithium-rich manganese-based positive electrode material with a hollow microsphere structure and its application as a positive electrode material for lithium-ion batteries. The material exhibits high rate performance and good cycle stability.

Description

Technical Field

[0001] The invention relates to a modified lithium-rich manganese-based positive electrode material with a hollow microsphere structure, a preparation method thereof, and application thereof as a positive electrode material for lithium ion batteries. Technical Background

[0002] Since lithium-ion batteries were first used in electronic products in the 1990s, their development has never stopped. Today, as a mature energy storage strategy, lithium-ion batteries have outstanding performance in energy density, driving range, and design flexibility, making them one of the most important chemical power sources. However, with the continuous development of the energy storage field and the electric vehicle industry, people have placed higher demands on the performance of lithium-ion batteries. As a bottleneck in battery capacity and energy density, positive electrode materials are considered the main factor in further improving the performance of lithium-ion batteries.

[0003] In the lithium-ion battery industry, consumer batteries targeting the 3C market still account for a large proportion, and they basically use lithium cobalt oxide as the positive electrode material. However, due to the low specific capacity, high cost and limited raw material resources of lithium cobalt oxide, it is difficult to meet the application of large-scale energy storage and power batteries. Although high-nickel materials have made great progress in recent years and have shown an actual discharge capacity far higher than that of traditional positive electrode materials, their energy density in the whole battery can only reach 300Wh·kg -1 , and power battery 400Wh·kg -1 To meet the increasing market demand, the development of a new generation of lithium-ion batteries with higher energy density and lower cost has become a top priority for the lithium battery industry.

[0004] Among many new cathode materials, lithium-rich manganese-based materials have excellent discharge capacity (>250mAh·g -1) and a high average operating voltage (>3.5V), becoming a research hotspot in recent years. Lithium-rich manganese-based materials use Mn as the main element, reducing the amount of Co used in the preparation process, significantly controlling production costs and minimizing environmental pollution during synthesis and recycling. Compared to high-nickel materials, they exhibit better thermal stability, significantly reduce heat generation during continuous cycling, and enhance safety. However, while Li-rich manganese-based materials offer significant advantages over traditional cathode materials in terms of energy density, power density, production cost, and safety, they still suffer from numerous drawbacks that hinder their development and application. First, during the first cycle of charging, Li-rich manganese-based materials undergo activation of Li2MnO3, a process accompanied by irreversible surface oxygen loss. Simultaneously, metal cations in the transition metal layer readily migrate and occupy existing lithium sites, resulting in low initial coulombic efficiency and surface structural transformations. As cycling continues, this structural transformation gradually propagates from the surface layer to the bulk, transforming the overall material configuration from a layered to a spinel structure, leading to capacity and voltage decay. In addition, the low electrical conductivity of the Li2MnO3 phase hinders the rapid insertion and extraction of lithium ions in the material to a certain extent, thereby limiting the rate performance of the material.

[0005] Therefore, selecting a suitable preparation method supplemented by a reasonable modification strategy is of great significance to the development of lithium-rich manganese-based materials. Summary of the Invention

[0006] In view of the above situation, the main purpose of the present invention is to provide a preparation and application of a modified lithium-rich manganese-based positive electrode material with a hollow microsphere structure. By utilizing the unique morphology and structure and in-situ doping and coating methods, the interface stability of the material surface is improved and the irreversible oxygen loss during the first cycle of charging is suppressed, so as to improve the problems of low first-cycle coulombic efficiency, severe cycle capacity attenuation, and poor rate performance of traditional lithium-rich manganese-based materials.

[0007] In the first aspect, the present invention provides a modified lithium-rich manganese-based positive electrode material with a hollow microsphere structure. The lithium-rich manganese-based material has a hollow microsphere structure. The microsphere is formed by self-assembly of primary nanoparticles. The outer layer of the microsphere is a LiCeO2 coating layer with a thickness of 1 to 10 nm. The main part of the coating layer is a cerium-doped lithium-rich manganese-based material. The interior of the microsphere presents a hollow structure. The overall molecular formula of the lithium-rich manganese-based material is Li 1+a Mn b Ni c Co d Ce e O2, where 0.1≤a≤0.4, 0≤b≤0.8, 0≤c≤0.3, 0≤d≤0.3, 0.005≤e≤0.1, a+b+c+d+e=1.

[0008] Preferably, the outer diameter of the microspheres of the lithium-rich manganese-based material is 500-2000 nm, and the particle size of the primary nanoparticles is 30-300 nm.

[0009] Preferably, e / (b+c+d+e)=1-3%, most preferably 3%.

[0010] In a second aspect, the present invention provides a method for preparing the modified lithium-rich manganese-based positive electrode material having a hollow microsphere structure according to the first aspect, the preparation method specifically comprising the following steps:

[0011] (1) Weighing a certain amount of lithium salt, nickel salt, cobalt salt and manganese salt, dissolving them in a solvent, and adding them to a stainless steel dynamic hydrothermal reactor, controlling the molar ratio of each metal element to conform to the ratio of each metal in the modified lithium-rich manganese-based positive electrode material;

[0012] (2) Weigh a certain amount of oxalic acid and dissolve it in a solvent, then add it dropwise into a stainless steel dynamic hydrothermal reactor, controlling the molar ratio of oxalate to total metal elements in the mixed system to be 0.8 to 1.2;

[0013] (3) Weighing a certain amount of cerium salt and dissolving it in a solvent, adding it to a stainless steel dynamic hydrothermal kettle, and controlling the molar ratio of cerium element to other metal elements to conform to the ratio of each metal in the modified lithium-rich manganese-based material;

[0014] (4) setting the speed of the stirrer of the stainless steel dynamic hydrothermal kettle to 80-120 rpm and the heating rate to 1.5-2.5°C / min, heating the mixed solution obtained in step (3) to 160-200°C for constant temperature reaction for 4-6 hours, and then allowing the system to cool naturally;

[0015] (5) After the system temperature drops to room temperature, the precipitate obtained in step (4) is collected and dried to obtain a precursor;

[0016] (6) placing the precursor obtained in step (5) in a sintering furnace for staged calcination, wherein the staged calcination includes two steps: low-temperature calcination and high-temperature calcination. The low-temperature calcination is calcined at 400-600°C for 4-6 hours, and the high-temperature calcination is calcined at 700-900°C for 10-15 hours. The calcination is carried out in an air atmosphere at a heating rate of 2°C to 5°C / min, thereby preparing the modified lithium-rich manganese-based positive electrode material with the hollow microsphere structure.

[0017] Preferably, in step (1):

[0018] The lithium salt is selected from one or both of lithium nitrate and lithium acetate;

[0019] The nickel salt is selected from one or both of nickel nitrate and nickel acetate;

[0020] The cobalt salt is selected from one or both of cobalt nitrate and cobalt acetate;

[0021] The manganese salt is selected from one or both of manganese nitrate and manganese acetate.

[0022] Preferably, the solvents used in steps (1-3) are the same, and the solvent is selected from a mixture of one or more of water, methanol, ethanol, n-propanol, and isopropanol.

[0023] Preferably, the cerium salt used in step (3) is selected from one or both of cerium nitrate and cerium acetate.

[0024] Preferably, the drying conditions in step (5) are: drying at 60-120° C. for more than 12 hours.

[0025] In the preparation method of the modified lithium-rich manganese-based positive electrode material with a hollow microsphere structure described in the present invention, the addition rate of the oxalic acid solution has a great influence on the material morphology. When the addition rate of the oxalic acid solution is too fast, a large amount of flocculent precipitates appear in the system in a short period of time, which to a certain extent breaks the kinetic balance of the nucleation and self-assembly process under ideal conditions, causing the morphology of the product to deviate from the design expectation. In addition, staged calcination also has an important influence on the morphology of the product. During the calcination process, it is necessary to pre-burn for a certain period of time in the range of 400-600°C to completely decompose the carbonate into metal oxides, so as to avoid the gasification phenomenon during the calcination process at a higher temperature, which affects the molten metal oxide to combine with oxygen in the air and gradually crystallize into a lithium-rich manganese-based solid solution material.

[0026] In a third aspect, the present invention provides an application of the modified lithium-rich manganese-based positive electrode material with a hollow microsphere structure described in the first aspect as a positive electrode material for a lithium-ion battery.

[0027] Compared with the prior art, the present invention has the following characteristics and advantages:

[0028] (1) The present invention provides a method for preparing a modified lithium-rich manganese-based cathode material with a hollow microsphere structure. The method employs a dynamic solvothermal method for precursor synthesis, thereby overcoming the drawbacks of conventional solvothermal methods, such as long reaction times and uneven elemental distribution in the resulting product. The method is simple, easy to operate, and has high production efficiency. The resulting precursor has a uniform distribution of metal elements, improving the consistency of the material after calcination.

[0029] (2) The lithium-rich manganese-based material prepared by the present invention has high rate performance and good cycle stability when used as a positive electrode material in lithium-ion batteries. The unique hollow microsphere structure enables the material to have a short Li + While controlling the migration path, it also controls the contact area between it and the electrolyte, thus improving the cycle stability of the material. 3 + / Ce 4+Ions are doped into the bulk phase, which expands the interlayer spacing of the material and increases the Li + The insertion and extraction dynamics of Ce-O are very strong, and the strong bonding force between Ce and O plays an anchoring role on O, stabilizing the structure of the material. Part of Ce forms CeO2 phase with rich oxygen vacancies, which, as a component with reversible oxygen storage function, reduces the oxygen partial pressure in the material and provides oxygen for O 2- The migration of Ce provides more active sites, thereby reducing oxygen release during the first charge cycle and during cycling. The remaining Ce is coated on the material surface as LiCeO2, preventing direct contact between the active material and the electrolyte, inhibiting various side reactions and improving the material's interfacial stability. Furthermore, the introduction of Ce simultaneously induces the formation of a layered-spinel heterostructure, giving the material higher conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 SEM images of the precursors and lithium-rich materials prepared at different oxalic acid solution addition rates in Comparative Examples 1-3: (a, b) rapid pouring in Comparative Example 1, (c, d) slow pouring in Comparative Example 2, and (e, f) dropwise addition in Comparative Example 3;

[0031] Figure 2 The XRD spectra of the materials prepared in Comparative Example 3 and Examples 1 to 3 are shown;

[0032] Figure 3 This is a scanning electron microscope image of the material prepared in Comparative Example 3;

[0033] Figure 4 This is a scanning electron microscope image of the material prepared in Example 2;

[0034] Figure 5 This is a scanning electron microscope image of the material prepared in Example 2;

[0035] Figure 6 This is a transmission electron micrograph of the material prepared in Example 2;

[0036] Figure 7 This is a high-magnification transmission electron microscopy image of the material prepared in Example 2;

[0037] Figure 8 The first cycle charge-discharge curves and corresponding dQ / dV curves of the materials prepared in Comparative Example 3 and Examples 1 to 3;

[0038] Figure 9 Graphs showing the cycle performance of the materials prepared in Comparative Example 3 and Examples 1 to 3;

[0039] Figure 10 This is a rate performance diagram of the materials prepared in Comparative Example 3 and Examples 1 to 3. DETAILED DESCRIPTION

[0040] The technical solution of the present invention is further described below through specific embodiments, but the protection scope of the present invention is not limited thereto:

[0041] Comparative Example 1:

[0042] 4.90g Mn(CH3COO)2·4H2O (20mmol), 1.25g Co(CH3COO)2·4H2O (5mmol), 1.24g Ni(CH3COO)2·4H2O (5mmol), and 4.82g CH3COOLi·2H2O (48mmol) were dissolved in a mixture of 120ml methanol and 80ml ethanol and added to a stainless steel dynamic hydrothermal reactor. 7.68g H2C2O4·2H2O (60mmol) was then dissolved in a mixture of 60ml methanol and 40ml ethanol and quickly poured into the stainless steel dynamic hydrothermal reactor. The stirrer speed of the hydrothermal reactor was set to 100 rpm, and the heating rate was set to 2°C / min. The mixed solution was heated to 180°C for 4 hours, then the system was allowed to cool naturally. After the system temperature dropped to room temperature, the resulting precipitate was collected and dried at 80°C for 12 hours to obtain the precursor. The obtained precursor was calcined in an air atmosphere. The calcination conditions were as follows: heating to 450°C at 5°C / min, keeping constant at this temperature for 4 hours, then heating to 800°C at 5°C / min, keeping constant at this temperature for 12 hours, and cooling to room temperature in the furnace to obtain a lithium-rich manganese-based positive electrode material with a hollow microsphere structure that does not contain Ce elements, which is recorded as LLO.

[0043] Comparative Example 2:

[0044] 4.90g Mn(CH3COO)2·4H2O (20mmol), 1.25g Co(CH3COO)2·4H2O (5mmol), 1.24g Ni(CH3COO)2·4H2O (5mmol), and 4.82g CH3COOLi·2H2O (48mmol) were weighed and dissolved in a mixed solvent of 120ml methanol and 80ml ethanol, and added to a stainless steel dynamic hydrothermal reactor. 7.68g H2C2O4·2H2O (60mmol) was then weighed and dissolved in a mixed solvent of 60ml methanol and 40ml ethanol, and slowly poured (2ml / s) into the stainless steel dynamic hydrothermal reactor. The stirrer speed of the hydrothermal reactor was set to 100 rpm, and the heating rate was set to 2°C / min. The mixed solution was heated to 180°C for a constant temperature reaction for 4 hours, and then the system was allowed to cool naturally. After the system temperature dropped to room temperature, the resulting precipitate was collected and dried at 80°C for 12 hours to obtain a precursor. The resulting precursor was calcined in air atmosphere at a rate of 5°C / min to 450°C, held constant for 4 hours, then increased to 800°C at 5°C / min and held constant for 12 hours. After cooling to room temperature in the furnace, a lithium-rich manganese-based cathode material with a hollow microsphere structure and no Ce element was obtained, which was denoted as LLO.

[0045] Comparative Example 3:

[0046] 4.90g Mn(CH3COO)2·4H2O (20mmol), 1.25g Co(CH3COO)2·4H2O (5mmol), 1.24g Ni(CH3COO)2·4H2O (5mmol), and 4.82g CH3COOLi·2H2O (48mmol) were dissolved in a mixed solvent of 120ml methanol and 80ml ethanol and added to a stainless steel dynamic hydrothermal reactor. 7.68g H2C2O4·2H2O (60mmol) was then dissolved in a mixed solvent of 60ml methanol and 40ml ethanol and added dropwise to the stainless steel dynamic hydrothermal reactor. The stirrer speed of the hydrothermal reactor was set to 100 rpm, and the heating rate was set to 2°C / min. The mixed solution was heated to 180°C for 4 hours, then the system was allowed to cool naturally. After the system temperature dropped to room temperature, the resulting precipitate was collected and dried at 80°C for 12 hours to obtain the precursor. The obtained precursor was calcined in an air atmosphere. The calcination conditions were as follows: heating to 450°C at 5°C / min, keeping constant at this temperature for 4 hours, then heating to 800°C at 5°C / min, keeping constant at this temperature for 12 hours, and cooling to room temperature in the furnace to obtain a lithium-rich manganese-based positive electrode material with a hollow microsphere structure that does not contain Ce elements, which is recorded as LLO.

[0047] Comparative Example 4:

[0048] 4.90 g Mn(CH3COO)2·4H2O (20 mmol), 1.25 g Co(CH3COO)2·4H2O (5 mmol), 1.24 g Ni(CH3COO)2·4H2O (5 mmol), and 4.82 g CH3COOLi·2H2O (48 mmol) were dissolved in a mixed solvent of 105 ml methanol and 70 ml ethanol, and added to a stainless steel dynamic hydrothermal reactor. 7.68 g H2C2O4·2H2O (60 mmol) was then dissolved in a mixed solvent of 60 ml methanol and 40 ml ethanol, and added dropwise to the stainless steel dynamic hydrothermal reactor. 0.40 g Ce(NO3)3·6H2O (0.9 mmol) was then dissolved in a mixed solvent of 15 ml methanol and 10 ml ethanol, and added to the stainless steel dynamic hydrothermal reactor. The speed of the hydrothermal kettle stirrer was set to 100 rpm, the heating rate was set to 2°C / min, the mixed solution was heated to 180°C and kept at this temperature for 4 hours, and then the system was cooled naturally. After the system temperature dropped to room temperature, the precipitate was collected and dried at 80°C for 12 hours to obtain a precursor. The obtained precursor was calcined in an air atmosphere under the calcination conditions of heating to 800°C at 5°C / min and keeping the temperature constant for 12 hours. After cooling to room temperature with the furnace, a modified lithium-rich manganese-based positive electrode material with a hollow microsphere structure containing 3% Ce element (in proportion to transition metal atoms) was obtained, which was recorded as LLO-3%Ce (comparison).

[0049] Example 1:

[0050] 4.90 g Mn(CH3COO)2·4H2O (20 mmol), 1.25 g Co(CH3COO)2·4H2O (5 mmol), 1.24 g Ni(CH3COO)2·4H2O (5 mmol), and 4.82 g CH3COOLi·2H2O (48 mmol) were dissolved in a mixed solvent of 105 ml methanol and 70 ml ethanol, and added to a stainless steel dynamic hydrothermal reactor. 7.68 g H2C2O4·2H2O (60 mmol) was then dissolved in a mixed solvent of 60 ml methanol and 40 ml ethanol, and added dropwise to the stainless steel dynamic hydrothermal reactor. 0.13 g Ce(NO3)3·6H2O (0.3 mmol) was then dissolved in a mixed solvent of 15 ml methanol and 10 ml ethanol, and added to the stainless steel dynamic hydrothermal reactor. The speed of the hydrothermal autoclave stirrer was set to 100 rpm, the heating rate was set to 2°C / min, the mixed solution was heated to 180°C and kept at this temperature for 4 hours, and then the system was cooled naturally. After the system temperature dropped to room temperature, the obtained precipitate was collected and dried at 80°C for 12 hours to obtain a precursor. The obtained precursor was calcined in an air atmosphere, and the calcination conditions were 5°C / min to 450°C, kept at this temperature for 4 hours, then heated to 800°C at 5°C / min, kept at this temperature for 12 hours, and cooled to room temperature with the furnace to obtain a modified lithium-rich manganese-based positive electrode material with a hollow microsphere structure containing 1% Ce element (in proportion to transition metal atoms), which was recorded as LLO-1%Ce.

[0051] Example 2:

[0052] 4.90 g Mn(CH3COO)2·4H2O (20 mmol), 1.25 g Co(CH3COO)2·4H2O (5 mmol), 1.24 g Ni(CH3COO)2·4H2O (5 mmol), and 4.82 g CH3COOLi·2H2O (48 mmol) were dissolved in a mixed solvent of 105 ml methanol and 70 ml ethanol, and added to a stainless steel dynamic hydrothermal reactor. 7.68 g H2C2O4·2H2O (60 mmol) was then dissolved in a mixed solvent of 60 ml methanol and 40 ml ethanol, and added dropwise to the stainless steel dynamic hydrothermal reactor. 0.40 g Ce(NO3)3·6H2O (0.9 mmol) was then dissolved in a mixed solvent of 15 ml methanol and 10 ml ethanol, and added to the stainless steel dynamic hydrothermal reactor. The speed of the hydrothermal kettle stirrer was set to 100 rpm, the heating rate was set to 2°C / min, the mixed solution was heated to 180°C for constant temperature reaction for 4 hours, and then the system was cooled naturally. After the temperature of the system dropped to room temperature, the obtained precipitate was collected and dried at 80°C for 12 hours to obtain a precursor. The obtained precursor was calcined in an air atmosphere, and the calcination conditions were 5°C / min to 450°C, constant temperature for 4 hours, 5°C / min to 800°C, constant temperature for 12 hours, and after cooling to room temperature with the furnace, a modified lithium-rich manganese-based positive electrode material with a hollow microsphere structure containing 3% Ce element (in proportion to transition metal atoms) was obtained, which was recorded as LLO-3%Ce.

[0053] Example 3:

[0054] 4.90 g Mn(CH3COO)2·4H2O (20 mmol), 1.25 g Co(CH3COO)2·4H2O (5 mmol), 1.24 g Ni(CH3COO)2·4H2O (5 mmol), and 4.82 g CH3COOLi·2H2O (48 mmol) were dissolved in a mixed solvent of 105 ml methanol and 70 ml ethanol, and added to a stainless steel dynamic hydrothermal reactor. 7.68 g H2C2O4·2H2O (60 mmol) was then dissolved in a mixed solvent of 60 ml methanol and 40 ml ethanol, and added dropwise to the stainless steel dynamic hydrothermal reactor. 0.69 g Ce(NO3)3·6H2O (1.59 mmol) was then dissolved in a mixed solvent of 15 ml methanol and 10 ml ethanol, and added to the stainless steel dynamic hydrothermal reactor. The speed of the hydrothermal kettle stirrer was set to 100 rpm, the heating rate was set to 2°C / min, the mixed solution was heated to 180°C and kept at this temperature for 4 hours, and then the system was cooled naturally. After the temperature of the system dropped to room temperature, the obtained precipitate was collected and dried at 80°C for 12 hours to obtain a precursor. The obtained precursor was calcined in an air atmosphere, and the calcination conditions were 5°C / min to 450°C, kept at this temperature for 4 hours, then 5°C / min to 800°C, kept at this temperature for 12 hours, and cooled to room temperature with the furnace to obtain a modified lithium-rich manganese-based positive electrode material with a hollow microsphere structure containing 5% Ce element (in proportion to transition metal atoms), which was recorded as LLO-5%Ce.

[0055] Example 4:

[0056] 4.90g Mn(CH3COO)2·4H2O (20mmol), 1.25g Co(CH3COO)2·4H2O (5mmol), 1.24g Ni(CH3COO)2·4H2O (5mmol), and 4.82g CH3COOLi·2H2O (48mmol) were weighed and dissolved in 180ml methanol and added to a stainless steel dynamic hydrothermal reactor. 7.68g H2C2O4·2H2O (60mmol) was then weighed and dissolved in 100ml methanol and added dropwise to the stainless steel dynamic hydrothermal reactor. 0.40g Ce(NO3)3·6H2O (0.9mmol) was then weighed and dissolved in 20ml methanol and added to the stainless steel dynamic hydrothermal reactor. The stirrer speed of the hydrothermal reactor was set to 100 rpm, the heating rate was set to 2°C / min, the mixed solution was heated to 180°C and the reaction was kept at this temperature for 4 hours, and then the system was allowed to cool naturally. After the system temperature dropped to room temperature, the resulting precipitate was collected and dried at 80°C for 12 hours to obtain a precursor. The resulting precursor was calcined in an air atmosphere under the following calcination conditions: heating to 450°C at 5°C / min, holding at this temperature for 4 hours, then heating to 800°C at 5°C / min, holding at this temperature for 12 hours, and then cooling to room temperature in the furnace to obtain a modified lithium-rich manganese-based positive electrode material with a hollow microsphere structure containing 3% Ce element (in terms of transition metal atomic ratio).

[0057] Example 5:

[0058] 4.90g Mn(CH3COO)2·4H2O (20mmol), 1.25g Co(CH3COO)2·4H2O (5mmol), 1.24g Ni(CH3COO)2·4H2O (5mmol), and 4.82g CH3COOLi·2H2O (48mmol) were weighed and dissolved in 180ml of ethanol and added to a stainless steel dynamic hydrothermal reactor. 7.68g H2C2O4·2H2O (60mmol) was then weighed and dissolved in 100ml of ethanol and added dropwise to the stainless steel dynamic hydrothermal reactor. 0.40g Ce(NO3)3·6H2O (0.9mmol) was then weighed and dissolved in 20ml of ethanol and added to the stainless steel dynamic hydrothermal reactor. The stirrer speed of the hydrothermal reactor was set to 100 rpm, and the heating rate was set to 2°C / min. The mixed solution was heated to 180°C for a constant temperature reaction for 4 hours, and then the system was allowed to cool naturally. After the system temperature dropped to room temperature, the resulting precipitate was collected and dried at 80°C for 12 hours to obtain a precursor. The resulting precursor was calcined in an air atmosphere under the following calcination conditions: heating to 450°C at 5°C / min, holding at this temperature for 4 hours, then heating to 800°C at 5°C / min, holding at this temperature for 12 hours, and then cooling to room temperature in the furnace to obtain a modified lithium-rich manganese-based positive electrode material with a hollow microsphere structure containing 3% Ce element (in terms of transition metal atomic ratio).

[0059] Example 6:

[0060] 5.74g Mn(NO3)2·6H2O (20mmol), 1.45g Co(NO3)2·6H2O (5mmol), 1.45g Ni(NO3)2·6H2O (5mmol), and 3.26g LiNO3 (47mmol) were weighed and dissolved in a mixed solvent of 105ml methanol and 70ml ethanol, and added to a stainless steel dynamic hydrothermal autoclave. 7.68g H2C2O4·2H2O (60mmol) was then weighed and dissolved in a mixed solvent of 60ml methanol and 40ml ethanol, and added dropwise to the stainless steel dynamic hydrothermal autoclave. 0.40g Ce(NO3)3·6H2O (0.9mmol) was then weighed and dissolved in a mixed solvent of 15ml methanol and 10ml ethanol, and added to the stainless steel dynamic hydrothermal autoclave. The speed of the hydrothermal kettle stirrer was set to 100 rpm, the heating rate was set to 2°C / min, the mixed solution was heated to 180°C for constant temperature reaction for 4 hours, and then the system was cooled naturally. After the temperature of the system dropped to room temperature, the obtained precipitate was collected and dried at 80°C for 12 hours to obtain a precursor. The obtained precursor was calcined in an air atmosphere, and the calcination conditions were 5°C / min to 450°C, constant temperature for 4 hours, 5°C / min to 800°C, constant temperature for 12 hours, and after cooling to room temperature with the furnace, a modified lithium-rich manganese-based positive electrode material with a hollow microsphere structure containing 3% Ce element (in proportion to transition metal atoms) was obtained, which was recorded as LLO-3%Ce.

[0061] Example 7:

[0062] 5.74g Mn(NO3)2·6H2O (20mmol), 1.45g Co(NO3)2·6H2O (5mmol), 1.45g Ni(NO3)2·6H2O (5mmol), and 3.26g LiNO3 (47mmol) were dissolved in a mixed solvent of 105ml ethanol and 70ml isopropanol, and added to a stainless steel dynamic hydrothermal reactor. 7.68g H2C2O4·2H2O (60mmol) was then dissolved in a mixed solvent of 60ml ethanol and 40ml isopropanol, and added dropwise to the stainless steel dynamic hydrothermal reactor. 0.40g Ce(NO3)3·6H2O (0.9mmol) was then dissolved in a mixed solvent of 15ml ethanol and 10ml isopropanol, and added to the stainless steel dynamic hydrothermal reactor. The speed of the hydrothermal kettle stirrer was set to 100 rpm, the heating rate was set to 2°C / min, the mixed solution was heated to 180°C for constant temperature reaction for 4 hours, and then the system was cooled naturally. After the temperature of the system dropped to room temperature, the obtained precipitate was collected and dried at 80°C for 12 hours to obtain a precursor. The obtained precursor was calcined in an air atmosphere, and the calcination conditions were 5°C / min to 450°C, constant temperature for 4 hours, 5°C / min to 800°C, constant temperature for 12 hours, and after cooling to room temperature with the furnace, a modified lithium-rich manganese-based positive electrode material with a hollow microsphere structure containing 3% Ce element (in proportion to transition metal atoms) was obtained, which was recorded as LLO-3%Ce.

[0063] The following describes the application of the modified lithium-rich manganese-based positive electrode material with a hollow microsphere structure prepared by the method of the present invention as a positive electrode material for lithium-ion batteries.

[0064] (1) Production of positive electrode

[0065] Using acetylene black as a conductive agent and PVDF as a binder, 0.4 g of the prepared lithium-rich manganese-based material powder, acetylene black and PVDF in a mass ratio of 8:1:1 was weighed, dissolved in an appropriate amount of N-methylpyrrolidone (NMP), fully mixed and evenly coated on aluminum foil. After vacuum drying at 120°C for 12 hours, it was cut into positive electrode sheets with a diameter of about 12 mm using a button battery slicer.

[0066] (2) Production of button batteries

[0067] The button cell was manufactured in an argon-filled glove box. The prepared electrode was used as the positive electrode, the metal lithium sheet was used as the negative electrode, and 1 mol / L LiPF6 / EC+EMC (V EC ∶V EMC =1:1) as the electrolyte, Celgard 2400 separator, assembled into CR2032 button half-cells, and various electrochemical performance tests were performed after pressing and sealing.

[0068] Figure 1 The SEM images of the precursor and lithium-rich material prepared at different oxalic acid solution addition rates are shown. Figure 1 (a, b)), the precursor is in the form of scattered flakes, while the lithium-rich material formed after calcination is uniformly distributed nanoparticles, and does not maintain the flake structure of the precursor. When oxalic acid solution is slowly poured (2ml / s) ( Figure 1 (c, d)), the sheet-like primary structure is stacked in a pine cone shape, but the morphology is not maintained after calcination. When the oxalic acid solution is added dropwise into the metal salt solution ( Figure 1 (e, f)) The flake-like structure shows a tendency to self-assemble, revealing a flower-like rudiment. After further calcination, the nanoparticles assemble into micron-sized secondary particles. Although their morphology is irregular, this indicates that the rate of oxalic acid addition has a significant impact on the material morphology.

[0069] Figure 2 The XRD spectra of the materials prepared in Comparative Example 3 and Examples 1 to 3 show that all four groups of materials have an α-NaFeO2 layered structure belonging to the R-3m space group. The weak diffraction peaks in the range of 20-22° can be attributed to the superlattice structure formed by the orderly arrangement of Li and Mn in Li2MnO3. The (003) peaks of the materials prepared in Examples 1 to 3 shift slightly to low angles, indicating that the unit cell parameters of the materials have increased. This is due to the partial embedding of Ce elements into the bulk phase of the material and the expansion of the interlayer spacing of the material, which facilitates the rapid insertion and extraction of lithium ions in the material. In addition, the materials prepared in Examples 1 to 3 show the presence of CeO2 and Li4Mn5O 12 The diffraction peaks indicate the existence of CeO2 and spinel heterostructures.

[0070] Figure 3 This scanning electron micrograph of the material prepared in Comparative Example 3 shows that the prepared lithium-rich manganese-based material exhibits microspherical morphology and a distinct hierarchical structure. The microspheres are approximately 1-1.5 μm in diameter, well dispersed, and self-assembled from primary particles with diameters of 50-200 nm. Furthermore, the mapping image shows that all elements are evenly distributed across the material surface, with no apparent segregation.

[0071] Figure 4 This is a scanning electron microscope image of the material prepared in Example 2. It can be seen that the introduction of the Ce element does not significantly change the morphological characteristics of the material, and the microspherical morphology and hierarchical structure are still maintained. The mapping image shows that the Ce element is evenly distributed on the surface of the material.

[0072] Figure 5This scanning electron micrograph of the material prepared in Example 2 shows partially broken lithium-rich manganese-based microspheres. The microspheres are not formed by tightly packed primary particles, but rather exhibit a hollow structure. Compared to nanomaterials, these microspheres have a higher tap density. Compared to self-assembled spherical materials with dense internal structures, they have shorter lithium ion diffusion paths, a larger contact area with the electrolyte, and minimize the impact of primary particle strain on the overall material configuration during charge and discharge, balancing the relationship between lithium ion diffusion kinetics and material stability.

[0073] Figure 6 This is a transmission electron microscope image of the material prepared in Example 2. There is a different contrast between the edge and the center of the material. The image of the center area is significantly brighter than the outer edge, indicating that there are more grains near the surface of the microsphere. The EDS line scan results further confirm the existence of this hollow structure (Figure b). The content of each element is high near the surface of the material. As the scan progresses toward the center of the microsphere, the signal intensity of each element gradually decreases. In addition, during the line scan from the blank area to the interior of the material, the Ce signal appears before other elements, indicating that some Ce exists on the surface of the material.

[0074] Figure 7 This is a high-magnification transmission electron micrograph of the material prepared in Example 2. As shown in Figure a, a uniform coating layer with a thickness of approximately 5 nm exists on the outside of the material particles. To further analyze the composition of the coating layer, this area was observed at a higher magnification. In Figure b, three distinct lattice fringes appear. The lattice fringes with spacings of 0.37 nm and 0.27 nm away from the surface correspond to the (-111) and (111) crystal planes of the layered structure component, respectively. The lattice fringes with spacings of 0.21 nm in the coating layer correspond to the (022) crystal plane of LiCeO2, proving that the coating layer is composed of LiCeO2.

[0075] The materials prepared in Examples 1 to 7 and Comparative Examples 1 to 4 were used as positive electrodes, and the lithium-ion battery manufacturing process described in the method of the present invention was adopted to assemble CR2032 button batteries for charge and discharge cycle testing.

[0076] Table 1 shows the discharge capacity of the lithium-rich manganese-based materials prepared in Examples 1 to 7 and Comparative Examples 1 to 4 at 0.1 C (20 mAh / g) and 2 to 4.8 V in the first and 50th cycles of charge and discharge.

[0077] Table 1: Comparison of the performance of lithium-rich manganese-based materials prepared in Examples 1 to 7 and Comparative Examples 1 to 4

[0078]

[0079] Figure 8The first cycle charge and discharge curves and corresponding dQ / dV curves of the materials prepared in Comparative Example 3 and Examples 1 to 3 are shown. As shown in the first cycle charge and discharge curves of the prepared materials (Figure a), the figure gives the first cycle discharge capacity and first cycle coulomb efficiency data. Since Ce does not undergo valence changes to provide capacity during the charge and discharge process, the first cycle discharge capacity of the materials prepared in Examples 1 to 3 is lower than that of Comparative Example 3, but the introduction of an appropriate amount of Ce element effectively improves the first cycle coulomb efficiency of the material. This can be attributed to the Ce in the bulk phase. 3+ / Ce 4+ It forms a strong Ce-O bond with O, which plays an anchoring role on the lattice oxygen, and the CeO2 phase containing rich oxygen vacancies is O 2- The migration of Ce provides more active sites, thereby reducing the irreversible oxygen loss during the activation of Li2MnO3. In addition, the LiCeO2 coating layer also plays a positive role in alleviating the harmful parasitic reactions between the active material and the electrolyte. However, when the amount of Ce introduced is increased to 5% (Example 3), the initial efficiency of the material is significantly reduced, which may be due to the excessive Ce in the bulk phase. 3+ / Ce 4+ To some extent, the layered structure is destroyed, thus hindering the Li + The insertion and extraction of Ce further aggravates the electrode polarization, resulting in a negative effect. As can be seen from the corresponding dQ / dV curve (Figure b), the presence of Ce further improves the electrode reaction kinetics, thereby reducing the electrode polarization during the activation process of Li2MnO3, making Li + Easier to deintercalate from this component.

[0080] Figure 9 The cycling performance graphs for the materials prepared in Comparative Example 3 and Examples 1-3 are shown. Although the discharge capacity of the materials prepared in Examples 1-3 is slightly lower than that of the material in Comparative Example 3 in the first few weeks of cycling, this phenomenon gradually disappears as the cycling continues. After 50 cycles, the discharge capacity of the material in Comparative Example 3 is only 218.1 mAh·g -1 The capacity retention rate was as low as 69.4%, and serious capacity decay occurred. The discharge capacities of the materials in Examples 1, 2, and 3 were 228.9 mAh·g -1 , 250.3mAh·g -1 and 218.2mAh·g -1 , and have capacity retention rates of 75.8%, 85.9% and 85.2% respectively. It can be seen that the introduction of Ce significantly inhibits the capacity decay during the cycle process and improves the cycle stability of the material.

[0081] Figure 10The rate performance diagram of the materials prepared in Comparative Example 3 and Examples 1 to 3. As the current density increases, each group of materials shows different degrees of capacity loss. When the rate is increased to 5C, the material in Comparative Example 3 only shows 145.8mAh·g -1 The specific capacity of the materials in Example 1, Example 2 and Example 3 is 169.2 mAh·g -1 、189.3mAh·g -1 and 158.7mAh·g -1 This can be attributed to the Ce 3+ / Ce 4+ The doping of α-doped ... + The intercalation and deintercalation of Ce enhances the electrode reaction kinetics and reduces electrode polarization at high current densities. Furthermore, the presence of layered-spinel heterointerfaces in Ce-containing materials promotes charge transfer, leading to higher electrical conductivity.

[0082] The above results show that the modified lithium-rich manganese-based cathode material with a hollow microsphere structure prepared in the present invention has a high specific capacity and good cycle stability, and is expected to be used in the new generation of lithium-ion batteries.

[0083] The above content is a detailed description of the content of the present invention in combination with preferred embodiments, but it cannot be considered that the specific implementation of the present invention is limited to the embodiments. All variations and replacements made within the scope of the claims of the present invention should fall within the scope of the claims of the present invention.

Claims

1. A modified lithium-rich manganese-based cathode material with a hollow microsphere structure, characterized by: The lithium-rich manganese-based positive electrode material has a hollow microsphere structure, which is formed by self-assembly of primary nanoparticles. The outer layer of the microsphere is a LiCeO2 coating layer with a thickness of 1 to 10 nm. The main part of the coating layer is a cerium-doped lithium-rich manganese-based material, and the interior of the microsphere presents a hollow structure. The molecular formula of the lithium-rich manganese-based positive electrode material is Li 1+a Mn b Ni c Co d Ce e O2, where 0.1≤a≤0.4, 0≤b≤0.8, 0≤c≤0.3, 0≤d≤0.3, 0.005≤e≤0.1, a+b+c+d+e=1.

2. The modified lithium-rich manganese-based cathode material with a hollow microsphere structure according to claim 1, characterized in that: The outer diameter of the microspheres of the lithium-rich manganese-based material is 500-2000 nm, and the particle size of the primary nanoparticles is 30-300 nm.

3. The modified lithium-rich manganese-based cathode material with a hollow microsphere structure according to claim 1, characterized in that: e / (b+c+d+e)=1-3%.

4. The modified lithium-rich manganese-based cathode material with a hollow microsphere structure according to claim 1, characterized in that: e / (b+c+d+e)=3%.

5. A method for preparing the modified lithium-rich manganese-based positive electrode material with a hollow microsphere structure as claimed in claim 1, characterized in that: The preparation method specifically comprises the following steps: (1) Weighing a certain amount of lithium salt, nickel salt, cobalt salt and manganese salt, dissolving them in a solvent, and adding them to a stainless steel dynamic hydrothermal reactor, controlling the molar ratio of each metal element to conform to the ratio of each metal in the modified lithium-rich manganese-based positive electrode material; (2) Weigh a certain amount of oxalic acid and dissolve it in a solvent, then add it dropwise into a stainless steel dynamic hydrothermal reactor, controlling the molar ratio of oxalate to total metal elements in the mixed system to be 0.8 to 1.2; (3) Weighing a certain amount of cerium salt and dissolving it in a solvent, adding it to a stainless steel dynamic hydrothermal kettle, and controlling the molar ratio of cerium element to other metal elements to conform to the ratio of each metal in the modified lithium-rich manganese-based material; (4) setting the speed of the stirrer of the stainless steel dynamic hydrothermal kettle to 80-120 rpm and the heating rate to 1.5-2.5°C / min, heating the mixed solution obtained in step (3) to 160-200°C for constant temperature reaction for 4-6 hours, and then allowing the system to cool naturally; (5) After the system temperature drops to room temperature, the precipitate obtained in step (4) is collected and dried to obtain a precursor; (6) placing the precursor obtained in step (5) in a sintering furnace for staged calcination, wherein the staged calcination includes two steps: low-temperature calcination and high-temperature calcination. The low-temperature calcination is calcined at 400-600°C for 4-6 hours, and the high-temperature calcination is calcined at 700-900°C for 10-15 hours. The calcination is carried out in an air atmosphere at a heating rate of 2°C to 5°C / min, thereby preparing the modified lithium-rich manganese-based positive electrode material with the hollow microsphere structure.

6. The preparation method according to claim 5, wherein: In step (1): The lithium salt is selected from one or both of lithium nitrate and lithium acetate; The nickel salt is selected from one or both of nickel nitrate and nickel acetate; The cobalt salt is selected from one or both of cobalt nitrate and cobalt acetate; The manganese salt is selected from one or both of manganese nitrate and manganese acetate.

7. The preparation method according to claim 5, wherein: The solvents used in steps (1-3) are the same, and the solvent is selected from a mixture of one or more of water, methanol, ethanol, n-propanol, and isopropanol.

8. The preparation method according to claim 5, wherein: The cerium salt used in step (3) is selected from one or both of cerium nitrate and cerium acetate.

9. The preparation method according to claim 5, wherein: The drying conditions in step (5) are: drying at 60-120° C. for more than 12 hours.

10. Use of the modified lithium-rich manganese-based positive electrode material with a hollow microsphere structure as claimed in claim 1 as a positive electrode material for lithium-ion batteries.

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