A modified lithium-rich layered cathode material and its preparation method, and a lithium-ion battery.

Abstract

This invention discloses a method for preparing a modified lithium-rich layered cathode material, comprising the following steps: mixing a dodecyl phosphate compound of a specific carbon chain length with deionized water to obtain a dodecyl phosphate compound solution; adding the lithium-rich layered cathode material to the dodecyl phosphate compound solution, dispersing and stirring to form a suspension; spray-drying the suspension to obtain a composite powder; and heat-treating the composite powder and cooling it to room temperature to obtain the modified lithium-rich layered cathode material. The dodecyl phosphate compound of the specific carbon chain length is an ester compound formed by a straight-chain alkyl group with 12 carbon atoms and a phosphate group. This invention also provides the modified lithium-rich layered cathode material and a lithium-ion battery based on the modified lithium-rich layered cathode material, solving the problem of capacity and voltage decay caused by surface oxygen release and structural phase transition during high-voltage cycling of the lithium-rich layered cathode material.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a modified lithium-rich layered cathode material and its preparation method, and a lithium-ion battery. Background Technology

[0002] Driven by the global energy structure transformation and the strategic goal of "carbon neutrality," lithium-ion batteries, with their excellent energy conversion efficiency (>90%) and long cycle life, have become the core power source for new energy vehicles, smart grid energy storage, and mobile terminal devices. As the core component of a lithium-ion battery system, the electrochemical performance of the cathode material directly determines key indicators such as energy density, voltage platform, and cycle life. However, current mainstream lithium-ion battery cathode materials (such as lithium iron phosphate and low-nickel ternary materials) are approaching their theoretical limits in terms of capacity and other performance aspects, making it difficult to meet the demands of high-energy-density applications. Therefore, developing cathode materials that combine high performance and controllable cost is of great practical significance.

[0003] Lithium-rich layered cathode materials (xLi₂MnO₃·(1-x)LiMO₂, where M is a transition metal such as Ni, Co, Mn, or Al) have become a hot topic in cathode material research due to their high specific capacity, good thermal stability, and low cobalt content dependence. However, during the first charge, these materials involve irreversible activation of the Li₂MnO₃ component, accompanied by redox reactions of lattice oxygen and release of surface oxygen, which in turn triggers severe interfacial side reactions, dissolution of transition metal ions, and an irreversible structural phase transition from the layered phase to the spinel phase. These intrinsic defects lead to core bottlenecks in the practical application of lithium-rich layered cathode materials, such as low initial coulombic efficiency and continuous capacity and voltage decay during long cycles, severely restricting their commercialization. Therefore, developing modification methods that can effectively stabilize the surface and interface structure of lithium-rich layered materials, suppress harmful bulk phase transitions, and are easy to implement on a large scale are currently urgent technical challenges to be solved in this field. Summary of the Invention

[0004] The purpose of this invention is to address the problem of capacity and voltage decay caused by surface oxygen release and structural phase change in lithium-rich layered cathode materials during high-voltage cycling. This invention provides a modified lithium-rich layered cathode material and its preparation method, as well as a lithium-ion battery, by using dodecyl phosphate compounds with specific carbon chain lengths to modify the surface of the lithium-rich layered cathode material.

[0005] Unlike existing technologies that use a wide range of alkyl phosphates in lithium-rich oxide supplementation materials, this invention, for the first time, specifically uses dodecyl phosphate compounds with a particular carbon chain length (specifically, monoester compounds with a long dodecyl chain, possessing optimal balanced performance advantages) for surface modification of lithium-rich layered cathode materials (preferably xLi2MnO3·(1-x)LiMO2), enabling them to serve as positive electrode active materials for lithium-ion batteries. This invention significantly improves high-voltage cycle stability while maintaining a simple and controllable process, suitable for large-scale continuous production.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a modified lithium-rich layered cathode material, comprising the following steps: A solution of dodecyl phosphate compound was prepared by mixing a dodecyl phosphate compound with deionized water; The lithium-rich layered cathode material is added to the solution of the dodecyl phosphate compound, and then dispersed and stirred to form a suspension. The suspension was spray-dried to obtain a composite powder; The composite powder was heat-treated and cooled to room temperature to obtain the modified lithium-rich layered cathode material. The dodecyl phosphate compounds with a specific carbon chain length are ester compounds formed by a straight-chain alkyl group (i.e., dodecyl) with 12 carbon atoms and a phosphate group, including one or more of mono-dodecyl phosphate, sodium lauryl phosphate monoester, and potassium dodecyl phosphate.

[0007] In some possible embodiments, the concentration of the dodecyl phosphate compound solution is 0.5 g / L to 5 g / L; The dodecyl phosphate compound with a specific carbon chain length accounts for 1% to 10% of the mass percentage of the lithium-rich layered cathode material.

[0008] In some possible implementations, the lithium-rich layered cathode material is prepared by one of the following methods: molten salt method, sol-gel method, and co-precipitation method, and its average particle size D50 is 100 nm to 800 nm.

[0009] In some possible implementations, the lithium-rich layered cathode material has a layered crystal structure with the general chemical formula xLi2MnO3·(1-x)LiMO2, where M is one or more of Mn, Ni, Co, and Al, and 0 < x < 1.

[0010] In some possible implementations, the stirring time is set to 1-8 hours, and the dispersion is ultrasonic dispersion, with the ultrasonic dispersion time set to 30-60 minutes.

[0011] In some possible implementations, the spray drying specifically includes: setting the air intake volume to 200-400 m³ / h. 3 / h, feed rate 10-30 ml / min, spray flow rate 500-700 L / h.

[0012] In some possible implementations, the heat treatment is carried out in an atmosphere of air, oxygen, nitrogen, or argon.

[0013] In some possible implementations, the heat treatment specifically includes: setting the heating rate to 1-10 ℃ / min, the calcination temperature to 200-600 ℃, and the holding time to 1-5 h.

[0014] In a second aspect, the present invention provides a modified lithium-rich layered cathode material, prepared by the preparation method described in any one of the first aspects, wherein the modified lithium-rich layered cathode material has a coating layer formed by a dodecyl phosphate compound of a specific carbon chain length on its surface, and when the modified lithium-rich layered cathode material is used as a cathode active material for lithium-ion batteries, the coating layer has the effect of suppressing voltage decay under high-voltage cycling.

[0015] Thirdly, the present invention also provides a lithium-ion battery, comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode comprises the modified lithium-rich layered positive electrode material described in the second aspect.

[0016] It should be noted that the dodecyl phosphate compounds of a specific carbon chain length selected in this invention (ester compounds formed by a straight-chain alkyl group with 12 carbon atoms and a phosphate group, i.e., monoester compounds with a dodecyl chain length) achieve a good balance between solubility and surface activity in water, enabling them to serve as highly efficient dispersants and form a coating layer of moderate thickness with both protective and ion-conducting functions after subsequent heat treatment. In contrast, diester compounds of the same chain length (such as di(dodecyl) phosphates) are unsuitable for the coating process of this invention due to their excessive hydrophobicity and poor solubility.

[0017] Compared with the prior art, the beneficial technical effects of the present invention are as follows: (1) Synergistic advantages of coating agent selection: This invention selects dodecyl phosphate compounds with specific carbon chain lengths as coating precursors. On the one hand, the phosphate groups in the dodecyl phosphate compound molecules have strong electronegativity, which can form coordination anchoring effects with transition metal ions or lattice oxygen on the surface of lithium-rich layered cathode materials, ensuring the firm adhesion and uniform coverage of the coating layer during subsequent processing and electrochemical cycling, effectively suppressing irreversible lattice oxygen release under high voltage, and fundamentally alleviating structural collapse and voltage decay caused by oxygen vacancies. On the other hand, dodecyl phosphate compounds have both hydrophilic phosphate end groups and hydrophobic alkyl chains, which can act as efficient dispersants when preparing aqueous solutions. They can significantly improve the suspension stability of lithium-rich layered cathode material powder in water through electrostatic repulsion and steric hindrance effects, thereby obtaining a uniformly dispersed suspension slurry. This characteristic makes the coating process of the present invention highly compatible with the subsequent spray drying granulation steps, ensuring the uniform and complete distribution of the coating layer on the particle surface and avoiding the problem of uneven coating caused by slurry sedimentation or agglomeration, thus providing convenience for large-scale continuous production.

[0018] (2) Beneficial control of material structure: The present invention uses spray drying to assemble particles, and the resulting modified lithium-rich layered cathode material exhibits a spherical secondary particle morphology with a uniform and moderately open pore structure. Compared with the dense microspheres prepared by the traditional co-precipitation method, this structure effectively increases the specific surface area of ​​the material, which is conducive to the full wetting of the electrolyte and shortens the solid-phase diffusion path of lithium ions, thereby ensuring the full utilization of the material's high specific capacity.

[0019] (3) Comprehensive improvement of electrochemical performance: Through the synergistic effect of the above-mentioned interface stabilization and bulk phase regulation, the modified lithium-rich layered cathode material prepared by the present invention exhibits significantly improved electrochemical performance: the first coulombic efficiency is significantly improved; the capacity retention rate during long cycling is greatly improved; the rate performance is improved; and most importantly, the average discharge voltage decay problem that is common in lithium-rich layered cathode materials is effectively suppressed.

[0020] (4) Simplicity and economy of process: This method adopts a wet mixing-spray drying-heat treatment process route, which is simple, easy to control the operating parameters, and has good compatibility with existing cathode material production lines. Dodecyl phosphate compounds are conventional industrial raw materials, widely available and inexpensive, and do not require special or strict preparation conditions, making them suitable for large-scale industrial production and commercial promotion. Attached Figure Description

[0021] Figure 1 A flowchart illustrating the preparation method of the modified lithium-rich layered cathode material provided by this invention; Figure 2 This is a scanning electron microscope image of the modified lithium-rich layered cathode material prepared in Example 1; Figure 3 Aberration-corrected electron microscope image of the modified lithium-rich layered cathode material prepared in Example 1; Figure 4 A comparison of the cycle life of the modified lithium-rich layered cathode material prepared in Example 1 and the lithium-rich layered cathode material prepared in Comparative Example 1 under 1 C conditions. Figure 5 The graph shows a comparison of the cycle life of the modified lithium-rich layered cathode material prepared in Example 2 and the lithium-rich layered cathode material prepared in Comparative Example 1 under 1 C conditions. Figure 6 The graph shows a comparison of the cycle life of the modified lithium-rich layered cathode material prepared in Example 3 and the lithium-rich layered cathode material prepared in Comparative Example 1 under 1 C conditions. Figure 7 This is a scanning electron microscope image of the lithium-rich layered cathode material in Comparative Example 1. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. At the same time, in the description of the embodiments of this application, the terms "first," "second," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0023] Example 1 This embodiment provides a modified lithium-rich layered cathode material, the preparation method of which includes the following steps: 0.5 g of mono-n-dodecyl phosphate was mixed with 100 mL of deionized water to prepare a mono-n-dodecyl phosphate solution with a concentration of 5 g / L; in other embodiments, sodium lauryl phosphate or potassium dodecyl phosphate can be used instead of mono-n-dodecyl phosphate.

[0024] The lithium-rich layered cathode material was added to a mono-dodecyl phosphate solution, and then ultrasonically dispersed for 50 min and stirred for 1 h to form a suspension. The lithium-rich layered cathode material was prepared by the sol-gel method, and its average particle size D50 was 200 nm. Lithium-rich layered cathode materials have a layered crystal structure and their general chemical formula is 0.5Li₂MnO₃·0.5LiMn 0.333 Ni 0.333 Co0.333 O2.

[0025] The suspension was spray-dried with an air intake of 400 m³. 3 The feed rate was 10 ml / min, the spray flow rate was 500 L / h, and the composite powder was obtained. The composite powder was heat-treated in a nitrogen atmosphere with a heating rate of 5℃ / min, a calcination temperature of 400℃, a holding time of 4h, and then cooled to room temperature to obtain a modified lithium-rich layered cathode material.

[0026] Weigh 0.16 g of modified lithium-rich layered cathode material, add 0.02 g of super P (conductive carbon black) as a conductive agent and 0.02 g of PVDF (polyvinylidene fluoride) as a binder, mix evenly and coat it on aluminum foil to form a cathode sheet. In a vacuum glove box, use a lithium metal sheet as the negative electrode, a polyethylene porous membrane as the separator, and 1 mol / L LiPF6 + 2 wt% LiBOB in EC:DMC:EMC (volume ratio 1:1:1) as the electrolyte to assemble a CR2032 coin cell.

[0027] Figure 2 The image shows a scanning electron microscope (SEM) image of the modified lithium-rich layered cathode material prepared in Example 1. As can be seen from the image, after spray drying and granulation, the material exhibits a regular spherical secondary particle morphology, with nanoscale primary particles tightly packed together to form a dense micron-sized assembly. This structure is beneficial for improving the material's tap density and electrode processing performance.

[0028] Figure 3 The image shows the aberration-corrected electron microscopy (EDS) spectrum of the modified lithium-rich layered cathode material prepared in Example 1. As can be seen from the image, C and P elements are uniformly distributed on the surface of the modified lithium-rich layered cathode material, confirming that the pyrolysis products of mono-dodecyl phosphate were successfully coated on the surface of the material, forming a uniform protective layer.

[0029] Example 2 The only difference between this embodiment and Embodiment 1 is that the lithium-rich layered cathode material is prepared by the molten salt method.

[0030] Example 3 The only difference between this embodiment and Example 1 is that mono-dodecyl phosphate is replaced with an equal mass of hexadecyl phosphate.

[0031] Comparative Example 1 The only difference between this comparative example and Example 1 is that the lithium-rich layered cathode material is not modified. 0.16 g of the lithium-rich layered cathode material prepared by the molten salt method is weighed, and 0.02 g of super P (conductive carbon black) and 0.02 g of PVDF (polyvinylidene fluoride) are added as conductive agents and binders. After being mixed evenly, the mixture is coated on aluminum foil to form a cathode sheet. In a vacuum glove box, a lithium metal sheet is used as the anode, a polyethylene porous membrane is used as the separator, and 1 mol / L LiPF6 + 2 wt% LiBOB is used as the electrolyte in EC:DMC:EMC (volume ratio 1:1:1) to assemble a CR2032 coin cell.

[0032] Figure 7 The image shows a scanning electron microscope (SEM) image of the lithium-rich layered cathode material in Comparative Example 1. As can be seen from the image, the unmodified lithium-rich layered cathode material has low particle uniformity, loose interparticle bonding, and gaps.

[0033] Figure 4 The graph shows a comparison of the cycle life of the coin cell prepared in Example 1 and the coin cell prepared in Comparative Example 1 using lithium-rich layered cathode material under 1C conditions. As can be seen from the graph, the cycle decay of the modified lithium-rich layered cathode material is significantly less than that of the unmodified lithium-rich layered cathode material.

[0034] Figure 5 The graph shows a comparison of the cycle life of the coin cell prepared in Example 2 and the coin cell prepared in Comparative Example 1 under 1C conditions. As can be seen from the graph, the cycle decay of the modified lithium-rich layered cathode material is significantly less than that of the unmodified lithium-rich layered cathode material.

[0035] Figure 6 The graph shows a comparison of the cycle life of the coin cell prepared in Example 3 and the coin cell prepared from the lithium-rich layered cathode material in Example 1 under 1C conditions. As can be seen from the graph, the lithium-rich layered cathode material coated with hexadecyl phosphate in Example 3 has a reduced capacity and poorer cycle performance due to excessive interfacial impedance. Its cycle decay is significantly greater than that of the lithium-rich layered cathode material coated with mono-dodecyl phosphate in Example 1.

[0036] The comparison graph of the cycle life of the coin cells prepared in Comparative Example 1 under 1 C conditions is shown in the figure. Figure 4 As shown, its cycle decay is significantly lower than that of the coin cell prepared from the modified lithium-rich layered cathode material in Example 1.

[0037] The modified lithium-rich layered cathode material of this invention comprises spherical secondary particles formed by spray drying, exhibiting a uniform and moderately open pore structure. Compared to dense microspheres prepared by traditional co-precipitation methods, this structure effectively increases the specific surface area of ​​the material, facilitating thorough electrolyte wetting and shortening the lithium-ion diffusion path, thereby ensuring full utilization of the material's capacity.

[0038] The phosphate group in dodecyl phosphate compounds has strong electronegativity and can form coordination with transition metal ions or lattice oxygen on the material surface. This coordination effect ensures the firm adhesion and uniform coverage of the coating layer on the material surface, preventing detachment during cycling. On the other hand, it effectively anchors lattice oxygen, inhibits irreversible oxygen evolution reaction under high voltage, thereby reducing the generation of oxygen vacancies and alleviating structural collapse and voltage decay caused by oxygen loss from the root.

[0039] Through the synergistic effect of the above-mentioned interface stabilization and bulk phase regulation, the modified lithium-rich layered cathode material exhibits significantly improved electrochemical performance: the initial coulombic efficiency is improved; the capacity retention rate during long-term cycling is greatly improved; the rate performance is improved; and the decay of the average discharge voltage is effectively suppressed.

[0040] At the process implementation level, this method adopts a wet mixing-spray drying-heat treatment process route, which is concise, easy to control operating parameters, and has good compatibility with existing cathode material production lines. In particular, the selected dodecyl phosphate compounds (such as mono-n-dodecyl phosphate) possess both hydrophilic phosphate end groups and hydrophobic alkyl chains in the aqueous phase, which can act as efficient dispersants to significantly improve the suspension stability of lithium-rich layered cathode material powder in the slurry. This creates excellent process synergy with the subsequent spray drying granulation step—the uniform and stable suspension ensures the uniform distribution of the coating agent on the particle surface and the regular assembly of spherical particles. At the same time, dodecyl phosphate compounds are conventional industrial raw materials, widely available and inexpensive, requiring no special or stringent preparation conditions, making them suitable for large-scale industrial production and commercialization.

[0041] Obviously, those skilled in the art can make various modifications and variations to the embodiments of the present invention without departing from the spirit and scope of the invention. Therefore, if these modifications and variations fall within the scope of the claims of the present invention and their equivalents, the present invention also intends to include these modifications and variations.

Claims

1. A method for preparing a modified lithium-rich layered cathode material, characterized in that, Includes the following steps: A solution of dodecyl phosphate compound was prepared by mixing a dodecyl phosphate compound with deionized water; The lithium-rich layered cathode material is added to the solution of the dodecyl phosphate compound, and then dispersed and stirred to form a suspension. The suspension was spray-dried to obtain a composite powder; The composite powder was heat-treated and cooled to room temperature to obtain the modified lithium-rich layered cathode material. The dodecyl phosphate compounds with a specific carbon chain length are ester compounds formed by a straight-chain alkyl group having 12 carbon atoms and a phosphate group, including one or more of mono-dodecyl phosphate, sodium lauryl phosphate, and potassium dodecyl phosphate.

2. The production method according to claim 1, characterized by, The concentration of the dodecyl phosphate compound solution is 0.5 g / L to 5 g / L; The dodecyl phosphate compound with a specific carbon chain length accounts for 1% to 10% of the mass percentage of the lithium-rich layered cathode material.

3. The preparation method according to claim 1, characterized in that, The lithium-rich layered cathode material is prepared by one of the following methods: molten salt method, sol-gel method, and co-precipitation method, and its average particle size D50 is 100 nm to 800 nm.

4. The preparation method according to claim 1, characterized in that, The lithium-rich layered cathode material has a layered crystal structure and its general chemical formula is xLi2MnO3·(1-x)LiMO2, where M is one or more of Mn, Ni, Co, and Al, and 0 < x < 1.

5. The preparation method according to claim 1, characterized in that, The stirring time is set to 1-8 hours, and the dispersion is ultrasonic dispersion, with the ultrasonic dispersion time set to 30-60 minutes.

6. The preparation method according to claim 1, characterized in that, The spray drying specifically comprises setting the air inlet amount to 200-400 m 3 / h, the feeding speed to 10-30 ml / min, and the spray flow rate to 500-700 L / h.

7. The preparation method according to claim 1, characterized in that, The heat treatment is carried out in an atmosphere of air, oxygen, nitrogen, or argon.

8. The preparation method according to claim 1, characterized in that, The heat treatment specifically includes: setting the heating rate to 1-10 ℃ / min, the calcination temperature to 200-600 ℃, and the holding time to 1-5 h.

9. A modified lithium-rich layered cathode material, characterized in that, The modified lithium-rich layered cathode material is prepared according to any one of claims 1-8, and its surface has a coating layer formed by a dodecyl phosphate compound of the specified carbon chain length. When the modified lithium-rich layered cathode material is used as a positive electrode active material for lithium-ion batteries, the coating layer has the effect of suppressing voltage decay under high voltage cycling.

10. A lithium-ion battery, comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that, The cathode comprises the modified lithium-rich layered cathode material as described in claim 9.

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