Preparation and application of lithium phosphate and lanthanum phosphate mixed coated lithium-rich manganese-based layered positive electrode material
By constructing a mixed coating layer of lithium phosphate and lanthanum phosphate on the surface of a lithium-rich manganese-based substrate cathode material, the problems of low initial coulombic efficiency and structural instability during cycling are solved, achieving efficient lithium-ion transport and interface stability, making it suitable for lithium-ion batteries.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- BEIJING INST OF TECH
- Filing Date
- 2026-04-07
- Publication Date
- 2026-06-09
AI Technical Summary
The lithium-rich manganese-based substrate cathode material exhibits low initial coulombic efficiency during the first charge, structural instability during long-term cycling, severe electrolyte side reactions under high voltage, and dissolution of transition metals, all of which affect the performance of lithium-ion batteries.
A method of mixed coating of lithium phosphate and lanthanum phosphate was adopted. The coating layer of lithium phosphate as fast ion conductor and lanthanum phosphate as inert polyanion was constructed on the surface of lithium-rich manganese-based cathode material by evaporation and drying of ethanol-water mixed solvent combined with low temperature sintering, forming a uniform composite coating layer.
It improves the lithium-ion migration rate, suppresses interfacial side reactions between the electrolyte and the cathode material, enhances the cycle stability and rate performance of the material, reduces production energy consumption, and is suitable for large-scale industrial production.
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Abstract
Description
Technical Field
[0001] This invention relates to the preparation and application of a lithium-rich manganese-based substrate cathode material coated with a mixture of lithium phosphate and lanthanum phosphate, belonging to the field of lithium-ion battery technology. Background Technology
[0002] Since 2015, hybrid electric vehicles and pure electric vehicles have experienced rapid development. Lithium-ion batteries, as the core component of electric vehicle energy storage systems, require high energy density and long cycle life. Layered cathode materials, with their high specific capacity, have become one of the key materials for improving the driving range of electric vehicles. Among them, lithium-rich manganese-based layered cathode materials (xLi2MnO3•(1-x)LiMO2, M=Ni, Co, Mn, etc.) are considered the most promising cathode material system for next-generation high-energy-density lithium-ion batteries due to their ultra-high specific capacity exceeding 250 mAh / g, and are expected to further alleviate users' range anxiety.
[0003] However, lithium-rich manganese-based cathode materials face numerous challenges in practical applications. During the initial charge, the irreversible release of lattice oxygen from the material surface leads to a low initial coulombic efficiency (typically below 85%). During long-term cycling, the material structure gradually transforms from layered to spinel and even rock salt phases, accompanied by a continuous decay of operating voltage and a rapid decrease in capacity. Furthermore, under high-voltage (>4.5 V) operating conditions, interfacial side reactions between the electrode material and the electrolyte intensify, causing transition metal ions (Mn, Ni, etc.) to dissolve and migrate to the negative electrode for deposition, further deteriorating the battery's cycle stability. These problems severely restrict the commercial application of lithium-rich manganese-based cathode materials.
[0004] To improve the electrochemical performance of lithium-rich manganese-based cathode materials, researchers have conducted extensive work on both bulk doping and surface coating. Bulk doping can stabilize the crystal structure to a certain extent, but it is difficult to effectively suppress surface side reactions. Surface coating, by constructing a protective layer on the surface of the cathode material, can physically isolate the direct contact between the electrolyte and the active material, and is currently the main strategy for improving interfacial stability. However, existing coating technologies still have many shortcomings: for example, common single coating materials (such as Al2O3, AlF3, etc.) are mostly electrochemically inert substances. Although they can suppress side reactions, they will hinder the interfacial transport of lithium ions, leading to a decrease in rate performance. In addition, traditional solid-phase physical coating methods are difficult to achieve a uniform distribution of the coating layer, while liquid-phase in-situ synthesis processes often involve complex reaction conditions or high-temperature heat treatment, which can easily damage the layered structure of the lithium-rich manganese matrix, exacerbating oxygen deficiency and lithium-nickel mixing.
[0005] Polyanionic cathode material systems (such as phosphates and pyrophosphates) exhibit unique advantages in improving the cycle life of electrode materials due to their excellent structural and thermal stability. Applying polyanionic compounds as coating layers to lithium-rich manganese-based cathode materials promises to achieve a combination of high capacity and high stability. Lithium phosphate (Li3PO4), as a fast ion conductor, provides an efficient lithium-ion transport channel and reduces the interfacial migration barrier; lanthanum phosphate (LaPO4), as an inert polyanionic compound, possesses excellent chemical stability and electrochemical inertness, effectively isolating it from electrolyte corrosion. The synergistic application of both to the surface coating of lithium-rich manganese-based cathode materials provides both enhanced ion conduction and interfacial stability protection, simultaneously improving the material's rate performance and cycle stability.
[0006] Existing patents mainly use single phosphate (such as lithium iron phosphate, lithium cobalt phosphate, etc.) coating layers to improve the interface stability of cathode materials. However, due to the poor uniformity and complex process of existing coating methods, most of them cannot achieve the ideal effect and are difficult to mass-produce. Summary of the Invention
[0007] In view of this, the purpose of the present invention is to provide a preparation and application of a lithium-rich manganese-based cathode material coated with a mixture of lithium phosphate and lanthanum phosphate.
[0008] To achieve the above objectives, the technical solution of the present invention is as follows: A lithium-rich manganese-based substrate cathode material co-coated with lithium phosphate and lanthanum phosphate is prepared by the following method, the steps of which are as follows: (1) Add lanthanum nitrate and ammonium phosphate to an appropriate amount of deionized water in proportion, and obtain a suspension containing a uniform white precipitate by continuous stirring. (2) After filtering the suspension, wash and filter it 3 to 5 times with deionized water. After testing with pH paper, pure lanthanum phosphate powder is obtained. (3) Add lithium phosphate and lithium-rich manganese-based cathode powder to an appropriate amount of deionized water and ethanol mixed solution in proportion. After ultrasonic dispersion, stir to obtain a uniform mixed solution П. Evaporate the mixed solution П by magnetic stirring and then transfer it to an oven to dry to obtain powder. (4) The lanthanum phosphate powder obtained in (2) and the mixed powder of lithium phosphate and lithium-rich manganese cathode obtained in (3) are ground and mixed evenly in a mortar and then transferred to a crucible. The crucible is then placed in a heating device for high-temperature treatment. The temperature is raised to 300℃~450℃ and calcined for 3h~15h. The calcination atmosphere is nitrogen or argon. After calcination, the temperature is lowered and cooled. A lithium-rich manganese-based cathode material with mixed coating of lithium phosphate and lanthanum phosphate is obtained in the crucible.
[0009] Among them, lithium phosphate and lanthanum phosphate coatings account for 2% to 6% of the total mass of the cathode material; Preferably, in step (1), the ratio is La:P=1:(1.05~1.2) (phosphorus excess 5%-20%).
[0010] Preferably, in step (3), the ultrasonic intensity during ultrasonic dispersion is 100~200 KHZ and the ultrasonic time is 0.5h~2h.
[0011] Preferably, in step (3), the lithium-rich manganese-based substrate cathode powder is xLi2MnO3•(1-x)LiMO2, where M is Mn, Ni, or Co, and O is 0. <x<1。
[0012] Preferably, in step (3), the temperature of the magnetic stirring is 80 ℃, the speed is 500~1500 rpm, and the stirring time is 0.25h~1h; the drying temperature of the oven is 100~120 ℃, and the drying time is 10~15h.
[0013] Preferably, in step (4), the heating device used is a tubular furnace, and an inert gas is introduced during the calcination process. The inert gas is nitrogen or argon, and the gas flow rate is 50cfm~300cfm.
[0014] Preferably, the particle diameter of the lithium-rich manganese-based substrate cathode material coated with a mixture of lithium phosphate and lanthanum phosphate is 2 to 15 μm, and the thickness of the mixed coating layer of lithium phosphate and lanthanum phosphate is 5 to 100 nm, more preferably 10 to 20 nm.
[0015] A lithium-ion battery, wherein the positive electrode material of the battery is a lithium-rich manganese-based substrate positive electrode material coated with a mixture of lithium phosphate and lanthanum phosphate as described in this invention. Beneficial effects
[0016] This invention provides a lithium-rich manganese-based cathode material with a lithium phosphate-lanthanum phosphate composite coating. The method employs an ethanol-water mixed solvent evaporation-drying combined with low-temperature sintering to uniformly construct a composite coating layer composed of ionicly conductive lithium phosphate and inert, stable lanthanum phosphate on the surface of the lithium-rich manganese-based cathode material. Lithium phosphate, as a fast-ion conductor coating layer, significantly improves the interfacial lithium-ion migration rate without affecting the electrochemical activity of the lithium-rich manganese matrix. Lanthanum phosphate, as an inert polyanionic coating layer, effectively suppresses interfacial side reactions between the electrolyte and the cathode material under high voltage due to its excellent chemical stability and structural rigidity. Compared to conventional pure water coating methods, the ethanol-water mixed solvent evaporation-drying process used in this invention effectively avoids agglomeration and cracking of the coating layer during the drying process by controlling the solvent polarity and surface tension, achieving uniform nucleation and conformal growth of the coating components on the surface of the lithium-rich manganese-based particles. Compared to traditional high-temperature solid-state coating processes, low-temperature sintering significantly reduces the damage to the lithium-rich manganese-based substrate structure caused by inert atmosphere calcination, reduces lattice oxygen deficiency and lithium-nickel mixing, and shortens heat treatment time, thus reducing production energy consumption. The resulting lithium phosphate-lanthanum phosphate composite coating is a mosaic coating. In this hybrid coating configuration, the lithium phosphate region acts as a fast ion conductor, providing an efficient cross-interface transport channel for lithium ions and ensuring the material's rate performance. The lanthanum phosphate region, with its excellent chemical inertness and structural stability, acts as a physical barrier, effectively suppressing interfacial side reactions between the electrolyte and the active material under high voltage. The functional complementarity and spatial synergistic distribution of lithium phosphate and lanthanum phosphate together achieve a comprehensive modification effect of "no decrease in ion transport and effective suppression of side reactions"—effectively solving key technical problems such as low initial coulombic efficiency, severe voltage decay during cycling, and transition metal dissolution in lithium-rich manganese-based cathode materials, meeting people's pursuit of comprehensive performance in high-energy-density lithium-ion battery cathode materials.
[0017] This invention provides a lithium-rich manganese-based cathode material with lithium phosphate-lanthanum phosphate composite coating. The composite coating layer is grown in situ on the surface of the lithium-rich manganese-based cathode material by evaporation and drying of ethanol-water mixed solvent combined with low-temperature sintering. The method is simple, controllable, and low-cost. The prepared material has a uniform and dense coating on the surface. The thickness and ratio of the coating layer can be flexibly adjusted, making it suitable for large-scale industrial production. Attached Figure Description
[0018] Figure 1 The image shows the energy dispersive spectroscopy (EDS) spectrum of the lithium-rich manganese-based cathode material coated with lithium phosphate-lanthanum phosphate composite prepared in Example 1.
[0019] Figure 2 The energy dispersive spectroscopy (EDS) spectrum of the lithium-rich manganese-based cathode material coated with lithium phosphate-lanthanum phosphate composite prepared in Example 2 is shown.
[0020] Figure 3The image shows the energy dispersive spectroscopy (EDS) spectrum of the lithium-rich manganese-based cathode material coated with lithium phosphate-lanthanum phosphate composite prepared in Example 3.
[0021] Figure 4 The image shows the first-cycle coulombic efficiency of batteries assembled from lithium-rich manganese-based cathode materials coated with lithium phosphate-lanthanum phosphate composites prepared in Examples 1-3. Detailed Implementation
[0022] The present invention will be further described in detail below with reference to specific embodiments. To better clarify and understand the purpose, process scheme, and advantages of the present invention, the technical solution and implementation methods of the present invention will be further clearly, completely, and in detail described below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the embodiments described in this invention are implemented under the premise of the technical solution of the present invention, providing detailed implementation methods and specific operating processes, but are only some embodiments of the present invention, not all embodiments. The specific implementation methods described are limited to illustrating and explaining the present invention and do not limit the present invention. Based on the embodiments of the present invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0023] Unless otherwise specified, the experimental methods and conditions used in the embodiments of this invention are conventional methods and conditions. The materials, reagents, and instruments used in the embodiments, unless otherwise specified, can be obtained commercially or prepared by conventional methods. The reaction conditions described in the invention can all achieve the reactions and obtain the desired products. Due to space limitations, some embodiments are listed below to further illustrate the advantages of the technical solution of this invention.
[0024] In the following embodiments or comparative examples: Assembly of button batteries: At room temperature, the working electrode is first prepared by mixing the materials prepared in the examples or comparative examples with binders and conductive agents in a ratio of 8:1:1 to prepare a uniform slurry; then, the obtained slurry is uniformly coated onto aluminum foil with a scraper and dried under vacuum at 100 °C for 12 h to obtain the working electrode; finally, the aluminum foil coated with the sample is pressed into small discs with a diameter of 1.1 cm using a punching machine as the positive electrode, lithium foil as the negative electrode material, and 1.0 M LiPF6 carbonate electrolyte to prepare the button battery.
[0025] The Blue Electric system is used to detect electrochemical performance, with a test voltage range of 2.5-4.8 V, a test temperature of 30℃, and a test current density of 1C (1C=250 mA / g).
[0026] Example 1 Take 18.5 mg (0.0428 mmol) of La(NO3). 3• 6.69 mg (0.0449 mmol) of (NH4)3PO4 was dissolved in 20 ml of deionized water and stirred continuously to obtain a homogeneous suspension. The suspension was filtered and then washed 3-5 times with deionized water. After pH testing, pure lanthanum phosphate powder was obtained. 10 mg of Li3PO4 and 1000 mg of lithium-rich manganese-based cathode material were added to a 1:1 ethanol-water mixture and stirred at 1000 rpm and 80 °C for 1 h to obtain a homogeneous, moist mixed powder. The resulting moist mixed powder was transferred to an oven and vacuum dried at 100 °C for 12 h to obtain a dry powder. The obtained powder was then ground with lanthanum phosphate in a mortar for 40 min and mixed. The mixture was then transferred to a crucible and heated at 400 °C for 12 h under an argon atmosphere to obtain LaPO4@Li3PO4@Li 1.2 Ni 0.2 Mn 0.6 In the O2 composite sample, the mixed coating layer accounts for approximately 2.0% of the total mass of the composite cathode material.
[0027] The energy spectrum of the composite layered cathode material is as follows: Figure 1 As shown, the results indicate that Li, La, and P elements are uniformly distributed on the surface of the composite material, indicating that the lithium-rich manganese-based material is uniformly coated with a lithium phosphate-lanthanum phosphate composite coating layer.
[0028] The first-cycle coulombic efficiency results of the assembled battery are as follows: Figure 2 As shown in the figure, the specific capacity is 79.17%. It can be seen from the figure that Example 1 has a voltage plateau similar to that of the lithium-rich cathode during the first charge, but exhibits a high discharge specific capacity of 249.71 mAh / g.
[0029] The cycle performance of the assembled battery is shown in Table 1. After 200 cycles at 1C, the average coulombic efficiency is 96.65%.
[0030] Example 2 Take 18.5 mg (0.0428 mmol) of La(NO3). 3•6.69 mg (0.0449 mmol) of (NH4)3PO4 was dissolved in 20 ml of deionized water and stirred continuously to obtain a homogeneous suspension. The suspension was filtered and then washed 3-5 times with deionized water. After pH testing, pure lanthanum phosphate powder was obtained. 20 mg of Li3PO4 and 1000 mg of lithium-rich manganese-based cathode material were added to a 1:1 ethanol-water mixture. The mixture was stirred at 1000 rpm and 80 °C for 1 h with a high-speed magnetic stirrer to obtain a homogeneous, moistened powder. The resulting moistened powder was transferred to an oven and vacuum dried at 100 °C for 12 h to obtain a dry powder. The obtained powder was then ground with lanthanum phosphate in a mortar for 40 min, mixed, and transferred to a crucible. The mixture was then heated at 400 °C for 12 h under an argon atmosphere to obtain LaPO4@Li3PO4@Li 1.2 Ni 0.2 Mn 0.6 In the O2 composite sample, the mixed coating layer accounts for approximately 2.9% of the total mass of the composite cathode material.
[0031] The energy spectrum of the composite layered cathode material is as follows: Figure 1 As shown, the results indicate that La and P elements are uniformly distributed on the surface of the composite material, indicating that the lithium-rich manganese-based material is uniformly coated with a lithium phosphate-lanthanum phosphate composite coating layer.
[0032] The first-cycle coulombic efficiency results of the assembled battery are as follows: Figure 2 As shown in the figure, the specific capacity is 86.08%. It can be seen from the figure that Example 2 has a voltage plateau similar to that of the lithium-rich cathode during the first charge, but exhibits a high discharge specific capacity of 276.29 mAh / g.
[0033] The cycle performance of the assembled battery is shown in Table 1. After 200 cycles at 1C, the average coulombic efficiency is 98.10%. Example 3
[0034] Take 18.5 mg (0.0428 mmol) of La(NO3). 3•6.69 mg (0.0449 mmol) of (NH4)3PO4 was dissolved in 20 ml of deionized water and stirred continuously to obtain a homogeneous suspension. The suspension was filtered and then washed 3-5 times with deionized water. After pH testing, pure lanthanum phosphate powder was obtained. 30 mg of Li3PO4 and 1000 mg of lithium-rich manganese-based cathode material were added to a 1:1 ethanol-water mixture. The mixture was stirred at 1000 rpm and 80 °C for 1 h with a high-speed magnetic stirrer to obtain a homogeneous, moistened powder. The resulting moistened powder was transferred to an oven and vacuum dried at 100 °C for 12 h to obtain a dry powder. The obtained powder was then ground with lanthanum phosphate in a mortar for 40 min, mixed, and transferred to a crucible. The mixture was then heated at 400 °C for 12 h under an argon atmosphere to obtain LaPO4@Li3PO4@Li 1.2 Ni 0.2 Mn 0.6 In the O2 composite sample, the mixed coating layer accounts for approximately 3.9% of the total mass of the composite cathode material.
[0035] The energy spectrum of the composite layered cathode material is as follows: Figure 1 As shown, the results indicate that La and P elements are uniformly distributed on the surface of the composite material, indicating that the lithium-rich manganese-based material is uniformly coated with a lithium phosphate-lanthanum phosphate composite coating layer.
[0036] The first-cycle coulombic efficiency results of the assembled battery are as follows: Figure 2 As shown in the figure, the voltage plateau of Example 3 during the first charge is similar to that of the lithium-rich cathode, but it exhibits a high discharge specific capacity of 265.42 mAh / g.
[0037] The cycle performance of the assembled battery is shown in Table 1. After 200 cycles at 1C, the average coulombic efficiency is 97.44%.
[0038] Comparative Example 1 Take LiNi 0.2 Mn 0.6 O2 cathode material was used as Comparative Example 1 to directly prepare electrode sheets for battery assembly. The cycle performance of the resulting battery is shown in Table 1. After 200 cycles at 1C, the average coulombic efficiency was 93.53%.
[0039] Comparative Example 2 Take LiNi 0.2 Mn 0.6 The O2 cathode material was heated at 400 °C for 12 h in an argon atmosphere as Comparative Example 2 to prepare an electrode sheet, which was then used for battery assembly. The cycle performance of the resulting battery is shown in Table 1. After 200 cycles at 1C, the average coulombic efficiency was 92.05%.
[0040] sample Coating amount (%) Average Coulomb efficiency (%) Example 1 2.0 96.65 Example 2 2.9 98.10 Example 3 3.9 97.44 Comparative Example 1 0 93.53 Comparative Example 2 0 92.05 Table 1. Performance comparison of different embodiments after 200 cycles at a current density of 1C.
Claims
1. A lithium-rich manganese layered cathode material co-coated with a mixture of lithium phosphate and lanthanum phosphate, characterized in that: The material is prepared by the following method, the steps of which are as follows: (1) Add lanthanum nitrate and ammonium phosphate to an appropriate amount of deionized water in proportion, and obtain a suspension containing a uniform white precipitate by continuous stirring. (2) After filtering the suspension, wash and filter it 3 to 5 times with deionized water. After testing with pH paper, pure lanthanum phosphate powder is obtained. (3) Add lithium phosphate and lithium-rich manganese cathode powder to an appropriate amount of deionized water and ethanol mixed solution in proportion. After ultrasonic dispersion, stir to obtain a uniform mixed solution П. Evaporate the mixed solution П by magnetic stirring and then transfer it to an oven to dry to obtain powder. (4) The lanthanum phosphate powder obtained in (2) and the mixed powder of lithium phosphate and lithium-rich manganese cathode obtained in (3) are ground and mixed evenly in a mortar and then transferred to a crucible. The crucible is then placed in a heating device for high-temperature treatment. The temperature is raised to 300℃~450℃ and calcined for 3h~15h. The calcination atmosphere is nitrogen or argon. After calcination, the temperature is lowered and cooled. A lithium-rich manganese layered cathode material with mixed coating of lithium phosphate and lanthanum phosphate is obtained in the crucible. The lithium phosphate and lanthanum phosphate coatings account for 2% to 6% of the total mass of the cathode material; the lithium phosphate and lanthanum phosphate are uniform AR-grade powders; the lithium-rich manganese cathode powder is xLi₂MnO₃•(1-x)LiMO₂, where M is Mn, Ni, or Co, and O₂ is 0. <x<1。 2. The lithium-rich manganese layered cathode material with lithium phosphate and lanthanum phosphate mixed coating as described in claim 1, characterized in that: In step (1), the ratio is La:P=1:(1.05~1.2) (phosphorus excess 5%-20%).
3. The lithium-rich manganese layered cathode material with lithium phosphate and lanthanum phosphate mixed coating as described in claim 1, characterized in that: In step (3), the ultrasonic intensity is 100~200 KHZ and the ultrasonic time is 0.5h~2h during ultrasonic dispersion.
4. The lithium-rich manganese layered cathode material with lithium phosphate and lanthanum phosphate mixed coating as described in claim 1, characterized in that: In step (3), the temperature of the magnetic stirring is 80℃, the speed is 500~1500 rpm, and the stirring time is 0.5h~1.5h; the drying temperature of the oven is 100~120℃, and the drying time is 10~15h.
5. The lithium-rich manganese layered cathode material with lithium phosphate and lanthanum phosphate mixed coating as described in claim 1, characterized in that: In step (4), the heating device used is a tubular furnace, and nitrogen or argon is introduced during the calcination process, with a gas flow rate of 50cfm ~ 300cfm.
6. The lithium-rich manganese layered cathode material with a mixture of lithium phosphate and lanthanum phosphate as described in claim 1, characterized in that: The lithium-rich manganese-based substrate cathode material with lithium phosphate and lanthanum phosphate mixed coating has a particle diameter of 2-15 μm and a thickness of 5-100 nm, more preferably 10-20 nm.
7. A lithium-ion battery, characterized in that: The positive electrode material of the battery is a lithium-rich manganese layered positive electrode material coated with a mixture of lithium phosphate and lanthanum phosphate as described in any one of claims 1 to 6.