Lithium-rich manganese-based positive electrode material with fast ion conductor coating and bulk doping and preparation method thereof

Abstract

The application discloses a lithium-rich manganese-based positive electrode material with a fast ion conductor coating layer and body phase doping and a preparation method thereof. 1+ a Mn b M c O2, M is one or more than one of Ni, Co, A1, Cr, Fe, Mg, Ce, and 0

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material technology, specifically relating to a method for synergistic modification of lithium-rich manganese-based cathode materials by surface coating and bulk doping, as well as the high-performance cathode material prepared therefrom and the lithium-ion battery containing the cathode material. Background Technology

[0002] Lithium-ion batteries have gained widespread application and development due to their advantages over traditional lead-acid and nickel-metal hydride batteries, such as high energy density, high output voltage, low self-discharge, no memory effect, and environmental friendliness. The performance of key materials in power and energy storage lithium-ion batteries is the ultimate determining factor in battery performance, and the research on cathode materials has always been a hot topic for scientists. LiCoO2, LiMnO4, LiFePO4, and LiNi are examples of materials that have been widely studied. x Co y Mn 1-x-y Cathode materials such as O2 have been extensively studied. However, lithium-ion battery systems assembled with these cathode materials suffer from drawbacks such as low specific energy density, high cost, and poor safety, making it difficult to meet the energy storage requirements of electric vehicles.

[0003] Lithium-rich manganese-based cathode materials are considered one of the ideal cathode materials for next-generation high-energy-density lithium-ion batteries due to their high reversible specific capacity (>250 mAh / g) and high operating voltage. However, the low initial coulombic efficiency, poor rate performance, and gradual voltage decrease during cycling of lithium-rich manganese-based cathode materials have seriously hindered their large-scale application.

[0004] To develop lithium-rich manganese-based cathode materials with excellent rate performance to meet the rate performance requirements of electric vehicles, researchers have developed various techniques to modify and improve these materials. Various inert substances, such as metal fluorides (AlF3), metal phosphates (AlPO4, Li-Ni-PO4), and metal oxides (Al2O3, ZnO, RuO, etc.), have been used to coat lithium-rich manganese-based cathode materials. Yu Yan et al. from the University of Science and Technology of China developed P-doped Li-based cathode materials using a simple one-step gas-solid reaction with trace amounts of red phosphorus mixed with LRMOs. 1.2 Mn 0.54 Ni 0.13 Co 0.13O2@Spinel@Li3PO4 materials (P-LRMOs). This method achieves synergistic modification of the surface, interface, and bulk phase. Xi'an University of Technology, Li Xifei et al., first proposed a low-temperature vapor-phase method for preparing LiF sub-nanometer layers on the surface of LRMOs. This LiF layer can effectively regulate the electric field distribution on the electrode surface, suppress side reactions between the electrode and electrolyte, and promote the formation of a uniform LiF-rich CEI layer on the LRMOs-F-1 surface. The optimized CEI not only promotes the formation of LiF-rich CEI layers on the electrode surface... + Flux homogenization also improved Li + The improved diffusion efficiency during the electrode insertion / extraction process contributes to the formation of a stable electrode-electrolyte interface. Furthermore, the LiF-rich CEI layer significantly suppresses the decomposition of lithium salts in the electrolyte and reduces autocatalytic side reactions initiated by byproducts. Simultaneously, the structural stability of LRMOs is enhanced by increasing the formation energies of oxygen and manganese vacancies. However, traditional modification methods typically involve coating and doping in steps, resulting in complex and time-consuming processes. Precise control of the distribution of the coating layer and dopant elements is also difficult, increasing production costs and hindering large-scale industrial applications.

[0005] Therefore, developing a simple, efficient, and industrially scalable one-step method to simultaneously achieve surface modification and bulk doping of lithium-rich manganese-based materials is of great significance for promoting their practical application. Summary of the Invention

[0006] The purpose of this invention is to provide a lithium-rich manganese-based cathode material with a fast-ion conductor coating layer and bulk doping, and its preparation method. By sintering a mixture of lithium-rich manganese-based cathode material precursor, lithium salt, and phosphate, the initial coulombic efficiency of the lithium-rich manganese-based cathode material is improved, as well as its cycle stability and rate performance, meeting the requirements of power batteries. The modification process is applicable to all lithium-rich manganese-based cathode materials, is simple and easy to implement, has low manufacturing cost, good reproducibility, and is suitable for large-scale industrial production.

[0007] The objective of this invention is achieved through the following technical solution: On one hand, this invention proposes a lithium-rich manganese-based cathode material with a fast-ion conductor coating layer and bulk doping. The surface of the lithium-rich manganese-based cathode material is coated with a coating layer composed of amorphous Li3PO4, and the bulk phase contains doping with other elements. The structural formula of the lithium-rich manganese-based cathode material is Li... 1+a Mn b M c O2, M is one or more of Ni, Co, Al, Cr, Fe, Mg, and Ce, 0 <a≤0.2,0<b≤1,0<c≤1,a+b+c=1。

[0008] On the other hand, the present invention proposes a method for preparing the above-mentioned lithium-rich manganese-based cathode material having a fast-ion conductor coating layer and bulk doping, comprising at least the following two steps: (1) A lithium-rich manganese-based precursor, a lithium salt, and an appropriate amount of phosphate are thoroughly mixed, wherein: the lithium-rich manganese-based precursor is not limited to one or more of carbonate precursors, hydroxide precursors, sol-gel precursors, and oxide precursors; the phosphate is one or a mixture of several of AlPO4, CaHPO4, MgHPO4.3H2O, (Mg)3(PO4)2, CePO4, LiH2PO4, K2HPO4, Na2HPO4, (NH4)3PO4, (NH4)2HPO4, and NH4H2PO4; the amount of phosphate added is 0.5-10% of the molar number of the lithium-rich manganese-based cathode material precursor; the lithium salt is one or more of lithium carbonate, lithium hydroxide, and lithium acetate; the mixing method is one of ball milling, grinding, jar milling, and magnetic stirring.

[0009] (2) The uniformly mixed sample is first pre-calcined at low temperature under a certain atmosphere, and then sintered at high temperature to obtain a lithium-rich manganese-based cathode material with a fast ion conductor coating layer and a bulk structure; wherein: the low-temperature pre-calcination temperature is 400-600℃, and the low-temperature pre-calcination time is 3-8h; the high-temperature sintering temperature is 700-900℃, and the high-temperature sintering time is 8-20h; the heating rate of the mixed sintering is 1-10℃ / min; the mixed sintering atmosphere is either oxygen or air. The coating layer is composed of amorphous Li3PO4 and bulk doping, thereby giving the lithium-rich manganese-based cathode material a high lithium-ion conductivity.

[0010] The relevant reaction mechanism is as follows: At high temperatures, lithium carbonate decomposes first: Li2CO3→ Li2O + CO2↑ Subsequently, the newly formed, highly reactive Li₂O will undergo a solid-phase reaction with the adjacent aluminum phosphate particles (taking AlPO₄ as an example): AlPO4 + Li2O → Li3PO4 + LiAlO2 (or related lithium aluminum oxides) This reaction is the crucial first step. It directly generates lithium phosphate at the interface between aluminum phosphate and the cathode material. Since the reaction occurs on the particle surface, the generated lithium phosphate coats the surface of the lithium-rich manganese-based material particles in the form of a thin film, forming a Li3PO4 coating layer.

[0011] At high temperatures, the thermal motion of atoms / ions intensifies, providing a driving force for diffusion into the bulk phase.

[0012] Phosphorus doping: The Li3PO4 produced by the reaction or the unreacted AlPO4 will release P. 5+Ions. P 5+ With a high charge and a small ionic radius, it tends to diffuse into the crystal lattice of lithium-rich manganese-based materials. 5+ The most likely replacement is the tetrahedral site in the crystal structure. This doping of high-valence cations introduces cation vacancies or alters the local electronic structure, thereby stabilizing the crystal structure and suppressing phase transitions and oxygen loss during cycling.

[0013] Aluminum doping: Similarly, reaction byproducts LiAlO2 or unreacted AlPO4 will provide Al. 3+ Ions. Al 3+ It is a classic doping element that tends to replace Ni in transition metal layers. 2+ Co 3+ or Mn 4+ Site.

[0014] Since the bond energy of Al-O bonds (~512 kJ / mol) is generally higher than that of Mn-O, Co-O, or Ni-O bonds, Al doping can significantly enhance lattice stability and suppress structural collapse during cycling. 3+ It is electrochemically inert; it does not participate in redox reactions, but it can inhibit the migration of transition metal ions (especially Ni). 2+ This reduces irreversible capacity loss. Other doping elements have similar effects.

[0015] The advantages of this invention are: by using lithium-rich manganese-based cathode precursor materials, lithium salts, and phosphates in a mixed sintering process, the initial coulombic efficiency of the lithium-rich manganese-based cathode material is improved through surface phosphate modification and bulk doping. Furthermore, its cycle stability and rate performance are also enhanced, meeting the requirements of power batteries. The modification process is applicable to all lithium-rich manganese-based cathode materials, is simple and easy to implement, has low manufacturing costs, good reproducibility, and is suitable for large-scale industrial production. This invention achieves doping of other elements such as P and Al simultaneously with coating, realizing a one-step coating and doping process. Moreover, by using a direct mixed sintering method with lithium-rich manganese-based cathode precursor materials, lithium salts, and phosphates, the original additional process steps requiring prior preparation of the cathode material are eliminated, significantly reducing preparation costs and simplifying the process. Attached Figure Description

[0016] Figure 1 The XRD patterns are of the lithium-rich manganese-based cathode material before modification (comparative example) and the lithium-rich manganese-based cathode material after phosphate modification (Example 2). Figure 2 SEM image of lithium-rich manganese-based cathode material before phosphate modification (comparative example); Figure 3 SEM image of the lithium-rich manganese-based cathode material modified with phosphate (Example 2); Figure 4 TEM image of the unmodified (Comparative Example 1) lithium-rich manganese-based cathode material; Figure 5 TEM image of lithium-rich manganese-based cathode material modified with phosphate (Example 2) Figure 6 The first charge-discharge curves are shown for the lithium-rich manganese-based cathode material before phosphate modification (comparative example) and the lithium-rich manganese-based cathode material after phosphate modification (Examples 2 and 3). Figure 7 Rate performance curves of lithium-rich manganese-based cathode material before phosphate modification (comparative example) and lithium-rich manganese-based cathode material after phosphate modification (Examples 2 and 3); Figure 8 Cycle stability of lithium-rich manganese-based cathode material before phosphate modification (comparative example) and lithium-rich manganese-based cathode material after phosphate modification (Examples 2 and 3). Detailed Implementation

[0017] The present invention will be further illustrated below with examples and comparative examples. These examples are for illustrative purposes only, and the present invention is not limited to the following examples. Any modifications or equivalent substitutions to the technical solutions of the present invention that do not depart from the spirit and scope of the technical solutions of the present invention should be covered within the protection scope of the present invention.

[0018] Comparative Example 1 1. Add 5g of lithium-rich manganese-based cathode material precursor Ni 0.166 Co 0.166 Mn 0.667 CO3 and 2.305g of lithium carbonate were thoroughly mixed by ball milling; 2. The material mixed uniformly in step 1 was heated in air at a heating rate of 5℃ / min, pre-sintered at a low temperature for 5 hours, and then sintered at a high temperature of 850℃ for 12 hours. After natural cooling, unmodified lithium-rich manganese-based material Li was obtained. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2.

[0019] X-ray diffraction (XRD) analysis showed that the product was a lithium-rich manganese-based cathode material with high material quality and no impurity phase formation.

[0020] Example 1

[0021] 1. Add 5g of lithium-rich manganese-based cathode material precursor Ni 0.166 Co 0.166 Mn 0.667 CO3, 105 mg AlPO4 and 2.305 g lithium carbonate were thoroughly mixed by ball milling; 2. The material mixed uniformly in step 1 is heated in air at a heating rate of 5℃ / min, pre-sintered at a low temperature for 5 hours, and then sintered at a high temperature of 850℃ for 12 hours, followed by natural cooling to obtain the modified lithium-rich manganese-based material Li. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2.

[0022] Example 2

[0023] 1. Add 5g of lithium-rich manganese-based cathode material precursor Ni 0.166 Co 0.166 Mn 0.667 CO3, 210 mg AlPO4 and 2.305 g lithium carbonate were thoroughly mixed by ball milling; 2. The material mixed uniformly in step 1 is heated in air at a heating rate of 5℃ / min, pre-sintered at a low temperature for 5 hours, and then sintered at a high temperature of 850℃ for 12 hours, followed by natural cooling to obtain the modified lithium-rich manganese-based material Li. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2.

[0024] It should be noted that the lithium-rich manganese-based cathode material precursor Ni used in the above embodiments and comparative examples 0.166 Co 0.166 Mn 0.667 CO3 can be obtained through synthesis or commercial purchase. The synthesis process is as follows: Nickel sulfate, cobalt sulfate, and manganese sulfate are added to an aqueous solution in a molar ratio of 1:1:4 to prepare a solution with a concentration of 2 mol / L. -1 A metal salt solution was prepared. Then, a sodium carbonate solution was prepared as a precipitant in the same molar ratio, and an appropriate amount of ammonia was added as a complexing agent. The metal salt solution and the precipitant solution were added to a continuous stirred tank reactor at a controlled flow rate. The pH was maintained at a constant value by controlling the feed rate of the precipitant solution. The reaction temperature was 55°C, and the stirring speed was 1000 rpm. After a certain reaction time, the precursor material was obtained.

[0025] Results Analysis

[0026] The lithium-rich manganese-based cathode material prepared in the laboratory exhibits a spherical morphology, with intact particles and no obvious breakage or agglomeration. The particle size is approximately 10-20 μm (see...). Figure 2 As shown); the modified lithium-rich manganese-based material also retains the spherical morphology of the lithium-rich manganese-based material (see...). Figure 3 (As shown).

[0027] like Figure 1As shown, X-ray diffraction (XRD) analysis indicates that the product is a lithium-rich manganese-based cathode material with high material density and no impurity phase formation. The shift of the (003) peak to the left indicates that the lattice spacing has increased after phosphate modification and bulk doping, which is beneficial to the diffusion of lithium ions.

[0028] TEM analysis revealed that the particle surface was coated with an amorphous layer of lithium phosphate. This coating prevents direct contact between the interface and the electrolyte, which helps reduce side reactions at the interface and improves the rate performance of the lithium-rich manganese-based cathode material (see...). Figure 5 The area outside the yellow line is the coating of lithium phosphate.

[0029] The phosphate-modified lithium-rich manganese-based cathode material exhibits an initial coulombic efficiency of 87.0% at 0.1C (see...). Figure 6 (As shown) For lithium-rich manganese-based cathode materials, the irreversible capacity decreased from 79 mAh / g to 40.3 mAh / g, while the coulombic efficiency increased from 70.7% to 87.0% (see...). Figure 6 This indicates that surface phosphate modification and bulk doping reduced the initial irreversible capacity of lithium-rich manganese-based cathode materials and improved the initial coulombic efficiency.

[0030] At current densities of 0.1C-5C, the discharge specific capacity of the surface-phosphate-modified lithium-rich manganese-based cathode material is significantly higher than that of the original material, indicating that surface phosphate modification and bulk doping also improve the rate performance of the lithium-rich manganese-based cathode material (see...). Figure 7 ).

[0031] The initial discharge capacity at 1C current density was 236 mAh / g, and the discharge capacity after 500 cycles was 192 mAh / g, with a retention rate of 82.6% (see...). Figure 8 The cycling stability of the phosphate-modified and bulk-doped lithium-rich manganese-based cathode material is significantly better than that of the original lithium-rich manganese-based cathode material, indicating that surface phosphate modification and bulk doping significantly improve the cycling stability of the lithium-rich manganese-based cathode material.

[0032] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a lithium-rich manganese-based cathode material with a fast-ion conductor coating layer and bulk doping, characterized in that, The surface of the lithium-rich manganese-based cathode material is coated with a coating layer composed of amorphous Li3PO4, and the bulk phase has element doping. The structural formula of the lithium-rich manganese-based cathode material is Li 1+a Mn b M c O2, where M is one or more of Ni, Co, Al, Cr, Fe, Mg, Ce, 0 < a ≤ 0.2, 0 < b ≤ 1, 0 < c ≤ 1, and a + b + c = 1. The method steps are as follows: (1) Thoroughly mix the lithium-rich manganese-based cathode material precursor, lithium salt, and an appropriate amount of phosphate, and control the amount of phosphate added to be 0.5-10% of the molar number of the lithium-rich manganese-based cathode material precursor; (2) The uniformly mixed sample is first pre-calcined at low temperature under a certain atmosphere, and then sintered at high temperature to obtain a lithium-rich manganese-based cathode material with a fast ion conductor coating layer and a bulk doped structure, wherein: the low temperature pre-calcination temperature is 400-600℃ and the low temperature pre-calcination time is 3-8h; the high temperature sintering temperature is 700-900℃ and the high temperature sintering time is 8-20h. The phosphate is AlPO4; the elements in the elemental doping are P and Al.

2. The method for preparing lithium-rich manganese-based cathode material with a fast-ion conductor coating layer and bulk doping according to claim 1, characterized in that, The lithium salt is one or a mixture of several of LiCO3, LiOH, and lithium acetate.

3. The method for preparing lithium-rich manganese-based cathode material with a fast-ion conductor coating layer and bulk doping according to claim 1, characterized in that, The lithium-rich manganese-based cathode material precursor and phosphate are mixed by one of the following methods: ball milling, jar milling, grinding, and magnetic stirring.

4. The method for preparing lithium-rich manganese-based cathode material with a fast-ion conductor coating layer and bulk doping according to claim 1, characterized in that, The sintering atmosphere is either oxygen or air.

5. The method for preparing lithium-rich manganese-based cathode material with a fast-ion conductor coating layer and bulk doping according to claim 1, characterized in that, The heating rate during the sintering process is 1-10℃ / min.

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