A nano cerium oxide coated cerium doped lithium-rich manganese-based positive electrode material and a preparation method thereof

Abstract

The application provides a nano cerium oxide coated cerium doped lithium-rich manganese-based positive electrode material, which comprises a lithium-rich manganese-based positive electrode material and nano cerium oxide coated on the surface of the lithium-rich manganese-based positive electrode material, the chemical formula of the lithium-rich manganese-based positive electrode material is xLi2MnO3·(1-x)LiTMO2, wherein TM is at least one element in Ni, Co and Mn, 0.2<=x<=0.8, and the lithium-rich manganese-based positive electrode material is doped with cerium elements. The application also provides a preparation method of the nano cerium oxide coated cerium doped lithium-rich manganese-based positive electrode material, and a precursor preparation method used in the method can use sodium carbonate as a precipitator, or can use ammonium bicarbonate as a precipitator, and then a one-step method is used to realize the effects of nano cerium oxide coating and surface cerium doping. Through the coating of the surface nano cerium oxide, oxygen vacancies are constructed on the surface of the lithium-rich manganese-based positive electrode material, and the release of irreversible oxygen on the surface of the material can be effectively inhibited.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material technology, and particularly relates to a lithium-rich manganese-based lithium-ion battery cathode material and its preparation method. Background Technology

[0002] As a new generation of green energy storage equipment, lithium-ion batteries have advantages such as high energy density, long cycle life, low environmental pollution, and no memory effect, injecting fresh vitality into the vigorous development of the new energy industry. Lithium-ion battery electric vehicles are an important part of the new energy vehicle industry, and high-energy-density lithium-ion power batteries, as core components of electric vehicles, can effectively solve the range anxiety problem in the electric vehicle field.

[0003] Lithium-rich manganese-based cathode materials exhibit excellent reversible capacity (>250 mAh / g) due to the combined effects of transition metal ions and oxygen anion redox reactions, making them one of the most promising cathode materials for rechargeable lithium-ion batteries. However, capacity decay and structural instability during cycling have hindered their market entry. Oxygen release from the surface due to oxygen anion redox reactions leads to structural instability, and oxygen anion redox reactions include reversible redox reactions within the bulk phase (O... 2- →O2 n- ) and irreversible lattice oxygen loss from the surface (O 2- →O2). Due to the irreversible loss of surface lattice oxygen, irreversible migration of transition metal ions is further induced, ultimately leading to problems such as poor cycle performance of the cathode material, unstable surface structure, and slow kinetics in the electrochemical reaction process. Therefore, the biggest challenge at present is to stabilize the surface structure changes and irreversible lattice oxygen loss caused by the redox process.

[0004] Chinese invention patent application CN 108172808 A (application number 201810039772.4.2) discloses a surface modification method for lithium-ion battery lithium-rich manganese-based cathode materials. This method achieves surface coating of lithium-rich manganese-based cathode materials through hydrothermal treatment. The preparation process is simple and, to some extent, inhibits the erosion of the cathode material by HF during charge and discharge, reducing the occurrence of side reactions. However, the crystal structure of the cathode material prepared by this method is not optimized and improved, and the surface structure is prone to phase transition during cycling, leading to severe capacity and voltage decay. Therefore, a "one-step-dual modification" method for modifying lithium-rich manganese-based cathode materials is needed, which is crucial for improving the capacity decay and rate performance of lithium-rich manganese-based cathode materials during cycling. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a cerium-doped lithium-rich manganese-based cathode material coated with nano-cerium oxide with good surface structure stability, good cycle performance, good rate performance and other electrochemical performance, and its preparation method.

[0006] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0007] A cerium-doped lithium-rich manganese-based cathode material coated with nano-cerium oxide includes a lithium-rich manganese-based cathode material and nano-cerium oxide coated on its surface. The chemical formula of the lithium-rich manganese-based cathode material is xLi2MnO3·(1-x)LiTMO2, where TM is at least one element selected from Ni, Co, and Mn, and 0.2≤x≤0.8. The lithium-rich manganese-based cathode material is doped with cerium.

[0008] Preferably, the molar ratio of cerium doping to the total molar amount of nickel, cobalt, and manganese in the lithium-rich manganese-based cathode material is (0.005-0.1):1, and the mass ratio of nano-cerium oxide to the lithium-rich manganese-based cathode material is (0.01-0.1):1.

[0009] Preferably, the cerium-doped lithium-rich manganese-based cathode material coated with nano-cerium oxide is a spherical secondary particle aggregate with a particle size of 8μm-12μm. The spherical shape of the surface-doped and nano-cerium-coated lithium-rich manganese-based cathode material ensures the morphology and particle size distribution of the secondary spherical particles in the unmodified lithium-rich manganese-based cathode material. The surface-doped and nano-cerium-coated lithium-rich manganese-based cathode material does not change the original spherical structure of the material, indicating that the doping and coating modification does not affect the morphology and particle size of the material.

[0010] Based on the overall inventive concept, this invention also provides a method for preparing a cerium-doped lithium-rich manganese-based cathode material coated with nano-cerium oxide, comprising the following steps:

[0011] (1) Nickel salt, cobalt salt and manganese salt are mixed and dissolved to obtain nickel cobalt manganese solution. After adding precipitant and complexing agent and reacting, nickel cobalt manganese carbonate precursor is obtained.

[0012] (2) Add the cerium source to the precipitant solution to react and prepare hydrated cerium carbonate. After grinding evenly, the ground hydrated cerium carbonate is obtained.

[0013] (3) After grinding and mixing the hydrated cerium carbonate obtained in step (2) with the nickel cobalt manganese carbonate precursor obtained in step (1) and the lithium source, the mixture is calcined, washed with water and dried to obtain a lithium-rich manganese-based cathode material with cerium doping and cerium oxide coating on the surface.

[0014] The precursor preparation method used in this invention can use either sodium carbonate or ammonium bicarbonate as a precipitant. Furthermore, the subsequent process employs a one-step method to achieve the effects of nano-cerium oxide coating and surface cerium doping. By coating the surface with nano-cerium oxide, oxygen vacancies are essentially constructed on the surface of the lithium-rich manganese-based cathode material, which can effectively suppress the release of irreversible oxygen from the material surface.

[0015] Preferably, the nickel source in step (1) is one or more of nickel sulfate and its hydrate, nickel acetate and its hydrate, nickel nitrate and its hydrate, and nickel chloride and its hydrate; the cobalt source is one or more of cobalt sulfate and its hydrate, cobalt acetate and its hydrate, cobalt nitrate and its hydrate, and cobalt chloride and its hydrate; the manganese source is one or more of manganese sulfate and its hydrate, manganese acetate and its hydrate, manganese nitrate and its hydrate, and manganese chloride and its hydrate; the molar ratio of nickel, cobalt, and manganese is (0-3):(0-3):(4-6). The total molar concentration of nickel, cobalt, and manganese ions in the nickel-cobalt-manganese solution is 0.1-4 mol / L (more preferably 1.5-2.5 mol / L). If the concentration of metal ions is too low, it is not conducive to the subsequent precipitation process, and the precipitation time is long, which is not conducive to improving production efficiency; if the concentration of metal ions is too high, it is not conducive to the complete dissolution of metal salts. The purpose of adding nickel, cobalt, and manganese is to form a nickel-cobalt-manganese precipitate, i.e., a lithium-rich manganese-based precursor material. Without this addition, a lithium-rich manganese-based precursor material without these elements can be formed, only the type of precursor will be different. The feeding rate of the nickel-cobalt-manganese solution is 75–130 mL / h (more preferably 95–115 mL / h). If the feeding rate into the reactor is too fast, it will lead to a large pH variation, making it difficult for the precipitant to effectively precipitate the metal ions, which is detrimental to the formation and growth of crystal nuclei during the reaction. If the feeding rate is too slow, the particles are prone to agglomeration and precipitation, which is not conducive to the formation of individual secondary spherical particles and also reduces production efficiency.

[0016] Preferably, step (1) is carried out under an inert atmosphere, the pH of the reaction system is between 7 and 9, the precipitant in step (1) is one or more combinations of sodium carbonate and ammonium bicarbonate, the molar concentration of the precipitant is 1.0 to 6.0 mol / L; the complexing agent is an ammonia solution with a molar concentration of 0.1 to 3 mol / L; the volume ratio of the complexing agent, precipitant and nickel-cobalt-manganese solution is (0.1 to 10):(0.5 to 3):(1 to 2). If the molar concentration of the ammonia solution is too low, the metal ions will be difficult to completely complex; if the molar concentration of the ammonia solution is too high, it will not be conducive to the formation of carbonate precipitates by the metal ions. The pH of the reaction system is adjusted to be between 7 and 9 using the precipitant solution; if the molar concentration of the carbonate precipitant solution is too high or too low, the reaction process cannot be properly controlled. At the above pH value, it is more conducive to controlling the growth rate of the particles to a moderate level. The volume ratio of complexing agent, precipitant and nickel-cobalt-manganese solution in the reactor is controlled to be (0.1-10):(0.5-3):(1-2); under the above feeding ratio, it is beneficial to the formation of grains and crystal growth in the crystallization process.

[0017] Step (1) is a coprecipitation reaction. During the coprecipitation reaction, the stirring speed is controlled at 600-1200 r / min, the temperature at 35℃-65℃ (more preferably 50-60℃), and the time at 30-50 h. If the stirring speed is too slow, the primary particles are prone to agglomeration; if the stirring speed is too fast, the newly grown crystals are prone to breakage. Within the above temperature range, crystal growth is more favorable. The reaction time is determined by the raw material content and the feeding rate. The aging temperature is 35℃-65℃ (more preferably 50-60℃), and the time is 10-30 h. Aging can displace anions such as sulfate ions inside the material, which is beneficial to the uniformity of the secondary particle surface. If the aging time is too short, it is difficult to ensure the ion exchange of anions, which will also affect the subsequent washing process. If the aging time is too long, it is not conducive to actual production applications. The above aging temperature is consistent with the coprecipitation temperature, which is conducive to the uniform dispersion of the material without agglomeration and ensures that the primary particles grow into secondary particles uniformly. The filter material is washed ≥8 times with deionized water and ethanol respectively. The drying temperature is 80-100℃ and the time is 12-20h. If the drying temperature is too low or the time is too short, the material will not dry completely. If the temperature is too high or the time is too long, the surface of the material will be easily oxidized, affecting the material performance. In addition, the drying cycle is too long, which is not conducive to industrial production.

[0018] Preferably, the cerium source in step (2) is one or more of cerium nitrate hexahydrate and cerium chloride heptahydrate, and the grinding aid is one or more of sodium chloride and ammonium chloride. The mass ratio of the grinding aid to hydrated cerium carbonate is (0.5-5):1. Step (2) involves adding the cerium source to the precipitant solution at a certain flow rate, stirring and reacting for a period of time after addition, aging, filtering, washing, and drying to obtain hydrated cerium carbonate, then adding the grinding aid, mixing and grinding evenly to obtain ground hydrated cerium carbonate. The mass ratio of the grinding aid to hydrated cerium carbonate is (0.5-5):1. During simultaneous lithiation, hydrated cerium carbonate decomposes to form cerium oxide. The thorough mixing of ammonium chloride or sodium chloride with the cerium carbonate raw material effectively prevents cerium oxide agglomeration. Under grinding force, hydrated cerium carbonate easily dissociates into small fragments, inevitably generating free valence bonds on the newly formed fractured surfaces. This drives adjacent particles to adhere and aggregate. At this point, ammonium chloride (sodium chloride) adsorbs onto the cerium carbonate surface, satisfying the unsaturated valence bonds on the newly formed surfaces, eliminating and weakening the tendency of cerium carbonate particles to aggregate, thus preventing agglomeration. Simultaneously, ammonium chloride (sodium chloride) also acts as a grinding aid. During calcination, ammonium chloride (sodium chloride) further inhibits cerium oxide particle agglomeration, achieving the purpose of refining. Nano-cerium oxide possesses abundant oxygen vacancies, which can suppress the release of lattice oxygen during charging. Furthermore, the oxidizing properties of cerium ions can be utilized to oxidize the surface Ni... 2+ Oxidation to Ni 3+ This process reduces the lithium / nickel mixing degree in the material, stabilizes the layered structure of the lithium-rich manganese-based cathode material, promotes lithium-ion insertion and extraction, and improves the cycle stability of the lithium-rich manganese-based cathode material. Furthermore, Ce doping into the lithium-rich manganese-based cathode material forms Ce-O bonds, stabilizing lattice oxygen and suppressing lattice oxygen release during charging, ultimately synergistically mitigating capacity decay during cycling. The hydrated cerium carbonate on the surface, under the uniform mixing of ammonium chloride and sodium chloride, reacts and decomposes at high temperatures to generate nano-cerium oxide with oxygen vacancies. The presence of these vacancies lowers the charge transfer barrier at the material-electrolyte interface, increasing the lithium-ion diffusion rate. Moreover, the uniformly distributed nano-cerium oxide coating effectively inhibits direct contact between the electrolyte and the active material, reduces side reactions at the material-electrolyte interface, and alleviates the dissolution and migration of surface transition metals, thereby improving the cycle stability of the material.

[0019] Preferably, the lithium source in step (3) includes one or more combinations of lithium carbonate, lithium hydroxide monohydrate, lithium hydroxide, and lithium nitrate; the molar ratio of the total molar amount of cerium in the cerium source and nickel, cobalt, and manganese in the nickel-cobalt-manganese carbonate precursor to the molar amount of lithium in the lithium source, Ce∶(Ni+Co+Mn):Li, is (0.005~0.1):1∶(1.5~1.7). Excessive use of cerium as a dopant will introduce too much inactive material, leading to a decrease in capacity; insufficient use of cerium as a dopant will result in uneven doping and excessive nano-cerium oxide coating, causing the coating layer on the material surface to be too thick or even agglomerated, thus affecting the material's performance. Insufficient nano-cerium oxide coating will make it difficult to achieve the desired coating effect, resulting in a waste of raw materials.

[0020] Preferably, the calcination process in step (3) employs a two-stage calcination method: the first stage involves calcination at 500–700°C for 4–8 hours, and the second stage involves calcination at 800–900°C for 10–15 hours, all within an oxygen atmosphere. The purpose of the first stage calcination is primarily to decompose the lithium source into oxides, while the second stage calcination process facilitates the formation of nano-cerium dioxide. The calcination process utilizes a tube furnace or a muffle furnace. The oxygen flow rate during the calcination process is controlled at 0.5–2.5 m³ / h. 3 The heating rate during calcination is 3–10 °C / min, and natural cooling is adopted after calcination is completed.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. The cathode material of this invention utilizes cerium to bulk dope lithium-rich manganese-based cathode materials while simultaneously coating the cathode material surface with nano-cerium oxide. Through dual modification and synergistic treatment of lithium-rich manganese-based cathode materials by ion doping and metal oxide coating, the problems of severe capacity decay and poor rate performance during cycling of existing cathode materials are overcome. Moreover, the preparation method of this cathode material is simple and low-cost, which is conducive to large-scale production. The dual-modified lithium-rich manganese-based cathode material was used for electrochemical performance testing of lithium-ion batteries. The results showed that after 100 cycles at a current density of 1C (2-4.8V, 250mA / g), the capacity retention rate was as high as 99.2%, indicating that the material of this invention has excellent discharge specific capacity retention rate as a cathode material for lithium-ion batteries.

[0023] 2. The preparation process of this invention is simple, the rare earth raw materials and process costs are low, and the experimental method is easy to promote. It is an effective method to suppress the capacity decay of lithium-rich manganese-based cathode materials during cycling. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 The images show the XRD patterns of the samples obtained in Comparative Example 1 and Example 1.

[0026] Figure 2 This is a SEM image of the lithium-rich manganese-based cathode material with surface cerium doping and nano-cerium oxide coating in Example 1.

[0027] Figure 3 This is a SEM image of the lithium-rich manganese-based cathode material with surface cerium doping and nano-cerium oxide coating in Example 1.

[0028] Figure 4 , Figure 5 EDS image of the lithium-rich manganese-based cathode material with surface cerium doping and nano-cerium oxide coating in Example 1.

[0029] Figure 6 Charge-discharge cycle curves of batteries assembled from lithium-rich manganese-based cathode materials with cerium doping and nano-cerium oxide coating in Comparative Example 1 and Example 1.

[0030] Figure 7 Charge-discharge cycle curves and charge-discharge coulomb curves of the batteries assembled from the lithium-rich manganese-based cathode materials with cerium doping and nano-cerium oxide coating in Comparative Example 1 and Example 1.

[0031] Figure 8 The discharge rate curves are for the batteries assembled from the lithium-rich manganese-based cathode materials with cerium doping and nano-cerium oxide coating in Comparative Example 1 and Example 1. Detailed Implementation

[0032] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0033] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0034] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0035] Example 1:

[0036] A lithium-rich manganese-based cathode material with cerium doping and nano-cerium oxide coating includes a cerium-doped lithium-rich manganese-based cathode material and oxygen-vacancy-rich nano-cerium oxide coated on its surface. The cerium-doped lithium-rich manganese-based cathode material refers to a lithium-rich manganese-based cathode material doped with cerium, where the molar ratio of cerium doping amount to the total molar amount of nickel, cobalt, and manganese transition metals in the lithium-rich manganese-based cathode material is (0.005–0.1):1, and the mass ratio of nano-cerium oxide coating amount to cerium-doped lithium-rich manganese-based cathode material is (0.01–0.1):1. The aforementioned lithium-rich manganese-based cathode material is Li... 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 is a spherical secondary particle agglomerate with a particle size of about 10 μm, regular morphology, and uniform distribution.

[0037] The preparation method of the above-mentioned lithium-rich manganese-based cathode material with cerium doping and nano-cerium oxide coating includes the following steps:

[0038] (1) A 4L mixed solution of transition metals, nickel sulfate, manganese sulfate and cobalt sulfate, wherein the total molar concentration of Ni, Co and Mn ions is 2.0 mol / L, is pumped into a reactor containing 2L of 0.3 mol / L ammonia solution at a feeding rate of 100 ml / h. At the same time, the ammonia concentration of the reaction system is adjusted to 0.3 mol / L with 25% ammonia solution. The pH of the reaction system is adjusted to 8.0 with 4L of 2 mol / L sodium carbonate precipitant solution. The reactor is purged with high-purity nitrogen atmosphere and heated and stirred at 1200 r / min and 60℃ for 40 h for co-precipitation. After that, it is aged at 60℃ for 20 h with stirring. The filter material is washed 8 times with deionized water and ethanol respectively. It is dried at 80℃ for 12 h to obtain nickel cobalt manganese carbonate precursor.

[0039] (2) 100 ml of cerium chloride solution, in which the total molar concentration of Ce ions is 0.5 mol / L, is added to 100 ml of 0.75 mol / L ammonium carbonate solution at a feeding rate of 100 ml / h. After the addition is complete, the solution is stirred at a stirring speed of 100 r / min for 10 min. The solution is aged at room temperature, and the filter material is washed 8 times with deionized water and ethanol respectively. The solution is dried at 60℃ for 12 h to obtain hydrated cerium carbonate precursor.

[0040] (3) Mix 0.0196g of hydrated cerium carbonate obtained in step (2) with 0.02g of grinding aid ammonium chloride and grind evenly to obtain ground hydrated cerium carbonate;

[0041] (4) 1.0g of nickel cobalt manganese carbonate precursor (Ni 1.31158mol, Co 1.35089mol, Mn 5.33753mol) obtained in step (1) was mixed and ground with 0.4742g (6.417474mmol) of lithium carbonate, 0.0196g (0.0425874mmol) of hydrated cerium carbonate obtained in step (3) and 0.02g (0.373902mmol) of ammonium chloride. Under a high-purity oxygen atmosphere, the temperature was first raised to 500℃ at a rate of 5℃ / min and calcined for 4h. Then, the temperature was raised to 850℃ at a rate of 5℃ / min and calcined for 12h. After natural cooling to room temperature, the material was washed and dried to obtain a lithium-rich manganese-based cathode material with cerium doping on the surface and nano-cerium oxide coating, named LRMO-1.

[0042] Comparative Example 1:

[0043] A lithium-rich manganese-based cathode material and its preparation method, comprising the following steps:

[0044] (1) Same as step (1) in Example 1;

[0045] (2) Take 1.0g of the nickel-cobalt-manganese carbonate precursor obtained in step (1) (Ni 1.31158mol, Co 1.35089mol, Mn

[0046] After mixing and grinding 5.33753 mol) of lithium carbonate with 0.4742 g (6.417474 mmol), the mixture was heated to 500 °C at a rate of 5 °C / min and calcined for 4 h in a high-purity oxygen atmosphere. Then, the mixture was heated to 850 °C at a rate of 5 °C / min and calcined for 12 h. After being naturally cooled to room temperature, washed, and dried, a lithium-rich manganese-based cathode material was obtained, named LRMO-P.

[0047] like Figure 1 As shown, XRD patterns were analyzed on the cerium-doped and nano-cerium oxide-coated lithium-rich manganese-based cathode materials synthesized in Example 1 and Comparative Example 1, as well as the untreated raw materials. The cerium-doped lithium-rich manganese-based cathode materials and raw materials obtained in the examples both have layered structures and are structurally complete. In addition, the main diffraction peaks in the XRD diffraction pattern of Example 1 are clear and have high intensity, which is significantly higher than that of Comparative Example 1. Furthermore, diffraction peaks matching standard PDF card #78-0694 were observed, indicating that nano-cerium dioxide was successfully coated on the surface of the material. This demonstrates that the cerium-doped and nano-cerium oxide-coated lithium-rich manganese-based cathode materials have good crystallinity and relatively pure crystal phase.

[0048] like Figure 2As shown, SEM tests were performed on the lithium-rich manganese-based cathode material with surface cerium doping and nano-cerium oxide coating synthesized in Example 1. The morphology of the lithium-rich manganese-based cathode material with surface cerium doping and nano-cerium oxide coating in Example 1 was good, with secondary particles being spherical and having a particle size distribution of about 10 μm.

[0049] Figure 3 This is a SEM image of a lithium-rich manganese-based cathode material. Figure 4 , Figure 5 The image shows the EDS pattern of the lithium-rich manganese-based cathode material. SEM results of the surface-doped and nano-cerium oxide-coated lithium-rich manganese-based cathode material in this embodiment show obvious coating marks on the material surface. Uniformly dispersed nanoparticles are clearly visible on the material surface in this embodiment, and the EDS mapping results show that cerium is uniformly distributed on the material.

[0050] Battery Assembly: 0.08g of the lithium-rich manganese-based cathode material prepared in Example 1 (surface cerium doped and nano-cerium oxide coated) and the lithium-rich manganese-based cathode material in Comparative Example 1 were weighed separately. 0.01g of acetylene black as a conductive agent and 0.01g of PVDF (polyvinylidene fluoride) as a binder were added respectively, and the mixtures were ground with N-methylpyrrolidone as a solvent to form cathode materials. The obtained cathode materials were coated onto the surface of aluminum foil to form electrode sheets. In a sealed glove box filled with argon gas, using the electrode sheets as the cathode, a lithium metal sheet as the anode, a microporous polypropylene membrane as the separator, and 1mol / L LiPF6 / EC:DMC:EMC (volume ratio 1:1:1) as the electrolyte, CR2025 coin cells were assembled, and charge-discharge performance tests were performed. Figure 6 , Figure 7 and Figure 8 The initial charge-discharge curve of the battery was performed with a current density of 25 mA / g and a voltage range of 2.0–4.8 V. Rate performance testing was conducted within the same 2.0–4.8 V voltage range at current densities of 25 mA / g, 50 mA / g, 125 mA / g, 250 mA / g, 500 mA / g, and 1250 mA / g, respectively. All electrochemical performance tests were performed at room temperature. The electrochemical performance test results show that the initial discharge capacity of the cerium-doped lithium-rich manganese-based cathode material coated with nano-cerium dioxide increased from 274.5 mAh / g to 280.7 mAh / g, and the initial charge-discharge efficiency increased from 79.6% to 81.5%, reducing the initial irreversible capacity loss. After 100 cycles, the discharge specific capacity remained as high as 210.3 mAh / g, with a capacity retention rate of 99.2%.

[0051] This indicates that the modification effectively inhibits direct contact between the electrolyte and the active material during charge and discharge, reduces the occurrence of side reactions at the interface between the material and the electrolyte, alleviates the dissolution and migration of surface transition metals, and thus improves the cycle stability of the material.

Claims

1. A method for preparing a cerium-doped lithium-rich manganese-based cathode material coated with nano-cerium oxide, characterized in that, The cerium-doped lithium-rich manganese-based cathode material coated with nano-cerium oxide comprises a lithium-rich manganese-based cathode material and nano-cerium oxide coated on its surface. The chemical formula of the lithium-rich manganese-based cathode material is xLi₂MnO₃·(1-x)LiTMO₂, where TM is at least one element selected from Ni, Co, and Mn, and 0.2≤x≤0.

8. The lithium-rich manganese-based cathode material is doped with cerium. Its preparation method includes the following steps: (1) Nickel salt, cobalt salt and manganese salt are mixed and dissolved to obtain nickel cobalt manganese solution. After adding precipitant and complexing agent and reacting, nickel cobalt manganese carbonate precursor is obtained; (2) Add the cerium source to the precipitant solution to react and prepare hydrated cerium carbonate. After grinding evenly, the hydrated cerium carbonate is obtained. (3) After grinding and mixing the hydrated cerium carbonate obtained in step (2) with the nickel cobalt manganese carbonate precursor obtained in step (1) and the lithium source, the mixture is calcined, washed with water and dried to obtain a lithium-rich manganese-based cathode material with cerium doping and cerium oxide coating on the surface.

2. The preparation method according to claim 1, characterized in that, The molar ratio of cerium doping to the total molar amount of nickel, cobalt, and manganese in the lithium-rich manganese-based cathode material is (0.005–0.1):1, and the mass ratio of nano-cerium oxide to the lithium-rich manganese-based cathode material is (0.01–0.1):

1.

3. The preparation method according to claim 1, characterized in that, The cerium-doped lithium-rich manganese-based cathode material coated with nano-cerium oxide is a spherical secondary particle aggregate with a particle size of 8μm-12μm.

4. The preparation method according to claim 1, characterized in that, The nickel salt in step (1) is one or more of nickel sulfate and its hydrate, nickel acetate and its hydrate, nickel nitrate and its hydrate, and nickel chloride and its hydrate; the cobalt salt is one or more of cobalt sulfate and its hydrate, cobalt acetate and its hydrate, cobalt nitrate and its hydrate, and cobalt chloride and its hydrate; the manganese salt is one or more of manganese sulfate and its hydrate, manganese acetate and its hydrate, manganese nitrate and its hydrate, and manganese chloride and its hydrate; the molar ratio of nickel, cobalt, and manganese is (0-3):(0-3):(4-6), and the total molar concentration of nickel, cobalt, and manganese ions in the nickel-cobalt-manganese solution is 0.1-4 mol / L.

5. The preparation method according to claim 1, characterized in that, Step (1) is carried out under an inert atmosphere, and the pH value of the reaction system is between 7 and 9. The precipitant in step (1) is one or more of sodium carbonate and ammonium bicarbonate, and the molar concentration of the precipitant is 1.0 to 6.0 mol / L. The complexing agent is an ammonia solution with a molar concentration of 0.1 to 3 mol / L. The volume ratio of the complexing agent, precipitant and nickel cobalt manganese solution is (0.1 to 10): (0.5 to 3): (1 to 2).

6. The preparation method according to claim 1, characterized in that, The cerium source in step (2) is one or more of cerium nitrate hexahydrate and cerium chloride heptahydrate; a grinding aid is added during grinding, and the grinding aid is one or more of sodium chloride and ammonium chloride, and the mass ratio of the grinding aid to hydrated cerium carbonate is (0.5-5):

1.

7. The preparation method according to claim 1, characterized in that, The lithium source in step (3) includes one or more combinations of lithium carbonate, lithium hydroxide monohydrate, lithium hydroxide, and lithium nitrate; the total molar amount of cerium in the cerium source and nickel, cobalt, and manganese in the nickel cobalt manganese carbonate precursor and the molar ratio of lithium in the lithium source Ce∶(Ni+Co+Mn)∶Li is (0.005~0.1)∶1∶(1.5~1.7).

8. The preparation method according to claim 1, characterized in that, The calcination process in step (3) is carried out in two stages: the first stage of calcination is carried out at 500-700℃ for 4-8 hours, and the second stage of calcination is carried out at 800-900℃ for 10-15 hours. The calcination process is carried out in an oxygen atmosphere.

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