Modified lithium-rich manganese-based positive electrode material and preparation method and application thereof

Abstract

The present invention provides a modified lithium-rich manganese-based positive electrode material, a preparation method thereof, and an application thereof. The preparation method of the modified lithium-rich manganese-based positive electrode material comprises the following steps: impregnating the lithium-rich manganese-based positive electrode material with a fluorocarbon surfactant and annealing at high temperature to obtain the modified lithium-rich manganese-based positive electrode material; the modified lithium-rich manganese-based positive electrode material is prepared by the preparation method of the modified lithium-rich manganese-based positive electrode material and is applied to the field of lithium-ion batteries. Compared with the prior art, the present invention not only retains the high theoretical specific capacity of the lithium-rich manganese-based positive electrode material itself, but also improves the surface stability of the material by fluorine doping the surface lattice of the material, thereby forming a modified lithium-rich manganese-based positive electrode material with excellent rate performance and more stable long-term cycle performance for application in the field of lithium-ion batteries. The preparation method is simple in process and highly operable.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a modified lithium-rich manganese-based positive electrode material and a preparation method and application thereof BACKGROUND

[0002] As an environmentally friendly new energy storage device, lithium ion batteries have been widely used in portable electronic devices, electric vehicles and large-scale energy storage since commercialization in the 1990s. In the past decade, although LiCoO2 and LiFePO4 have successfully realized large-scale commercial application, they still have many problems to be solved. For example, LiCoO2 is unstable after delithiation, and is prone to side reactions with electrolyte, resulting in irreversible capacity loss and safety problems. In addition, their low available capacity (theoretical capacity < 200 mAh / g) has failed to meet the demand for longer endurance of electric vehicles. Therefore, developing a lithium ion battery positive electrode material with high capacity, long life, high stability, high safety and low cost has become the key to breaking through the bottleneck of energy development.

[0003] Among the currently common material systems, layered oxide positive electrode materials have attracted widespread attention due to their high theoretical capacity. Among them, lithium-rich manganese-based layered positive electrode materials have a theoretical specific capacity as high as 250 mAh / g and are considered to be a highly potential next-generation high-performance lithium ion battery positive electrode material. Its chemical formula can be expressed as xLi2MnO3·(1-x)LiMO2. According to the two-phase structure theory, we believe that it is composed of layered Li2MnO3 and LiMO2 (M = Ni, Co, Mn), where one-third of Li in the Li2MnO3 phase is replaced by Mn + 4+ to form a monoclinic crystal with a space group of C / 2m, while LiMO2 has a layered structure similar to lithium cobaltate with a space group of R-3m. This unique two-phase chelation structure allows transition metal ions and oxygen anions in the lithium-rich manganese-based positive electrode material to participate in electrochemical reactions, thereby providing higher theoretical specific capacity than traditional ternary materials. Currently, to achieve large-scale commercialization of lithium-rich manganese-based positive electrode materials, the key scientific problem to be solved is how to better stabilize the lattice oxygen and reduce the surface oxygen loss of the material during the cycle process to improve the long-term cycle stability of the material. Currently, surface treatment, surface coating and anion and cation doping are often used to enhance the stability of the material, but these methods often result in a decrease in the specific capacity of the material due to the introduction of electrochemically inert components. Therefore, finding a modification method that can improve the cycle stability of lithium-rich manganese-based positive electrode materials without affecting their actual discharge specific capacity is a key problem to be solved. SUMMARY

[0004] ​In view of the defects in the prior art, the purpose of the present application is to provide a modified lithium-rich manganese-based positive electrode material and a preparation method and application thereof, which not only retains the relatively high theoretical specific capacity of the lithium-rich manganese-based positive electrode material itself, but also improves the surface stability of the material by fluorine doping of the surface lattice of the material, thereby forming a modified lithium-rich manganese-based positive electrode material with excellent rate performance and more stable long-term cycling performance for application in the field of lithium ion batteries.

[0005] To solve the above technical problems, the present application provides the following technical solutions:

[0006] According to a first aspect of an embodiment of the present application, a preparation method of a modified lithium-rich manganese-based positive electrode material is provided, which comprises the following steps:

[0007] The lithium-rich manganese-based positive electrode material is impregnated with a fluorocarbon surfactant and then subjected to high-temperature annealing, thereby obtaining the modified lithium-rich manganese-based positive electrode material.

[0008] In a further preferred embodiment, the fluorocarbon surfactant is at least one of perfluorooctylsulfonic acid, perfluorooctanoic acid, perfluorobutylsulfonic acid, perfluorooctyl alcohol, perfluorohexylsulfonic acid, perfluorohexanoic acid or perfluorodecylsulfonic acid.

[0009] In a further preferred embodiment, the preparation method specifically comprises the following steps:

[0010] In step one, the powder of the lithium-rich manganese-based positive electrode material is uniformly dispersed in an aqueous solution containing the fluorocarbon surfactant, and then impregnated at room temperature, the concentration of the aqueous solution of the fluorocarbon surfactant used is 0.5-50%, the impregnation time is 2-24 h, and after the impregnation is completed, the powder is separated and dried to obtain a lithium-rich manganese-based positive electrode material with the fluorocarbon surfactant adsorbed on the surface;

[0011] In step two, the powder of the lithium-rich manganese-based positive electrode material with the fluorocarbon surfactant adsorbed on the surface is uniformly mixed with a certain amount of lithium hydroxide monohydrate or lithium carbonate in a mortar, and then subjected to high-temperature calcination to obtain the modified lithium-rich manganese-based positive electrode material.

[0012] In a further preferred embodiment, the fluorine content of the modified lithium-rich manganese-based positive electrode material in step two is between 0.1-10%.

[0013] In a further preferred embodiment, the addition amount of the lithium hydroxide monohydrate or the lithium carbonate in step two is 0.1-5 wt%.

[0014] In a further preferred embodiment, the high-temperature calcination in step two adopts a one-step sintering method, and is reacted at a temperature of 600-900 o C under an oxygen or air atmosphere for 1-10 h.

[0015] In a further preferred embodiment, the powder is separated and dried after the impregnation in step 2 to obtain a lithium-rich manganese-based positive electrode material with a fluorocarbon surfactant adsorbed on the surface, which specifically includes:

[0016] After the impregnation is completed, the powder is separated by centrifugation and heated at 80-120 o C, and drying the powder to obtain a lithium-rich manganese-based positive electrode material with a fluorocarbon surfactant adsorbed on the surface.

[0017] In a further preferred embodiment, the lithium-rich manganese-based positive electrode material in any one of the above-mentioned modified lithium-rich manganese-based positive electrode material preparation methods is cobalt-free Li 1.2 Ni 0.2 Mn 0.6 O2 or Li containing cobalt 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2

[0018] At least one of .

[0019] According to a second aspect of an embodiment of the present invention, a modified lithium-rich manganese-based positive electrode material is provided, which is prepared by using any one of the above methods for preparing a modified lithium-rich manganese-based positive electrode material.

[0020] According to a third aspect of an embodiment of the present invention, an application of a modified lithium-rich manganese-based positive electrode material is provided. The modified lithium-rich manganese-based positive electrode material is prepared by any of the above-mentioned methods for preparing the modified lithium-rich manganese-based positive electrode material and is applied to the field of lithium-ion batteries.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) Compared with the untreated material, the cycle stability of the doped material is significantly improved. Fluoride ions are doped in the surface lattice of the modified lithium-rich manganese-based cathode material. Since the strength of the TM-F bond is higher than that of the TM-O bond, the surface transition metal of the modified material dissolves less during the cycle. Therefore, surface F doping can reduce the transition metal dissolution of the lithium-rich manganese-based cathode material during the cycle.

[0023] (2) The introduction of fluorine is beneficial to stabilizing the oxygen skeleton on the surface of the material, improving the stability of the lattice oxygen on the surface of the lithium-rich manganese-based positive electrode material, reducing the irreversible oxygen loss during the cycle when the material is charged to a high voltage, and thus improving the long-term cycle stability of the material.

[0024] (3) Because the trace surface doping does not introduce too much electrochemical inert component, the obtained modified lithium-rich manganese-based positive electrode material still has a high discharge specific capacity, and is more suitable for large-scale commercial application.

[0025] (4) The method of the carbon-fluorine surfactant aqueous solution impregnation combined with high-temperature calcination is simple to realize, and is beneficial to commercialization.

[0026] In summary, the present application not only retains the high theoretical specific capacity of the lithium-rich manganese-based positive electrode material itself, but also improves the surface stability of the material through fluorine doping of the surface lattice of the material, forms a modified lithium-rich manganese-based positive electrode material applied in the field of lithium ion batteries, which has excellent rate performance and more stable long-term cycle performance, and the preparation method provided by the present application is simple in process and strong in operability. BRIEF DESCRIPTION OF DRAWINGS

[0027] Other features, objects, and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments, read in conjunction with the accompanying drawings:

[0028] Figure 1 X-ray diffraction spectra of the lithium-rich manganese-based positive electrode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 before and after modification provided by the embodiments of the present application;

[0029] Figure 2 Scanning electron microscope spectra of the lithium-rich manganese-based positive electrode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 before modification provided by the embodiments of the present application;

[0030] Figure 3 Scanning electron microscope spectra of the lithium-rich manganese-based positive electrode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 after modification provided by the embodiments of the present application;

[0031] Figure 4 XPS full spectra of the lithium-rich positive electrode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 before and after modification provided by the embodiments of the present application;

[0032] Figure 5 XPS full spectra of the lithium-rich positive electrode material Li 1.2 Ni 0.13 Co 0.13Mn 0.54 Electrochemical test discharge data graph of O2 as a positive electrode material at 1 C rate (1C = 250 mAh / g) (the first circle uses 0.1 C rate to form the battery);

[0033] Figure 6 The modified lithium-rich positive electrode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 The cyclic voltammetry graph of O2;

[0034] Figure 7 The modified lithium-rich positive electrode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 The cyclic voltammetry graph of O2;

[0035] Figure 8 The lithium-rich positive electrode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 The impedance graph of O2 after 50 cycles at 2C rate. DETAILED DESCRIPTION

[0036] The present application will be described in detail below with specific embodiments. The following examples will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present application. These all belong to the protection scope of the present application.

[0037] The unique properties of fluorocarbon surfactants are directly related to the fluorocarbon chain, and further depend on the unique properties of the fluorine element. Fluorine is the most electronegative element, which has high oxidation potential and high ionization energy. This property causes the fluorine-carbon bond (F-C) to have high bond energy (in fact, the fluorine-carbon bond is the highest covalent bond known). The fluorocarbon surfactant molecules have a stronger tendency to separate from the aqueous solution than other surfactant molecules, and are arranged in a molecular film on the liquid / gas interface, thereby having two different properties from other surfactants. Using these properties of fluorocarbon surfactants, the present application proposes that the aqueous solution thereof can be used to impregnate a lithium-rich manganese-based positive electrode material, and then the lithium-rich manganese-based positive electrode material is obtained by centrifugal separation and drying, and the surface of the lithium-rich manganese-based positive electrode material is covered with a fluorocarbon surfactant molecular film. Finally, after high-temperature calcination, the fluorine ions contained in the fluorocarbon surfactant diffuse into the crystal lattice on the surface of the lithium-rich manganese-based positive electrode material to replace the surface oxygen ions. Since the strength of the TM-F bond is higher than that of the TM-O bond, surface F doping can reduce the transition metal dissolution of the lithium-rich manganese-based positive electrode material during the cycle process. In addition, the introduction of fluorine elements can also improve the stability of the surface lattice oxygen of the lithium-rich manganese-based positive electrode material, reduce the irreversible oxygen loss during the cycle process, and thus improve the long-term cycle stability of the material. At the same time, since this trace surface doping does not introduce too many electrochemically inert components, the modified lithium-rich manganese-based positive electrode material obtained still has a relatively high specific discharge capacity, and is more suitable for large-scale commercial application.

[0038] Example 1:

[0039] The preparation method of the modified lithium-rich manganese-based positive electrode material provided by the embodiment of the present application adopts the following steps:

[0040] (1) The powder of the lithium-rich manganese-based positive electrode material is uniformly dispersed in an aqueous solution containing fluorocarbon surfactant, and then impregnated at room temperature. After the impregnation is completed, the powder is separated by a centrifuge and fully dried in an oven.

[0041] (2) The powder of the impregnated lithium-rich manganese-based positive electrode material prepared in step (1) is mixed with a certain amount of lithium hydroxide monohydrate or lithium carbonate in a mortar, and then high-temperature calcination is performed in a muffle furnace to obtain a modified lithium-rich manganese-based positive electrode material.

[0042] In step (1):

[0043] The impregnation method is to pour the powder of the lithium-rich manganese-based positive electrode material into an aqueous solution containing a certain concentration of fluorocarbon surfactant, and impregnate at room temperature for 2-24 h. Then, through centrifugation and drying, the lithium-rich manganese-based positive electrode material with fluorocarbon surfactant adsorbed on the surface is obtained. After the impregnation is completed, the powder is separated by centrifugation, and dried at 80-120 oThe lithium-rich manganese-based positive electrode material powder with carbon fluoride surfactant adsorbed on the surface is fully dried in an oven under the condition of 80 oC.

[0044] In step (2):

[0045] High-temperature calcination is to fully mix the lithium-rich manganese-based positive electrode material powder with carbon fluoride surfactant adsorbed on the surface with a certain amount of lithium carbonate or lithium hydroxide monohydrate in a mortar, and then calcine in a muffle furnace at 600-900 oC for 1-10 h under the condition of 80 oC. o C, to obtain the modified lithium-rich manganese-based positive electrode material.

[0046] In one specific embodiment, the modified lithium-rich manganese-based positive electrode material is prepared by the following steps:

[0047] First step, 2 g of lithium-rich positive electrode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 is added to 50 mL of aqueous solution containing 0.5 mol% of perfluorooctanoic acid, and the solution is stirred at room temperature for 4 h, then the mixed solution is transferred to a centrifuge tube, and the powder is separated out using a centrifuge, and then placed in an 80 oC oven for drying for 12 h. o C.

[0048] Second step, 1 g of the treated lithium-rich positive electrode material powder obtained in the first step is weighed, and mixed with 0.01 g of lithium carbonate in a mortar. Then, the mixed powder is transferred to a box-type muffle furnace and heat-treated at 800 oC for 4 h to obtain the modified lithium-rich manganese-based positive electrode material target product.

[0049] See Figures 1-4 , which are the X-ray diffraction spectra, scanning electron microscope spectra and transmission electron microscope spectra of the lithium-rich manganese-based material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 prepared before and after modification in this embodiment. From the X-ray spectra, it can be seen that the diffraction peaks of the material before and after modification are consistent with the characteristics of the lithium-rich layered positive electrode material, and the diffraction peaks correspond well to the R-3m and C / 2m space groups, the (003) peak of the material is significantly higher than the (104) peak, indicating that the degree of Li / Ni ion mixing of the material is low, and the (018) peak and (110) peak are relatively obvious, which shows that the material before and after modification has a good layered structure. Figure 4 The XPS full spectrum in shows that the signal of F element is increased in the modified lithium-rich material, which shows that F is successfully introduced into the surface of the material; from Figure 2 and Figure 3The scanning electron microscopy spectrum can also show that after the lithium-rich material is impregnated with the aqueous solution of fluorocarbon surfactant and subsequent high-temperature treatment, the morphology of the material will not be damaged, and it can still maintain the morphology of a microsphere, which is beneficial to improve the compaction density of the material.

[0050] Example 2:

[0051] Different from Example 1, the modified lithium-rich manganese-based positive electrode material in this embodiment is prepared by the following steps:

[0052] First step, 2 g of lithium-rich positive electrode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 is added to 50 mL of aqueous solution containing 1 mol% of perfluorobutyl sulfonic acid, the solution is stirred at room temperature for 6 h, then the mixed solution is transferred to a centrifuge tube, and the powder is separated out using a centrifuge, and then placed in a 120 oC oven for drying for 12 h.

[0053] Second step, 1 g of the treated lithium-rich positive electrode material powder obtained in the first step is weighed and mixed uniformly with 0.03 g of lithium carbonate in a mortar. Then, the mixed powder is transferred to a box muffle furnace and heat treated at 750 o C for 4 h to obtain the target product of the modified lithium-rich positive electrode material.

[0054] Example 3:

[0055] Different from Example 1, the modified lithium-rich manganese-based positive electrode material in this embodiment is prepared by the following steps:

[0056] First step, 2 g of lithium-rich positive electrode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 is added to 50 mL of aqueous solution containing 2 mol% of heptafluorobutyric acid, the solution is stirred at room temperature for 6 h, then the mixed solution is transferred to a centrifuge tube, and the powder is separated out using a centrifuge, and then placed in an 80 o C oven for drying for 12 h.

[0057] Second step, 1 g of the treated lithium-rich positive electrode material powder obtained in the first step is weighed and mixed uniformly with 0.02 g of lithium hydroxide monohydrate in a mortar. Then, the mixed powder is transferred to a box muffle furnace and heat treated at 850 o C for 6 h to obtain the target product of the modified lithium-rich positive electrode material.

[0058] Example 4: Unlike Example 1, the modified lithium-rich manganese-based cathode material in this example was prepared by the following steps:

[0059] Step 1, 2 g of lithium-rich cathode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2was added to 50 mL of aqueous solution containing 1 mol% of perfluorohexanoic acid, the solution was stirred for 4 h under 50 o C water bath conditions, then the mixed solution was transferred to a centrifuge tube, and the powder was separated out using a centrifuge, and then placed in an 80 oC oven to dry for 12 h.

[0060] Step 2, 1 g of the treated lithium-rich cathode material powder obtained in Step 1 was weighed out and mixed uniformly with 0.02 g of lithium hydroxide monohydrate in a mortar. After that, the mixed powder was transferred to a box muffle furnace and heat treated at 800 o C for 2 h to obtain the target product of the modified lithium-rich cathode material.

[0061] Example 5:

[0062] Unlike Example 1, the modified lithium-rich manganese-based cathode material in this example was prepared by the following steps:

[0063] Step 1, 2 g of lithium-rich cathode material Li 1.2 Ni 0.2 Mn 0.6 O2was added to 50 mL of aqueous solution containing 1 mol% of perfluorohexanoic acid, the solution was stirred for 6 h under 50 o C water bath conditions, then the mixed solution was transferred to a centrifuge tube, and the powder was separated out using a centrifuge, and then placed in an 80 oC oven to dry for 12 h.

[0064] Step 2, 1 g of the treated lithium-rich cathode material powder obtained in Step 1 was weighed out and mixed uniformly with 0.02 g of lithium carbonate in a mortar. After that, the mixed powder was transferred to a box muffle furnace and heat treated at 600 o C for 6 h to obtain the target product of the modified lithium-rich cathode material.

[0065] Example 6:

[0066] Unlike Example 1, the modified lithium-rich manganese-based cathode material in this example was prepared by the following steps:

[0067] Step 1, 2 g of lithium-rich cathode material Li 1.2 Ni 0.2 Mn 0.6O2 was added to 50 mL of aqueous solution containing 2 mol% of perfluorodecanesulfonic acid, the solution was stirred at room temperature for 12 h, then the mixed solution was transferred to a centrifuge tube, and the powder was separated out using a centrifuge, and then placed in a 80 o C oven for 12 h.

[0068] Second step, 1 g of the treated lithium-rich cathode material powder obtained in the first step was weighed and mixed uniformly with 0.02 g of lithium hydroxide in a mortar. Then, the mixed powder was transferred to a box muffle furnace and heat-treated at 900 o C for 1 h to obtain the modified lithium-rich cathode material target product.

[0069] Example 7:

[0070] Different from Example 1, the modified lithium-rich manganese-based cathode material in this example was prepared by the following steps:

[0071] First step, 2 g of lithium-rich cathode material Li 1.2 Ni 0.2 Mn 0.6 O2 was added to 50 mL of aqueous solution containing 2 mol% of perfluorodecanesulfonic acid, the solution was stirred at room temperature for 12 h, then the mixed solution was transferred to a centrifuge tube, and the powder was separated out using a centrifuge, and then placed in a 80 o C oven for 12 h.

[0072] Second step, 1 g of the treated lithium-rich cathode material powder obtained in the first step was weighed and mixed uniformly with 0.02 g of lithium hydroxide in a mortar. Then, the mixed powder was transferred to a box muffle furnace and heat-treated at 900 o C for 1 h to obtain the modified lithium-rich cathode material target product.

[0073] Example 8:

[0074] This example illustrates the performance test of the battery prepared from the lithium-rich manganese-based material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 before and after modification provided by the present application.

[0075] Electrochemical performance test:

[0076] (1) Preparation of the battery

[0077] The sample needs to be made into a button type lithium battery before electrochemical performance test. The sample acts as the positive material of the electrode in the lithium battery, and the lithium sheet is used as the negative electrode. The production process is four processes in turn, namely pretreatment, slurry preparation, electrode production and battery assembly. The synthesized W-doped lithium-rich layered positive material (80%) is mixed with conductive agent Super-P (10%) and binder polyvinylidene fluoride (10%) (mass ratio), NMP is added and ground thoroughly, then uniformly coated on aluminum foil, and then placed in a vacuum drying box at 120 o C for 12 h, and then dried. After drying, the positive sheet of the button cell is made by using a cutting machine, and the sheet is pressed at 4-6 atm. The weight of the active material coated on the sheet is weighed, and the weight of the blank aluminum foil is subtracted. Then, according to the proportion of the active material, the weight of the active material in each electrode sheet is calculated. The weighed sheet is placed in an argon glove box.

[0078] The metal lithium sheet is used as the negative electrode of the battery, and the 1 M LiPF6-EC:DMC:EMC = 1:1:1 electrolyte is used. The assembly of the button cell is carried out in an argon-filled anhydrous and oxygen-free glove box. The assembly process of the battery is as follows: 1) the positive sheet is placed in the middle of the battery shell, and 1-3 drops of electrolyte are added by using a pipette; 2) the PP separator is evenly laid on the electrode sheet; 3) 1-3 drops of electrolyte are added to the center of the PP separator by using a pipette, and the separator is completely wetted; 3) the metal lithium sheet is placed in the center of the separator, and it cannot touch the battery shell to avoid short circuit of the battery; 4) the stainless steel gasket and spring sheet are placed on the lithium sheet in sequence and aligned with the lithium sheet; 5) the negative electrode shell is covered and tightly pressed, and the battery is sealed by using a sealing machine, and the assembly is completed. The battery is placed for 5-12 h before electrochemical test.

[0079] (2) Electrochemical performance test

[0080] The constant current charge-discharge cycle test of the sample is carried out on a LAND-201A battery test system, and the test voltage range is 2.0-4.8 V. The electrochemical impedance test is carried out on a CHIS600B electrochemical workstation (Shanghai Chenhua Instrument Co., Ltd.). Figure 5 The constant current charge-discharge test of the lithium-rich manganese-based material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 before and after modification, Figure 6 and Figure 7 The cyclic voltammetry curve of the lithium-rich manganese-based material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 before and after modification. From Figure 5It can be seen from the constant current charge-discharge test diagram that after 1 cycle of formation at 0.1 C rate, the discharge specific capacity of the modified lithium-rich manganese-based positive electrode material is 189.74 mAh / g and the capacity retention rate is 91.7% after 300 cycles at 1 C rate (1 C = 250 mAh / g); while the discharge specific capacity of the unmodified lithium-rich manganese-based positive electrode material is only 155.97 mAh / g and the capacity retention rate is only 70.8%, which shows that the modification method of the application can significantly improve the cycle stability of the lithium-rich material. Figure 6 And Figure 7 It can be seen from the cyclic voltammetry curve that the electrochemical reversibility of the modified lithium-rich manganese-based positive electrode material is enhanced, which shows that the modification method adopted by the application is beneficial to improve the surface structure stability of the material, so as to alleviate the phase change that may occur when the material is charged to high voltage, combined with Figure 8 It can be seen from the impedance diagram that after 50 cycles at 2 C high rate, the modified lithium-rich positive electrode material has smaller charge transfer impedance, which shows that its structure is well maintained after cycling, which explains its better cycle stability.

[0081] The specific embodiments of the application are described above. It should be understood that the application is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essential content of the application. In the case of no conflict, the embodiments of the application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A method for preparing a modified lithium-rich manganese-based positive electrode material, characterized in that: The following steps are involved: impregnating the lithium-rich manganese-based positive electrode material with a fluorocarbon surfactant and annealing at high temperature to obtain the modified lithium-rich manganese-based positive electrode material; The fluorocarbon surfactant is at least one of perfluorooctane sulfonic acid, perfluorooctanoic acid, perfluorobutyl sulfonic acid, perfluorooctylethanol, perfluorohexyl sulfonic acid, perfluorohexanoic acid or perfluorodecyl sulfonic acid; The preparation method specifically comprises the following steps: Step 1: Evenly disperse the powder of the lithium-rich manganese-based positive electrode material in an aqueous solution containing the fluorocarbon surfactant, and then immerse it at room temperature. The concentration of the aqueous solution of the fluorocarbon surfactant used is 0.5-50%, and the immersion time is 2-24 hours. After the immersion is completed, the powder is separated and dried to obtain a lithium-rich manganese-based positive electrode material with the fluorocarbon surfactant adsorbed on the surface; Step 2: Evenly mix the powder of the lithium-rich manganese-based positive electrode material with the carbon-fluorosurfactant adsorbed on the surface with a certain amount of lithium hydroxide monohydrate or lithium carbonate in a mortar, and then calcine at a high temperature to obtain the modified lithium-rich manganese-based positive electrode material.

2. The method for preparing the modified lithium-rich manganese-based positive electrode material according to claim 1, characterized in that: The fluorine content of the modified lithium-rich manganese-based positive electrode material in step 2 is between 0.1% and 10%.

3. The method for preparing the modified lithium-rich manganese-based positive electrode material according to claim 2, characterized in that: The amount of the lithium hydroxide monohydrate or the lithium carbonate added in step 2 is 0.1-5 wt %.

4. The method for preparing the modified lithium-rich manganese-based positive electrode material according to claim 3, characterized in that: The high temperature calcination in step 2 is carried out by a one-step sintering method at 600-900 o C temperature in an oxygen or air atmosphere for 1-10 h.

5. The method for preparing the modified lithium-rich manganese-based positive electrode material according to claim 4, characterized in that: The step 2 of separating the powder after the impregnation and drying it to obtain a lithium-rich manganese-based positive electrode material with a fluorocarbon surfactant adsorbed on the surface specifically includes: After the impregnation is completed, the powder is separated by centrifugation and heated at 80-120 o C, and drying the powder to obtain a lithium-rich manganese-based positive electrode material with a fluorocarbon surfactant adsorbed on the surface.

6. The method for preparing a modified lithium-rich manganese-based positive electrode material according to any one of claims 1 to 5, characterized in that: The lithium-rich manganese-based positive electrode material is cobalt-free Li 1.2 Ni 0.2 Mn 0.6 O2 or Li containing cobalt 1.2 Ni 0.13 Co 0.13 Mn 0.54 At least one of O2.

7. A modified lithium-rich manganese-based positive electrode material, characterized in that: The modified lithium-rich manganese-based positive electrode material is prepared by the preparation method according to any one of claims 1 to 6.

8. An application of a modified lithium-rich manganese-based positive electrode material, characterized in that: The modified lithium-rich manganese-based positive electrode material prepared by the preparation method of the modified lithium-rich manganese-based positive electrode material according to any one of claims 1 to 6 is applied to the field of lithium-ion batteries.

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