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

Abstract

The application relates to the technical field of lithium batteries, in particular to a coated lithium-rich manganese-based positive electrode material and a preparation method and application thereof. The coated lithium-rich manganese-based positive electrode material comprises a main body material and a coating layer formed on the surface of the main body material, the main body material is a lithium-rich manganese-based positive electrode material, the material of the coating layer comprises LiGdO2, the content of the LiGdO2 is 1%-5% according to the mass percentage of the coated lithium-rich manganese-based positive electrode material, and the surface of the main body material has oxygen vacancies. The above-mentioned coated lithium-rich manganese-based positive electrode material has high initial efficiency and energy density and low voltage attenuation rate.

Description

TECHNICAL FIELD

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

[0002] With the gradual increase of people's demand for energy, traditional non-renewable energy such as oil, coal and natural gas has been widely used, but these traditional energy has caused great pollution to the environment, and these energy can not meet the current economic development demand for energy. At this time, in order to protect the environment and realize sustainable development, it has become a trend to develop new energy.

[0003] Since the advent of lithium ion battery, due to its high working voltage and specific energy, long cycle life, low self-discharge, no memory effect and environmental protection, it is a promising energy storage device. But with the development of industrialization, large electric tools, energy storage power stations, Internet of Things, intelligent electronics and other fields have put forward new requirements for the safety, cycle life, energy density and low cost of lithium ion battery. Compared with the negative electrode material of lithium ion battery, the specific capacity of the positive electrode material of lithium ion battery is lower. Due to the structural instability in the cycle process and other factors, the actual available capacity of the lithium ion battery positive electrode material is lower than the theoretical capacity, so it is urgent to develop lithium ion battery positive electrode material with higher capacity.

[0004] Lithium-rich manganese-based positive electrode material is widely considered as one of the most attractive positive electrode materials due to its high specific capacity and high voltage (>4.5V). However, the traditional layered lithium-rich manganese-based positive electrode material such as LiCoO2 has problems such as high capacity attenuation rate, poor rate performance and high voltage attenuation rate, which seriously hinders its application in the field of lithium ion battery. SUMMARY

[0005] Therefore, it is necessary to provide a coated lithium-rich manganese-based positive electrode material which can improve the first efficiency and energy density of lithium-rich manganese-based positive electrode material and reduce the voltage attenuation rate, and a preparation method and application thereof.

[0006] In a first aspect, the present application provides a coated lithium-rich manganese-based positive electrode material, which comprises a main body material and a coating layer formed on the surface of the main body material; the main body material is a lithium-rich manganese-based positive electrode material, the surface of the main body material has oxygen vacancies, and the material of the coating layer comprises LiGdO2, and the content of the LiGdO2 is 1% to 5% according to the mass percentage of the coated lithium-rich manganese-based positive electrode material.

[0007] In some embodiments, the material of the coating layer is LiGdO2, and the content of the LiGdO2 is 2.5% to 4%.

[0008] In a second aspect, the present application also provides a preparation method of the coated lithium-rich manganese-based positive electrode material according to the first aspect, which comprises the following steps:

[0009] The host material and the gadolinium source are dissolved in an alcohol solvent, and after heating to remove the alcohol solvent, annealing is performed under an oxygen-containing atmosphere, and the annealing temperature is 400-780°C.

[0010] In some embodiments, the gadolinium source is a gadolinium salt, and the gadolinium salt comprises gadolinium nitrate and / or gadolinium chloride.

[0011] In some embodiments, the alcohol solvent comprises one or more of methanol, ethanol, ethylene glycol and propylene glycol.

[0012] In some embodiments, the heating temperature is 80-100°C.

[0013] In some embodiments, the host material is prepared by a method comprising the following steps:

[0014] After mixing the precursor material with a lithium source, calcination is performed under an oxygen-containing atmosphere, and the molecular formula of the precursor material is Ni x Mn y (OH)2, wherein 0

[0015] In some embodiments, the lithium source comprises one or more of lithium carbonate, lithium hydroxide, lithium nitrate and lithium chloride.

[0016] In some embodiments, the calcination conditions comprise: first, heating at a temperature increasing rate of 1-3°C / min to 350-500°C, and maintaining for 3-5h; and then, heating at a temperature increasing rate of 2-5°C / min to 900-1050°C, and maintaining for 9-15h.

[0017] In a third aspect, the present application further provides a lithium battery, wherein the positive electrode material of the lithium battery comprises the coated lithium-rich manganese-based positive electrode material according to the first aspect.

[0018] In a fourth aspect, the present application provides an electric drive device, which comprises the lithium battery according to the third aspect.

[0019] The coated lithium-rich manganese-based positive electrode material provided in the application can prevent the reaction of the lithium-rich manganese-based positive electrode material with the electrolyte, and avoid the problems of capacity attenuation and poor cycle performance of the coated lithium-rich manganese-based positive electrode material. The surface of the main material has a large number of oxygen vacancies, and the concentration of the oxygen vacancies can be further improved by setting the LiGdO2 coating layer. The existence of the oxygen vacancies not only provides more active sites for the overflowed oxygen ions, effectively alleviates the loss of the lattice oxygen of the lithium-rich manganese-based positive electrode material in the high voltage range, but also enhances the reversibility of the anion oxidation and reduction, and improves the initial specific discharge capacity of the coated lithium-rich manganese-based positive electrode material. In addition, LiGdO2 is an excellent lithium ion conductor, which greatly reduces the transmission rate of lithium ions, and improves the capacity and rate performance of the coated lithium-rich manganese-based positive electrode material. Moreover, a small amount of Gd element is doped into the lithium-rich manganese-based positive electrode material in the process of forming the coating layer, which further inhibits the voltage attenuation of the coated lithium-rich manganese-based positive electrode material.

[0020] In addition, by adjusting the content, on the one hand, the uniform LiGdO2 coating layer can be ensured to be formed; on the other hand, the formation of the uniform LiGdO2 coating layer can make the surface of the lithium-rich manganese-based positive electrode material form an appropriate GdO2 layer, which can not only avoid the agglomeration of LiGdO2, but also inhibit the release of oxygen, thereby improving the coating effect and the safety of the coated lithium-rich manganese-based positive electrode material. Moreover, by adjusting the content of LiGdO2 within the range, the oxygen vacancy concentration can be maintained at a high concentration, thereby increasing the number of active sites on the surface of the coated lithium-rich manganese-based positive electrode material. Moreover, the high concentration of oxygen vacancies can inhibit the generation of oxygen, thereby improving the capacity of the coated lithium-rich manganese-based positive electrode material.

[0021] Further, the preparation method adopted in the application is a liquid phase method, the LiGdO2 coating layer prepared by the method is more uniform, and by adjusting the annealing temperature within the above range, the uniform coating of the LiGdO2 coating layer can be ensured, and the doping effect of gadolinium element can also be achieved. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the description of the embodiments or the prior art will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0023] Figures 1-3 The first charge-discharge performance test diagram, cycle performance diagram and voltage attenuation diagram of the lithium-rich manganese-based positive electrode material prepared in Examples 1-4, respectively;

[0024] Figures 4-6The first charge-discharge performance test chart, cycle performance chart and voltage attenuation chart of the lithium-rich manganese-based positive electrode material prepared by Comparative Examples 1-4, respectively. DETAILED DESCRIPTION

[0025] For the purpose of facilitating the understanding of the present application, a more complete understanding of the present application can be had by reference to the relevant drawings in which the preferred embodiments of the application are illustrated. The application may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the application to those skilled in the art.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0027] Terms and definitions:

[0028] "Oxygen vacancy" refers to the oxygen atom (oxygen ion) in the oxygen-containing compound lattice being detached, resulting in oxygen deficiency, forming a vacancy, i.e. the defect left by the oxygen ion escaping from its lattice.

[0029] The conventional lithium-rich manganese-based positive electrode material often has problems of high capacity attenuation rate, poor rate performance, high voltage attenuation rate, etc. To solve this problem, the present application provides a coated lithium-rich manganese-based positive electrode material to improve its capacity, rate and cycle performance.

[0030] In a first aspect, the present application provides a coated lithium-rich manganese-based positive electrode material, which comprises a main body material and a coating layer formed on the surface of the main body material; wherein the main body material is a lithium-rich manganese-based positive electrode material, the surface of the main body material has oxygen vacancies, and the material of the coating layer comprises LiGdO2, and the content of LiGdO2 is 1% to 5% according to the mass percentage of the coated lithium-rich manganese-based positive electrode material.

[0031] The LiGdO2 coating layer can prevent the reaction of the lithium-rich manganese-based positive electrode material with the electrolyte, avoid the capacity attenuation and poor cycle performance of the coated lithium-rich manganese-based positive electrode material. The surface of the main material has a large number of oxygen vacancies, and the LiGdO2 coating layer can further increase the concentration of the oxygen vacancies. The existence of the oxygen vacancies not only provides more active sites for the overflowed oxygen ions, effectively alleviates the loss of the lattice oxygen of the lithium-rich manganese-based positive electrode material in the high voltage range, but also enhances the reversibility of the anion oxidation and reduction, and improves the initial discharge specific capacity of the coated lithium-rich manganese-based positive electrode material. In addition, LiGdO2 is an excellent lithium ion conductor, which greatly reduces the transmission rate of lithium ions and improves the capacity and rate performance of the coated lithium-rich manganese-based positive electrode material. Moreover, a small amount of Gd element is doped into the lithium-rich manganese-based positive electrode material during the formation of the coating layer, which further inhibits the voltage attenuation of the coated lithium-rich manganese-based positive electrode material.

[0032] In addition, by adjusting the content, on the one hand, the uniform LiGdO2 coating layer can be formed, and on the other hand, the formation of the uniform LiGdO2 coating layer can form an appropriate amount of GdO2 layer on the surface of the lithium-rich manganese-based positive electrode material, which can avoid the agglomeration of LiGdO2 and inhibit the release of oxygen, thereby improving the coating effect and safety of the coated lithium-rich manganese-based positive electrode material. Moreover, by adjusting the content of LiGdO2 within the range, the oxygen vacancy concentration can be maintained at a high concentration, thereby increasing the number of active sites on the surface of the coated lithium-rich manganese-based positive electrode material. Moreover, the high concentration of oxygen vacancies can inhibit the generation of oxygen, thereby improving the capacity of the coated lithium-rich manganese-based positive electrode material.

[0033] In some embodiments, the chemical formula of the lithium-rich manganese-based positive electrode material is Li x Ni y Mn z O2, wherein 0.8≤x≤1.2, 0<y<1, and 0<z<1.

[0034] In some embodiments, the material of the coating layer is LiGdO2.

[0035] In some embodiments, the content of LiGdO2 is any value between 1% and 5%, and can also be 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, or 4.5%. Preferably, the content of LiGdO2 is any value between 2.5% and 4%. By adjusting the content of LiGdO2 to 2.5% to 4%, the capacity and initial efficiency of the coated lithium-rich manganese-based positive electrode material can be further improved, and the coated lithium-rich manganese-based positive electrode material has excellent electrochemical performance.

[0036] It can be understood that in the process of forming the LiGdO2coating layer, Gd elements are inevitably doped in the host material (lithium-rich manganese-based positive electrode material), and the content of the doped Gd elements in the host material is in a positive proportional relationship with the content of the LiGdO2coating layer, so that the content of the doped Gd elements in the host material can be regulated by regulating the content of the LiGdO2, and the doping of the Gd elements can inhibit the voltage attenuation of the coated lithium-rich manganese-based positive electrode material.

[0037] In a second aspect, the application further provides a preparation method of the coated lithium-rich manganese-based positive electrode material according to the first aspect, which comprises the following steps:

[0038] The host material and the gadolinium source are dissolved in an alcohol solvent, and after heating to remove the alcohol solvent, annealing is performed in an oxygen-containing atmosphere; wherein the annealing temperature is 400-780°C.

[0039] The formation principle of the LiGdO2coating layer is specifically that in the annealing process, the gadolinium source reacts with lithium elements in the lithium-rich manganese-based positive electrode material, thereby forming a LiGdO2nanolayer with high ionic and electronic conductivity on the outermost layer.

[0040] The above preparation method is a liquid phase method, compared with a solid phase method, the prepared LiGdO2coating layer is more uniform, and regulating the annealing temperature in the above range can ensure that the LiGdO2coating layer is uniformly coated. Moreover, the solvent used is an alcohol solvent rather than pure water phase, and the alcohol solvent can be easily evaporated, which can avoid the loss of the coated lithium-rich manganese-based positive electrode material during evaporation.

[0041] In some embodiments, the gadolinium source is a gadolinium salt, which can or can not be in a hydrate form. Specifically, the gadolinium salt comprises gadolinium nitrate and / or gadolinium chloride; wherein the gadolinium nitrate is specifically gadolinium nitrate hexahydrate.

[0042] In the present application, the alcohol solvent can be any alcohol solvent commonly used in the art. In some embodiments, the alcohol solvent comprises one or more of methanol, anhydrous ethanol, ethylene glycol and propylene glycol. Specifically, the ethanol is anhydrous ethanol.

[0043] In some embodiments, the annealing temperature can also be 420°C, 450°C, 480°C, 500°C, 550°C, 580°C, 600°C, 620°C, 650°C, 680°C, 700°C, 720°C, 750°C.

[0044] In some embodiments, the annealing temperature is raised to 400-780°C at a temperature raising rate of 3-5°C / min, and the annealing time is 3-8h.

[0045] In the present application, the heating condition is not limited, and is determined according to the complete removal of the alcohol solvent. In some embodiments, the heating temperature is 80-100°C, and the heating time is 15-30 min.

[0046] In some embodiments, during the heating process, stirring can be performed synchronously for quickly and completely removing the alcohol solvent. The stirring mode and condition can be selected from those commonly used in the art, and are not limited herein, for example, mechanical stirring and / or magnetic stirring. The stirring rate can be 300-600 rpm / min, and the time can be 15-30 min.

[0047] In some embodiments, the oxygen-containing atmosphere specifically refers to an atmosphere containing oxygen, for example, an air atmosphere, an oxygen atmosphere, etc.

[0048] In some embodiments, the host material is prepared by a method comprising the following steps:

[0049] After mixing the precursor material and the lithium source, the mixture is calcined under an oxygen-containing atmosphere. The molecular formula of the precursor material is Ni x Mn y (OH)2, 0

[0050] In the present application, the lithium source can be any lithium-containing compound known in the art. In some embodiments, the lithium source comprises one or more of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium chloride.

[0051] In some embodiments, the molar ratio between the lithium element in the lithium source, the Ni element in the precursor material, and the Mn element in the precursor material is 1:x:y, wherein 0

[0052] In some embodiments, the calcination conditions comprise: first, increasing the temperature to 350-500°C at a temperature increasing rate of 1-3°C / min, and maintaining the temperature for 3-5 h; and then, increasing the temperature to 900-1050°C at a temperature increasing rate of 2-5°C / min, and maintaining the temperature for 9-15 h.

[0053] According to one specific embodiment, the preparation method of the coated lithium-rich manganese-based positive electrode material comprises the following steps:

[0054] S10: After mixing the precursor material and the lithium source, the mixture is calcined under an oxygen-containing atmosphere to form a host material. The molecular formula of the precursor material is Ni x Mn y (OH)2, 0

[0055] S20: mixing the host material prepared in step S10 with a gadolinium source in an alcohol solvent to form a mixed solution; wherein the mass percentage of the gadolinium source in the total amount of the host material and the gadolinium source is 1% to 5%;

[0056] S30: heating the mixed solution prepared in step S30 to remove the alcohol solvent to prepare a mixed powder;

[0057] S40: annealing the mixed powder prepared in step S30 at a temperature of 400°C to 780°C.

[0058] In a third aspect, the present application further provides a lithium battery, wherein the positive electrode material of the lithium battery comprises the coated lithium-rich manganese-based positive electrode material according to the first aspect.

[0059] It can be understood that the lithium battery is a lithium secondary battery, and specifically can be a lithium ion battery.

[0060] In the present application, the lithium battery can further comprise a negative electrode material, an electrolyte, a separator and other components or components necessary for the lithium battery. Specifically, the negative electrode material can comprise one or more of graphite, mesocarbon microbeads and silicon-carbon negative electrodes; the electrolyte can be an electrolyte or a solid-state electrolyte, and the solid-state electrolyte can be composed of components including a polymer matrix and a lithium salt.

[0061] As an exemplary illustration, the polymer matrix can comprise one or more of polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, polyvinyl chloride, polycarbonate, polysulfone, polyvinylpyrrolidone, polyethylene-vinyl acetate copolymer and polyvinyl butyral; and the lithium salt can comprise any one or more of lithium difluorophosphate, lithium difluorobisoxalate phosphate, lithium tetrafluoroborate, lithium difluoro oxalate borate, lithium bisoxalate borate, lithium bis(trifluoromethylsulfonyl)imide and lithium bisfluorosulfonylimide.

[0062] In some embodiments, the separator is a polyethylene film or a polypropylene film.

[0063] In a fourth aspect, the present application provides an electrically driven device comprising the lithium battery according to the third aspect.

[0064] In some embodiments, the electrically driven device specifically refers to a device using the above-mentioned lithium battery as a power supply, as an exemplary illustration, the electrically driven device comprises an electronic intelligent device (mobile phone, computer, etc.), can also be an electric vehicle, and can also be an electric tool, for example, a power drill, a power saw, etc.

[0065] The present application will be further described in detail below in combination with specific embodiments.

[0066] Embodiment 1

[0067] In this embodiment, LiGdO2 accounts for 1% of the mass percentage of the coated lithium-rich manganese-based cathode material.

[0068] 1. Preparation of lithium-rich manganese-based cathode materials

[0069] 1) Add 2g Ni 0.25 Mn 0.75 (OH)₂ was mixed with 1.3726g Li₂CO₃ to form a mixture, which was then placed in a tube furnace under an oxygen atmosphere and calcined. The calcined material was passed through a 300-mesh sieve to obtain lithium-rich manganese-based cathode material (Li₂CO₃) with a particle size of ~5μm. 1.2 Ni 0.2 Mn 0.6 O2); the calcination process is as follows: first, heat to 500℃ at a heating rate of 3℃ / min, hold for 5h, then heat to 1000℃ at a heating rate of 2℃ / min, and hold for 15h.

[0070] 2. Preparation of coated lithium-rich manganese-based cathode materials

[0071] 1) Take 1g of the Li obtained in step 1 1.2 Ni 0.2 Mn 0.6 O2 and 0.025g (Gd)3NO 3.6 H2O was dissolved in ethanol and heated at 90°C while being stirred at 500 rpm for 25 min to obtain a mixed powder.

[0072] 2) The mixed powder obtained in step 1) was placed in a tube furnace under an oxygen atmosphere and annealed at 600°C for 6 hours. After cooling to room temperature, it was passed through a 300-mesh sieve to obtain LiGdO2-coated lithium-rich manganese-based cathode material with a particle size of ~6μm.

[0073] Example 2

[0074] In this embodiment, LiGdO2 accounts for 3% of the mass percentage of the coated lithium-rich manganese-based cathode material.

[0075] 1. Preparation of lithium-rich manganese-based cathode materials

[0076] 1) Add 2g Ni 0.25 Mn 0.75 (OH)₂ was mixed with 1.3726g Li₂CO₃ to form a mixture, which was then placed in a tube furnace under an oxygen atmosphere and calcined. The calcined material was passed through a 300-mesh sieve to obtain lithium-rich manganese-based cathode material (Li₂CO₃) with a particle size of ~5μm. 1.2 Ni 0.2 Mn 0.6O2); wherein the calcination process is as follows: first, increase the temperature to 500°C at a rate of 3°C / min, keep the temperature for 5h, then increase the temperature to 1000°C at a rate of 2°C / min, keep the temperature for 15h.

[0077] 2. Preparation of coated lithium-rich manganese-based positive electrode material

[0078] 1) Take 1 g of Li 1.2 Ni 0.2 Mn 0.6 O2 prepared in step 1) and 0.03 g of (Gd)3NO 3.6 H2O dissolved in ethanol, and heated at 90°C while stirring at 500 rpm for 25 min to obtain a mixed powder

[0079] 2) Put the mixed powder obtained in step 1) into a tube furnace in an oxygen atmosphere, and anneal at 600°C for 6h. After cooling to room temperature, pass through a 300 mesh sieve to obtain a lithium-rich manganese-based positive electrode material coated with LiGdO2 with a particle size of about 6 μm.

[0080] Example 3

[0081] In this example, the mass percentage of LiGdO2 in the coated lithium-rich manganese-based positive electrode material is 5%.

[0082] 1. Preparation of lithium-rich manganese-based positive electrode material

[0083] 1) Mix 2 g of Ni 0.25 Mn 0.75 (OH)2 and 1.3726 g of Li2CO3 to form a mixture, then put the mixture into a tube furnace in an oxygen atmosphere, and calcine, pass the calcined material through a 300 mesh sieve to obtain a lithium-rich manganese-based positive electrode material (Li 1.2 Ni 0.2 Mn 0.6 O2) with a particle size of about 5 μm; wherein the calcination process is as follows: first, increase the temperature to 500°C at a rate of 3°C / min, keep the temperature for 5h, then increase the temperature to 1000°C at a rate of 2°C / min, keep the temperature for 15h.

[0084] 2. Preparation of coated lithium-rich manganese-based positive electrode material

[0085] 1) Take 1 g of Li 1.2 Ni 0.2 Mn 0.6 O2 prepared in step 1) and 0.04 g of (Gd)3NO 3.6 H2O dissolved in ethanol, and heated at 90°C while stirring at 500 rpm for 25 min to obtain a mixed powder

[0086] 2) The mixed powder obtained in step 1) was placed in a tube furnace in an oxygen atmosphere and annealed at 600°C for 6h. After cooling to room temperature, the LiGdO2-coated lithium-rich manganese-based positive electrode material with a particle size of ~6μm was obtained after sieving through a 300-mesh sieve.

[0087] Example 4

[0088] The preparation method in this example was basically the same as that in Example 1, except that the annealing temperature in step 2) was 500°C.

[0089] 1. Preparation of a lithium-rich manganese-based positive electrode material

[0090] 1) 2g Ni 0.25 Mn 0.75 (OH)2was mixed with 1.3726g Li2CO3to form a mixture, and then the mixture was placed in a tube furnace in an oxygen atmosphere and calcined. The calcined material was sieved through a 300-mesh sieve to obtain a lithium-rich manganese-based positive electrode material (Li 1.2 Ni 0.2 Mn 0.6 O2) with a particle size of ~5μm; wherein the calcination process was as follows: first, the temperature was raised to 500°C at a rate of 3°C / min, and then held for 5h; then, the temperature was raised to 1000°C at a rate of 2°C / min, and then held for 15h.

[0091] 2. Preparation of a coated lithium-rich manganese-based positive electrode material

[0092] 1) 1g of Li 1.2 Ni 0.2 Mn 0.6 O2prepared in step 1) was mixed with 0.035g (Gd)3NO 3.6 H2O was dissolved in ethylene glycol and heated at 90°C while stirring at 500rpm for 25min to remove the ethylene glycol, and then a mixed powder was prepared;

[0093] 2) The mixed powder obtained in step 1) was placed in a tube furnace in an oxygen atmosphere and annealed at 500°C for 4h. After cooling to room temperature, the LiGdO2-coated lithium-rich manganese-based positive electrode material with a particle size of ~6μm was obtained after sieving through a 300-mesh sieve.

[0094] Comparative Example 1

[0095] The lithium-rich manganese-based positive electrode material in this comparative example was not coated. The specific steps were as follows:

[0096] 2g Ni 0.25 Mn 0.75Li2CO3 to form a mixture, and then the mixture is placed in a tube furnace in an oxygen atmosphere and calcined, and the calcined material is sieved through a 300 mesh screen to produce a lithium-rich manganese-based positive electrode material (Li 1.2 Ni 0.2 Mn 0.6 O2); wherein the calcination process is as follows: first, the temperature is raised to 500°C at a rate of 3°C / min, and then the temperature is held for 5h, and then the temperature is raised to 1000°C at a rate of 2°C / min, and then the temperature is held for 15h.

[0097] Comparative Example 2

[0098] The preparation method of Comparative Example 2 is basically the same as that of Example 2, except that the mass percentage of LiGdO2 in the coated lithium-rich manganese-based positive electrode material is 0.5%. The specific steps are as follows:

[0099] 1. Preparation of a lithium-rich manganese-based positive electrode material

[0100] 1) 2g of Ni 0.25 Mn 0.75 (OH)2 is mixed with 1.3726g of Li2CO3 to form a mixture, and then the mixture is placed in a tube furnace in an oxygen atmosphere and calcined, and the calcined material is sieved through a 300 mesh screen to produce a lithium-rich manganese-based positive electrode material (Li 1.2 Ni 0.2 Mn 0.6 O2); wherein the calcination process is as follows: first, the temperature is raised to 500°C at a rate of 3°C / min, and then the temperature is held for 5h, and then the temperature is raised to 1000°C at a rate of 2°C / min, and then the temperature is held for 15h.

[0101] 2. Preparation of a coated lithium-rich manganese-based positive electrode material

[0102] 1) 1g of Li 1.2 Ni 0.2 Mn 0.6 O2 prepared in step 1 is mixed with 0.005g of (Gd)3NO 3.6 H2O is dissolved in ethanol and heated at 90°C while stirring at 500rpm for 25min to remove the ethanol, and then a mixed powder is prepared;

[0103] 2) The mixed powder obtained in step 1) is placed in a tube furnace in an oxygen atmosphere and annealed at 600°C for 6h. Then, after cooling to room temperature, sieving through a 300 mesh screen, a LiGdO2-coated lithium-rich manganese-based positive electrode material with a particle size of ~6μm is obtained.

[0104] Comparative Example 3

[0105] The preparation method of Comparative Example 3 is substantially the same as that of Example 2, except that the mass percentage of LiGdO2 in the coated lithium-rich manganese-based positive electrode material is 6%. The specific steps are as follows:

[0106] 1. Preparation of a lithium-rich manganese-based positive electrode material

[0107] 1) 2 g of Ni 0.25 Mn 0.75 (OH)2was mixed with 1.3726 g of Li2CO3to form a mixture, and then the mixture was placed in a tube furnace in an oxygen atmosphere and calcined. The calcined material was sieved through a 300-mesh sieve to obtain a lithium-rich manganese-based positive electrode material (Li 1.2 Ni 0.2 Mn 0.6 O2) with a particle size of about 5 μm; wherein the calcination process was as follows: first, the temperature was raised to 500°C at a rate of 3°C / min, and then the temperature was raised to 1000°C at a rate of 2°C / min, and the temperature was maintained for 15 h.

[0108] 2. Preparation of a coated lithium-rich manganese-based positive electrode material

[0109] 1) 1 g of Li 1.2 Ni 0.2 Mn 0.6 O2obtained in step 1 was mixed with 0.06 g of (Gd)3NO 3.6 H2O was dissolved in ethanol and heated at 90°C while stirring at 500 rpm for 25 min to remove the ethanol, and then a mixed powder was obtained;

[0110] 2) The mixed powder obtained in step 1) was placed in a tube furnace in an oxygen atmosphere and annealed at 600°C for 6 h. Then, after cooling to room temperature, sieving through a 300-mesh sieve, a LiGdO2-coated lithium-rich manganese-based positive electrode material with a particle size of about 6 μm was obtained.

[0111] Comparative Example 4

[0112] The preparation method of Comparative Example 4 is substantially the same as that of Example 2, except that the annealing temperature in step 2 is 900°C. The specific steps are as follows:

[0113] 1. Preparation of a lithium-rich manganese-based positive electrode material

[0114] 1) 2 g of Ni 0.25 Mn 0.75 (OH)2was mixed with 1.3726 g of Li2CO3to form a mixture, and then the mixture was placed in a tube furnace in an oxygen atmosphere and calcined. The calcined material was sieved through a 300-mesh sieve to obtain a lithium-rich manganese-based positive electrode material (Li 1.2 Ni0.2 Mn 0.6 O2); wherein the calcination process is as follows: first, heating to 500℃ at a heating rate of 3℃ / min, holding for 5h, then heating to 1000℃ at a heating rate of 2℃ / min, holding for 15h.

[0115] 2. Preparation of coated lithium-rich manganese-based positive electrode material

[0116] 1) Take 1g of Li 1.2 Ni 0.2 Mn 0.6 O2 and 0.03g (Gd)3NO 3.6 H2O is dissolved in ethanol, and after heating at 90℃ while stirring at 500rpm for 25min to remove ethanol, a mixed powder is prepared;

[0117] 2) The mixed powder obtained in step 1) is placed in a tube furnace in an oxygen atmosphere, and annealed at 900℃ for 6h. After cooling to room temperature, it is sieved through a 300 mesh sieve to obtain a lithium-rich manganese-based positive electrode material coated with LiGdO2 with a particle size of ~6μm.

[0118] The positive electrode materials prepared in Examples 1-4 and Comparative Examples 1-4 are subjected to electrochemical performance testing, and the test results are shown in Table 1 below.

[0119] Wherein the test conditions for each performance test item are as follows:

[0120] 1) First charge-discharge test: the lithium-rich manganese-based positive electrode materials prepared in Examples 1-4 and Comparative Examples 1-4 are subjected to constant current charge-discharge testing by assembling button cells using the LAND battery testing system. The test voltage range is 2.0V-4.8V, and the test current is 0.05C, 1C=200mAg -1 .

[0121] 2) Cycle performance test: the lithium-rich manganese-based positive electrode materials prepared in Examples 1-4 and Comparative Examples 1-4 are tested for cycle performance at a constant current density of 0.5C, 1C=200mAg -1

[0122] The electrochemical performance of the positive electrode materials prepared in Examples 1-4 and Comparative Examples 1-4 is shown in Table 1 below.

[0123] Table 1

[0124]

[0125] Figures 1-3 The first charge-discharge curve, cycle performance curve and voltage attenuation graph of the lithium-rich manganese-based positive electrode materials prepared in Examples 1-4, respectively.​Figures 4-6 The first charge-discharge curves, cycle performance curves and voltage attenuation diagrams of the lithium-rich manganese-based positive electrode materials prepared in Comparative Examples 1-4, respectively. From Table 2 above and Figures 1-6 It can be seen that the lithium-rich manganese-based positive electrode materials in Examples 1-4 have higher oxygen vacancy concentration on the surface, and have more excellent electrochemical performance, higher capacity and efficiency. Moreover, the content of LiGdO2 has a more obvious effect on the capacity and efficiency of the coated lithium-rich manganese-based positive electrode material, and the content of LiGdO2 is preferably 2.5%-4%. When the preferred coating ratio is 3%, the lithium-rich manganese-based positive electrode material prepared has the highest first discharge specific capacity of 265 mAh / g. Comparative Example 1 is a lithium-rich manganese-based positive electrode material without coating. Compared with Comparative Example 1, the electrochemical performance of the lithium-rich manganese-based positive electrode materials prepared in Examples 1-4 is significantly improved, and the first discharge specific capacity of the lithium-rich manganese-based positive electrode material prepared in Example 2 is most obviously improved. From the test results of Comparative Examples 2 and 3, it can be seen that when the coating amount is not within the range of 1%-5%, the discharge specific capacity of the prepared lithium-rich manganese-based positive electrode material is obviously reduced, and the cycle stability is also obviously deteriorated. From the test results of Examples 2 and 4, it can be seen that when the annealing temperature exceeds the temperature range of 400°C-780°C, the capacity of the lithium-rich manganese-based positive electrode material is obviously reduced, the cycle stability is obviously deteriorated, and the voltage attenuation is more serious. Figure 3 and Figure 6 It can be seen that the voltage attenuation of the coated lithium-rich manganese-based positive electrode material is obviously smaller than that of the uncoated sample, which fully embodies the effect of Gd element doping. From the test results of Example 2 and Comparative Example 4, it can be seen that when the annealing temperature exceeds the temperature range of 400°C-780°C, the capacity of the lithium-rich manganese-based positive electrode material is obviously reduced, the cycle stability is obviously deteriorated, and the voltage attenuation is more serious.

[0126] The technical features of the above-described embodiments can be combined in any manner. To make the description concise, all possible combinations of the technical features in the above-described embodiments are not described, but as long as the combinations of the technical features do not contradict each other, they should be considered within the scope of the present disclosure.

[0127] The above-described embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are within the scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims, and the description and drawings can be used to explain the scope of the claims.

Claims

1. A coated lithium-rich manganese-based positive electrode material, characterized in that, The coated lithium-rich manganese-based positive electrode material comprises a main material and a coating layer formed on the surface of the main material; the main material is a lithium-rich manganese-based positive electrode material, the main material is doped with Gd element, the surface of the main material has oxygen vacancies, and the material of the coating layer comprises LiGdO2, and the content of the LiGdO2 is 1% to 5% according to the mass percentage of the coated lithium-rich manganese-based positive electrode material. 2.The coated lithium-rich manganese-based cathode material of claim 1, wherein, The material of the coating layer is LiGdO2, and the content of the LiGdO2 is 2.5% to 4%.

3. A method for preparing the coated lithium-rich manganese-based positive electrode material according to claim 1 or 2, characterized in that, The method comprises the following steps: The main material and the gadolinium source are dissolved in an alcohol solvent, the alcohol solvent is removed by heating, and then annealing is performed in an oxygen-containing atmosphere, and the annealing temperature is 400 DEG C to 780 DEG C.

4. The method of claim 3, wherein the coated lithium-rich manganese-based cathode material is prepared by the steps of: preparing a lithium-rich manganese-based cathode material; and coating the lithium-rich manganese-based cathode material with a coating layer. The preparation method satisfies at least one of the following conditions: 1) the gadolinium source is a gadolinium salt, and the gadolinium salt comprises gadolinium nitrate and / or gadolinium chloride; 2) the alcohol solvent comprises one or more of methanol, ethanol, ethylene glycol and propylene glycol.

5. The method of claim 3, wherein the coated lithium-rich manganese-based cathode material is prepared by the steps of: preparing a lithium-rich manganese-based cathode material; and coating the lithium-rich manganese-based cathode material with a coating layer. The heating temperature is 80 DEG C to 100 DEG C.

6. The method for preparing a coated lithium-rich manganese-based positive electrode material according to any one of claims 3 to 5, characterized in that, The main material is prepared by a method comprising the following steps: After mixing the precursor material with a lithium source, the precursor material has a molecular formula of Ni x Mn y (OH)2, wherein 0 < x < 0.3, 0.7 < y < 1, and x + y = 1.

7. The method of claim 6, wherein the coated lithium-rich manganese-based cathode material is prepared by the steps of: mixing a lithium source, a manganese source, and a transition metal source to form a mixture; adding a binder to the mixture; and sintering the mixture to form the coated lithium-rich manganese-based cathode material. The lithium source comprises one or more of lithium carbonate, lithium hydroxide, lithium nitrate and lithium chloride.

8. The method of claim 6, wherein the coated lithium-rich manganese-based cathode material is prepared by the steps of: mixing a lithium source, a manganese source, and a transition metal source to form a mixture; adding a binder to the mixture; and sintering the mixture to form the coated lithium-rich manganese-based cathode material. The calcination conditions comprise: first, heating at a temperature increasing rate of 1 DEG C / min to 3 DEG C / min to 350 DEG C to 500 DEG C, maintaining for 3 h to 5 h, and then heating at a temperature increasing rate of 2 DEG C / min to 5 DEG C / min to 900 DEG C to 1050 DEG C, maintaining for 9 h to 15 h.

9. A lithium battery, characterized by The positive electrode material of the lithium battery comprises the coated lithium-rich manganese-based positive electrode material according to claim 1 or 2.

10. An electric drive device, characterized by The lithium battery comprises the lithium battery according to claim 9.

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