Lithium-rich manganese-based cathode materials, their preparation methods and applications

Abstract

The present invention relates to the field of lithium battery materials. Specifically, it relates to a lithium-rich manganese-based cathode material, a preparation method thereof, and an application. The surface of the lithium-rich manganese-based cathode material has oxygen vacancies, and its molecular formula is Li 1+a Mn b M c O2, wherein Mn includes trivalent manganese and tetravalent manganese, and the molar percentage of trivalent manganese in the overall Mn is 20% to 60%. M includes one or more of Ni, Co, Al, Mo, Ti, and Zr, 0

Description

Technical Field

[0001] The present invention relates to the field of lithium battery materials, and in particular, to a lithium-rich manganese-based cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, the rapid development of new energy vehicles has put forward higher requirements for the energy density of lithium-ion secondary batteries. The cathode material is a key factor in achieving a high energy density of lithium-ion secondary batteries. However, currently mature cathode materials such as lithium cobaltate, spinel lithium manganate, lithium iron phosphate, and nickel cobalt manganese ternary materials are difficult to meet the requirements for high specific energy of lithium-ion secondary batteries in fields such as electric vehicles. Therefore, there is an urgent need for new cathode materials with low cost, high energy density, and good safety.

[0003] The lithium-rich manganese-based layered cathode material has a high specific capacity of more than 250 mAh / g and a high working voltage of 4.8 V, and is inexpensive, which has received extensive attention from researchers. However, it still faces problems such as low initial Coulomb efficiency, serious capacity and voltage decay, and poor rate performance, which have hindered the industrial application of this material in lithium-ion secondary batteries. The low initial Coulomb efficiency and serious voltage decay of the lithium-rich manganese-based layered cathode material are mainly due to irreversible oxygen evolution during the first cycle, which on the one hand causes a large irreversible capacity loss, and on the other hand reduces the binding energy between transition metal ions and oxygen, inducing the migration and valence change of transition metal ions, resulting in the occurrence of irreversible phase transformation and voltage decay.

[0004] At present, the methods for improving the electrochemical performance of the lithium-rich manganese-based layered cathode material often lead to the destruction of its structure and easy precipitation and loss of lithium while improving the initial Coulomb efficiency and rate performance of the lithium-rich manganese-based layered cathode material. Summary of the Invention

[0005] Based on this, the present invention provides a lithium-rich manganese-based cathode material with self-regulated oxygen vacancies, which can inhibit voltage decay during battery cycling while improving the initial Coulomb efficiency, and a preparation method and an application thereof.

[0006] On the one hand, the present invention provides a lithium-rich manganese-based cathode material, the surface of the lithium-rich manganese-based cathode material has oxygen vacancies, and its molecular formula is Li 1+a Mn b M c O2, wherein, Mn includes trivalent manganese and tetravalent manganese, and the molar percentage of trivalent manganese in the overall Mn is 20% to 60%, M includes one or more of Ni, Co, Al, Mo, Ti, and Zr, 0 < a ≤ 0.25, b ≥ 0.5, 0.8 ≤ a + b + c ≤ 1.2.

[0007] In some of these embodiments, the lithium-rich manganese-based cathode material is a layered material and has a stacking fault structure, and the thickness of the stacking fault structure is ≤50 nm.

[0008] In some of these embodiments, the lithium-rich manganese-based cathode material satisfies at least one of the following properties:

[0009] (1) The particle size D50 is 3 μm to 15 μm;

[0010] (2) The specific surface area is 0.3 m 2 / g to 6.0 m 2 / g;

[0011] (3) The tap density is 1.5 g / cm 3 to 2.8 g / cm 3 .

[0012] On the one hand, the present invention also provides a preparation method of the lithium-rich manganese-based cathode material as described above, which includes the following steps:

[0013] Mix a lithium source, a manganese source, an M source, and an organic substance to prepare a mixed powder, and the organic substance is used to provide a nitrogen source and / or a carbon source; and

[0014] Calcine and cool the mixed powder.

[0015] In some of these embodiments, the organic substance includes one or more of sucrose, glucose, chitosan, urea, and citric acid.

[0016] In some of these embodiments, in the mixed powder, the mass percentage of the organic substance is 0.5% to 10%.

[0017] In some of these embodiments, it has at least one of the following characteristics:

[0018] (1) The lithium source includes one or more of LiOH, Li2CO3, Li2SO4, LiCl, and LiNO3;

[0019] (2) The manganese source includes one or more of MnO, MnO2, Mn3O4, MnCO3, and MnSO4;

[0020] (3) The M source is one or more of an oxide, a hydroxide, a carbonate, and a sulfate of a metal element containing M.

[0021] In some of these embodiments, the calcination is a segmented calcination, and the specific process of the segmented calcination is as follows:

[0022] In an oxygen-containing atmosphere, first control the intake rate to be 0.5 m 3 / h to 5 m 3 / h, heat up to 300°C to 600°C at a heating rate of 1.0°C / min to 5.0°C / min, and keep the temperature for 2h to 8h; then control the intake rate to be 0.5m 3 / h to 5m 3 / h, heat up to 800°C to 1000°C at a heating rate of 1.0°C / min to 5.0°C / min, and keep the temperature for 10h to 20h.

[0023] In some of the embodiments, the cooling method is air cooling or liquid nitrogen quenching;

[0024] Optionally, the air intake rate of the air cooling is 5m 3 / h to 30m 3 / h.

[0025] In some of the embodiments, the method for preparing the mixed powder is specifically as follows:

[0026] Dissolve the lithium source, the manganese source, the M source and the organic matter in a solvent, and dry;

[0027] Optionally, the drying method is spray drying, and the liquid inlet rate of the spray drying is 0.5L min -1 ~5Lmin -1 , the inlet air temperature is 150°C to 300°C, the outlet air temperature is 80°C to 200°C, and the carrier gas rate is 20L min -1 ~200Lmin -1 .

[0028] On the other hand, the present invention further provides a positive electrode, which includes a positive electrode current collector and a positive electrode active material layer located on one or both sides of the positive electrode current collector, and the positive electrode active material in the positive electrode active material layer is the above-mentioned lithium-rich manganese-based positive electrode material.

[0029] On yet another aspect, the present invention further provides a lithium secondary battery, which includes the above-mentioned positive electrode.

[0030] On the other hand, the present invention further provides an electrical device, which includes the above-mentioned lithium secondary battery.

[0031] It is found through research that during the first charging process of traditional lithium-rich manganese-based cathode materials, some oxygen ions escape from the lattice, resulting in irreversible capacity. This makes the first Coulombic efficiency of lithium-rich manganese-based cathode materials relatively low. Moreover, the oxygen vacancies left after the oxygen ions escape can cause the migration of transition metal ions, leading to irreversible phase transformation and voltage decay of lithium-rich manganese-based cathode materials. The above-provided lithium-rich manganese-based cathode materials introduce oxygen vacancy defects on their surface, and through the regulation of the type and content of organic substances and in combination with the calcination and cooling processes, the local oxygen partial pressure of the raw materials during the calcination process is precisely controlled, realizing the self-regulation of the number of oxygen vacancies and the stacking fault thickness in the lithium-rich manganese-based cathode materials. Thereby, the surface and interface stability of the lithium-rich manganese-based cathode materials are improved, the first Coulombic efficiency is increased, and the voltage decay during the battery cycling process is inhibited.

[0032] In addition, the self-regulation of oxygen vacancies can induce the molar percentage content of trivalent manganese in the material to be within a specific range of 20% - 60%, which is beneficial to the improvement of the conductivity of lithium-rich manganese-based cathode materials, promotes the charge transport and transfer on the material surface, enhances the diffusion and reaction kinetics of lithium ions, and improves the rate performance of lithium-rich manganese-based cathode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0034] Figure 1 XRD pattern of the lithium-rich manganese-based layered cathode material prepared in Example 1 of the present invention;

[0035] Figure 2 TEM image of the lithium-rich manganese-based layered cathode material prepared in Example 1 of the present invention;

[0036] Figure 3 XPS spectrum of Mn element on the surface of the lithium-rich manganese-based layered cathode materials prepared in Example 1 and Comparative Example 1;

[0037] Figure 4 TEM image of the lithium-rich manganese-based layered cathode material prepared in Comparative Example 3 of the present invention;

[0038] Figure 5 Graph showing the test results of the rate performance of the lithium-ion secondary batteries formed by the lithium-rich manganese-based layered cathode materials in Example 1 and Comparative Examples 1 and 2;

[0039] Figure 6It is a graph showing the test results of the cycling performance of the lithium-rich manganese-based layered cathode material in Example 1 and Comparative Examples 1 and 2 for the lithium-ion secondary battery. Detailed Description of the Invention

[0040] Reference will now be made in detail to embodiments of the invention, one or more examples of which are described below. Each example is provided by way of explanation and not limitation of the invention. Indeed, it will be apparent to those skilled in the art that various modifications and variations can be made to the invention without departing from the scope or spirit of the invention. For example, features illustrated or described as part of one embodiment can be used in another embodiment to yield a still further embodiment.

[0041] Accordingly, it is intended that the invention cover such modifications and variations that fall within the scope of the appended claims and their equivalents. Other objects, features, and aspects of the invention are disclosed in or are apparent from the following detailed description. Those of ordinary skill in the art will understand that this discussion is only a description of exemplary embodiments and is not intended to limit the broader aspects of the invention.

[0042] 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 invention belongs. The terms used in the description of the invention herein are for the purpose of describing particular embodiments only and are not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0043] A first object of the present invention is to provide a lithium-rich manganese-based cathode material, wherein the surface of the lithium-rich manganese-based cathode material has oxygen vacancies, and its molecular formula is Li 1+a Mn b M c O2, wherein Mn includes trivalent manganese and tetravalent manganese, and the molar percentage of trivalent manganese in the overall Mn is 20% to 60%, M includes one or more of Ni, Co, Al, Mo, Ti, and Zr, 0 < a ≤ 0.25, b ≥ 0.5, 0.8 ≤ a + b + c ≤ 1.2.

[0044] Through research, it is found that during the first charging process of traditional lithium-rich manganese-based cathode materials, some oxygen ions escape from the lattice, generating irreversible capacity, resulting in a low initial Coulombic efficiency of the lithium-rich manganese-based cathode materials. Moreover, the oxygen vacancies left after the escape of oxygen ions will cause the migration of transition metal ions, resulting in irreversible phase transformation and voltage decay of the lithium-rich manganese-based cathode materials. The above-provided lithium-rich manganese-based cathode materials introduce oxygen vacancy defects on their surfaces, and the self-regulation of oxygen vacancies can make the valence states of manganese elements on the surface of the lithium-rich manganese-based cathode materials present a mixed state of +3 and +4, which is conducive to promoting charge transport and transfer on the surface of the lithium-rich manganese-based cathode materials, enhancing the diffusion and reaction kinetics of lithium ions, and improving the rate performance of the lithium-rich manganese-based cathode materials. Further regulating the molar percentage of trivalent manganese in manganese elements within a specific range is beneficial to the improvement of the conductivity of the lithium-rich manganese-based cathode materials.

[0045] In some embodiments, the molar percentage of trivalent manganese can be any value between 20% and 60%. For example, it can also be 25%, 30%, 35%, 40%, 45%, 50%.

[0046] In some embodiments, the lithium-rich manganese-based cathode material is a layered material and has a stacking fault structure, and the thickness of the stacking fault structure ≤ 50 nm.

[0047] In some embodiments, the lithium-rich manganese-based cathode material satisfies at least one of the following properties:

[0048] (1) The particle size D50 is 3 μm to 15 μm;

[0049] (2) The specific surface area is 0.3 m 2 / g to 6.0 m 2 / g;

[0050] (3) The tapped density is 1.5 g / cm 3 to 2.8 g / cm 3 .

[0051] In some embodiments, the lithium-rich manganese-based cathode material particles (i.e., secondary particles) are formed by the agglomeration of primary particles. Among them, the particle size D50 of the primary particles in the lithium-rich manganese-based cathode material can be any value between 50 nm and 500 nm.

[0052] The second object of the present invention also provides a preparation method of the lithium-rich manganese-based cathode material as described above, which includes steps S100 to S200:

[0053] Step S100: Mix a lithium source, a manganese source, an M source, and an organic substance to prepare a mixed powder, and the organic substance is used to provide a nitrogen source and / or a carbon source.

[0054] In some embodiments, the organic matter includes, but is not limited to, one or more of sucrose, glucose, chitosan, urea, and citric acid.

[0055] In some embodiments, in the mixed powder, the mass percentage of the organic matter can be any value between 0.5% and 10%, for example, it can also be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%.

[0056] In some embodiments, the choice of the lithium source is not restricted, and any lithium source well-known in the art can be selected, including but not limited to one or more of LiOH, Li2CO3, Li2SO4, LiCl, and LiNO3.

[0057] It can be understood that the choice of the manganese source is also not restricted. For example, the manganese source can be selected from one or more of MnO, MnO2, Mn3O4, MnCO3, and MnSO4.

[0058] Similarly, those skilled in the art are capable of selecting the M source according to needs. For example, it can be one or more of oxides, hydroxides, carbonates, and sulfates of M metal elements. Specifically, the M source can be one or more of nickel oxide, nickel hydroxide, nickel carbonate, nickel sulfate, cobalt oxide, cobalt hydroxide, cobalt carbonate, cobalt sulfate, aluminum oxide, aluminum hydroxide, aluminum carbonate, aluminum sulfate, molybdenum oxide, molybdenum hydroxide, molybdenum carbonate, molybdenum sulfate, titanium oxide, titanium hydroxide, titanium sulfate, zirconium oxide, zirconium hydroxide, zirconium carbonate, and zirconium sulfate.

[0059] In some embodiments, the method used to prepare the mixed powder can be any mixing method well-known in the art, such as dry mixing or wet mixing. In the present invention, the mixing method can be specifically as follows:

[0060] Dissolve the lithium source, manganese source, M source, and organic matter in a solvent and dry.

[0061] It can be understood that the solvent can be any commonly used solvent in the art. For example, it can be an alcohol solvent and / or water, and the alcohol solvent can be methanol and / or ethanol.

[0062] Furthermore, the mass ratio of the solvent to the total mass of the lithium source, manganese source, M source, and organic matter is (0.5 - 1.5):1.

[0063] In some embodiments, the drying method is not restricted either. Spray drying is preferred; more preferably, the liquid inlet rate of spray drying can be 0.5 L / min -1 ~5 L / min -1 、the inlet air temperature can be 150°C - 300°C, the outlet air temperature can be 80°C - 200°C, and the carrier gas rate can be 20 L / min -1~200 L / min -1 。

[0064] Step S200: Calcinate and cool the mixed powder obtained in Step S100.

[0065] In some embodiments, the calcination is segmented calcination, and the specific process of the segmented calcination is as follows:

[0066] Under an oxygen-containing atmosphere, first control the intake rate to be 0.5 m 3 / h to 5 m 3 / h, heat up to 300°C to 600°C at a heating rate of 1.0 °C / min to 5.0 °C / min, and keep warm for 2 h to 8 h; then control the intake rate to be 0.5 m 3 / h to 5 m 3 / h, heat up to 800°C to 1000°C at a heating rate of 1.0 °C / min to 5.0 °C / min, and keep warm for 10 h to 20 h.

[0067] In some embodiments, the cooling method is air cooling or liquid nitrogen quenching. By selecting the above cooling methods, rapid cooling can be achieved, thereby ensuring the formation of better oxygen vacancies.

[0068] Preferably, the air intake rate of air cooling can be any value between 5 m 3 / h and 30 m 3 / h. For example, it can also be 10 m 3 / h, 12 m 3 / h, 15 m 3 / h, 20 m 3 / h, 25 m 3 / h, 28 m 3 / h.

[0069] For the above preparation method of the lithium-rich manganese-based cathode material, due to the differences in the decomposition temperatures of different organic substances and the gas products generated by the decomposition, the local oxygen partial pressure of the raw materials during the calcination process can be controlled, and by finely regulating the calcination formula, the coupling of the temperature field and the mixed gas flow field during the calcination process can be realized, and oxygen vacancy defects are introduced into the structure of the lithium-rich manganese-based cathode material. Further optimize the cooling process after calcination, induce the self-limited diffusion of vacancy defects on the surface, and realize the self-regulation of oxygen vacancies (such as the number and stacking fault thickness of oxygen vacancies) in the lithium-rich manganese-based cathode material, thereby improving the surface and interface stability of the lithium-rich manganese-based cathode material, increasing the initial Coulombic efficiency, and suppressing the voltage decay during the battery cycling process.

[0070] The third object of the present invention further provides a cathode, which includes a cathode current collector and a cathode active material layer located on one or both sides of the cathode current collector, and the cathode active material in the cathode active material layer is the above-mentioned lithium-rich manganese-based cathode material.

[0071] A fourth object of the present invention further provides a lithium ion secondary battery, which includes the positive electrode described above.

[0072] A fifth object of the present invention further provides an electrical device, which includes the lithium secondary battery described above.

[0073] The present invention will be further described in detail below with reference to specific examples and comparative examples.

[0074] Example 1

[0075] 1) Weigh 530 g of lithium hydroxide (LiOH·H2O), 458 g of manganese tetraoxide (Mn3O4), 92 g of nickel hydroxide (Ni(OH)2), 93 g of cobalt hydroxide (Co(OH)2), 59 g of glucose, 3.2 g of aluminum oxide (Al2O3) and 2.8 g of zirconium dioxide (ZrO2), add them to 1000 mL of deionized water, stir and mix evenly to obtain a first mixture;

[0076] 2) Pump the first mixture prepared in step 1) into a spray drying device through a peristaltic pump, set the liquid inlet rate to 0.8 L / min -1 , set the inlet air temperature of spray drying to 250 °C, the outlet air temperature to 120 °C, and the carrier gas rate to 50 L / min -1 , evaporate the liquid in the first mixture to obtain a powder with uniformly mixed metal ions;

[0077] 3) Place the powder prepared in step 2) in an air atmosphere furnace for calcination. The calcination process is as follows: first, raise the temperature to 450 °C at a heating rate of 3 °C / min and calcine for 4 h, where the inlet gas rate is 3 m 3 / h; then raise the temperature to 900 °C at a heating rate of 3 °C / min and calcine for 12 h, where the inlet gas rate is 2 m 3 / h. Subsequently, continue to introduce air into the air atmosphere furnace for air cooling, where the inlet gas rate is 10 m 3 / h. Then pulverize and screen the product to obtain an oxygen vacancy self-regulated lithium-rich manganese-based layered cathode material (Li 1.2 Mn 0.6 Ni 0.1 Co 0.1 O2) with a stacking fault thickness of 4 nm. Among them, in step 1), lithium hydroxide is in an excess of 5 wt.%, which can make up for the loss of lithium during high-temperature calcination.

[0078] The XRD pattern of the lithium-rich manganese-based layered cathode material was measured as Figure 1 shown. From Figure 1It can be seen that except for the relatively weak diffraction peaks of the Li2MnO3 structure belonging to the C2 / m space group between 20° and 25°, the remaining diffraction peaks can correspond to the hexagonal layered structure, and the introduction of oxygen vacancies does not change the bulk structure characteristics of the lithium-rich manganese-based layered cathode material. In addition, I(003) / I(104) > 1.2, indicating that Li + / Ni 2+ has a low degree of cation mixing. From Figure 2 it can be seen that there are local structural stacking faults introduced by oxygen vacancy defects on the surface of the lithium-rich manganese-based layered cathode material, and the stacking fault thickness is about 4 nm. From Figure 3 it can be seen that since there is a linear relationship between the valence state of the Mn element and the splitting energy of the Mn 3s doublet, that is, O Mn = 9.67 - 1.27ΔE 3s . Among them, ΔE 3s of the prepared lithium-rich manganese-based layered cathode material is 4.73 eV, that is, the average valence state of Mn in the lithium-rich manganese-based layered cathode material is +3.66. It can be seen that due to the generation of oxygen vacancies on the surface of the lithium-rich manganese-based layered cathode material, the relative content of +3 valence Mn in the Mn element is higher (about 32.5%). This highly mixed valence state is beneficial to improving the electronic conductivity of the lithium-rich manganese-based layered cathode material.

[0079] Example 2

[0080] 1) Weigh 466 g of lithium carbonate (Li2CO3), 632 g of manganese carbonate (MnCO3), 184 g of nickel hydroxide (Ni(OH)2), 310 g of cobalt sulfate (CoSO4), 48 g of sucrose, 2.2 g of aluminum oxide (Al2O3), 4.5 g of molybdenum trioxide (MoO3) and 2.5 g of titanium dioxide (TiO2), add them to 1300 mL of ethanol, stir and mix evenly to obtain a first mixture;

[0081] 2) Pump the first mixture prepared in step 1) into a spray drying device through a peristaltic pump, set the liquid inlet rate to 1 L min -1 , set the inlet air temperature of spray drying to 220 °C, the outlet air temperature to 100 °C, and the carrier gas rate to 150 Lmin -1 , evaporate the liquid in the first mixture to obtain a powder with uniformly mixed metal ions;

[0082] 3) Place the powder prepared in step 2) in an air atmosphere furnace for calcination. The calcination process is as follows: first, raise the temperature to 400 °C at a heating rate of 2.5 °C / min and calcine for 6 h, where the inlet gas rate is 6 m 3 / h; then raise the temperature to 920 °C at a heating rate of 2.5 °C / min and calcine for 10 h, where the inlet gas rate is 3 m 3 / h. Subsequently, continue to introduce air in an air atmosphere furnace for air cooling, with an intake rate of 15 m 3 / h. Then, pulverize and screen the product to obtain an oxygen vacancy self-regulated lithium-rich manganese-based layered cathode material (Li 1.1 Mn 0.55 Ni 0.2 Co 0.2 O2) with a stacking fault thickness of 10 nm. Among them, in step 1), lithium carbonate is in excess by 5 wt.%, which can compensate for the loss of lithium volatilization during high-temperature calcination. The relative content of +3 valence Mn in the Mn element of the lithium-rich manganese-based layered cathode material is measured to be approximately 36.8%.

[0083] Example 3

[0084] 1) Weigh 466 g of lithium carbonate (Li2CO3), 522 g of manganese dioxide (MnO2), 308 g of nickel sulfate (NiSO4), 26 g of chitosan, 5.0 g of molybdenum trioxide (MoO3) and 3.0 g of zirconium dioxide (ZrO2), add them to 1350 mL of ethanol, stir and mix evenly to obtain a first mixture;

[0085] 2) Pump the first mixture prepared in step 1) into a spray drying device through a peristaltic pump, set the liquid inlet rate to 0.8 L min -1 , set the inlet air temperature of spray drying to 200 °C, the outlet air temperature to 80 °C, and the carrier gas rate to 80 Lmin -1 , evaporate the liquid in the first mixture to obtain a powder with uniformly mixed metal ions;

[0086] 3) Place the powder prepared in step 2) in an air atmosphere furnace for calcination. The calcination process is as follows: first, raise the temperature to 500 °C at a heating rate of 4 °C / min and calcine for 3 h, with an intake rate of 2 m 3 / h; then raise the temperature to 940 °C at a heating rate of 4 °C / min and calcine for 10 h, with an intake rate of 3 m 3 / h. Subsequently, continue to introduce air in the air atmosphere furnace for air cooling, with an intake rate of 12 m 3 / h. Then, pulverize and screen the product to obtain an oxygen vacancy self-regulated lithium-rich manganese-based layered cathode material (Li 1.2 Mn 0.6 Ni 0.2 O2) with a stacking fault thickness of 8 nm. Among them, in step 1), lithium carbonate is in excess by 5 wt.%, which can compensate for the loss of lithium volatilization during high-temperature calcination. The relative content of +3 valence Mn in the Mn element of the lithium-rich manganese-based layered cathode material is measured to be approximately 30.5%.

[0087] Example 4

[0088] 1) Weigh 664 g of lithium sulfate (Li2SO4), 845 g of manganese sulfate (MnSO4), 177 g of nickel oxide (NiO), 169 g of glucose, 2.4 g of zirconium dioxide (ZrO2) and 3.6 g of titanium dioxide (TiO2), add them to 2250 mL of deionized water, stir and mix evenly to obtain a first mixture;

[0089] 2) Pump the first mixture prepared in step 1) into a spray drying device through a peristaltic pump, set the liquid inlet rate to 3 L / min -1 , set the inlet air temperature of spray drying to 280 °C, the outlet air temperature to 120 °C, and the carrier gas rate to 180 L / min -1 , evaporate the liquid in the first mixture to obtain a powder with uniformly mixed metal ions;

[0090] 3) Place the powder prepared in step 2) in an air atmosphere furnace for calcination. The calcination process is as follows: First, raise the temperature to 450 °C at a heating rate of 5 °C / min and calcine for 6 h, with an inlet gas rate of 4 m 3 / h; then raise the temperature to 880 °C at a heating rate of 5 °C / min and calcine for 16 h, with an inlet gas rate of 5 m 3 / h. Subsequently, continue to introduce air in the air atmosphere furnace for air cooling, with an inlet gas rate of 25 m 3 / h. Then pulverize and screen the product to obtain an oxygen vacancy self-regulated lithium-rich manganese-based layered cathode material (Li 1.15 Mn 0.56 Ni 0.24 O2) with a stacking fault thickness of 12 nm. Among them, in step 1), lithium sulfate is in an excess of 5 wt.%, which can compensate for the loss of lithium volatilization during high-temperature calcination. The relative content of +3 valence Mn in the Mn element of the lithium-rich manganese-based layered cathode material is measured to be approximately 36.2%.

[0091] Example 5

[0092] 1) Weigh 529 g of lithium chloride (LiCl), 397 g of manganese monoxide (MnO), 110 g of nickel hydroxide (Ni(OH)2), 110 g of cobalt oxyhydroxide (CoOOH), 46 g of citric acid, 1.2 g of aluminum hydroxide (Al(OH)3) and 4.0 g of zirconium dioxide (ZrO2), add them to 1400 mL of methanol, stir and mix evenly to obtain a first mixture;

[0093] 2) Pump the first mixture prepared in step 1) into a spray drying device through a peristaltic pump, set the liquid inlet rate to 1 L / min -1 , set the inlet air temperature of spray drying to 240 °C, the outlet air temperature to 160 °C, and the carrier gas rate to 150 L / min -1, evaporate the liquid in the first mixture to obtain a powder with uniformly mixed metal ions;

[0094] 3) Place the powder prepared in step 2) in an air atmosphere furnace for calcination. The calcination process is as follows: First, raise the temperature to 350 °C at a heating rate of 2 °C / min and calcine for 8 h, with an air inlet rate of 4.5 m 3 / h; then raise the temperature to 850 °C at a heating rate of 2 °C / min and calcine for 20 h, with an air inlet rate of 5 m 3 / h. Subsequently, continue to introduce air in the air atmosphere furnace for air cooling, with an air inlet rate of 20 m 3 / h. Then pulverize and screen the product to obtain an oxygen vacancy self-regulated lithium-rich manganese-based layered cathode material (Li 1.2 Mn 0.56 Ni 0.12 Co 0.12 O2) with a stacking fault thickness of 23 nm. Among them, in step 1), lithium chloride is in excess by 5 wt.%, which can make up for the volatilization loss of lithium during high-temperature calcination. The relative content of +3 valence Mn in the Mn element of the lithium-rich manganese-based layered cathode material is measured to be approximately 40.2%.

[0095] Example 6

[0096] 1) Weigh 466 g of lithium carbonate (Li2CO3), 435 g of manganese dioxide (MnO2), 186 g of cobalt hydroxide (Co(OH)2), 11 g of urea, 51 g of aluminum oxide (Al2O3), 4.5 g of molybdenum trioxide (MoO3) and 2.4 g of titanium dioxide (TiO2), add them to 1450 mL of methanol, stir and mix evenly to obtain a first mixture;

[0097] 2) Pump the first mixture prepared in step 1) into a spray drying device through a peristaltic pump. Set the liquid inlet rate to 0.8 L min -1 , set the inlet air temperature of the spray drying to 300 °C, the outlet air temperature to 100 °C, and the carrier gas rate to 30 Lmin -1 , evaporate the liquid in the first mixture to obtain a powder with uniformly mixed metal ions;

[0098] 3) Place the powder prepared in step 2) in an air atmosphere furnace for calcination. The calcination process is as follows: First, raise the temperature to 550 °C at a heating rate of 3.5 °C / min and calcine for 4 h, with an air inlet rate of 1.5 m 3 / h; then raise the temperature to 900 °C at a heating rate of 3.5 °C / min and calcine for 14 h, with an air inlet rate of 0.5 m 3 / h. Subsequently, perform liquid nitrogen quenching. Then pulverize and screen the product to obtain an oxygen vacancy self-regulated lithium-rich manganese-based layered cathode material (Li 1.2Mn 0.5 Co 0.2 Al 0.1 O2). Among them, in step 1), lithium carbonate is in excess by 5 wt.%, which can make up for the volatilization loss of lithium during high-temperature calcination. The relative content of Mn with a +3 valence in the Mn element of the lithium-rich manganese-based layered cathode material is measured to be about 30.6%.

[0099] Comparative Example 1

[0100] The preparation method of this comparative example is basically the same as that of Example 1, the difference being that: no organic matter is added. The specific steps are as follows:

[0101] 1) Weigh 530 g of lithium hydroxide (LiOH·H2O), 458 g of manganese tetroxide (Mn3O4), 92 g of nickel hydroxide (Ni(OH)2), 93 g of cobalt hydroxide (Co(OH)2), 3.2 g of aluminum oxide (Al2O3) and 2.8 g of zirconium dioxide (ZrO2), add them to 1000 mL of deionized water, stir and mix evenly to obtain a first mixture;

[0102] 2) Pump the first mixture prepared in step 1) into a spray drying device through a peristaltic pump, set the liquid inlet rate to 0.8 L min -1 , set the inlet air temperature of spray drying to 250 °C, the outlet air temperature to 120 °C, and the carrier gas rate to 50 Lmin -1 , evaporate the liquid in the first mixture to obtain a powder with uniformly mixed metal ions;

[0103] 3) Place the powder prepared in step 2) in an air atmosphere furnace for calcination. The calcination process is as follows: first raise the temperature to 450 °C at a heating rate of 3 °C / min and calcine for 4 h, where the inlet gas rate is 3 m 3 / h; then raise the temperature to 900 °C at a heating rate of 3 °C / min and calcine for 12 h, where the inlet gas rate is 2 m 3 / h. Subsequently, continue to pass air in the air atmosphere furnace for air cooling, where the inlet gas rate is 10 m 3 / h. Then pulverize and screen the product to obtain a lithium-rich manganese-based layered cathode material (Li 1.2 Mn 0.6 Ni 0.1 Co 0.1 O2). Among them, in step 1), lithium hydroxide is in excess by 5 wt.%, which can make up for the volatilization loss of lithium during high-temperature calcination. It can be seen from Figure 3 that since there is a linear relationship between the valence state of the Mn element and the Mn 3s doublet splitting energy, that is, O Mn = 9.67 - 1.27ΔE 3s . Among them, ΔE of the lithium-rich manganese-based layered cathode material prepared above 3sIt is 4.50 eV, that is, the average valence state of Mn in the lithium-rich manganese-based layered cathode material is +3.96. It can be seen that since there are no oxygen vacancies on the surface of the above-prepared lithium-rich manganese-based layered cathode material, the relative content of Mn with a valence of +3 in the Mn element is lower (about 4%), and the electronic conductivity of the lithium-rich manganese-based layered cathode material is lower.

[0104] Comparative Example 2

[0105] The preparation method of this comparative example is to form oxygen vacancies by acid etching. The specific steps are as follows:

[0106] 1) According to the molar ratio of Mn:Ni:Co of 6:1:1, 245.2 g of manganese acetate tetrahydrate, 41.6 g of cobalt acetate tetrahydrate and 41.6 g of nickel acetate tetrahydrate were respectively taken and dissolved in 4 L of ethylene glycol solution to obtain a first metal salt solution with a molar concentration of 2 mol / L;

[0107] 2) 350 g of ammonium bicarbonate was dissolved in a mixed solution of 2.5 L of water and polyethylene glycol 400 (volume ratio 1:1) to obtain a second solution; under magnetic stirring, the second solution was pumped into the first metal salt solution prepared in step 1) through a peristaltic pump, and then placed in a high-pressure reactor at 180 °C for heat preservation for 10 h; then cooled and centrifuged to obtain a precipitate;

[0108] 3) The precipitate prepared in step 2) was placed in a muffle furnace and heat-preserved at 500 °C for 5 h to obtain a lithium-rich manganese-based material precursor. After mixing according to the molar ratio of the metal elements in the lithium-rich manganese-based material precursor to lithium hydroxide of 1:1.06, it was ground evenly and placed in a muffle furnace, and heated to 800 °C at a heating rate of 3 °C / min for calcination for 12 h, and taken out after cooling to room temperature to obtain a pre-modified lithium-rich manganese-based material;

[0109] 4) 50 g of the pre-modified lithium-rich manganese-based material prepared in step 3) was dissolved in an oxalic acid solution with a concentration of 0.02 mol / L and stirred for 30 min, then filtered and dried by suction, placed in a muffle furnace, and heat-treated at 500 °C for 5 h to obtain an acid-treated modified lithium-rich manganese-based layered cathode material (Li 1.2 Mn 0.6 Ni 0.1 Co 0.1 O2).

[0110] Comparative Example 3

[0111] The preparation method of this comparative example is basically the same as that of Example 1, the difference is that: the mass percentage of the organic matter is 15%. The specific steps are as follows:

[0112] 1) Weigh 530 g of lithium hydroxide (LiOH·H2O), 458 g of manganese tetroxide (Mn3O4), 92 g of nickel hydroxide (Ni(OH)2), 93 g of cobalt hydroxide (Co(OH)2), 177 g of glucose, 3.2 g of aluminum oxide (Al2O3) and 2.8 g of zirconium dioxide (ZrO2), add them to 1000 mL of deionized water, stir and mix evenly to obtain the first mixture;

[0113] 2) Pump the first mixture prepared in step 1) into a spray drying device through a peristaltic pump, set the liquid inlet rate to 0.8 L / min -1 , set the inlet air temperature of spray drying to 250 °C, the outlet air temperature to 120 °C, and the carrier gas rate to 50 L / min -1 , evaporate the liquid in the first mixture to obtain a powder with uniformly mixed metal ions;

[0114] 3) Place the powder prepared in step 2) in an air atmosphere furnace for calcination. The calcination process is as follows: first, raise the temperature to 450 °C at a heating rate of 3 °C / min and calcine for 4 h, where the inlet gas rate is 3 m 3 / h; then raise the temperature to 900 °C at a heating rate of 3 °C / min and calcine for 12 h, where the inlet gas rate is 2 m 3 / h. Subsequently, continue to introduce air in the air atmosphere furnace for air cooling, where the inlet gas rate is 10 m 3 / h. Then crush and screen the product to obtain a lithium-rich manganese-based layered cathode material (Li 1.2 Mn 0.6 Ni 0.1 Co 0.1 O2). Among them, in step 1), the lithium hydroxide is in an excess of 5 wt.%, which can compensate for the loss of lithium volatilization during high-temperature calcination.

[0115] The TEM image of the lithium-rich manganese-based layered cathode material is shown as Figure 4 . As can be seen from Figure 4 , a spinel structure and an electrochemically inert rock salt structure appear on the surface of the above-prepared lithium-rich manganese-based layered cathode material, and the relative content of +3 valence Mn in the Mn element is too high (about 60.4%), and the lithium ion diffusion of the lithium-rich manganese-based layered cathode material is inhibited.

[0116] The lithium-rich manganese-based layered cathode materials prepared in Examples 1 to 6 and Comparative Examples 1 to 3 are prepared into coin-type lithium-ion secondary batteries according to the following method to test the electrochemical performance of the lithium-rich manganese-based layered cathode materials. The specific preparation steps are as follows:

[0117] The lithium-rich manganese-based layered cathode material powders prepared in Examples 1 to 6 and Comparative Examples 1 to 3 were respectively mixed with acetylene black and polyvinylidene fluoride (mass ratio 90:6:4), and an appropriate amount of N-methylpyrrolidone was added as a dispersant and ground into a slurry; subsequently, the slurry was uniformly coated on aluminum foil, vacuum-dried at 120 °C for 10 h, and then the dried electrode was roll-pressed using a roll press, and the aluminum foil was cut using a slicing machine into circular electrodes with a diameter of 1.3 cm. Among them, the loading amount of the lithium-rich manganese-based layered cathode material loaded on the circular electrode was controlled at ~10 mg cm -2 . A half-cell was assembled in an argon atmosphere glove box, where the water partial pressure ≤ 0.1 ppm and the oxygen partial pressure ≤ 0.1 ppm. Using metallic lithium as the counter electrode and a 1 M LiPF6 (FEC / EC / DMC, volume ratio 1:1:1) solution as the electrolyte, a CR2032-type coin lithium-ion secondary battery was assembled. Subsequently, a constant current charge-discharge test was carried out at room temperature conditions, with a voltage range of 2.0 V to 4.65 V and a current density of 50 mA / g (0.2 C rate) for 100 charge-discharge cycles. The lithium-ion diffusion coefficients of different lithium-rich manganese-based layered cathode materials were compared through electrochemical impedance EIS tests, and the test frequency range was 100 kHz to 0.01 Hz. The current densities for the battery rate performance tests were 50 mA / g, 500 mA / g, 1250 mA / g, and 2500 mA / g, corresponding to 0.2 C, 2 C, 5 C, and 10 C respectively.

[0118] Among them, the rate performance test results of the CR2032-type coin lithium-ion secondary batteries formed using the lithium-rich manganese-based layered cathode materials prepared in Example 1 and Comparative Examples 1 to 2 are as Figure 5 shown.

[0119] The cycle performance test results of the CR2032-type coin lithium-ion secondary batteries formed using the lithium-rich manganese-based layered cathode materials prepared in Example 1 and Comparative Examples 1 to 2 are as Figure 6 shown.

[0120] The first-week charge specific capacity, first-week discharge specific capacity, first-week Coulomb efficiency, capacity retention rate after 100 weeks, discharge mid-voltage decay, and lithium-ion diffusion coefficient of the above-mentioned CR2032-type coin lithium-ion secondary batteries were measured as shown in Table 1:

[0121] Table 1

[0122]

[0123] The rate performance of the above-mentioned CR2032-type coin lithium-ion secondary batteries was measured as shown in Table 2:

[0124] Table 2

[0125]

[0126]

[0127] As can be seen from the above test results, for the lithium-rich manganese-based layered cathode material provided by the present invention, by adding an organic substance and regulating its content during the preparation process, and further optimizing the calcination and cooling processes, the local oxygen partial pressure in the raw materials of the lithium-rich manganese-based layered cathode material during the calcination process can be accurately controlled, inducing the formation of oxygen vacancies on the surface of the lithium-rich manganese-based layered cathode material, and self-regulation of the oxygen vacancies in terms of quantity and stacking fault thickness can be achieved. As a result, the lithium-rich manganese-based layered cathode material with self-regulated oxygen vacancies exhibits a higher initial Coulombic efficiency, and the capacity retention rate is still significantly higher than that of the lithium-rich manganese-based layered cathode material prepared in the comparative example after 100 cycles, and the voltage decay is significantly inhibited. In addition, the rate performance test at different current densities from 0.2C to 8C shows that the discharge capacity retention rate (8C discharge capacity / 0.2C discharge capacity) of the lithium-rich manganese-based layered cathode material provided by the present invention is above 80% at a high rate of 8C, which is much higher than that of the lithium-rich manganese-based layered cathode material prepared in the comparative example. It can be seen from the lithium ion diffusion coefficient obtained by the EIS test that the lithium-rich manganese-based layered cathode material provided by the present invention has a higher lithium ion diffusion coefficient, showing stronger reaction kinetics.

[0128] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0129] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent should be subject to the appended claims.

Claims

1. A lithium-rich manganese-based cathode material, characterized in that, The surface of the lithium-rich manganese-based cathode material has oxygen vacancies, and its molecular formula is Li 1+a Mn b M c O2, where Mn includes trivalent manganese and tetravalent manganese, and the molar percentage of trivalent manganese in the overall Mn is 20% to 60%, M includes one or more of Ni, Co, Al, Mo, Ti, and Zr, 0 < a ≤ 0.25, b ≥ 0.5, 0.8 ≤ a + b + c ≤ 1.2; The preparation method of the lithium-rich manganese-based cathode material comprises the following steps: Mix a lithium source, a manganese source, an M source, and an organic substance to prepare a mixed powder, where the organic substance is used to provide a nitrogen source and / or a carbon source; Calcine and cool the mixed powder; The organic substance includes one or more of sucrose, glucose, chitosan, urea, and citric acid; In the mixed powder, the mass percentage of the organic substance is 0.5% to 10%; The calcination is carried out in stages, and the specific process of the staged calcination is as follows: under an oxygen-containing atmosphere, first control the inlet gas rate to be 0.5 m 3 / h to 5 m 3 / h, and heat up to 300°C to 600°C at a heating rate of 1.0°C / min to 5.0°C / min, and keep the temperature for 2 h to 8 h; then control the inlet gas rate to be 0.5 m 3 / h to 5 m 3 / h, and heat up to 800°C to 1000°C at a heating rate of 1.0°C / min to 5.0°C / min, and keep the temperature for 10 h to 20 h; The cooling method is air cooling or quenching with liquid nitrogen.

2. The lithium-rich manganese-based cathode material according to claim 1, wherein The lithium-rich manganese-based cathode material is a layered material and has a stacking fault structure, and the thickness of the stacking fault structure is ≤ 50 nm.

3. The lithium-rich manganese-based cathode material according to claim 1 or 2, characterized in that, The lithium-rich manganese-based cathode material satisfies at least one of the following properties: (1) The particle size D50 is 3 μm to 15 μm; (2) The specific surface area is 0.3 m 2 / g to 6.0 m 2 / g; (3) The tapped density is 1.5 g / cm 3 ~2.8 g / cm 3 .

4. A method for preparing a lithium-rich manganese-based cathode material according to any one of claims 1 to 3, characterized in that, Comprises the following steps: Mix a lithium source, a manganese source, an M source, and an organic substance to prepare a mixed powder, where the organic substance is used to provide a nitrogen source and / or a carbon source; Calcine and cool the mixed powder; the organic substance includes one or more of sucrose, glucose, chitosan, urea, and citric acid; In the mixed powder, the mass percentage of the organic substance is 0.5% to 10%; The calcination is a segmented calcination, and the specific process of the segmented calcination is as follows: Under an oxygen-containing atmosphere, first control the intake rate to be 0.5 m 3 / h to 5 m 3 / h, and heat up to 300 °C to 600 °C at a heating rate of 1.0 °C / min to 5.0 °C / min, and keep the temperature for 2 h to 8 h; then control the intake rate to be 0.5 m 3 / h to 5 m 3 / h, and heat up to 800 °C to 1000 °C at a heating rate of 1.0 °C / min to 5.0 °C / min, and keep the temperature for 10 h to 20 h; The cooling method is air cooling or quenching with liquid nitrogen.

5. The preparation method of the lithium-rich manganese-based cathode material according to claim 4, wherein, Has at least one of the following characteristics: (1) The lithium source includes one or more of LiOH, Li2CO3, Li2SO4, LiCl, and LiNO3; (2) The manganese source includes one or more of MnO, MnO2, Mn3O4, MnCO3, and MnSO4; (3) The M source is one or more of an oxide, hydroxide, carbonate, and sulfate of a metal element containing M.

6. The preparation method of the lithium-rich manganese-based cathode material according to claim 4, wherein, The air intake rate of the air-cooling is 5m 3 / h to 30m 3 / h.

7. The preparation method of the lithium-rich manganese-based cathode material according to any one of claims 4 to 6, characterized in that The method adopted for preparing the mixed powder is specifically as follows: Dissolve the lithium source, the manganese source, the M source, and the organic substance in a solvent and dry.

8. The preparation method of the lithium-rich manganese-based cathode material according to claim 7, wherein The drying method is spray drying, and the liquid inlet rate of the spray drying is 0.5 L / min -1 ~5 L / min -1 , the inlet air temperature is 150°C to 300°C, the outlet air temperature is 80°C to 200°C, and the carrier gas rate is 20 L / min -1 ~200 L / min -1 .

9. A positive electrode, characterized in that, Comprises a positive electrode current collector and a positive electrode active material layer located on one or both sides of the positive electrode current collector, and the positive electrode active material in the positive electrode active material layer is the lithium-rich manganese-based cathode material according to any one of claims 1 to 3.

10. A lithium secondary battery, characterized in that, Comprises the positive electrode according to claim 9.

11. An electrical device, characterized in that, Comprises the lithium secondary battery according to claim 10.

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