Lithium manganese oxide cathode material and its preparation method, lithium battery

Abstract

This application belongs to the field of lithium battery technology, and particularly relates to a lithium manganese oxide cathode material and its preparation method, and a lithium battery. The method includes: adding manganese sulfate solution, precipitant and complexing agent in parallel to a reaction vessel, reacting under a first preset reaction condition, and simultaneously introducing a first oxidant to obtain a mixed solution; concentrating the mixed solution to a preset solid content, and adding a ripening agent to perform a ripening reaction to obtain a manganese tetroxide slurry; adding manganese sulfate solution, precipitant and complexing agent in parallel to the reaction vessel again, reacting with the manganese tetroxide slurry under a second preset reaction condition, and simultaneously introducing a second oxidant to obtain a composite manganese oxide mixed solution; filtering, washing and drying to obtain a composite manganese oxide; mixing the composite manganese oxide with lithium carbonate, calcining, crushing and classifying to obtain a lithium manganese oxide cathode material, thereby improving the electrochemical performance of the lithium manganese oxide cathode material.

Description

Technical Field

[0001] This application belongs to the field of lithium battery technology, and particularly relates to a lithium manganese oxide cathode material and its preparation method, and a lithium battery. Background Technology

[0002] Lithium spinel manganese oxide (LiMn2O4) is one of the cathode materials for lithium batteries, with a theoretical specific capacity of 148 mAh / g. Currently, manganese tetroxide is mainly used as a precursor or by high-temperature calcination of manganese tetroxide and manganese dioxide to prepare lithium manganese oxide. However, the manganese atoms in spinel lithium manganese oxide are densely arranged on the (111) crystal plane, which cannot further improve the diffusion rate of lithium ions, thus limiting the electrochemical performance of lithium manganese oxide cathode materials.

[0003] Existing technologies suffer from limitations in the electrochemical performance of spinel lithium manganese oxide, which cannot meet the requirements of various applications. Summary of the Invention

[0004] This application provides a lithium manganese oxide cathode material and its preparation method, as well as a lithium battery, aiming to solve to some extent the problem that the electrochemical performance of spinel lithium manganese oxide is limited and cannot meet the needs of various applications.

[0005] In a first aspect, this application provides a method for preparing a lithium manganese oxide cathode material, comprising:

[0006] Manganese sulfate solution, precipitant, and complexing agent are added to a reactor in parallel flow and reacted under a first preset reaction condition. A first oxidant is introduced into the reactor while the reaction is underway to obtain a manganese tetroxide mixed solution. The inflow rate of the manganese sulfate solution is the first inflow rate.

[0007] The manganese tetroxide mixed solution is concentrated to a preset solid content, and a curing agent is added to carry out a curing reaction to obtain manganese tetroxide slurry;

[0008] The manganese sulfate solution, the precipitant, and the complexing agent are added to the reactor in parallel flow again, and reacted with the manganese tetroxide slurry under the second preset reaction conditions. While reacting, a second oxidant is introduced into the reactor to obtain a composite manganese oxide mixed solution. The inlet rate of the manganese sulfate solution is the second inlet rate.

[0009] The composite manganese oxide mixture solution is filtered, washed, and dried to obtain a composite manganese oxide compound, wherein the composite manganese oxide compound is manganese trioxide in the form of a regular hexagonal single crystal embedded on a spinel manganese tetroxide substrate.

[0010] The composite manganese oxide compound was mixed with lithium carbonate, calcined in air, and then crushed and graded to obtain lithium manganese oxide cathode material.

[0011] Secondly, this application provides a lithium manganese oxide cathode material, which is prepared according to the preparation method of lithium manganese oxide cathode material according to any one of the contents of the first aspect.

[0012] Thirdly, this application provides a lithium battery, including a positive electrode, wherein the positive electrode includes a lithium manganese oxide positive electrode material prepared by the method for preparing lithium manganese oxide positive electrode material described in the second aspect.

[0013] It is understood that the beneficial effects of the second and third aspects mentioned above can be found in the relevant descriptions in the first aspect above, and will not be repeated here.

[0014] The advantages of this application compared to the prior art are:

[0015] Compared with the prior art, the preparation method of lithium manganese oxide cathode material of this application first prepares manganese tetroxide substrate material, and then oxidizes part of the manganese oxidation state from +2 to +3 under a strong oxidizing atmosphere to obtain a composite manganese oxide compound including manganese tetroxide. Since the liquid phase co-precipitation method is used to embed manganese tetroxide in the form of a regular hexagonal single crystal on the spinel manganese tetroxide substrate to form a composite manganese oxide compound, the number of (100) crystal faces in lithium manganese oxide is increased, and then the lithium manganese oxide cathode material is obtained. This method not only improves the discharge capacity of lithium manganese oxide cathode material, but also improves the capacity retention rate of lithium manganese oxide cathode material, thereby improving the electrochemical performance of lithium manganese oxide cathode material. Moreover, the liquid phase co-precipitation method reduces the manufacturing cost of lithium manganese oxide cathode material. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic flowchart of a method for preparing lithium manganese oxide cathode material according to an embodiment of this application;

[0018] Figure 2 This is an XRD pattern of the composite manganese oxide provided in Example 1 of this application;

[0019] Figure 3 This is a SEM schematic diagram of the composite manganese oxide provided in Example 1 of this application;

[0020] Figure 4 This is an XRD pattern of the composite manganese oxide provided in Comparative Example 1 of this application;

[0021] Figure 5 This is a SEM image of the composite manganese oxide provided in Comparative Example 1 of this application;

[0022] Figure 6 This is a SEM schematic diagram of the composite manganese oxide provided in Comparative Example 3 of this application. Detailed Implementation

[0023] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0024] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0025] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, a~b (i.e., a and b), a~c, b~c, or a~b~c, where a, b, and c can be single or multiple.

[0026] The terms "first" and "second" are used only to describe the purpose and to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the provisions of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature.

[0027] The terminology used in the embodiments of this application is for the purpose of describing particular implementations only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the implementations of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0028] It should be understood that in the various embodiments of this application, the sequence number of each process does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the implementation regulations of this application.

[0029] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a mass unit known in the chemical industry, such as μg, mg, g, or kg.

[0030] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0031] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application are available on the market or can be prepared by existing methods.

[0032] Lithium spinel manganese oxide (LiMn2O4) is one of the cathode materials for lithium batteries, with a theoretical specific capacity of 148 mAh / g. Currently, manganese tetroxide is mainly used as a precursor or by high-temperature calcination of manganese tetroxide and manganese dioxide to prepare lithium manganese oxide. Due to the unique three-dimensional tunnel structure of lithium spinel manganese oxide, lithium ions can be reversibly inserted and extracted from the spinel lattice. However, the manganese atoms in lithium spinel manganese oxide are densely arranged on the (111) crystal plane, which cannot further improve the diffusion rate of lithium ions, thus limiting the electrochemical performance of lithium manganese oxide cathode materials.

[0033] To address the aforementioned problems to some extent, the first aspect of this application provides a method for preparing a lithium manganese oxide cathode material, comprising:

[0034] S100, manganese sulfate solution, precipitant and complexing agent are added to the reactor in parallel flow, and the reaction is carried out under the first preset reaction conditions. The first oxidant is introduced into the reactor while the reaction is underway to obtain a manganese tetroxide mixed solution. The inlet rate of manganese sulfate solution is the first inlet rate.

[0035] S200, concentrate the manganese tetroxide mixed solution to the preset solid content, and add a curing agent to carry out a curing reaction to obtain manganese tetroxide slurry;

[0036] S300, manganese sulfate solution, precipitant and complexing agent are added to the reactor in parallel flow again, and reacted with manganese tetroxide slurry under the second preset reaction conditions. A second oxidant is introduced into the reactor while the reaction is underway to obtain a composite manganese oxide mixed solution. The inlet rate of manganese sulfate solution is the second inlet rate.

[0037] S400, the mixed solution of composite manganese oxide is filtered, washed and dried to obtain composite manganese oxide, which is manganese trioxide in the form of a regular hexagonal single crystal embedded on a spinel manganese tetroxide substrate.

[0038] S500 is a process in which a composite manganese oxide compound is mixed with lithium carbonate, calcined in air, and then crushed and graded to obtain lithium manganese oxide cathode material.

[0039] Compared with the prior art, this application first prepares a manganese tetroxide substrate material, and then oxidizes part of the manganese valence from +2 to +3 under a strong oxidizing atmosphere to obtain a composite manganese oxide compound including manganese tetroxide. Since the manganese tetroxide is embedded in the spinel manganese tetroxide substrate in the form of a regular hexagonal single crystal by liquid phase co-precipitation to form a composite manganese oxide compound, the number of (100) crystal faces in lithium manganese oxide is increased, and then lithium manganese oxide cathode material is obtained. This not only improves the discharge capacity of lithium manganese oxide cathode material, but also improves the capacity retention rate of lithium manganese oxide cathode material, thereby improving the electrochemical performance of lithium manganese oxide cathode material. Moreover, the use of liquid phase co-precipitation method reduces the manufacturing cost of lithium manganese oxide cathode material. In step S200, the concentrated manganese tetroxide mixed solution is brought to a preset solid content, and a curing agent is added to carry out a curing reaction. As the solid content of the manganese tetroxide mixed solution is increased, the probability of collision between particles is increased. After adding the curing agent, the oxidation activity of the manganese tetroxide surface is increased while the manganese tetroxide mixed solution is homogenized. It also acts as a template agent to guide the formation of manganese tetroxide into the substrate material.

[0040] It should be noted that lithium manganese oxide (LiMn2O4) crystals synthesized using manganese tetroxide exhibit low distortion, uniform morphology and size. This favorable morphology facilitates lithium ion insertion / extraction, reduces crystal structure changes caused by insertion / extraction, and results in excellent rate performance, stability, and safety, thus improving the cycle performance of LiMn2O4. Existing methods for preparing manganese trioxide primarily involve the potassium permanganate hydrothermal method and the high-temperature calcination method of manganese salts. These methods place high demands on reaction equipment and temperatures, and cubic-shaped manganese trioxide is obtained through high-temperature sintering of manganese carbonate, increasing manufacturing costs. For example, manganese carbonate can be prepared using potassium manganate or manganese salts as raw materials, and then sintered at 400-600℃ to obtain manganese trioxide. The chemical reaction formula is as follows:

[0041]

[0042] MnCO3 + O2 → 2Mn2O3 + 4CO2↑

[0043] MnO3 is a precipitate, while CO2 and NH3 are gases.

[0044] This embodiment employs a liquid-phase co-precipitation method to prepare an in-situ composite manganese oxide of manganese tetroxide and manganese trioxide. This allows the manganese oxide to maintain the cycle performance of lithium manganese oxide while also improving the discharge capacity of lithium manganese oxide. Furthermore, the reaction conditions are relatively mild, reducing manufacturing costs. Due to the addition of a ripening reaction and a secondary strong oxidation reaction, hexagonal single-crystal manganese trioxide is precipitated and grown on a spinel manganese tetroxide substrate, subsequently intercalating to form a composite manganese oxide. The manganese tetroxide and manganese trioxide are tightly bonded and not easily detached, resulting in a composite manganese oxide with good processability. The chemical reaction is as follows:

[0045]

[0046] In some embodiments, the first preset reaction conditions include: maintaining the pH of the mixed solution in the reaction vessel at 8.5–9.0, the reaction temperature at 50°C–70°C, and the reaction time at 12–18 h; the second preset reaction conditions include: maintaining the pH of the mixed solution in the reaction vessel at 9.2–9.8, the reaction temperature at 70°C–90°C, and the reaction time at 15–25 h. In this embodiment, since the pH of the second preset reaction conditions is greater than that of the first preset reaction conditions, and the reaction temperature of the second preset reaction conditions is also greater than that of the first preset reaction conditions, the redox potential of the mixed solution in the reaction vessel is increased, which is beneficial to the oxidation reaction and promotes the oxidation of manganese ions from +2 to +3, thereby increasing the rate of manganese trioxide formation.

[0047] In some embodiments, the molar ratio of manganese sulfate solution, precipitant, and complexing agent initially added to the reactor in a co-current manner is 10:(18-26):(8-13); the molar ratio of manganese sulfate solution, precipitant, and complexing agent added to the reactor in a co-current manner again is 10:(24-30):(1-16). Using the ratio range of this embodiment can improve the reaction efficiency of liquid-phase co-precipitation method to embed manganese trioxide in the morphology of a regular hexagonal single crystal on a spinel manganese tetroxide substrate to form a composite manganese oxide compound.

[0048] In some embodiments, the radius of manganese trioxide is 0.5 μm to 5 μm, and the mass percentage of manganese trioxide in the composite manganese oxide compound is less than or equal to 30%, that is, the mass ratio of manganese trioxide to manganese tetroxide in the composite manganese oxide compound is (1-3):7. In this embodiment, controlling the radius of manganese trioxide allows it to have a hexagonal single crystal morphology that is more conducive to its embedding on the spinel manganese tetroxide substrate. When the mass percentage of manganese trioxide in the composite manganese oxide compound is controlled to be less than or equal to 30%, increasing the mass percentage of manganese trioxide can... Increasing the number of (100) crystal planes in lithium manganese oxide increases the diffusion rate of lithium ions in the lithium manganese oxide cathode material, thereby increasing the discharge capacity of lithium manganese oxide. This is because the density of manganese atoms in the (100) crystal plane is less than that in the (111) crystal plane, and the diffusion channels of lithium ions are in the same direction as those of the (100) crystal plane.

[0049] In some embodiments, the first liquid inlet rate is 3% to 8% of the reactor volume per hour; the second liquid inlet rate is 1% to 5% of the reactor volume per hour. The liquid inlet rate of this embodiment is beneficial for controlling the reaction rate and forming a composite manganese oxide with better morphology.

[0050] In some embodiments, the concentration of the manganese sulfate solution is 50 g / L to 300 g / L, the mass percentage of the precipitant is 20% to 35%, and the mass percentage of the complexing agent is 5% to 25%. Controlling the concentration of the manganese sulfate solution and the mass percentages of the precipitant and complexing agent is beneficial for forming a better multidimensional structure, allowing manganese trioxide to be embedded in the spinel manganese tetroxide substrate in the form of a regular hexagonal single crystal, thereby improving structural stability.

[0051] In some embodiments, the preset solid content ranges from 20% to 30%, and the mass percentage of the curing agent is 0.5% to 2%. The curing agent includes F127 nonionic surfactant, sodium hypochlorite, and ammonium bicarbonate, with a mass ratio of F127 nonionic surfactant, sodium hypochlorite, and ammonium bicarbonate of 40:(10-30):(15-25). This increases the solid content of the manganese tetroxide mixed solution and increases the probability of collision between particles. After adding the curing agent in the mass ratio of this embodiment, the F127 nonionic surfactant emulsifies the manganese tetroxide mixed solution, and the sodium hypochlorite creates an active oxygen atmosphere. While homogenizing the manganese tetroxide mixed solution, it also increases the oxidation activity of the manganese tetroxide surface. Ammonium bicarbonate also acts as a template agent, guiding manganese tetroxide to form a substrate material, which facilitates the formation of hexagonal single crystals of manganese tetroxide and their precipitation on the substrate formed by manganese tetroxide.

[0052] In some embodiments, the ripening reaction temperature is 70°C to 90°C and the ripening time is 6h to 10h, providing a better reaction environment for the formation of complex manganese oxides.

[0053] In some embodiments, the first oxidant is air or oxygen. When forming a manganese tetroxide mixed solution, the oxidizing power of the first oxidant is relatively low because there is no need to oxidize the +2 manganese ions. The second oxidant is any one or a combination of oxygen, hydrogen peroxide, sodium persulfate, ozone, sodium hypochlorite, or potassium dichromate. Since it is necessary to oxidize the +2 manganese ions to the +3 manganese ions, the oxidizing power of the second oxidant is greater than that of the first oxidant. The precipitant is any one or a combination of sodium hydroxide, potassium hydroxide, sodium methoxide, or sodium ethoxide. The complexing agent is any one or a combination of ammonia, ammonium sulfate, disodium ethylenediaminetetraacetate, polyethylene glycol, triethanolamine, or sodium dodecyl sulfonate. Using the precipitant and complexing agent of this embodiment is beneficial for forming hexagonal single crystals of manganese tetroxide and precipitating them on the substrate formed by manganese tetroxide.

[0054] In some embodiments, the molar ratio of lithium in lithium carbonate to manganese in the composite manganese oxide is (0.5~0.55):1, the calcination temperature is 700℃~800℃, and the calcination time is 10h~14h. Using the lithium-manganese ratio of this embodiment improves the electrochemical performance of lithium manganese oxide. The calcination reaction conditions allow lithium ions to combine better with the composite manganese oxide, thereby improving the electrochemical performance of lithium manganese oxide.

[0055] The technical solution of this application will be illustrated below through specific embodiments and comparative examples.

[0056] Example 1

[0057] A method for preparing a lithium manganese oxide cathode material includes:

[0058] 1) A manganese sulfate solution with a volume concentration of 180 g / L, sodium hydroxide with a mass percentage of 28%, and disodium ethylenediaminetetraacetate with a mass percentage of 20% were added to the reactor in a parallel flow. The manganese sulfate solution was added at a rate of 6% of the reactor volume per hour. The pH of the mixed solution in the reactor was maintained at 8.6. The reaction temperature was 60°C and the reaction time was 14 hours. Oxygen was introduced into the reactor during the reaction to obtain a manganese tetroxide mixed solution.

[0059] 2) Concentrate the manganese tetroxide mixed solution to 25% using a concentrator, and add 0.6% by mass of a curing agent to carry out a curing reaction to obtain manganese tetroxide slurry. The curing agent includes F127 nonionic surfactant, sodium hypochlorite, and ammonium bicarbonate. The mass ratio of F127 nonionic surfactant, sodium hypochlorite, and ammonium bicarbonate is 40:25:18. The reaction temperature of the curing reaction is 80℃, and the curing time is 6h.

[0060] 3) A manganese sulfate solution with a volume concentration of 180 g / L, 28% sodium hydroxide by mass, and 20% disodium ethylenediaminetetraacetate by mass are added to the reactor in a parallel flow. The manganese sulfate solution is added at a rate of 4% of the reactor volume per hour. The pH of the mixed solution in the reactor is maintained at 9.3. The reaction temperature is 70°C and the reaction time is 16 hours. The mixture is then reacted with manganese tetroxide slurry. Ozone is introduced into the reactor during the reaction to obtain a composite manganese oxide mixed solution.

[0061] 4) The mixed solution of the composite manganese oxide is filtered, washed, and dried to obtain the composite manganese oxide.

[0062] 5) The composite manganese oxide compound is mixed with lithium carbonate, and the molar ratio of lithium in lithium carbonate to manganese in composite manganese oxide compound is 0.53:1. The mixture is calcined in air at a temperature of 780℃ for 12 hours. After crushing and grading, lithium manganese oxide cathode material is obtained.

[0063] The XRD pattern of the composite manganese oxide formed in Example 1 is shown below. Figure 2 As shown, the SEM schematic diagram of the composite manganese oxide provided in Example 1 is as follows. Figure 3 As shown.

[0064] Example 2: The difference between Example 2 and Example 1 is that the concentration of the manganese sulfate solution in the first injection, the mass percentage of the precipitant sodium hydroxide and the complexing agent ammonia, the first injection rate, the first preset reaction conditions, the preset solid content, the second preset reaction conditions, and the second oxidant are different. All other contents are the same.

[0065] 1) A manganese sulfate solution with a volume concentration of 200 g / L, sodium hydroxide solution with a mass percentage of 25%, and ammonia solution with a mass percentage of 18% were added to the reactor in a parallel flow. The manganese sulfate solution was added at a rate of 5% of the reactor volume per hour. The pH of the mixed solution in the reactor was maintained at 8.7. The reaction temperature was 65°C and the reaction time was 14 hours. Oxygen was introduced into the reactor during the reaction to obtain a manganese tetroxide mixed solution.

[0066] 2) Concentrate the manganese tetroxide mixed solution to 20% using a concentrator, and add 0.7% by mass of a curing agent to carry out a curing reaction to obtain manganese tetroxide slurry. The curing agent includes F127 nonionic surfactant, sodium hypochlorite, and ammonium bicarbonate. The mass ratio of F127 nonionic surfactant, sodium hypochlorite, and ammonium bicarbonate is 40:16:15. The reaction temperature of the curing reaction is 80℃, and the curing time is 6h.

[0067] 3) A manganese sulfate solution with a volume concentration of 180 g / L, 28% sodium hydroxide by mass, and 20% disodium ethylenediaminetetraacetate by mass are added to the reactor in a parallel flow. The manganese sulfate solution is added at a rate of 6% of the reactor volume per hour. The pH of the mixed solution in the reactor is maintained at 9.2. The reaction temperature is 75℃ and the reaction time is 12 hours. The mixture is then reacted with manganese tetroxide slurry. Sodium persulfate is continuously introduced into the reactor during the reaction to obtain a composite manganese oxide mixed solution.

[0068] Example 3: The difference between Example 3 and Example 1 is that the concentration of manganese sulfate solution, the complexing agent is ammonium sulfate, the first liquid inlet rate, the first preset reaction conditions, the preset solid content, the mass percentage of ripening agent, the ripening time, the second preset reaction conditions, and the second oxidizing agent are different. The rest are the same.

[0069] 1) A manganese sulfate solution with a volume concentration of 120 g / L, sodium hydroxide with a mass percentage of 28%, and ammonium sulfate with a mass percentage of 20% were added to the reactor in a parallel flow. The manganese sulfate solution was added at a rate of 5% of the reactor volume per hour. The pH of the mixed solution in the reactor was maintained at 8.9. The reaction temperature was 65°C and the reaction time was 14 hours. Oxygen was introduced into the reactor during the reaction to obtain a manganese tetroxide mixed solution.

[0070] 2) Concentrate the manganese tetroxide mixed solution to 30% using a concentrator, and add 0.9% by mass of a curing agent to carry out a curing reaction to obtain manganese tetroxide slurry. The curing agent includes F127 nonionic surfactant, sodium hypochlorite, and ammonium bicarbonate. The mass ratio of F127 nonionic surfactant, sodium hypochlorite, and ammonium bicarbonate is 40:28:20. The reaction temperature of the curing reaction is 80℃, and the curing time is 12h.

[0071] 3) A manganese sulfate solution with a volume concentration of 120 g / L, 28% sodium hydroxide by mass, and 20% ammonium sulfate by mass are added to the reactor in parallel. The manganese sulfate solution is added at a rate of 3% of the reactor volume per hour. The pH of the mixed solution in the reactor is maintained at 9.6, the reaction temperature is 80℃, and the reaction time is 18 hours. The mixture is then reacted with manganese tetroxide slurry. Hydrogen peroxide is continuously introduced into the reactor during the reaction to obtain a composite manganese oxide mixed solution.

[0072] Comparative Example 1: The difference from Example 1 is that the concentration of manganese sulfate solution, the mass percentage of precipitant sodium hydroxide and complexing agent ammonia, and the pH value of the first preset reaction conditions are different, and the aging reaction and the secondary reaction in step 3) are not carried out.

[0073] 1) A manganese sulfate solution with a volume concentration of 200 g / L, sodium hydroxide with a mass percentage of 25%, and ammonium sulfate with a mass percentage of 18% were added to the reactor in a parallel flow. The manganese sulfate solution was added at a rate of 5% of the reactor volume per hour. The pH of the mixed solution in the reactor was maintained at 8.7, the reaction temperature was 65°C, and the reaction time was 14 hours. Oxygen was introduced into the reactor during the reaction to obtain a manganese tetroxide mixed solution.

[0074] 2) Turn on the thickener to concentrate the manganese tetroxide mixed solution to 30% to obtain manganese tetroxide slurry;

[0075] 3) The mixed solution of the composite manganese oxides is filtered, washed, and dried to obtain the composite manganese oxides;

[0076] 4) The composite manganese oxide compound is mixed with lithium carbonate, and the molar ratio of lithium in lithium carbonate to manganese in composite manganese oxide compound is 0.53:1. The mixture is calcined in air at a temperature of 780℃ for 12 hours. After crushing and grading, lithium manganese oxide cathode material is obtained.

[0077] The XRD pattern of the composite manganese oxide formed in Comparative Example 1 is shown below. Figure 4 As shown, the SEM schematic diagram of the composite manganese oxide provided in Comparative Example 1 is as follows. Figure 5 As shown.

[0078] Comparative Example 2: Manganese tetroxide and manganese trioxide were mixed using a solid-state method.

[0079] 1) Mix manganese tetroxide and manganese trioxide evenly in a mass ratio of 3.2:1;

[0080] 2) The composite manganese oxide compound was mixed with lithium carbonate, and the molar ratio of lithium in the lithium carbonate to manganese in the composite manganese oxide compound was 0.53:1. The mixture was calcined in air at a temperature of 780℃ for 12 hours. After crushing and grading, lithium manganese oxide cathode material was obtained.

[0081] Comparative Example 3 differs from Example 1 in that the mass percentages of the precipitant sodium hydroxide and the complexing agent, the first liquid inlet rate, and the first preset reaction conditions are different, and the aging reaction and the secondary reaction in step 3) are not performed; all other contents are the same.

[0082] 1) A manganese sulfate solution with a volume concentration of 180 g / L, sodium hydroxide with a mass percentage of 26%, and disodium ethylenediaminetetraacetate with a mass percentage of 10% were added to the reactor in a parallel flow. The manganese sulfate solution was added at a rate of 4% of the reactor volume per hour. The pH of the mixed solution in the reactor was maintained at 8.6, the reaction temperature was 65°C, and the reaction time was 15 hours. Oxygen was introduced into the reactor during the reaction to obtain a manganese tetroxide mixed solution.

[0083] 2) Turn on the thickener to concentrate the manganese tetroxide mixed solution to 25% to obtain manganese tetroxide slurry;

[0084] 3) A manganese sulfate solution with a volume concentration of 180 g / L, 28% sodium hydroxide by mass, and 10% disodium ethylenediaminetetraacetate by mass are added to the reactor in a parallel flow. The manganese sulfate solution is added at a rate of 4% of the reactor volume per hour. The pH of the mixed solution in the reactor is maintained at 9.3. The reaction temperature is 70°C and the reaction time is 16 hours. The mixture is then reacted with manganese tetroxide slurry. Ozone is introduced into the reactor during the reaction to obtain a composite manganese oxide mixed solution.

[0085] The XRD pattern of the composite manganese oxide formed in Example 1 is shown below. Figure 2 As shown, the SEM schematic diagram of the composite manganese oxide provided in Example 1 is as follows. Figure 3 As shown.

[0086] Performance / Data Testing:

[0087] Using lithium foil as the negative electrode, and the lithium manganese oxide positive electrode materials prepared in the above examples and comparative examples respectively as the positive electrode, the particle morphology and mass ratio of manganese trioxide (Mn2O3) of the composite manganese oxide compounds in Examples 1, 2, and 3 and Comparative Examples 1, 2, and 3 were tested to prepare secondary button batteries, model CR2025. Under a voltage of 3.0–4.2V, the batteries were first charged at 0.2C and discharged at 0.2C for two cycles, and then cycled under 1C charging and discharging conditions. The initial charge capacity at 0.2C, the initial discharge capacity at 0.2C, the initial charge-discharge efficiency at 0.2C, the initial discharge capacity at 1C, and the capacity retention rate after 60 cycles were tested. The test results are shown in Tables 1 and 2.

[0088] Table 1

[0089]

[0090]

[0091] Table 2

[0092]

[0093] Comparative Example 2 is a ball milling solid-phase dry method for mixing manganese trioxide. Since Comparative Example 3 did not undergo aging reaction and secondary strong oxidation reaction, neither Comparative Example 2 nor Comparative Example 3 formed a composite manganese oxide compound with single-crystal hexahedral manganese trioxide embedded in a spinel manganese tetroxide substrate.

[0094] Since Comparative Example 1 did not mix manganese trioxide, while Comparative Example 2 mixed manganese trioxide by ball milling solid phase dry method, Comparative Example 2 improved the 1C initial discharge capacity, but compared with Comparative Example 1, the cycle performance of Comparative Example 2 decreased significantly.

[0095] Since Comparative Example 3 uses a liquid-phase method to mix manganese tetroxide and manganese trioxide at the nanoscale, while Comparative Example 2 uses a ball-milled solid-phase dry method to mix manganese trioxide, Comparative Example 3 shows a more significant improvement in the 1C initial discharge capacity.

[0096] The results of Examples 1 and 3 show that the composite manganese oxide compound, which is a single-crystal hexahedral manganese oxide embedded in a spinel manganese tetroxide substrate prepared by the liquid phase method, not only improves the discharge capacity, but also significantly enhances the cycle stability compared with Comparative Examples 2 and 3.

[0097] The test results of Examples 1, 2, and 3 show that as the content of single-crystal manganese oxide increases, the 1C discharge capacity of lithium manganese oxide cathode material continuously increases. However, when the content of single-crystal manganese oxide exceeds 30%, the cycle stability of lithium manganese oxide decreases, resulting in a decrease in capacity retention.

[0098] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0099] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0100] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A method for preparing a lithium manganese oxide cathode material, characterized in that, include: Manganese sulfate solution, precipitant, and complexing agent are added to a reactor in parallel flow and reacted under a first preset reaction condition. A first oxidant is introduced into the reactor while the reaction is underway to obtain a manganese tetroxide mixed solution. The inflow rate of the manganese sulfate solution is the first inflow rate. The manganese tetroxide mixed solution is concentrated to a preset solid content, and a curing agent is added to carry out a curing reaction to obtain manganese tetroxide slurry; The manganese sulfate solution, the precipitant, and the complexing agent are added to the reactor in parallel flow again, and reacted with the manganese tetroxide slurry under the second preset reaction conditions. While reacting, a second oxidant is introduced into the reactor to obtain a composite manganese oxide mixed solution. The inlet rate of the manganese sulfate solution is the second inlet rate. The composite manganese oxide mixture solution is filtered, washed, and dried to obtain a composite manganese oxide compound. The composite manganese oxide compound is manganese trioxide in the form of a regular hexagonal single crystal embedded on a spinel manganese tetroxide substrate. The mass percentage of manganese trioxide in the composite manganese oxide compound is less than or equal to 30%. The composite manganese oxide compound was mixed with lithium carbonate, calcined in air, and then crushed and graded to obtain lithium manganese oxide cathode material. The first preset reaction conditions include: maintaining the pH value of the mixed solution in the reaction vessel at 8.5~9.0 and the reaction temperature at 50 ℃~70 ℃; The second preset reaction conditions include: maintaining the pH value of the mixed solution in the reaction vessel at 9.2~9.8 and the reaction temperature at 70 ℃~90 ℃; The first liquid inlet rate is 3% to 8% of the reactor volume per hour; the second liquid inlet rate is 1% to 5% of the reactor volume per hour. The concentration of the manganese sulfate solution is 50 g / L to 300 g / L, the mass percentage of the precipitant is 20% to 35%, and the mass percentage of the complexing agent is 5% to 25%. The preset solid content ranges from 20% to 30%, and the mass percentage of the curing agent is 0.5% to 2%. The curing agent includes F127 nonionic surfactant, sodium hypochlorite and ammonium bicarbonate, wherein the mass ratio of F127 nonionic surfactant, sodium hypochlorite and ammonium bicarbonate is 40:(10~30):(15~25). The first oxidant is air, and the second oxidant is any one or a combination of oxygen, hydrogen peroxide, sodium persulfate, ozone, sodium hypochlorite, or potassium dichromate. Alternatively, the first oxidant is oxygen, and the second oxidant is a combination of multiple of oxygen, hydrogen peroxide, sodium persulfate, ozone, sodium hypochlorite, or potassium dichromate. Alternatively, the first oxidant may be oxygen, and the second oxidant may be any one of hydrogen peroxide, sodium persulfate, ozone, sodium hypochlorite, or potassium dichromate.

2. The method for preparing the lithium manganese oxide cathode material as described in claim 1, characterized in that, The first preset reaction conditions also include: a reaction time of 12 h to 18 h; The second preset reaction conditions also include a reaction time of 15 h to 25 h.

3. The method for preparing the lithium manganese oxide cathode material as described in claim 1, characterized in that, The ripening reaction is carried out at a temperature of 70℃ to 90℃ and for a ripening time of 6 h to 10 h.

4. The method for preparing the lithium manganese oxide cathode material as described in claim 1, characterized in that, The precipitant is any one or a combination of sodium hydroxide, potassium hydroxide, sodium methoxide, or sodium ethoxide; The complexing agent is any one or a combination of ammonia, ammonium sulfate, disodium ethylenediaminetetraacetate, polyethylene glycol, triethanolamine, or sodium dodecyl sulfonate.

5. The method for preparing the lithium manganese oxide cathode material as described in claim 1, characterized in that, The molar ratio of lithium in the lithium carbonate to manganese in the composite manganese oxide is (0.5~0.55):1, the calcination temperature is 700℃~800℃, and the calcination time is 10 h~14 h.

6. A lithium manganese oxide cathode material, characterized in that, The lithium manganese oxide cathode material is prepared according to any one of claims 1 to 5.

7. A lithium battery, characterized in that, Includes a positive electrode, wherein the positive electrode comprises the lithium manganese oxide positive electrode material prepared by the preparation method of the lithium manganese oxide positive electrode material as described in claim 6.

Images