Positive electrode material, preparation method and lithium ion battery

Abstract

The invention discloses a positive electrode material, a preparation method and a lithium ion battery, and belongs to the field of lithium ion battery positive electrode materials. Potassium permanganate is used as a manganese source and is mixed with a salt solution of transition metal elements, and nano-microsphere-shaped manganous-manganic oxide is prepared by adopting a reduction method. In a reduction reaction process, a reducing agent is accurately controlled to be dropwise added from fast to slow, a large number of crystal nucleuses are formed in an explosive manner at the initial stage of the reaction, and fast growth of the crystal nucleuses is inhibited at the later stage, so that the nano-microsphere-shaped manganous-manganic oxide with a relatively small particle size is obtained. Meanwhile, gullies on the surface of manganous-manganic oxide are filled with transition metal, and manganous-manganic oxide with small particle size and large specific surface area is finally prepared on the premise of not influencing the spherical structure of manganous-manganic oxide, so that more active sites are provided for electrode reaction. It is proved that the transition metal doped modified manganous-manganic oxide serves as the battery positive electrode material, and the prepared battery has high specific capacity and good cycle performance and stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery cathode material, and particularly relates to a cathode material, a preparation method and a lithium ion battery. BACKGROUND

[0002] Lithium manganate (LiMn2O4) is one of the cathode materials of lithium ion batteries, and has a good application prospect due to its low price, excellent performance and high safety. In recent years, manganese tetroxide (Mn3O4) as a precursor for preparing lithium manganate has attracted much attention, and has the same spinel structure as lithium manganate, has a small phase change stress in the preparation of lithium manganate, and will not cause severe structural changes, which is beneficial to the capacity retention of lithium batteries. The main preparation methods of manganese tetroxide include metal manganese oxidation method, manganese carbonate calcination method and manganese salt method (also known as solution precipitation oxidation method). Among them, the manganese salt method is widely used due to its low production cost, which uses soluble divalent manganese as raw material, precipitates and hydrolyzes divalent manganese by adjusting pH, and then adds an oxidizing agent to generate manganese tetroxide. Common manganese salts include manganese sulfate (MnSO4), manganese chloride (MnCl2), manganese nitrate (Mn(NO3)2) and the like.

[0003] Lithium manganate as a cathode material has a series of problems. On the one hand, the existence of Mn 3+ may cause Jahn-Teller effect, induce the collapse of lithium manganate structure, and reduce the cycle performance of the material; on the other hand, Mn 2+ may be dissolved in the electrolyte to make its structure unstable. Therefore, in order to further improve the performance of lithium manganate product, element doping means is often used to improve its structural stability, such as doping metal ions such as Al 3+ , Ti 4+, rare earth ions, etc. For example, a spherical aluminum-doped trimanganese tetroxide and a preparation method thereof are disclosed in Chinese Patent Application Publication No. CN 102544472A. A mixed solution containing trivalent aluminum and divalent manganese is first prepared by a manganese salt method, then the mixed solution is co-precipitated with a sodium hydroxide solution, and finally the spherical aluminum-doped trimanganese tetroxide is obtained by oxidation treatment. This method can effectively control the impurity content and range of the product, uniformly dopes aluminum at the molecular level, and significantly improves the cycle performance and high-temperature performance of the lithium manganate product. For another example, a ferrum-doped trimanganese tetroxide material and a preparation method thereof are disclosed in Chinese Patent Application Publication No. CN 120057991A. In view of the problems of high sulfur content and Jahn-Teller effect in the preparation of trimanganese tetroxide using manganese sulfate as the manganese source, DTPA ferric ammonium salt is used as a complexing agent and a doping agent, and ammonia is used as the lye, which improves the uniformity of iron element doping, and obtains trimanganese tetroxide with uniform particle size and high tap density. At the same time, ethanol is introduced as a dispersing agent to reduce the sulfur content in the product, and a lithium manganate precursor material with excellent cycle life and good rate performance is prepared. The deficiency is that the above-mentioned element doping methods cannot well improve the problem of large particle size of trimanganese tetroxide. For example, the particle size of spherical aluminum-doped trimanganese tetroxide (Mn3O4·0.052Al2O3) D 50 is 9.7 μm, and the particle size index D 50 increases continuously with the increase of the percentage content of aluminum ions.

[0004] The particle size of trimanganese tetroxide can directly affect the crystal structure, electrochemical performance, and cycle stability of lithium manganate. Specifically, 1) improving battery performance: trimanganese tetroxide with small particle size has a larger specific surface area, which can increase the contact area of active substances, thereby improving the charge and discharge efficiency and energy density of the battery; 2) improving the cycle stability of the battery: trimanganese tetroxide with small particle size can be better dispersed in the positive electrode material of the battery, reducing the agglomeration phenomenon between particles, which helps to improve the cycle stability and service life of the battery; 3) reducing the internal resistance of the battery: trimanganese tetroxide with small particle size can reduce the ion transport path inside the battery, reduce the internal resistance of the battery, and improve the working efficiency of the battery. SUMMARY

[0005] 1. Problem to be solved In view of the problem that the manganese salt method for preparing trimanganese tetraoxide has a large product particle size, which may affect the crystal structure, electrochemical performance and cycle stability of lithium manganate material, a positive electrode material, a preparation method and a lithium ion battery are provided. A nano microspherical trimanganese tetraoxide is prepared by a reduction method using potassium permanganate as a manganese source and mixing it with a salt solution of transition metal elements. Among them, by controlling the addition speed of the reducing agent, a large number of crystal nuclei are formed in the early stage of the reaction, and in the later stage, the rapid generation of crystal nuclei is inhibited, and then nano microspherical trimanganese tetraoxide with small particle size is obtained. At the same time, the transition metal ions effectively fill in the grooves on the surface of the nano microspheres, and finally the trimanganese tetraoxide with small particle size (D 50 is 3-5 μm) and large specific surface area (75-120 m 2 / g) is prepared, which exhibits good charge and discharge and cycle performance as a battery positive electrode material.

[0006] 2. Technical solutions In order to solve the above problems, the technical solutions adopted by the present application are as follows: The present application provides a positive electrode material, which comprises transition metal doped modified trimanganese tetraoxide. The transition metal doped modified trimanganese tetraoxide is in the form of nano microspheres, and a large number of grooves are distributed on the surface, and transition metals fill in the groove gaps. The particle size D 50 of the transition metal doped trimanganese tetraoxide is 3-7 μm. The specific surface area of the transition metal doped trimanganese tetraoxide is 75-120 m 2 / g.

[0007] Further, the above positive electrode material is prepared by mixing the transition metal doped modified trimanganese tetraoxide with a conductive agent and a binder, then adding an organic reagent, and then performing ultrasonic, demulsification and drying treatment, and then coating on a nickel sheet net, and then drying, pressing, and drying.

[0008] Further, the transition metal doped modified trimanganese tetraoxide and the conductive agent and the binder are mixed in a mass ratio of (15-19):(1-3):1.

[0009] Further, the conductive agent comprises acetylene black.

[0010] Further, the binder comprises polytetrafluoroethylene.

[0011] Further, the organic reagent comprises anhydrous ethanol.

[0012] Further, the preparation method of the transition metal doped modified trimanganese tetraoxide comprises the following steps: S1, adding a soluble salt of heptavalent manganese and a soluble salt of a transition metal into deionized water to configure a mixed salt solution containing heptavalent manganese ions and transition metal ions; S2, adding a reducing agent into the mixed salt solution of S1 and continuously stirring to obtain a turbid solution containing flocculent precipitate; S3, aging the turbid solution of S2 at room temperature, filtering by precipitation to obtain transition metal doped modified trimanganese tetraoxide.

[0013] Further, the soluble salt of heptavalent manganese is added into deionized water at a final concentration of 0.05-0.1 mol / L.

[0014] Further, the soluble salt of heptavalent manganese is added into deionized water at a final concentration of 0.05 mol / L.

[0015] Further, the soluble salt of heptavalent manganese includes any one of potassium permanganate, sodium permanganate, calcium permanganate, silver permanganate, and zinc permanganate; it should be noted that the soluble salt of heptavalent manganese in the present application refers to all soluble salts containing permanganate ions (MnO4 - ), and is not limited to the above representative salt classes.

[0016] Further, the soluble salt of heptavalent manganese is potassium permanganate and / or sodium permanganate.

[0017] Further, the soluble salt of transition metal is added at 3%-5% of the molar percentage of the soluble salt of heptavalent manganese.

[0018] Further, the soluble salt of transition metal is added at 3% of the molar percentage of the soluble salt of heptavalent manganese.

[0019] Further, the soluble salt of transition metal includes any one of ferrous sulfate, ferrous chloride, ferrous nitrate, manganese dioxide, and manganese chloride; it should be noted that the soluble salt of transition metal in the present application refers to all soluble metal salts with reducing properties in low valence state, and is not limited to the above representative salt classes.

[0020] Further, the reducing agent is added into the mixed salt solution in the form of dropwise addition, which includes: using a dropwise addition device to continuously add 2-3 drops / min for 10-15 min; then stopping dropwise addition and continuously stirring for 10-15 min; and then continuously adding 1-2 drops / min until the dropwise addition of the reducing agent is completed; it should be noted that the trimanganese tetraoxide is prepared by the reduction method in the present application, and a large number of crystal nuclei are explosively generated at the initial stage of the reaction by faster dropwise addition, and the slow dropwise addition of the reducing agent at the later stage can inhibit the rapid growth of the crystal nuclei, thereby obtaining trimanganese tetraoxide with smaller particle size.

[0021] Further, the amount of the reducing agent is 3-5 times the amount of the soluble salt of the heptavalent manganese.

[0022] Further, the amount of the reducing agent is 4 times the amount of the soluble salt of the heptavalent manganese.

[0023] Further, the reducing agent includes ethylene glycol.

[0024] Further, the stirring is performed for 3-4 hours on a magnetic stirrer.

[0025] Further, the aging time is 12-14 hours.

[0026] Further, after the filtration and precipitation, the precipitate is dried and ground.

[0027] Further, the drying is performed in a constant temperature oven at 80-90°C.

[0028] Further, the grinding is performed in a mortar.

[0029] The application also provides a transition metal doped modified trimanganese tetraoxide, which is prepared by the above-mentioned method for preparing a transition metal doped modified trimanganese tetraoxide.

[0030] Further, the transition metal doped modified trimanganese tetraoxide is in the form of nanometer microspheres, and a large number of grooves are distributed on the surface of the nanometer microspheres, and the transition metal fills the groove gaps.

[0031] Further, the particle size D50 of the transition metal doped modified trimanganese tetraoxide is 3-7 μm. 50

[0032] Further, the specific surface area of the transition metal doped modified trimanganese tetraoxide is 75-120 m 2 / g.

[0033] Further, the transition metal doped modified trimanganese tetraoxide is iron doped modified trimanganese tetraoxide.

[0034] Further, the particle size D50 of the iron doped modified trimanganese tetraoxide is 3-5 μm.

[0035] Further, the specific surface area of the transition metal doped modified trimanganese tetraoxide is 80-110 m 2 ​ / g; it is to be noted that, since the particle size of trimanganese tetraoxide can directly affect the crystal structure, electrochemical performance and cycle stability of the lithium ion battery cathode material, the present application obtains nanometer microspherical trimanganese tetraoxide with smaller particle size by precisely controlling the addition speed of the reducing agent in the reduction reaction process; meanwhile, the transition metal iron ions are effectively filled in the grooves on the surface of the nanometer microspheres, and the trimanganese tetraoxide with smaller particle size (D 50 of 3-5 μm and larger specific surface area (75-120 m 2 / g) is prepared under the premise of not affecting the spherical structure, so as to provide more active sites for the electrode reaction.

[0036] The present application also provides the application of the above-mentioned transition metal doped modified trimanganese tetraoxide in the preparation of a cathode material.

[0037] The present application also provides the application of the above-mentioned transition metal doped modified trimanganese tetraoxide or the above-mentioned cathode material in the preparation of a lithium ion battery; it is to be noted that, by preparing trimanganese tetraoxide with smaller particle size (D 50 of 3-5 μm and larger specific surface area (75-120 m 2 / g), it is proved that, as a battery cathode material, it has good conductivity and stable charge and discharge performance; at the same time, due to the smaller particle size, the electrochemical embedding / extraction capacity of lithium ions in the cathode material is enhanced, and the prepared battery shows high discharge specific capacity and good cycle performance, so it has good application prospect in the preparation of lithium ion batteries.

[0038] The present application also provides a lithium ion battery, which comprises the above-mentioned transition metal doped modified trimanganese tetraoxide or the above-mentioned cathode material.

[0039] 3. Beneficial effects Compared with the prior art, the present application has the following beneficial effects: (1) The present application provides a cathode material, a preparation method and a lithium ion battery. Potassium permanganate is used as a manganese source, mixed with a salt solution of a transition metal element, and nanometer microspherical trimanganese tetraoxide is prepared by reduction method. By precisely controlling the dropping speed of the reducing agent from fast to slow in the reduction reaction process, a large number of crystal nuclei are formed in the early stage of the reaction, and the rapid growth of the crystal nuclei is inhibited in the later stage, so as to obtain nanometer microspherical trimanganese tetraoxide with smaller particle size. At the same time, the transition metal ions are filled in the grooves on the surface of the trimanganese tetraoxide, and the trimanganese tetraoxide with smaller particle size (D 50 of 3-7 μm and larger specific surface area (75-120 m 2 / g) is prepared under the premise of not affecting the spherical structure, so as to provide more active sites for the electrode reaction.

[0040] (2) The application provides a positive electrode material, a preparation method and a lithium ion battery. Experiments prove that the transition metal (Fe) doped modified trimanganese tetraoxide in the application has good conductivity and stable charge and discharge performance as a battery positive electrode material. Meanwhile, the small particle size enhances the electrochemical embedding and disembedding capacity of lithium ions in the positive electrode material, and the prepared battery has high discharge specific capacity and good cycle performance.

[0041] (3) The application provides a positive electrode material, a preparation method and a lithium ion battery. The high-valence reduction method is used to prepare smaller particles, and the preparation conditions and maintenance costs are not complex, the energy consumption is lower, and the method is suitable for large-scale commercial application. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 is a preparation flowchart of the transition metal doped modified trimanganese tetraoxide in the application.

[0043] Figure 2 is an XRD graph of the iron doped modified trimanganese tetraoxide prepared in the application.

[0044] Figures 3~4 is a micro-morphology graph of the iron doped modified trimanganese tetraoxide prepared in the application scanned by an electron microscope.

[0045] Figure 5 is a conductivity performance test graph of the iron doped modified trimanganese tetraoxide material prepared in the application.

[0046] Figure 6 is a cyclic voltammetry (CV) graph of the iron doped modified trimanganese tetraoxide material prepared in the application. DETAILED DESCRIPTION

[0047] The application will be further described below in combination with specific embodiments.

[0048] 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 the application belongs; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0049] Unless otherwise specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturers are used. The reagents or instruments used are not specified by the manufacturers, and are all conventional products that can be purchased on the market.

[0050] As used herein, the term "about" is used to provide flexibility to a given term, measurement, or value associated with a term, measurement, or value. The degree of flexibility of a specific variable can be readily determined by one of skill in the art. As used herein, the term "at least one of" is intended to mean one or more of. For example, "at least one of A, B and C" means A alone; B alone; C alone; A and B; A and C; B and C; or A, B and C. Concentrations, amounts, and other numerical data can be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted -flexibly to avoid limiting to the specific data recited as the fine ends of the range. It should be further understood that it is thereby incorporated to also cover any and all sub-ranges of the same, and that the phrases "less than" and "greater than" mean "less than or equal to" and "greater than or equal to," respectively. For example, "from about 1 to about 4.5" should be interpreted to include not only the explicitly recited limits of 1 to about 4.5, but also the inclusion of individual numbers, for example, 2, 3 and 4, within the defined range, as well as an inclusion of fractions within that range, e.g., 1.5 and 3.3. This same principle applies to ranges reciting only one numerical value, such as "less than about 4.5," which should be interpreted to include all values up to and including the value 4.5.

[0051] Embodiment 1 The present embodiment provides a preparation method of transition metal doped modified trimanganese tetraoxide, and a prepared trimanganese tetraoxide and a study on its related performance.

[0052] Specifically, transition metal iron is selected to dope and modify the trimanganese tetraoxide.

[0053] The preparation flow is shown in Figure 1 The preparation flow is shown in S1, 0.01 mol of potassium permanganate is added into 200 mL of deionized water, and placed on a magnetic stirrer for stirring for 30 min for dissolution, and then 0.0003 mol of ferrous sulfate is added to configure a mixed salt solution containing heptavalent manganese ions and transition metal iron ions; S2, 0.04 mol of ethylene glycol is added into the mixed salt solution in S1, and continuously stirred on the magnetic stirrer for 3-4 h until a turbid liquid containing flocculent precipitate is obtained; S3, the turbid liquid in S2 is placed at room temperature for aging for 12 h, then the flocculent precipitate therein is subjected to sedimentation filtration, the obtained precipitate is placed in a constant temperature oven at 80°C for drying, and the dried sample is placed in a mortar for grinding to prepare the iron doped modified trimanganese tetraoxide.

[0054] In S2, the ethylene glycol is added into the mixed salt solution in a dropwise form, and the specific dropwise form is as follows: a rubber bulb dropper is used, 3 drops / min are continuously added for 15 min; then the dropwise addition is stopped, and stirring is continuously performed for 15 min; then 1 drop / min is continuously added until the addition of ethylene glycol is completed.

[0055] Figure 2The image shows the X-ray diffraction (XRD) results of iron-doped modified manganese tetroxide. It can be seen that the positions and intensities of each diffraction peak are consistent with those in the Mn3O4 standard card PDF#24-0734 (see the attached figures in the specification of Chinese invention patent publication number CN 108212147A). Figure 1 The results were consistent with the above, and no other impurities were observed, indicating that the prepared manganese tetroxide sample was relatively pure and homogeneous.

[0056] Figure 3 and Figure 4 The image shown is a scanning electron microscope image of iron-doped modified manganese tetroxide. It can be seen that there are many grooves distributed on the surface of manganese tetroxide nanospheres. These grooves can increase the specific surface area of ​​the material and provide more active sites for electrode reactions. At the same time, more transition metal ions can effectively fill these groove gaps, thus not affecting the spherical structure of manganese tetroxide.

[0057] The following are experiments investigating the performance of iron-doped modified manganese tetroxide: Preparation of battery positive electrode sheet: The above-mentioned iron-doped modified manganese tetroxide is mixed with conductive agent (acetylene black) and binder (polytetrafluoroethylene) in a mass ratio of 17:2:1, and then added to anhydrous ethanol as an organic reagent. After ultrasonic treatment, demulsification and drying, it is coated on a nickel mesh with a diameter of about 1.5 cm. After drying, pressing and baking, the positive electrode sheet of lithium-ion battery is obtained. Assemble lithium-ion batteries: In a glove box filled with argon atmosphere, lithium metal sheets are used as negative electrodes, KOH solution (6 mol / L) is used as electrolyte, and the prepared positive electrode sheets are assembled to prepare lithium-ion batteries.

[0058] Charge and discharge test: After the assembled lithium-ion battery was placed at high temperature (40℃) for 12 h, it was charged and discharged cycled at a current rate of 0.2C (36 mA / g) in the range of -0.2~0.4V on the Xinwei (BTS-5V6A) charge and discharge test system.

[0059] Specific capacity test: Charge and discharge test was performed on the Xinwei (BTS-5V6A) test system at laboratory ambient temperature (20℃) and a current rate of 0.2C (36 mA / g).

[0060] Figure 5 The charge-discharge cycle test curves shown in the figure demonstrate that the voltage changes linearly with the accumulation and release of charge on the electrodes, indicating that the sample has good conductivity and good reversibility.

[0061] Figure 6The CV curve related to the specific capacity test is shown, and it can be seen that the CV curve current response presents a trend of first increasing and then decreasing, the sample has the maximum i-V response value, indicating that it has a high specific capacity, and the specific capacity can reach 598 mAh / g through calculation.

[0062] Example 2 The embodiment provides a preparation method of transition metal doped modified trimanganese tetraoxide and the prepared trimanganese tetraoxide.

[0063] In contrast to Example 1, in the embodiment, the addition amount of potassium permanganate in S1 is changed from 0.01 mol to 0.015 mol, and other conditions are the same as in Example 1.

[0064] Example 3 The embodiment provides a preparation method of transition metal doped modified trimanganese tetraoxide and the prepared trimanganese tetraoxide.

[0065] In contrast to Example 1, in the embodiment, the addition amount of potassium permanganate in S1 is changed from 0.01 mol to 0.02 mol, and other conditions are the same as in Example 1.

[0066] Example 4 The embodiment provides a preparation method of transition metal doped modified trimanganese tetraoxide and the prepared trimanganese tetraoxide.

[0067] In contrast to Example 1, in the embodiment, the addition amount of ferrous sulfate in S1 is changed from 0.0003 mol to 0.0004 mol, and other conditions are the same as in Example 1.

[0068] Example 5 The embodiment provides a preparation method of transition metal doped modified trimanganese tetraoxide and the prepared trimanganese tetraoxide.

[0069] In contrast to Example 1, in the embodiment, the addition amount of ferrous sulfate in S1 is changed from 0.0003 mol to 0.0005 mol, and other conditions are the same as in Example 1.

[0070] Example 6 The embodiment provides a preparation method of transition metal doped modified trimanganese tetraoxide and the prepared trimanganese tetraoxide.

[0071] In contrast to Example 1, in the embodiment, the addition amount of ethylene glycol in S2 is changed from 0.04 mol to 0.02 mol, and other conditions are the same as in Example 1.

[0072] Comparative Example 1 The comparative example provides a preparation method of trimanganese tetraoxide without transition metal doping modification and the prepared trimanganese tetraoxide.

[0073] Compared with Example 1, the comparative example does not add ferrous sulfate component in S1, and other conditions are the same as Example 1.

[0074] Example 7 In this example, the related properties of the transition metal doped modified trimanganese tetroxide prepared in Examples 1-6 are compared.

[0075] First, the positive electrode sheet of the battery was prepared: the transition metal doped modified trimanganese tetroxide prepared in Examples 1-6 and the trimanganese tetroxide without transition metal doped modification prepared in Comparative Example 1 were mixed with conductive agent (acetylene black) and binder (polytetrafluoroethylene) in a mass ratio of 17:2:1, then added to organic reagent anhydrous ethanol for ultrasonic, demulsification, drying treatment, then coated on a nickel sheet net with a diameter of about 1.5 cm, dried, pressed, and dried to prepare a lithium ion battery positive electrode sheet; Then, the lithium ion battery was assembled: in an argon-filled glove box, with lithium metal sheet as the negative electrode and KOH solution (6 mol / L) as the electrolyte, the positive electrode sheet prepared above was assembled to prepare a lithium ion battery; Finally, the performance test: the prepared lithium ion battery was tested at 25℃ for charge and discharge, and the 1 / 3C, 0.5C charge and discharge capacity was tested, and the 1C charge and discharge cycle test was carried out (the test system was the same as Example 1), and the results are shown in Table 1.

[0076] Table 1. Related properties of lithium ion batteries assembled with different trimanganese tetroxide as positive electrode material

[0077] In summary, the potassium permanganate and transition metal element salt solution are mixed in this application, and the nano microspherical trimanganese tetroxide with small particle size is prepared by reduction method; at the same time, the transition metal fills in the grooves on the surface of the nano microspheres, and does not affect the spherical structure of the trimanganese tetroxide under the premise of further stabilizing the stability of its structure. Combined with Table 1, it is confirmed that the transition metal doped modified trimanganese tetroxide as the battery positive electrode material in this application has a higher specific capacity and good cycle performance.

Claims

1. A positive electrode material, characterized by, The positive electrode material comprises transition metal doped modified trimanganese tetroxide; The transition metal doped modified trimanganese tetroxide is in the form of nanometer microspheres, and a plurality of gullies are distributed on the surface of the nanometer microspheres, and the transition metal fills the gaps of the gullies. The particle size D of the transition metal-doped trimanganese tetraoxide 50 is 3-7 μm; The specific surface area of the transition metal-doped trimanganese tetraoxide is 75-120 m 2 / g.

2. The positive electrode material of claim 1, wherein, The positive electrode material is prepared by mixing the transition metal doped modified trimanganese tetroxide, a conductive agent and a binder, adding an organic reagent, and then performing ultrasonic treatment, demulsification, drying treatment, coating on a nickel sheet net, drying, sheet pressing and drying.

3. The positive electrode material according to claim 2, characterized in that, The transition metal doped modified trimanganese tetroxide, the conductive agent and the binder are mixed in a mass ratio of (15-19):(1-3):

1.

4. The positive electrode material according to claim 3, characterized in that, The conductive agent comprises acetylene black; and / or The binder comprises polytetrafluoroethylene; and / or The organic reagent comprises anhydrous ethanol.

5. The positive electrode material according to any one of claims 1 to 4, characterized in that, The preparation method of the transition metal doped modified trimanganese tetroxide comprises the following steps: S1, adding a soluble salt of heptavalent manganese and a soluble salt of a transition metal into deionized water to prepare a mixed salt solution containing heptavalent manganese ions and transition metal ions; S2, adding a reducing agent into the mixed salt solution of S1 and continuously stirring to obtain a turbid liquid containing flocculent precipitate; S3, aging the turbid liquid in S2 at room temperature, and filtering the precipitate to obtain the transition metal doped modified trimanganese tetroxide.

6. The positive electrode material according to claim 5, wherein the soluble salt of heptavalent manganese is added into deionized water in a final concentration of 0.05-0.1 mol / L; and / or the soluble salt of heptavalent manganese comprises any one of potassium permanganate, sodium permanganate, calcium permanganate, silver permanganate and zinc permanganate.

7. The positive electrode material according to claim 5 or 6, wherein the soluble salt of the transition metal is added in a molar percentage of 3%-5% of the soluble salt of heptavalent manganese; and / or the soluble salt of the transition metal comprises any one of ferrous sulfate, ferrous chloride, ferrous nitrate, manganese dioxide and manganese chloride.

8. The positive electrode material according to claim 7, wherein the reducing agent is added into the mixed salt solution in a dropwise form, and the dropwise form comprises: using a dropwise device, first continuously dropping at 2-3 drops / min for 10-15 min; then stopping dropping, continuously stirring for 10-15 min; and then continuously dropping at 1-2 drops / min until the reducing agent is completely dropped; and / or the amount of the reducing agent is 3-5 times of the amount of substance of the soluble salt of heptavalent manganese; and / or the reducing agent comprises ethylene glycol. The transition metal doped modified trimanganese tetroxide is prepared by the preparation method of any one of claims 5-8. The battery comprises the positive electrode material of any one of claims 1-8 or the transition metal doped modified trimanganese tetroxide of claim 9. ​ ​ ​ ​ ​ 9. A transition metal doped modified trimanganese tetraoxide characterized by, ​ 10. A lithium-ion battery, characterized by, ​

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