A lithium manganate positive electrode material and preparation method thereof

Abstract

The present invention belongs to the technical field of lithium ion batteries, and discloses a lithium manganate positive electrode material and a preparation method thereof. The lithium manganate positive electrode material is prepared by sequentially mixing and sintering a lithium compound, manganese tetraoxide, an oxidant and niobium oxide; wherein the molar ratio of lithium to manganese in the lithium compound and manganese tetraoxide is 1.03-1.05:2, the amount of the oxidant added is 1-1.5wt% of the lithium manganate, and the amount of the niobium oxide added is 0.3-1wt% of the lithium manganate. The present invention can effectively and synergistically promote the addition of Mn in the preparation process of lithium manganate by doping with the oxidant and the niobium oxide. 2+ and Mn 3+ The oxidation of lithium manganese oxide accelerates the reaction rate and reduces production costs, while also effectively improving the performance of lithium manganese oxide positive electrode materials.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a lithium manganate positive electrode material and a preparation method thereof. Background Art

[0002] There are two main manganese sources for synthetic lithium manganate currently used in the market. One is manganese dioxide, which is prepared from a manganese sulfate solution. For example, prior art 1: Chinese patent application 200410009004.2 discloses spherical lithium manganate and a preparation method, which comprises reacting manganese sulfate or manganese chloride or manganese nitrate with permanganate or peroxodisulfate in a liquid medium and adding an impurity-removing additive, controlling the pH value, temperature and feed rate of the reaction solution to produce spherical manganese dioxide, then mixing the spherical manganese dioxide with battery-grade lithium hydroxide or lithium nitrate or lithium carbonate and zinc or aluminum or zirconium in an organic solvent, uniformly drying the mixture, and then calcining the dried mixture to produce spherical lithium manganate.

[0003] The spherical lithium manganate produced by prior art 1 has excellent physical, chemical and electrochemical properties and is an excellent positive electrode material for lithium-ion batteries. However, due to the use of manganese sulfate as a raw material, the impurity content of the generated manganese dioxide is high, and the purity is between 90-92%. Due to the high impurity content, the charge capacity is generally 123-125 mAh / g, which is insufficient to meet the current battery development needs.

[0004] The other is manganese tetraoxide, which is formed by oxidation of metallic manganese or precipitation of manganese sulfate, with less impurities and a purity of more than 99%. Because of the low impurity content and higher effective Mn content, lithium manganate prepared from manganese source can exert a higher capacity, and the charge capacity is generally between 128-132 mAh / g; such as prior art 2: Chinese patent application 201310574431.4 discloses a method for producing high-capacity lithium manganate from manganese tetraoxide, which uses manganese tetraoxide and lithium carbonate as main raw materials, and according to the lithium-manganese molar ratio of 0.48-0.58, the additive corresponds to the finished product mass percentage of 0.1%-1%, and a dry method is used to mix evenly to form a semi-finished product, and then a high-capacity lithium manganate is produced by a sintering and post-treatment process.

[0005] Prior art 2 is to prepare lithium manganate positive electrode material by manganese tetraoxide, and the 1C gram capacity of the obtained lithium manganate positive electrode material is between 124-126 mAh / g. However, in order to ensure that the Mn in the manganese tetraoxide is 2+ and Mn 3+ Oxidized to Mn 3+ and Mn 4+ It takes a long time to sinter to obtain lithium manganese oxide positive electrode materials with excellent performance. The existing technology 2 needs to sinter for more than 18 hours, which will lead to higher production costs.

[0006] Therefore, it is necessary to find a method for preparing lithium manganese oxide materials that can effectively reduce production costs and ensure that the performance of the lithium manganese oxide positive electrode material will not decrease, so as to obtain a lithium manganese oxide positive electrode material with excellent performance. Summary of the invention

[0007] One of the purposes of the present invention is to provide a lithium manganate positive electrode material, which is prepared by mixing specific raw materials and can fully catalyze the oxidation of Mn under the synergistic effect of an oxidant and niobium oxide. 2+ and Mn 3+ The oxidation reaction not only increases the reaction rate but also synergistically improves the electrical performance of the lithium manganese oxide positive electrode material.

[0008] Another object of the present invention is to provide a method for preparing a lithium manganese oxide positive electrode material. The method has a short sintering time and can effectively obtain a lithium manganese oxide positive electrode material with excellent performance. It not only optimizes the reaction conditions and improves the material activity, but also greatly reduces the production cost.

[0009] To achieve the above-mentioned purpose, the present invention provides a lithium manganate positive electrode material, which is prepared by sequentially mixing and sintering a lithium compound, manganese tetraoxide, an oxidant and niobium oxide; wherein the molar ratio of lithium to manganese in the lithium compound and manganese tetraoxide is 1.03-1.05:2, the added amount of the oxidant is 1-1.5wt% of the lithium manganate, and the added amount of the niobium oxide is 0.3-1wt% of the lithium manganate.

[0010] In order to maximize the Mn 2+ and Mn 3+ The oxidation degree of Mn can generally be changed by adopting pure oxygen sintering, increasing the sintering temperature, extending the sintering time or doping with individual additives to change the reaction path and rate; among them, the technical solutions of adopting pure oxygen sintering, increasing the sintering temperature and extending the sintering time can effectively increase the oxidation degree of Mn 2+ and Mn 3+ The degree of oxidation can be increased, but its production cost will be greatly increased; and the choice of doping with individual additives, such as phosphorus doping, can change the crystal structure and electrochemical properties of lithium manganese oxide, thereby affecting the reaction rate, but due to phosphorus doping, it will limit the conductivity of the positive electrode material, thereby affecting the performance of the battery, and it is impossible to improve the reaction rate of lithium manganese oxide from the root.

[0011] The present invention promotes the rapid oxidation of low-valent manganese to the required high-valent manganese by doping with an oxidant, and further increases the Mn 2+ and Mn 3+ The degree of oxidation is increased to ensure that the manganese ions are fully oxidized, thereby obtaining a positive electrode material with excellent electrical properties and improving the performance of the battery.

[0012] In this process, niobium oxide not only synergistically increases the Mn 2+ and Mn 3+ The degree of oxidation is increased, and the electrical properties of the positive electrode material are further improved by doping with niobium.

[0013] Preferably, the lithium compound is at least one of lithium oxide, lithium hydroxide and lithium carbonate.

[0014] Preferably, the oxidant is one of sodium dichromate, potassium permanganate, ammonium persulfate, cobalt oxyhydroxide, potassium chloride, and sodium percarbonate.

[0015] Preferably, the niobium oxide is niobium monoxide, niobium dioxide, niobium trioxide or niobium pentoxide.

[0016] Experiments have found that niobium oxides have a certain synergistic catalytic effect with strong oxidants on the oxidation of low-valent manganese to high-valent manganese. However, when niobium monoxide, niobium dioxide, and niobium trioxide are used as synergistic oxidizing dopants, strong oxidants will also promote the oxidation of niobium, which will result in the need to supply more oxygen to complete the Mn 2+ and Mn 3+ The oxidation degree of Mn increases, which increases the production cost to a certain extent and reduces 2+ and Mn 3+ degree of oxidation; therefore, as a more preferred technical solution, the niobium oxide is niobium pentoxide.

[0017] The present invention also discloses a method for preparing a lithium manganate positive electrode material, comprising the following steps:

[0018] Step 1: mixing a lithium compound, manganese tetraoxide, an oxidant and niobium oxide to obtain a mixture;

[0019] Step 2: Sinter the mixture at 400-500° C. for 3-5 h, and then sinter at 600-800° C. for 4-10 h to obtain a lithium manganese oxide positive electrode material.

[0020] Preferably, in order to reduce production costs, step 2 of the above two preparation methods is sintered in an air atmosphere.

[0021] Furthermore, the method further comprises step 3: crushing and classifying the lithium manganese oxide positive electrode material to obtain lithium manganese oxide positive electrode material powder with a particle size D50 of 8-12 μm.

[0022] Beneficial Effects

[0023] Compared with the prior art, the present invention has at least the following advantages:

[0024] (1) The present invention can effectively promote the synthesis of Mn in the preparation process of lithium manganate by doping with oxidant and niobium oxide. 2+and Mn 3+ The oxidation of lithium manganese oxide accelerates the reaction rate and reduces production costs, while also effectively improving the performance of lithium manganese oxide positive electrode materials;

[0025] (2) The present invention discloses a method for preparing a lithium manganese oxide positive electrode material, which not only optimizes the reaction conditions and improves the material activity, but also significantly reduces the production cost. DETAILED DESCRIPTION

[0026] The present invention will be further described below in conjunction with the embodiments, but it does not constitute any limitation to the present invention. Any limited number of modifications made within the scope of the claims of the present invention are still within the scope of the claims of the present invention.

[0027] In order to explain the technical content of the present invention in detail, further description is given below in conjunction with the implementation modes.

[0028] In the following examples and comparative examples, the sintering treatment in step 2 was carried out in a roller hearth furnace in an air atmosphere, and compressed air was continuously introduced during the process, with a flow rate of 1.8 m 3 / h; the mixing in step 1 is carried out using a high-speed mixer.

[0029] In the following examples and comparative examples, the trimanganese tetraoxide is quasi-spherical trimanganese tetraoxide purchased from Sinosteel Tianyuan Co., Ltd., with a manganese content of 72%; the lithium carbonate is battery-grade lithium carbonate purchased from Guangdong Shengxiang New Materials Technology Co., Ltd., with a purity of 99.7%.

[0030] In the following examples and comparative examples, the theoretical weight of lithium manganate = (weight of manganese tetraoxide + weight of lithium carbonate) × 0.945. The calculation formula for the theoretical weight of lithium manganate is a calculation formula obtained through multiple experiments.

[0031] Example 1

[0032] A lithium manganate positive electrode material is prepared by the following steps:

[0033] Step 1: 101.6 g of lithium carbonate, 400 g of manganese tetraoxide, 4.977 g of potassium permanganate and 3.39 g of niobium pentoxide are uniformly mixed to obtain a mixture;

[0034] Step 2: sintering the mixture at 480°C for 4 hours and then sintering at 800°C for 5 hours to obtain a lithium manganese oxide positive electrode material;

[0035] Step 3: crushing and classifying the lithium manganese oxide positive electrode material to obtain a lithium manganese oxide positive electrode material powder with a particle size D50 of 10 μm;

[0036] According to calculation, the addition amount of potassium permanganate is 1.05wt% of the theoretical weight of lithium manganate, and the addition amount of niobium pentoxide is 0.5wt% of the theoretical weight of lithium manganate.

[0037] Example 2

[0038] A lithium manganate positive electrode material is prepared by the following steps:

[0039] Step 1: 104.6 g of lithium carbonate, 400 g of manganese tetraoxide, 7.153 g of potassium permanganate and 6.822 g of niobium pentoxide are uniformly mixed to obtain a mixture;

[0040] Step 2: sintering the mixture at 480°C for 3 hours and then sintering at 720°C for 4 hours to obtain a lithium manganese oxide positive electrode material;

[0041] Step 3: crushing and classifying the lithium manganese oxide positive electrode material to obtain a lithium manganese oxide positive electrode material powder with a particle size D50 of 10 μm;

[0042] According to calculation, the addition amount of potassium permanganate is 1.5wt% of the theoretical weight of lithium manganate, and the addition amount of niobium pentoxide is 1wt% of the theoretical weight of lithium manganate.

[0043] Example 3

[0044] The method is substantially the same as Example 1, except that niobium pentoxide is replaced by niobium dioxide, and step 2 is changed to: sintering the mixture at 480° C. for 5 h, and then sintering at 720° C. for 8 h to obtain a lithium manganate positive electrode material.

[0045] Example 4

[0046] The method is substantially the same as Example 2, except that step 2 is changed to: sintering the mixture at 480° C. for 5 h, and then sintering at 600° C. for 10 h to obtain a lithium manganate positive electrode material.

[0047] Example 5

[0048] The method is substantially the same as Example 2, except that step 2 is changed to: sintering the mixture at 450° C. for 5 h, and then sintering at 800° C. for 8 h to obtain a lithium manganese oxide positive electrode material.

[0049] Example 6

[0050] The method is substantially the same as Example 1, except that niobium pentoxide is replaced by niobium trioxide, and step 2 is changed to: sintering the mixture at 480° C. for 4 hours, and then sintering at 720° C. for 7 hours to obtain a lithium manganese oxide positive electrode material.

[0051] Comparative Example 1

[0052] It is generally the same as Example 1, except that potassium permanganate is not added.

[0053] Comparative Example 2

[0054] The method is generally the same as Example 1, except that potassium permanganate is not added, and step 2 is changed to: sintering the mixture at 480° C. for 5 h, and then sintering at 720° C. for 14 h to obtain a lithium manganate positive electrode material.

[0055] Comparative Example 3

[0056] The method is substantially the same as Example 1, except that niobium pentoxide is replaced by ferrosoferric oxide, and step 2 is changed to: sintering the mixture at 480° C. for 5 h, and then sintering at 720° C. for 8 h to obtain a lithium manganese oxide positive electrode material.

[0057] Comparative Example 4

[0058] It is generally the same as Example 1, except that niobium pentoxide is replaced by ferroferric oxide and potassium permanganate is not added, and step 2 is changed to: sintering the mixture at 480° C. for 5 hours and then sintering at 720° C. for 8 hours to obtain a lithium manganese oxide positive electrode material.

[0059] Comparative Example 5

[0060] The method is substantially the same as Example 1, except that niobium pentoxide is replaced by nickel oxide, and step 2 is changed to: sintering the mixture at 480° C. for 5 h, and then sintering at 720° C. for 8 h to obtain a lithium manganese oxide positive electrode material.

[0061] Comparative Example 6

[0062] It is generally the same as Example 1, except that niobium pentoxide is replaced by nickel oxide and potassium permanganate is not added, and the step 2 is changed to: sintering the mixture at 480° C. for 5 hours and then sintering at 720° C. for 8 hours to obtain a lithium manganate positive electrode material.

[0063] Comparative Example 7

[0064] The method is generally the same as Example 1, except that the amount of potassium permanganate used is 8.058 g. After calculation, the amount of potassium permanganate added is 1.7 wt % of the theoretical weight of lithium manganate.

[0065] Comparative Example 8

[0066] The method is substantially the same as Example 1, except that niobium pentoxide is replaced by manganese dioxide, and step 2 is changed to: sintering the mixture at 480° C. for 5 h, and then sintering at 720° C. for 8 h to obtain a lithium manganate positive electrode material.

[0067] Comparative Example 9

[0068] It is generally the same as Example 1, except that niobium pentoxide is replaced by manganese dioxide and potassium permanganate is not added, and the step 2 is changed to: sintering the mixture at 480° C. for 5 hours and then sintering at 720° C. for 8 hours to obtain a lithium manganate positive electrode material.

[0069] Comparative Example 10

[0070] It is substantially the same as Example 1, except that the amount of niobium pentoxide is 1.695 g. According to calculation, the amount of niobium pentoxide added is 0.25 wt % of the theoretical weight of lithium manganate.

[0071] Comparative Example 11

[0072] It is substantially the same as Example 1, except that the amount of niobium pentoxide is 8.137 g. According to calculation, the amount of niobium pentoxide added is 1.2 wt % of the theoretical weight of lithium manganate.

[0073] Comparative Example 12

[0074] The process is substantially the same as Example 1, except that niobium pentoxide is not added.

[0075] Performance Testing

[0076] The lithium manganese oxide positive electrode materials obtained in Examples 1-6 and Comparative Examples 1-12 were subjected to a full electrical test and tested at a cut-off voltage of 4.2 V: the lithium manganese oxide positive electrode materials obtained in Examples 1-6 and Comparative Examples 1-12 were used to prepare positive electrode slurry and negative electrode slurry, respectively, and then the positive electrode slurry was coated on aluminum foil, and the negative electrode slurry was coated on copper foil. After drying, rolling, powdering, welding of pole ears, winding, liquid injection, sealing and other processes, soft-pack batteries were prepared, and the battery capacity and cycle performance were tested.

[0077] The preparation method of the positive electrode slurry is:

[0078] Step 1: prepare lithium manganese oxide positive electrode material, PVDF, and carbon nanotube slurry in a mass ratio of 97:1.5:1.5;

[0079] Step 2: Dissolve PVDF in NMP to prepare a glue with a solid content of 8%, then add carbon nanotube slurry to mix and disperse at high speed for 1.5 hours, then knead and stir the lithium manganese oxide positive electrode material for 6 hours, add an appropriate amount of NMP to adjust the slurry viscosity to 5500mPa.s, control the solid content to 50%, apply it on the aluminum foil current collector, and vacuum dry it to obtain the positive electrode sheet.

[0080] The negative electrode slurry preparation method is as follows: dissolve the graphite material, carboxymethyl cellulose and styrene-butadiene rubber in deionized water at a mass ratio of 96.5:1.5:1, control the solid content to 50%, coat it on the copper foil current collector, and vacuum dry it to obtain the negative electrode sheet.

[0081] The battery was assembled and tested in the dew point room. After activation, the charge and discharge test was performed at room temperature of 25°C with a charge and discharge range of 3V~4.2V. The specific charge and discharge conditions were:

[0082] Step 1: The battery is placed at room temperature 25℃ for 1h, first charged to 4.2V at 1C constant current and constant voltage, with a cut-off current of 0.1C, and placed for 5min, then discharged at a constant current of 1C, with a cut-off voltage of 3V, and placed for 5min, and the 1C discharge gram capacity of the whole battery is recorded.

[0083] Step 2: Then charge at 1C constant current and constant voltage to 4.2V, cut off current 0.1C, rest for 5 minutes, discharge at 8C constant current, cut off voltage 3V, rest for 5 minutes, repeat this step 2 until the cycle retention rate is less than 80%, and record the number of cycles.

[0084] The full electrical test performance results of the lithium manganate positive electrode materials obtained in Examples 1-6 and Comparative Examples 1-12 are shown in Table 1;

[0085] Table 1 Full electrical test performance results of lithium manganate positive electrode materials obtained in Examples 1-6 and Comparative Examples 1-12

[0086] 1C gram capacity (mAh / g) 8C / 1C capacity ratio (%) 1C charge 8C discharge cycle life Example 1 121.2 91 450 weeks retention rate 80% Example 2 120.8 92 500-week retention rate 80% Example 3 120.6 91 450 weeks retention rate 80% Example 4 120.5 92 550 weeks retention rate 80% Example 5 117.3 84 300-week retention rate 80% Example 6 120.6 91 450 weeks retention rate 80% Comparative Example 1 103.0 80 300-week retention rate 80% Comparative Example 2 122.1 92 350 weeks retention rate 80% Comparative Example 3 110.1 82 350 weeks retention rate 80% Comparative Example 4 102.8 80 350 weeks retention rate 80% Comparative Example 5 110.3 83 300-week retention rate 80% Comparative Example 6 103.9 78 300-week retention rate 80% Comparative Example 7 110.4 80 500-week retention rate 80% Comparative Example 8 108.5 76 250-week retention rate 80% Comparative Example 9 105.8 77 200-week retention rate 80% Comparative Example 10 113.7 88 350 weeks retention rate 80% Comparative Example 11 122.2 84 250-week retention rate 80% Comparative Example 12 112.8 83 200-week retention rate 80%

[0087] According to the results in Table 1, we can see that:

[0088] According to the data comparison between Example 1 and Example 2, the technical solutions of the present invention can obtain lithium manganese oxide positive electrode materials with excellent electrical properties, and among them, within the addition amount range of potassium permanganate and niobium pentoxide of the present invention, increasing the addition amount of potassium permanganate and niobium pentoxide can effectively improve the 1C charge 8C discharge cycle life of the battery. The reason is that the potassium ions in potassium permanganate and the niobium ions in niobium pentoxide can effectively improve the cycle performance of the lithium manganese oxide positive electrode material.

[0089] However, according to the data comparison between Example 1 and Comparative Examples 1, 2 and 7, it can be seen that in Comparative Example 1, since no oxidant potassium permanganate is added, Mn 2+ and Mn 3+The oxidation efficiency is reduced. At the same sintering time and sintering temperature, due to the lack of oxidant, the valence state of the lithium manganese oxide positive electrode material cannot be completely converted. This directly affects the crystallization process of the material. The crystal structure is not perfect and regular, resulting in a significant decrease in the 1C gram capacity, 8C / 1C capacity ratio and 1C charge 8C discharge cycle life of the lithium manganese oxide positive electrode material. In view of the insufficient sintering, Comparative Example 2 prolongs the sintering time without adding potassium permanganate to obtain the grown lithium manganese oxide positive electrode material. However, it can be seen that the 1C gram capacity and 8C / 1C capacity ratio are reversed without adding potassium permanganate. Compared with Example 1, there is a slight improvement, but the 1C charge 8C discharge cycle life is significantly reduced. The reason is that although the potassium ions of potassium permanganate can effectively improve the 1C charge 8C discharge cycle life, potassium ions will enter the structure after the reaction decomposition, which will affect the capacity. Similarly, according to the data of Comparative Example 7, when the addition amount of potassium permanganate exceeds the scope of the present invention, the 1C gram capacity and 8C / 1C capacity ratio of the prepared lithium manganate positive electrode material are significantly reduced. Combined with the data of Comparative Example 2 and Example 1, it can be seen that the addition of niobium pentoxide not only synergistically promotes the Mn 2+ and Mn 3+ It also effectively inhibits the oxidation of potassium ions entering the structure and affecting the capacity.

[0090] It should be noted that the sodium ions and potassium ions in other oxidants such as sodium dichromate, ammonium persulfate, cobalt hydroxide oxide, potassium chloride, and sodium percarbonate will also enter the structure and affect the capacity of the lithium manganese oxide positive electrode material. The technical solution of the present invention promotes the catalytic conversion of Mn by niobium oxide on the basis of the oxidant. 2+ and Mn 3+ While preventing oxidation, it also effectively inhibits the entry of potassium ions and sodium ions into the structure, avoiding affecting the capacity of the lithium manganese oxide positive electrode material.

[0091] According to the performance of Examples 3 and 6, niobium dioxide, niobium trioxide and other niobium oxides can also cooperate with potassium permanganate to promote the 2+ and Mn 3+ The oxidation of niobium can improve the reaction efficiency, but because the valence state of niobium will also change and consume part of the oxygen, in this case it is necessary to increase the sintering time to promote the full growth of the lithium manganese oxide positive electrode material.

[0092] According to the data comparison between Example 1 and Comparative Example 1, Comparative Examples 3-6, it can be seen that in Comparative Examples 1, Comparative Examples 4, and Comparative Examples 6, without adding potassium permanganate as an oxidant, niobium pentoxide, ferroferric oxide, and nickel oxide are difficult to promote the Mn 2+ and Mn 3+The oxidation of Mn increases the sintering reaction rate; Comparative Examples 3 and 5 reflect that ferroferric oxide and nickel oxide can also effectively promote the sintering reaction rate together with potassium permanganate. 2+ and Mn 3+ The oxidation of the lithium manganese oxide increases the sintering reaction rate, but compared with the data of Example 1, it can be seen that ferroferric oxide and nickel oxide cannot effectively solve the problem of decreased capacity of the lithium manganese oxide positive electrode material due to the addition of potassium permanganate.

[0093] According to the data comparison between Example 3 and Comparative Examples 8 and 9, the addition of manganese dioxide can effectively increase the sintering reaction rate, but the effect is not significant. The reason may be that the role of manganese dioxide is not to synergistically promote the reaction of Mn with potassium permanganate. 2+ and Mn 3+ The effect of oxidation efficiency is that the addition of manganese dioxide can release oxygen during the sintering process, thereby increasing the Mn 2+ and Mn 3+ The oxidation efficiency of Mn was improved, but it did not cooperate with potassium permanganate, and only produced a simple effect superposition; therefore, although Comparative Example 8 effectively promoted the 2+ and Mn 3+ The oxidation efficiency is good, but the fluxing effect of niobium pentoxide is lacking, resulting in insufficient crystallinity of the material, which affects the electrochemical performance.

[0094] According to the data comparison between Example 1 and Comparative Example 10, too little addition of niobium pentoxide will lead to a significant decrease in the electrical performance of the lithium manganese oxide positive electrode material. The possible reasons are speculated to be:

[0095] (1) The amount of niobium pentoxide added is too small to produce significant synergistic Mn with potassium permanganate. 2+ and Mn 3+ The effect of oxidation efficiency;

[0096] (2) Too little addition of niobium pentoxide results in a significant decrease in its ability to inhibit potassium ions from entering the structure, thereby affecting the electrical performance of the lithium manganese oxide positive electrode material.

[0097] According to the data comparison between Example 1 and Comparative Example 11, it can be seen that excessive addition of niobium pentoxide leads to an increase in the 1C gram capacity of the lithium manganese oxide positive electrode material, but a decrease in the 8C / 1C capacity ratio and the 1C charge-8C discharge cycle life. It is speculated that the possible reason is that niobium pentoxide has a fluxing effect. Adding too much flux causes the lithium manganese oxide positive electrode material to exceed the normal sintering temperature range, destroying the crystal structure of the material, thereby affecting the electrochemical performance.

[0098] According to the data comparison between Example 1 and Comparative Examples 1 and 12, it can be seen that in the case of no addition of niobium pentoxide, although potassium permanganate is added to promote the 2+ and Mn3+ The oxidation efficiency can be improved, but it cannot solve the problem of decreased capacity of lithium manganese oxide positive electrode materials caused by the addition of potassium permanganate.

[0099] The embodiments presented herein are only embodiments selected according to the combination of all possible embodiments. The appended claims should not be limited by the embodiments describing the present invention. Some numerical ranges used in the claims include sub-ranges therein, and the changes in these ranges should also be covered by the appended claims.

Claims

1. A lithium manganate positive electrode material, characterized in that: The invention is prepared by sequentially mixing and sintering a lithium compound, manganese tetraoxide, an oxidant and niobium oxide; wherein the molar ratio of lithium to manganese in the lithium compound and manganese tetraoxide is 1.03-1.05:2, the amount of the oxidant added is 1-1.5wt% of the lithium manganate, and the amount of the niobium oxide added is 0.3-1wt% of the lithium manganate; the oxidant is one of sodium dichromate, potassium permanganate and sodium percarbonate; and the niobium oxide is niobium pentoxide; The preparation method of the lithium manganese oxide positive electrode material comprises the following steps: Step 1: mixing a lithium compound, manganese tetraoxide, an oxidant and niobium oxide to obtain a mixture; Step 2: Sinter the mixture at 400-500° C. for 3-5 h, and then sinter at 600-800° C. for 4-10 h to obtain a lithium manganese oxide positive electrode material.

2. The lithium manganate positive electrode material according to claim 1, characterized in that The lithium compound is at least one of lithium oxide, lithium hydroxide and lithium carbonate.

3. A method for preparing the lithium manganate positive electrode material according to claim 1 or 2, characterized in that: The steps include: Step 1: mixing a lithium compound, manganese tetraoxide, an oxidant and niobium oxide to obtain a mixture; Step 2: Sinter the mixture at 400-500° C. for 3-5 h, and then sinter at 600-800° C. for 4-10 h to obtain a lithium manganese oxide positive electrode material.

4. The method for preparing the lithium manganate positive electrode material according to claim 3, characterized in that: The method also includes step 3: crushing and classifying the lithium manganese oxide positive electrode material to obtain lithium manganese oxide positive electrode material powder with a particle size D50 of 8-12 μm.