A manganese-rich cathode material, its preparation method, a battery cathode, and a lithium-ion battery.

Abstract

This invention provides a manganese-rich cathode material, a preparation method, a battery cathode, and a lithium-ion battery. The method includes: dissolving a manganese source in an aqueous solution of citric acid and heating it in a water bath to react the manganese source and citric acid to generate nucleation sites, wherein the manganese source includes manganese dioxide; mixing and reacting the nucleation sites, a lithium source, a nickel source, and a cobalt source, followed by drying to form a precursor; and sintering the precursor to obtain the manganese-rich cathode material. Compared to existing technologies, this invention significantly reduces the raw material cost of the lithium-rich manganese-based cathode material by replacing at least a portion of the manganese source with manganese dioxide, while maintaining the chemical formula and crystal structure of the lithium-rich manganese-based cathode material without significant changes, ensuring its fundamental performance. Furthermore, with the addition of citric acid treatment, the specific surface area of ​​the lithium-rich manganese-based cathode material is significantly increased, further improving battery performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion batteries, in particular to a manganese-rich cathode material, a preparation method, a battery cathode and a lithium ion battery. BACKGROUND

[0002] At present, the manganese source used in the lithium-rich manganese-based cathode material is generally manganese acetate, which is used to control the charge transfer and ion diffusion rate. However, with the development of lithium batteries, the research and development of lithium-rich manganese-based cathode materials has become mature, and the performance of the materials has been difficult to further improve, and the research and development of lithium-rich manganese-based cathode materials has gradually encountered a bottleneck. In order to further improve the performance of lithium-rich manganese-based cathode materials, the main research idea at present is to dope in the lithium-rich manganese-based cathode material.

[0003] Doping generally destroys the crystal structure of the lithium-rich manganese-based cathode material itself, so there is great uncertainty in the influence on the performance of the battery, and it is often limited or harmful. In addition, the cost of the doped elements is high, so the cost of doping is high. Therefore, how to obtain a lithium-rich manganese-based cathode material with better performance at a lower cost is an important research goal of the lithium-rich manganese-based cathode material at present. SUMMARY

[0004] Therefore, it is necessary to provide a manganese-rich cathode material, a preparation method, a battery cathode and a lithium ion battery in order to solve the problems of high modification cost and insufficient modification effect of the lithium-rich manganese-based cathode material.

[0005] The technical scheme provided by the present application is as follows:

[0006] A preparation method of a manganese-rich cathode material, the preparation method comprising:

[0007] dissolving a manganese source in a citric acid aqueous solution and performing water bath heating to make the manganese source and the citric acid react to generate nucleation points, wherein the manganese source comprises manganese dioxide;

[0008] mixing and reacting the nucleation points, a lithium source, a nickel source and a cobalt source, and then drying to form a precursor;

[0009] sintering the precursor to obtain the manganese-rich cathode material.

[0010] The water bath heating temperature in the present application is 60℃.

[0011] The manganese source in the present application comprises manganese acetate.

[0012] The molar ratio of the manganese dioxide and the manganese acetate in the present application is 4:6.

[0013] The lithium source is lithium hydroxide, the nickel source is one or more of nickel carbonate, nickel sulfate and nickel hydroxide, and the cobalt source is one or more of cobalt carbonate, cobalt oxide and cobalt sulfate.

[0014] The lithium ion molar amount in the lithium source is a, the manganese ion molar amount in the manganese source is b, the cobalt ion molar amount in the cobalt source is c, the nickel ion molar amount in the nickel source is d, a: (b+c+d)=1.58:1, and the molar amount of citric acid is e, e: (a+b+c+d)=1:2.

[0015] A manganese-rich positive electrode material is obtained by the preparation method.

[0016] The chemical formula of the manganese-rich positive electrode material is Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2.

[0017] A battery positive electrode is made of the manganese-rich positive electrode material.

[0018] A lithium ion battery comprises the battery positive electrode.

[0019] The manganese-rich positive electrode material has the following advantages:

[0020] The manganese dioxide is treated with citric acid to obtain nucleation points with a large specific surface area, so that the nucleation points are more uniform and sufficient when reacting with the lithium source, the nickel source and the cobalt source, thereby improving the synthesis quality of the manganese-rich positive electrode material.

[0021] Compared with the prior art, at least part of the manganese source is replaced by manganese dioxide, the raw material cost of the lithium-rich manganese-based positive electrode material is significantly reduced, the chemical formula and the crystal structure of the lithium-rich manganese-based positive electrode material do not change significantly, the basic performance of the lithium-rich manganese-based positive electrode material is ensured, on this basis, the specific surface area of the lithium-rich manganese-based positive electrode material is significantly increased, and the battery performance is further improved. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 SEM of the manganese-rich positive electrode material in Example 1 of the present application;

[0023] Figure 2 The first charge-discharge curve of the lithium ion battery in Comparative Examples 1-3 and Example 1 of the present application;

[0024] Figure 3 The first charge-discharge curve of the lithium ion battery in Comparative Example 1 and Examples 2-4 of the present application;

[0025] Figure 4The images show the XRD patterns of the manganese-rich cathode materials in Comparative Example 1 and Examples 2-4 of this invention.

[0026] Figure 5 The graph shows the cycle performance of the lithium-ion batteries in Comparative Example 1 and Examples 2-4 of this invention after 200 cycles at 1C.

[0027] Figure 6 The graph shows the performance of lithium-ion batteries in Comparative Example 1 and Examples 2-4 of this invention after 500 cycles at 5C.

[0028] Figure 7 The graphs show the rate performance of lithium-ion batteries in Comparative Example 1 and Examples 2-4 of this invention at 0.1C-10C.

[0029] Figure 8 The first charge-discharge curves of the lithium-ion batteries in Comparative Example 4 and Example 4 of the present invention are shown. Detailed Implementation

[0030] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0031] Comparative Example 1:

[0032] This comparative embodiment provides a method for preparing a manganese-rich cathode material, including the following steps:

[0033] Step S1: Dissolve the manganese source (in this comparative example, the manganese source only includes manganese acetate tetrahydrate) in an aqueous solution of citric acid (citric acid concentration is e, in this comparative example, e=0.5mol / L), and heat it in a water bath at 60°C. During the reaction with citric acid, the manganese source gradually transforms into nucleation sites with a large specific surface area.

[0034] Step S2: Using lithium hydroxide as the lithium source, nickel acetate tetrahydrate as the nickel source, and cobalt acetate tetrahydrate as the cobalt source, the lithium source, nickel source, cobalt source, and nucleation site are mixed and reacted. The molar amount of lithium ions in the lithium source is a, the molar amount of manganese ions in the manganese source is b, the molar amount of cobalt ions in the cobalt source is c, and the molar amount of nickel ions in the nickel source is d. The total molar concentration of lithium ions, manganese ions, cobalt ions, and nickel ions is 1 mol / L, where a:(b+c+d)=1.58:1.

[0035] In some other comparative examples, the nickel source can also be one or more of nickel carbonate, nickel sulfate and nickel hydroxide, and the cobalt source is one or more of cobalt carbonate, cobalt oxide and cobalt sulfate.

[0036] Step S3: The reaction product obtained in step S2 is transported to an air flow spray drying device for drying, wherein the inlet air temperature is 230°C and the outlet air temperature is 110°C, so as to obtain a precursor.

[0037] Step S4: The precursor is transferred to a muffle furnace for sintering under an air atmosphere, the sintering process is to increase the temperature to 450°C at a temperature increasing rate of 2°C / min, then keep the temperature for 4h, and then increase the temperature to 850°C at a temperature increasing rate of 5°C / min, and keep the temperature for 20h.

[0038] Step S5: The sintered product is scattered by using an air flow mill, and then sieved and demagnetized, so as to obtain a manganese-rich positive electrode material with a chemical formula of Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2.

[0039] The manganese-rich positive electrode material, a conductive agent (SP) and a binder (PVDF) are mixed in a mass ratio of 8:1:1, an appropriate amount of NMP is added to prepare a mixed slurry, the mixed slurry is mixed in a debubbling machine, and then uniformly coated on an aluminum foil, and then transferred to a vacuum oven for drying at 110°C after primary baking at 100°C. The dried electrode sheet is cut into small pieces, and then subjected to rolling and punching treatment, so as to obtain a battery positive electrode.

[0040] A lithium ion battery is assembled by using a negative electrode (metal lithium sheet), the battery positive electrode, an electrolyte (DMC / EC / DEC=1 / 1 / 1 (1mol / L LiPF6)) and a cut piece separator (Celgard 2400), and the charge-discharge voltage range of the lithium ion battery is 2.0V-4.8V, the battery rate performance and capacity are tested at 0.1C / 1C / 2C / 5C / 10C rate.

[0041] Comparative Example 2:

[0042] The difference between this comparative example and comparative example 1 is that the manganese source only includes manganese sulfate.

[0043] Comparative Example 3:

[0044] The difference between this comparative example and comparative example 1 is that the manganese source only includes manganese nitrate.

[0045] Example 1:

[0046] The difference between this example and comparative example 1 is that the manganese source only includes manganese dioxide.

[0047] The specific surface area of the manganese-rich positive electrode material in Example 1 is shown in Table 1

[0048] Table 1

[0049]

[0050] As can be seen from Table 1, in the case of using manganese dioxide as the manganese source, the specific surface area of the manganese-rich positive electrode material is greatly improved, and the improvement effect is much greater than that of Comparative Example 1-3, thereby providing great potential for improving the performance of lithium ion batteries. The SEM of the manganese-rich positive electrode material in Example 1 is shown in Figure 1 which exhibits a loose and porous structure, fully illustrating that manganese dioxide plays a very important role in improving the specific surface area of the manganese-rich positive electrode material.

[0051] Referring to Figure 2 For the lithium ion batteries in Comparative Example 1-3 and Example 1, the discharge capacity of Example 1 is the largest, followed by Comparative Example 1, and the overall change trend of the discharge capacity meets the change trend of the specific surface area BET, but the discharge capacity of Comparative Example 3 is slightly less than that of Comparative Example 2, which reflects that there is a certain abnormality between the specific surface area BET and the battery performance.

[0052] Based on the abnormal correlation between the specific surface area BET and the battery performance, in order to obtain the maximum battery performance, additional experiments are supplemented, and considering the supporting effect of manganese acetate tetrahydrate on the battery performance, part of the manganese acetate tetrahydrate is replaced with manganese dioxide, as shown in Example 2-4.

[0053] Example 2:

[0054] The difference between this example and Comparative Example 1 is that the manganese source also includes manganese dioxide, and the total amount of manganese ions remains unchanged, part of the manganese acetate tetrahydrate is replaced with manganese dioxide, and the molar ratio of manganese dioxide to manganese acetate tetrahydrate is 2:8, that is, 20% of the manganese acetate tetrahydrate is replaced with manganese dioxide.

[0055] Example 3:

[0056] The difference between this example and Example 2 is that the molar ratio of manganese dioxide to manganese acetate tetrahydrate is 4:6, that is, 40% of the manganese acetate tetrahydrate is replaced with manganese dioxide.

[0057] Example 4:

[0058] The difference between this example and Example 2 is that the molar ratio of manganese dioxide to manganese acetate tetrahydrate is 6:4, that is, 60% of the manganese acetate tetrahydrate is replaced with manganese dioxide.

[0059] The specific surface area data of the manganese-rich positive electrode materials in Examples 2-4 are shown in Table 2.

[0060] Table 2

[0061]

[0062] As can be seen from Table 2, the increase in the content of manganese dioxide does not always increase the specific surface area BET of the manganese-rich positive electrode material, but there is a process of first increasing and then decreasing. The specific surface area BET of the manganese-rich positive electrode material can reach a maximum value when 60% of manganese dioxide is combined with 40% of manganese acetate tetrahydrate. This indicates that when manganese dioxide and manganese acetate tetrahydrate are used together as a manganese source, there is a greater probability that the lithium ion battery can obtain more excellent performance.

[0063] The battery performance in Comparative Example 1 and Examples 2-4 is described in Table 3 to demonstrate the improvement effect of the combination of manganese dioxide and manganese acetate tetrahydrate on the performance of the lithium ion battery.

[0064] Table 3

[0065]

[0066] In combination Figures 5-8 It can be seen that as the manganese acetate tetrahydrate is gradually replaced by manganese dioxide, the rate performance of the battery gradually increases and then decreases, and the initial coulombic efficiency and capacity retention rate also show the same trend. As shown in Figure 4 The improvement in performance is largely due to the fact that manganese dioxide does not change the crystal structure of the lithium-rich manganese-based material, ensuring the basic performance of the lithium-rich manganese-based material.

[0067] However, it is worth noting that the optimal value of the battery performance is actually in Example 3, not in the case of the maximum specific surface area of the manganese-rich positive electrode material in Example 4. Referring to Figure 3 , the initial discharge capacity of the lithium ion battery in Example 3 is the largest, followed by Example 2, Comparative Example 1, and Example 4.

[0068] This indicates that the specific surface area cannot be equated with the battery performance, and the reason may be that the increase in the specific surface area of the lithium-rich manganese-based material may also be accompanied by some negative effects. For example, a larger specific surface area can increase the contact area between the material and the electrolyte, increasing the loss and irreversible reaction of lithium ions in the electrolyte. In addition, a larger specific surface area can also lead to an increase in particle aggregation and structural instability of the material, thereby reducing the cycle stability and life of the electrode. This can demonstrate that when using a combination of manganese acetate tetrahydrate and manganese dioxide as a manganese source, the specific surface area of the lithium-rich manganese-based material needs to be controlled within a reasonable range in order to improve the performance of the battery.

[0069] Further, in order to demonstrate the cost advantage in embodiment 3, the prices of different manganese sources are shown in Table 4.

[0070] Table 4

[0071]

[0072] It can be seen that the manganese content in manganese dioxide is about half of that in manganese acetate tetrahydrate, which indicates that by replacing part of manganese acetate tetrahydrate with manganese dioxide, the battery performance is improved and the battery production cost is greatly reduced.

[0073] Comparative example 4:

[0074] The difference between this comparative example and embodiment 4 is that e = 1 mol / L, i.e. compared with the manganese source, the citric acid is in an excess state.

[0075] Referring to Figure 8 , the excess citric acid leads to a decrease in the discharge capacity of the battery, which indicates that the content ratio between citric acid and manganese source has a very important influence on the battery performance.

[0076] The appropriate amount of citric acid can homogenize the particles formed by the manganese source and increase the specific surface area, thereby improving the surface energy of the unit mass of manganese source, and thus improving the reaction quality of the lithium-rich manganese-based material. At the same time, the interface impedance is also reduced, the energy loss in the ion transport process in the battery is reduced, and the ion migration speed and efficiency are improved. In addition, the homogenization of the particles can also improve the battery capacity and cycle performance, thereby making the battery better store and release energy and improving the service life. If the manganese source, nickel source, cobalt source and lithium source are mixed with citric acid at the same time, the reactions between them and citric acid will be in competition, which is not conducive to the homogenization of the particles. If an excess of citric acid is used to pursue homogenization, the manganese ions will form unstable compounds by excessive complexation, and due to the decrease in pH during the reaction process, the manganese ions cannot produce sufficient aggregation, making it difficult to ensure the formation of nucleation points with a relatively uniform size. As a result, the uniformity of the manganese-rich positive electrode material cannot be guaranteed, and the battery will also have defects such as capacity decay and reduced cycle life during the charging and discharging process. In addition, the introduction of excess citric acid will also change the uneven distribution of electrolyte concentration in the battery, thereby increasing the safety hazard. Therefore, it also reflects the importance of the reaction between the manganese source and citric acid to form nucleation points in the synthesis process.

[0077] Any combination of the technical features of the above-described embodiments can be made, and in order to make the description concise, not all possible combinations of the technical features in the above-described embodiments are described, however, as long as the combinations of the technical features do not exist, they should be considered as the scope of the description.

[0078] The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are within the scope of protection of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A method for preparing a manganese-rich cathode material, characterized in that, The preparation method comprises: dissolving a manganese source in an aqueous solution of citric acid and heating in a water bath to react the manganese source and the citric acid to form nucleation points, the manganese source comprising manganese dioxide and manganese acetate; mixing and reacting the nucleation points, a lithium source, a nickel source and a cobalt source, and then drying to form a precursor; sintering the precursor to obtain a manganese-rich positive electrode material.

2. The method for preparing the manganese-rich cathode material according to claim 1, characterized in that, The water bath heating temperature is 60℃.

3. The method for preparing the manganese-rich cathode material according to claim 2, characterized in that, The molar ratio of the manganese dioxide and the manganese acetate is 4:

6.

4. The method of claim 3, wherein the manganese-rich cathode material is prepared by the steps of: preparing a precursor solution by dissolving manganese acetate, lithium acetate, and a binder in a solvent; coating the precursor solution on a substrate; and drying the coated substrate. The lithium source is lithium hydroxide, the nickel source is one or more of nickel carbonate, nickel sulfate and nickel hydroxide, and the cobalt source is one or more of cobalt carbonate, cobalt oxide and cobalt sulfate.

5. The method for preparing the manganese-rich cathode material according to claim 4, characterized in that, The molar amount of lithium ions in the lithium source is a, the molar amount of manganese ions in the manganese source is b, the molar amount of cobalt ions in the cobalt source is c, the molar amount of nickel ions in the nickel source is d, a:(b+c+d)=1.58:1, and the molar amount of citric acid is e, e:(a+b+c+d)=1:

2.

6. A manganese-rich cathode material, characterized in that, The preparation method is obtained by any one of claims 1-5.

7. The Mn-rich cathode material of claim 6, wherein, Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2.

8. A battery positive electrode, characterized by, The manganese-rich positive electrode material is prepared by claim 7.

9. A lithium-ion battery, characterized by The battery positive electrode comprises claim 8.

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