A surface structure modified lithium cobalt oxide cathode material and a preparation method and application thereof

Abstract

The application relates to a surface structure modified lithium cobalt oxide positive electrode material and a preparation method and application thereof, wherein the surface structure and the morphology of the lithium cobalt oxide positive electrode material are microstructured by an alkaline solution, the alkali treated lithium cobalt oxide positive electrode material is repeatedly washed after filtration, then dried, and finally high-temperature calcined to obtain the surface structure modified lithium cobalt oxide positive electrode material. Compared with the prior art, the preparation method is simple, raw materials are extensive, and the cost is low; and the lithium cobalt oxide positive electrode material obtained through alkali treatment has excellent structural stability and electrochemical performance, especially a higher specific capacity and excellent cycle performance under high voltage.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material technology, and in particular relates to a surface-structure modified lithium cobalt oxide cathode material, its preparation method and application. Background Technology

[0002] With the increasing demand for portable electronic products in modern society, the development of battery technology has become increasingly important. Since Sony successfully commercialized lithium-ion batteries in 1992, they have been widely used in various electronic devices due to their advantages of high operating voltage, high energy density, and long cycle life. Compared with nickel lithium oxide and manganese lithium oxide, lithium cobalt oxide cathode materials still hold a dominant position in the development of 3C digital products due to their superior energy density, cycle performance, high-temperature performance, and low-temperature performance. Since the introduction of 4.45V lithium cobalt oxide cathode materials to the market, they have basically met the application needs of 3C electronic products. However, as a reserve of high-end battery technology, the energy density and cycle life of lithium cobalt oxide cathode materials still need to be improved.

[0003] The theoretical capacity of lithium cobalt oxide cathode material is 274 mAh / g, and when the charging cutoff voltage is increased to 4.45V, the capacity is approximately 175 mAh / g. Although increasing the charging cutoff voltage gives the lithium cobalt oxide cathode material a higher specific capacity, excessive lithium ions extracted from the lattice can cause the crystal structure to collapse, leading to an irreversible phase transition. Simultaneously, when the degree of delithiation on the cathode material surface increases, the lithium cobalt oxide structure will extend from the particle surface to the particle interior, undergoing a phase transition. Furthermore, under high voltage, Co ions are more easily dissolved in the electrolyte, and tetravalent cobalt ions have strong oxidizing properties, leading to electrolyte decomposition. These factors all contribute to a decrease in the cycle performance of lithium cobalt oxide, thus affecting its practical application under high voltage. Chinese patent CN116314783A discloses a nanoscale high-voltage lithium cobalt oxide cathode material and its preparation method. By doping with magnesium, aluminum, and titanium and undergoing a high-temperature solid-state reaction, a lithium cobalt oxide cathode material with good electrochemical performance under high voltage is obtained. However, its preparation process is complex and involves a large number of doping elements.

[0004] Therefore, further research is needed to improve the electrochemical performance of lithium cobalt oxide cathode materials at a cutoff voltage of 4.45V and to simplify the preparation process. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the prior art by providing a surface-structure modified lithium cobalt oxide cathode material, its preparation method and application. By treating the cathode material with an alkaline solution, a lithium cobalt oxide cathode material with stable structure and excellent cycle performance is obtained. Moreover, the preparation method is simple, the raw materials are readily available, and the cost is low.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] This invention provides a method for preparing a surface-structure modified lithium cobalt oxide cathode material, comprising the following steps:

[0008] S1: Immerse the lithium cobalt oxide cathode material in an alkaline solution, stir at room temperature, and replace the alkaline solution periodically. After stirring, filter to obtain the alkaline-treated lithium cobalt oxide cathode material.

[0009] S2: Wash the alkali-treated lithium cobalt oxide cathode material obtained in S1 to remove the alkali solution remaining on the surface of the cathode material, and then dry it to obtain lithium cobalt oxide cathode material powder.

[0010] S3: The powder obtained in S2 is sintered at high temperature. After sintering is completed, it is cooled to room temperature to obtain a lithium cobalt oxide cathode material with modified surface structure.

[0011] Furthermore, in S1, the mass ratio of the lithium cobalt oxide cathode material to the alkaline solution is 1:4 to 1:40.

[0012] Further, in S1, the alkaline solution is one of LiOH solution, NaOH solution, KOH solution, Li2CO3 solution, and ammonia water; the concentration of the alkaline solution is 0.05M-1M.

[0013] Furthermore, in S1, the stirring time is 12h-120h, and the stirring speed is 600r / min.

[0014] Furthermore, in S1, the alkaline solution is replaced every 12 hours.

[0015] Furthermore, in S2, the drying conditions are vacuum drying, the drying temperature is 80℃, and the drying time is 12h.

[0016] Furthermore, in S2, the washing process uses deionized water and continues until the pH of the washing water is neutral.

[0017] Furthermore, in S3, the sintering temperature is 500–800℃, the sintering time is 300 min, the sintering atmosphere is air, and the heating rate is 10℃ / min.

[0018] The present invention also provides a lithium cobalt oxide cathode material with modified surface structure.

[0019] The present invention also provides an application of a surface-modified lithium cobalt oxide cathode material, which is applied to a working scenario with a cutoff voltage of 4.45V.

[0020] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0021] 1. The method for surface modification of lithium cobalt oxide cathode material in this invention is simple and easy to operate, and the raw materials are widely available and inexpensive.

[0022] 2. The modified lithium cobalt oxide cathode material of this invention has excellent structural stability and electrochemical performance, especially high specific capacity and excellent cycle performance under high voltage.

[0023] 3. The modified lithium cobalt oxide cathode material of this invention can reduce the side reactions between the lithium cobalt oxide cathode material and the electrolyte during charging and discharging, thereby improving the electrochemical performance of the material.

[0024] 4. The surface modification method of the present invention belongs to the surface in-situ construction method. Compared with the traditional coating method, the present invention can more easily form a uniform and dense coating layer on the surface of lithium cobalt oxide cathode material. Attached Figure Description

[0025] Figure 1 These are scanning electron microscope (SEM) images of the lithium cobalt oxide cathode material before and after surface modification in Example 1.

[0026] Figure 2 The images show the XRD patterns of the lithium cobalt oxide cathode material before and after surface modification in Example 1.

[0027] Figure 3 This is a TEM image of the lithium cobalt oxide cathode material after surface modification in Example 1;

[0028] Figure 4 The above are charge-discharge curves of the lithium cobalt oxide cathode material before and after surface modification in Example 1.

[0029] Figure 5 The graph shows the cycle performance of the lithium cobalt oxide cathode material before and after surface modification in Example 1.

[0030] Figure 6 The graph shows the cycle performance of the lithium cobalt oxide cathode material before and after surface modification in Example 2.

[0031] Figure 7 The graph shows the cycle performance of the lithium cobalt oxide cathode material before and after surface modification in Example 3. Detailed Implementation

[0032] The following examples illustrate specific implementations of the present invention. These examples are carried out based on the solution described in the present invention, and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following examples.

[0033] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Any preparation methods, materials, structures, or composition ratios not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0034] Example 1

[0035] This invention provides a method for surface structure modification of lithium cobalt oxide cathode materials, comprising the following steps:

[0036] S1: Prepare 20 ml of 0.1 M LiOH solution, immerse 1 g of LiCoO2 cathode material in the LiOH solution, replace with fresh 0.1 M LiOH solution every 12 hours, stir at room temperature for 72 h and then filter to obtain LiOH solution treated lithium cobalt oxide cathode material;

[0037] S2: The lithium cobalt oxide cathode material treated with LiOH solution in S1 is washed with deionized water until the pH is neutral to remove the alkaline solution remaining on the surface of the cathode material, and then vacuum dried at 80℃ for 12 hours to obtain the dried lithium cobalt oxide cathode material.

[0038] S3: The dried lithium cobalt oxide cathode material from S2 is placed in a muffle furnace for high-temperature sintering. It is calcined at 600°C in air for 300 minutes with a heating rate of 10°C / min. After sintering is completed, the surface-modified lithium cobalt oxide cathode material is obtained by cooling to room temperature.

[0039] The surface-modified lithium cobalt oxide cathode material (R-LCO) and the unmodified lithium cobalt oxide cathode material (LCO) were characterized and tested, and the results are as follows: Figure 1 , Figure 2 and Figure 3 As shown. Figure 1 In the image, 'a' is a SEM image of LCO, and 'b' is a SEM image of R-LCO. (From...) Figure 1 It can be seen that after surface modification, the surface of R-LCO is rougher than that of LCO, and its particle size is smaller. The particle size of LCO is 5-25 μm, while that of R-LCO is 3-20 μm. Figure 2 It can be seen that R-LCO can still maintain a good layered structure after surface modification; Figure 3 It can be seen that after surface modification, a uniform and dense coating layer with a thickness of 5nm is formed on the surface of the lithium cobalt oxide cathode material.

[0040] R-LCO and LCO were respectively used to prepare half-cells with lithium metal as the negative electrode for electrochemical performance testing. The specific test conditions were: 0.4C / 0.4C charge-discharge tests were conducted at 25℃ and within a voltage range of 3.0–4.45V. Figure 4In diagram a, the charge-discharge curve of LCO is shown, and in diagram b, the charge-discharge curve of R-LCO is shown. Figure 4 It can be seen that the LCO exhibits significant voltage decay after 200 cycles, while the charge-discharge curve of the R-LCO remains almost unchanged.

[0041] Long-cycle testing was performed on half-cells assembled from R-LCO and LCO, and the results are as follows: Figure 5 As shown, after 300 cycles, the discharge specific capacity of LCO is only 50.5 mAh / g, while the discharge specific capacity of R-LCO after 300 cycles is 162.1 mAh / g; when cycled to 1000 cycles, the capacity retention rate of R-LCO is still maintained at 94%, thus demonstrating that the surface-modified lithium cobalt oxide cathode material has excellent cycle stability.

[0042] Example 2

[0043] This embodiment is basically the same as Embodiment 1, except that in S1 of this embodiment, the LiOH solution is replaced with a NaOH solution. Figure 6 As shown, using 0.1M NaOH solution as the alkali, the modified lithium cobalt oxide cathode material (R-LCO(NaOH)) retained 78.5% of its capacity after 500 cycles at a current density of 0.4C.

[0044] Example 3

[0045] This embodiment is basically the same as Embodiment 1, except that in S1 of this embodiment, the LiOH solution is replaced with an ammonia solution. Figure 7 As shown, using 0.1M ammonia water as the alkaline solution, the modified lithium cobalt oxide cathode material (R-LCO(NH3·H2O)) retained 69.7% of its capacity after 500 cycles at a current density of 0.4C.

[0046] Example 4

[0047] This embodiment is basically the same as embodiment 1, except that in S1 of this embodiment, the LiOH solution is replaced with KOH solution.

[0048] Example 5

[0049] This embodiment is basically the same as Embodiment 1, except that in S1 of this embodiment, the stirring time is changed from 72 hours to 120 hours. After stirring for 120 hours, the cathode material exhibits a discharge specific capacity of 68.8 mAh g after 300 cycles. -1 It is 93.3 mAh higher than that in Example 1. -1 Its corresponding capacity retention rate is 42%.

[0050] Example 6

[0051] This embodiment is basically the same as embodiment 1, except that in S1 of this embodiment, the stirring time of 72 hours is changed to 12 hours.

[0052] Example 7

[0053] This embodiment is basically the same as embodiment 1, except that in S3 of this embodiment, the heating temperature of 600℃ is changed to 800℃.

[0054] Example 8

[0055] This embodiment is basically the same as embodiment 1, except that in S3 of this embodiment, the heating temperature of 600℃ is changed to 500℃.

[0056] Example 9

[0057] This embodiment is basically the same as Embodiment 1, except that in S1 of this embodiment, the concentration of LiOH solution is changed to 0.05M.

[0058] Example 10

[0059] This embodiment is basically the same as embodiment 1, except that in S1 of this embodiment, the concentration of LiOH solution is changed to 1M.

[0060] Example 11

[0061] This embodiment is basically the same as embodiment 1, except that in S1 of this embodiment, the 20ml LiOH solution is replaced with 40ml LiOH solution.

[0062] Example 12

[0063] This embodiment is basically the same as embodiment 1, except that in S1 of this embodiment, 1g of LiCoO2 cathode material is replaced with 5g of LiCoO2 cathode material.

[0064] Comparative Example 1

[0065] This comparative example used a 0.1M hydrochloric acid solution, and the remaining steps were the same as in Example 1, to prepare a surface-modified lithium cobalt oxide cathode material. After 50 cycles, its discharge specific capacity was only 28 mAh g⁻¹. -1 .

[0066] Comparative Example 2

[0067] This comparative example used a 0.01M LiOH alkaline solution, and the remaining steps were the same as in Example 1 to prepare the surface-modified cathode material. After 300 cycles, its discharge specific capacity was only 40.4 mAh g⁻¹. -1 The corresponding capacity retention rate is 25.4%.

[0068] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a surface-structure modified lithium cobalt oxide cathode material, characterized in that, Includes the following steps: S1: Immerse the lithium cobalt oxide cathode material in an alkaline solution, stir at room temperature, and replace the alkaline solution periodically. After stirring, filter to obtain alkaline-treated lithium cobalt oxide cathode material. The mass ratio of the lithium cobalt oxide cathode material to the alkaline solution is 1:4 to 1:

40. The alkaline solution is one of LiOH solution, NaOH solution, KOH solution, Li2CO3 solution, or ammonia water. The concentration of the alkaline solution is 0.05M-1M. S2: Wash the alkali-treated lithium cobalt oxide cathode material obtained in S1 to remove the alkali solution remaining on the surface of the cathode material, and then dry it to obtain lithium cobalt oxide cathode material powder. S3: The powder obtained in S2 is sintered at high temperature. After sintering is completed, it is cooled to room temperature to obtain a lithium cobalt oxide cathode material with modified surface structure. The sintering temperature is 500~800 ℃, the sintering time is 300 min, the sintering atmosphere is air atmosphere, and the heating rate is 10℃ / min.

2. The method for preparing a surface-structure modified lithium cobalt oxide cathode material according to claim 1, characterized in that, In S1, the stirring time is 12h-120h, and the stirring speed is 600r / min.

3. The method for preparing a surface-structure modified lithium cobalt oxide cathode material according to claim 1, characterized in that, In S1, the alkaline solution is replaced every 12 hours.

4. The method for preparing a surface-structure modified lithium cobalt oxide cathode material according to claim 1, characterized in that, In S2, the drying conditions are vacuum drying, the drying temperature is 80℃, and the drying time is 12h.

5. The method for preparing a surface-structure modified lithium cobalt oxide cathode material according to claim 1, characterized in that, In S2, the washing process uses deionized water and continues until the pH of the washing water is neutral.

6. A surface-structure modified lithium cobalt oxide cathode material prepared by the method according to any one of claims 1-5.

7. An application of a surface-structure modified lithium cobalt oxide cathode material as described in claim 6, characterized in that, Surface-modified lithium cobalt oxide cathode material is applied to working scenarios with a cutoff voltage of 4.45V.

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