A method for in-situ coating of a chromium oxide positive electrode material

Abstract

The application discloses a method for in-situ coating of a chromium oxide positive electrode material, and belongs to the technical field of preparation of lithium ion battery positive electrode materials, and a specific scheme is as follows: the chromium oxide material is composed of an inner layer of high specific capacity chromium oxide and an outer layer of high chromium content oxide material coated thereon. The application aims at the prominent problem of low structural stability of the high capacity chromium oxide material, coats a layer of chromium oxide material with good structural stability on the high capacity chromium oxide material through high temperature quenching, and improves the storage performance and cycle stability of the material through the stable effect of the outer coating layer.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium battery cathode materials, and particularly relates to a method for in-situ coating of a chromium oxide cathode material. BACKGROUND

[0002] Lithium ion batteries (LIBs) have higher energy density and cycle life compared to other rechargeable batteries, making them widely used in various fields. Currently, commercially available cathode materials such as LiCoO2, LiFePO4, LiMn2O4, and ternary cathodes (NCM or NCA) have increased their specific energy from 120 Wh / kg to 300 Wh / kg, but are close to the theoretical limit. Therefore, researchers have turned their attention to the development of new materials. In recent years, chromium oxides have attracted attention due to their high energy density and high capacity at low discharge rates. Chromium oxides with multiple electron reactions, such as Cr8O 21 (Cr(III)2[Cr(VI)O4]2Cr(VI)4O 13 ), have attracted attention due to their high theoretical specific capacity (642 mAh / g, 1210 Wh / kg) and high operating voltage (3.0 V vs. Li+ / Li). The theoretical specific capacity is more than twice that of conventional ternary materials LiNi 0.8 Co 0.1 Mn 0.1 O2 (280 mAh / g). As a cathode material for lithium ion batteries, it is also relatively low in cost, thus having good competitiveness and prospects.

[0003] In recent years, chromium oxides have attracted widespread attention as an important cathode material in the field of batteries. Traditionally, research on chromium oxides has mainly focused on the optimization of sintering processes, the compounding of other active materials to improve battery performance, and the improvement of cycle performance through material coating. Although existing composite cathodes, such as CF x / Cr8O 21 composite cathodes, can improve battery capacity to some extent, they also have problems affecting rate performance. In addition, the use of atomic layer deposition (ALD) technology to coat an Al2O3 layer on the surface of chromium oxides can effectively improve the cycle stability of the battery, but significantly increases the production cost of the battery. In order to overcome the above problems, related research is exploring simpler and more economical coating techniques to maintain the excellent cycle performance of chromium oxides and avoid cost increases. SUMMARY

[0004] The purpose of the present application is to solve the problems of high cost and poor rate performance of existing chromium oxides, and to provide a method for in-situ coating of a chromium oxide cathode material. Specifically, a layer of CrO xThe chromium oxide protective layer material. Compared with the traditional chromium oxide material, the modified material has superior surface structure stability, significantly improves the air stability of the material, and the CrO x The chromium oxide protective layer reduces the side reaction of the positive electrode and the electrolyte, improves the cycle life and storage life of the chromium oxide positive electrode material, and significantly improves the cycle stability of the assembled lithium-chromium oxide battery.

[0005] To achieve the above-mentioned purpose, the technical solutions adopted by the present application are as follows:

[0006] A method for in-situ coating of a chromium oxide positive electrode material, the method comprising:

[0007] Step one: chromium trioxide is treated by high temperature calcination, and after grinding, active chromium oxide material is obtained;

[0008] Step two: a protective chromium oxide is in-situ coated on the surface of the active chromium oxide material of step one.

[0009] Further, in step one, the high temperature calcination time is 6-48h, the temperature is 250-375℃, and the heating rate is 1-10℃ / min. According to the sintering temperature and sintering time, the obtained active chromium oxide material is Cr8O 21 , Cr2O5, Cr5O 12 or a mixed phase thereof.

[0010] Further, in step one, the grinding includes manual grinding, ball mill grinding or breaking by a cell wall breaking machine.

[0011] Further, in step two, the in-situ coating specifically refers to quenching the active chromium oxide material of step one at high temperature to generate CrO x chromium oxide protective layer on the surface thereof.

[0012] Further, in step two, the specific conditions of the in-situ coating are: the quenching temperature is 375-1000℃, and the time is 10s-60min. According to the quenching temperature and time, the CrO x chromium oxide protective layer material has a specific structure of Cr2O5, Cr5O 12 and Cr2O3 or a mixed phase thereof. Due to the difference in quenching temperature and time, the CrO x chromium oxide protective layer material has a coating thickness of 1nm-50μm.

[0013] Compared with the prior art, the present application has the following beneficial effects:

[0014] Compared with Cr8O 21 , Cr2O5, Cr5O 12and Cr2O3 material has more excellent stability, can be stored for more than a month at room temperature without obvious deterioration. These chromium oxides not only have high chemical stability, but also are not easy to react with electrolyte, so as to effectively avoid the performance decline of the battery due to material degradation or reaction with electrolyte during use. The application provides a method for coating Cr2O5, Cr5O 12 or Cr2O3 and other high-stability chromium oxides on the surface of chromium oxide material by a simple in-situ coating technology. This coating method can not only significantly improve the air stability of chromium oxide, but also effectively improve its cycle stability and long-term performance, and will not significantly increase the production cost of the material. The application of such coating technology has significant advantages, which can provide stronger guarantee for the long-term stable operation of chromium oxide battery, and has wide application prospect.

[0015] Cr8O 21 has higher electrochemical capacity, but its structure is not the most stable form, and the capacity layer can be dissolved by water, so the air stability is poor. While other chromium oxides such as Cr2O5, Cr5O 12 and Cr2O3 material has better structural stability, can be stored in air for a long time, so the stable Cr2O5, Cr5O 12 and Cr2O3 coated on the active chromium oxide material can improve its storage capacity; at the same time, Cr2O5, Cr5O 12 and Cr2O3 have good chemical stability, are not easy to react with electrolyte, and the cycle stability of the battery is obviously improved. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is the scanning electron microscope photo of the Cr8O 21 material coated with Cr2O3 in Example 1;

[0017] Figure 2 is the long cycle curve diagram of Li||Cr8O 21 @Cr2O3 battery in Example 1;

[0018] Figure 3 is the long cycle curve diagram of Li||Cr2O5@Cr2O3 battery in Example 2;

[0019] Figure 4 is the long cycle curve diagram of Li||Cr8O 21 @Cr2O5 battery in Example 3;

[0020] Figure 5 is the long cycle curve diagram of Li||Cr8O 21 @Cr5O 12 battery in Example 4;

[0021] Figure 6 For Comparative Example 1 Li||Cr8O 21 Long cycle curve of the battery;

[0022] Figure 7 For Comparative Example 1 Li||Cr8O 21 Long cycle curve of the battery. DETAILED DESCRIPTION

[0023] The technical solutions in the present application will be described clearly and completely in combination with the drawings and examples. Obviously, the described examples are only some of the examples of the present application, but not all the examples. Based on the examples in the present application, all the other examples obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0024] The present application aims to provide a method for in-situ coating of a chromium oxide positive electrode material to improve its cycle life and storage life. The specific method is to coat a layer of CrO x on the surface of the active chromium oxide by high-temperature quenching. Compared with traditional chromium oxide materials, the modified material can isolate air due to its inert surface, significantly improving the air stability of the material. At the same time, CrO x The protective layer reduces the side reaction of the positive electrode and the electrolyte, thereby reducing the capacity decay of the chromium oxide as a battery material when it is stored.

[0025] Example 1

[0026] 5.0 g of chromium trioxide crystal powder was weighed and placed in a ceramic capsule, which was placed in a tube furnace for pyrolysis at 270℃ for 24 h in an air atmosphere, with a heating rate of 5℃ / min. The product was ground and sieved to obtain the product Cr8O 21 . The obtained Cr8O 21 was placed in a tube furnace fired at 800℃ for 10 s to obtain Cr2O3-coated Cr8O 21 material. The morphology of the obtained material is shown in Figure 1 . The specific battery assembly process and electrochemical performance test are as follows:

[0027] The Cr2O3-coated Cr8O 21The material was dissolved in N-methyl pyrrolidone (NMP) with Super P and PVDF at a mass ratio of 8:1:1 and stirred for 12 h. The slurry was scraped on an Al current collector with a coater and placed in a vacuum oven at 120°C for 12 h to dry, obtaining a coated chromium oxide positive electrode. A CR2025 type button cell was assembled using a lithium metal wafer as the negative electrode, with EC / DEC (1:1)-LiPF6 (1 mol / L) as the electrolyte, the amount of electrolyte being 50 μL, and a commercial PP separator. The charge and discharge performance of the battery at 0.1C was tested, with the voltage test interval being 1.5-4.5 V. The battery test results are shown in Table 1. Figure 2

[0028] Example 2

[0029] 5.0 g of chromium trioxide crystal powder was weighed into a ceramic boat and placed in a tube furnace for pyrolysis at 350°C for 12 h under an air atmosphere, with a heating rate of 5°C / min. The product was ground and sieved to obtain the product Cr2O5. The obtained Cr2O5 was placed in a tube furnace at 800°C for pyrolysis for 10 s, and quenched to obtain Cr2O3-coated Cr2O5 material. The specific battery assembly process and electrochemical performance test are as follows:

[0030] The Cr2O3-coated Cr2O5 material obtained in the above process was dissolved in N-methyl pyrrolidone (NMP) with Super P and PVDF at a mass ratio of 8:1:1 and stirred for 12 h. The slurry was scraped on an Al current collector with a coater and placed in a vacuum oven at 120°C for 12 h to dry, obtaining a coated chromium oxide positive electrode. A CR2025 type button cell was assembled using a lithium metal wafer as the negative electrode, with EC / DEC (1:1)-LiPF6 (1 mol / L) as the electrolyte, the amount of electrolyte being 50 μL, and a commercial PP separator. The charge and discharge performance of the battery at 0.1C was tested, with the voltage test interval being 1.5-4.5 V. The capacity retention rate of the battery after being placed at 55°C for 1 month was 98%. The test results of the battery at room temperature are shown in Table 2. Figure 3

[0031] Example 3

[0032] 5.0 g of chromium trioxide crystal powder was weighed into a ceramic boat and placed in a tube furnace for pyrolysis at 270°C for 24 h under an air atmosphere, with a heating rate of 5°C / min. The product was ground and sieved to obtain the product Cr8O 21 The obtained Cr8O 21 was placed in a tube furnace at 375°C for pyrolysis for 30 s, and quenched to obtain Cr2O5-coated Cr8O 21 material. The specific battery assembly process and electrochemical performance test are as follows:

[0033] ​​The Cr2O5-coated Cr8O 21 The material was dissolved with Super P and PVDF in N-methyl pyrrolidone (NMP) at a mass ratio of 8:1:1 and stirred for 12 h. The slurry was doctor-bladed on an Al current collector and placed in a vacuum oven at 120°C for 12 h to dry, obtaining a coated chromium oxide positive electrode. A CR2025 button cell was assembled using a lithium metal wafer as the negative electrode, with an electrolyte of EC / DEC (1:1)-LiPF6 (1 mol / L) at a dosage of 50 μL, and a commercial PP separator. The charge-discharge performance of the battery at 0.1 C was tested, with a voltage test range of 1.5-4.5 V. The battery test results are shown in Figure 4 .

[0034] Example 4

[0035] 5.0 g of chromium trioxide crystal powder was weighed into a ceramic canister and placed in a tube furnace for pyrolysis at 270°C for 12 h in an air atmosphere at a heating rate of 5°C / min. The product was ground and sieved, obtaining a product of Cr8O 21 . The obtained Cr8O 21 was placed in a tube furnace that was air-fired at 400°C for pyrolysis for 30 s, and was quenched to obtain Cr5O 12 -coated Cr8O 21 material. The specific battery assembly process and electrochemical performance testing are as follows:

[0036] The Cr5O 12 -coated Cr8O 21 material was dissolved with Super P and PVDF in N-methyl pyrrolidone (NMP) at a mass ratio of 8:1:1 and stirred for 12 h. The slurry was doctor-bladed on an Al current collector and placed in a vacuum oven at 120°C for 12 h to dry, obtaining a coated chromium oxide positive electrode. A CR2025 button cell was assembled using a lithium metal wafer as the negative electrode, with an electrolyte of EC / DEC (1:1)-LiPF6 (1 mol / L) at a dosage of 50 μL, and a commercial PP separator. The charge-discharge performance of the battery at 0.1 C was tested, with a voltage test range of 1.5-4.5 V. The battery test results are shown in Figure 5 .

[0037] Comparative Example 1

[0038] The difference between this comparative example and Example 1 is that the secondary pyrolysis operation of the obtained chromium oxide was not performed. The test results of Comparative Example 1 are shown in Figure 6 .

[0039] Comparative Example 2

[0040] The present comparative example differs from Example 2 in that the secondary pyrolysis operation of the resulting chromium oxide is not performed. The test results for Comparative Example 2 are shown in Table 1. Figure 7

[0041] The electrochemical performance of each example and comparative example is shown in Table 1.

[0042] Table 1. Cycle retention rate comparison of Examples 1-4 and Comparative Examples 1, 2

[0043] Sample Fold Capacity retention (from second week) Example 1 0.1C 76.4％ Example 2 0.1C 71.0％ Example 3 0.1C 61.2％ Example 4 0.1C 59.4％ Comparative Example 1 0.1C 33.9％ Comparative Example 2 0.1C 32.7％

[0044] Furthermore, it should be understood that although the present specification describes particular embodiments, each of which contains only a single independent technical solution, the specification is merely a single representative set of embodiments and that the description of features in the specification can be combined and recombined in many ways, and that the description of features in the specification can be implemented and / or combined with other features described in other specifications to provide one or more other technical solutions not expressly described. Thus, the scope of the disclosure should not be limited to the specific illustrative embodiments described in this specification, but rather is instead determined by the claims.​

Claims

1. A method for in-situ coating of a chromium oxide positive electrode material, characterized in that: The method is: Step 1: calcining chromium trioxide at high temperature and grinding it to obtain an active chromium oxide material; the high temperature calcination time is 6 to 48 hours, the temperature is 250 to 375°C, and the heating rate is 1 to 10°C / min; Step 2: In-situ coating of protective chromium oxide on the surface of the active chromium oxide material in step 1; the in-situ coating is specifically to quench the active chromium oxide material in step 1 at a high temperature to generate CrO on its surface. x Chromium oxide protective layer; the specific conditions of the in-situ coating are: quenching temperature of 375~800℃, time of 10s~60min.

2. The method for in-situ coating of a chromium oxide positive electrode material according to claim 1, characterized in that: In step 1, the grinding includes manual grinding, ball milling or crushing with a wall breaking machine.

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