Method for determining stability of bulk structure of sodium-ion battery positive electrode material

Abstract

The application provides a method for determining the bulk phase structure stability of a sodium ion battery cathode material, which comprises the following steps: (1) dividing the sodium ion battery cathode material into two groups, and mixing each group with ultrapure water to obtain suspension 1 and suspension 2; (2) stirring suspension 1 and suspension 2 respectively, and performing one-step standing on suspension 1 to test the supernatant pH, and performing two-step standing on suspension 2 after being transferred to a sealed container to test the supernatant pH, and determining the bulk phase structure stability of the sodium ion battery cathode material according to the difference between the pH of suspension 1 and the pH of suspension 2, wherein the method does not need to assemble a button cell and perform tests on cycle life, XRD and other items, can qualitatively determine the bulk phase stability of different types of sodium battery transition metal layered oxide cathode materials, thereby shortening the cathode material screening time and product development time, effectively reducing the product development cost, and achieving good actual verification effect.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology and relates to a method for determining the bulk structure stability of sodium-ion battery cathode materials. Background Technology

[0002] Since the advent of lithium-ion batteries in 1990, their performance has improved significantly with in-depth research, leading to their widespread application in various fields such as 3C (computers, communications, and consumer electronics), electric vehicles, and energy storage. With increasing concerns about pollution from fossil fuel use and the comprehensive electrification of society, the demand for highly reliable and stable chemical power sources is growing daily. Although lithium-ion batteries possess advantages such as high energy density and long cycle life, global lithium reserves are limited (relative abundance in the Earth's crust is only 20 ppm), and with increasing application, lithium resources are becoming increasingly expensive. This makes it increasingly difficult for lithium-ion batteries to meet people's demand for reliable, convenient, and stable energy at low cost.

[0003] As an alkali metal, sodium ions possess similar chemical properties to lithium ions. Sodium is inexpensive and widely distributed globally, and its development and utilization are not limited by cost or resource scarcity. Therefore, sodium-ion batteries can serve as a supplement to lithium-ion batteries and are widely used in various applications where energy density requirements are not high. Currently, there are three main development directions for sodium-ion battery cathode materials: transition metal layered oxides, polyanionic materials, and Prussian blue / white materials. Among these, transition metal oxide materials have the best development prospects due to their simple material preparation process, high operating voltage, high energy density, and moderate cycle life. Despite these advantages, transition metal layered oxide materials also face some challenges in practical applications. For example, exposure to air leads to an increase in surface residual alkali, and contact with moisture in the environment causes bulk sodium ions to dissolve through proton exchange, resulting in decreased structural stability. These problems also significantly deteriorate the processing and electrical performance of transition metal layered oxide materials, hindering their large-scale application.

[0004] Currently, the commonly used methods for assessing the stability of transition metal layered oxide cathode materials mainly involve assembling the cathode materials into batteries and conducting cycle performance tests. This is achieved through: ① comparing cycle life decay curves; and ② performing XRD or dQ / dV tests on the cathode materials / electrodes after different cycle counts, observing changes in the intensity and shift of characteristic peaks to characterize the stability of different materials. While these two methods are relatively accurate, they require assembling the cathode materials into coin cells / batteries and conducting tests at a certain cycle life before XRD or dQ / dV tests can be performed. Therefore, determining the bulk stability of materials using these methods is time-consuming, which is not conducive to the extensive screening and verification of a large number of transition metal layered oxide cathode materials. Consequently, it is not conducive to selecting materials with superior bulk structural stability for cell design and product development. Summary of the Invention

[0005] The purpose of this invention is to provide a method for determining the bulk structural stability of sodium-ion battery cathode materials. This method does not require the assembly of coin cells or the testing of cycle life, XRD, etc. It can conveniently and quickly qualitatively determine the bulk stability of different types of sodium-ion battery transition metal layered oxide cathode materials, thereby shortening the cathode material screening time and product development time, effectively reducing the cost of product development, and achieving better results.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for determining the bulk structural stability of a sodium-ion battery cathode material, the method comprising the following steps:

[0008] (1) The sodium-ion battery cathode material was divided into two groups and mixed with ultrapure water to obtain suspension 1 and suspension 2 respectively.

[0009] (2) Stirring is performed on suspension 1 and suspension 2 respectively. Suspension 1 is allowed to stand for one step and the pH of the supernatant is tested. Suspension 2 is transferred to a sealed container and allowed to stand for two steps and the pH of the supernatant is tested. The bulk structure stability of the sodium-ion battery cathode material is determined based on the pH difference between suspension 1 and suspension 2.

[0010] Bulk stability of cathode materials is a crucial parameter. Within their normal operating voltage range, the degree of bulk stability is a key factor determining the cycle life of the battery cell. Cathode materials with high bulk stability typically contribute to improved cycle life, thus extending the cell's lifespan. For sodium-ion battery transition metal layered oxide cathode materials, the bulk phase undergoes two main changes during cycling: ① O→P phase transition; ② distortion and misalignment of the layered structure. Both of these changes in the cathode material's bulk structure lead to a rapid decline in cycle life, accelerating cell failure.

[0011] The method described in this invention can quickly determine the system stability of transition metal layered oxide cathode materials for sodium-ion batteries, thereby facilitating the rapid screening of cathode materials with superior bulk stability for product development. The use of this method not only saves significant time in sodium-ion battery product development but also reduces costs during the development process, thus demonstrating good economic and practical value.

[0012] The theoretical basis of the method described in this invention is that when the transition metal layered oxide cathode material of a sodium-ion battery comes into contact with H2O, the Na in the bulk phase of the material... + It undergoes a proton exchange reaction with H2O, gradually migrating from the interior of the material to the surface. To ensure the material remains electrically neutral, the H in H2O... + It will also gradually migrate into the interior of the material. This process mainly produces the following two effects: ① Na in the bulk phase of the material + After migration, the bulk structure becomes unstable or even collapses locally; ②H + The migration of H2O into the material causes it to become alkaline, and as H2O migrates into the material, it becomes alkaline. + As the migration of H2O increases, the alkalinity of H2O also increases. Therefore, the bulk stability of different layered transition metal oxide materials for sodium-ion batteries can be indirectly characterized by measuring the pH changes of different layered transition metal oxide materials in water.

[0013] Preferably, the sodium-ion battery cathode material in step (1) includes a sodium-ion battery transition metal layered oxide cathode material.

[0014] Preferably, the sodium-ion battery cathode material in suspension 1 and suspension 2 in step (1) has the same mass concentration.

[0015] Preferably, the mass concentration of sodium-ion battery cathode material in suspension 1 and suspension 2 is 50-150 g / L, for example: 50 g / L, 80 g / L, 100 g / L, 120 g / L or 150 g / L, etc.

[0016] Preferably, the stirring speed in step (2) is 100 to 800 rpm, for example: 100 rpm, 200 rpm, 300 rpm, 500 rpm or 800 rpm.

[0017] Preferably, the stirring time in step (2) is 8 to 12 minutes, for example: 8 minutes, 9 minutes, 10 minutes, 11 minutes or 12 minutes.

[0018] Preferably, the settling time in step (2) is 20 to 40 minutes, for example: 20 minutes, 25 minutes, 30 minutes, 35 minutes or 40 minutes.

[0019] Preferably, the two-step settling time in step (2) is 20 to 30 hours, for example: 20 hours, 22 hours, 25 hours, 28 hours or 30 hours.

[0020] Preferably, the pH difference between suspension 1 and suspension 2 in step (2) is ≤1.1, and the bulk structure stability of the sodium-ion battery cathode material is relatively high.

[0021] As a preferred embodiment of the present invention, the method includes the following steps:

[0022] (1) The sodium-ion battery cathode material was divided into two groups and mixed with ultrapure water to obtain suspension 1 and suspension 2 with the same mass concentration of 50-150 g / L.

[0023] (2) Stir suspension 1 and suspension 2 at 500-600 rpm for 8-12 min respectively. Let suspension 1 stand for 20-40 min and test the pH of the supernatant. Transfer suspension 2 to a sealed container and let it stand for 20-30 h. Test the pH of the supernatant. Determine the bulk structure stability of the sodium-ion battery cathode material based on the pH difference between suspension 1 and suspension 2.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] This invention provides a consistent, rapid, convenient, and low-cost method for determining the bulk phase stability of layered oxide transition metals in sodium-ion battery cathodes. This method is based on the reaction of sodium-ion battery cathode materials with water, and the change in Na+ in the bulk phase... +It will undergo an exchange reaction with protons in H2O and gradually precipitate to the surface of the material, thereby causing the pH of the solution to rise continuously. Therefore, by using the method described in this invention, the bulk stability of transition metal layered oxide materials for sodium-ion batteries on the market can be qualitatively screened. This allows for the efficient and low-cost screening of cathode materials with better bulk stability for sodium-ion battery product development, thereby shortening development time and reducing development costs, demonstrating good practical effects and economic feasibility. Attached Figure Description

[0026] Figure 1 This is a comparison chart of pH changes in the supernatant of the suspension 2 of the three sodium-ion battery cathode materials described in Examples 1-3 of this invention. Cathode material A is Example 1, cathode material B is Example 2, and cathode material C is Example 3.

[0027] Figure 2 This is a pH comparison chart of the supernatant of suspension 2 described in Examples 1 and 4-6.

[0028] Figure 3 This is a comparison chart of the cycle performance of batteries made from the three sodium-ion battery cathode materials described in Examples 1-3. Cathode material A is from Example 1, cathode material B is from Example 2, and cathode material C is from Example 3. Detailed Implementation

[0029] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0030] Example 1

[0031] This embodiment provides a method for determining the bulk structural stability of a sodium-ion battery cathode material, the method comprising the following steps:

[0032] (1) Select sodium nickel iron manganese oxide developed by manufacturer A and label it A. Take 20g of material A and divide it into two groups (10g of positive electrode material in each group). Mix each group of positive electrode material with 100ml of ultrapure water to obtain suspension 1 and suspension 2.

[0033] (2) Stir the mixture at 550 rpm for 10 min at room temperature using a magnetic stirrer to ensure that the surface of the positive electrode material can be in full contact with H2O. After the suspension 1 is left to stand for 30 min, test the pH of the supernatant. After the suspension 2 is transferred to a sealed container, it is left to stand at room temperature for 24 h and the pH of its supernatant is tested. The test results are shown in Table 1.

[0034] Example 2

[0035] This embodiment provides a method for determining the bulk structural stability of a sodium-ion battery cathode material, the method comprising the following steps:

[0036] (1) Select sodium nickel iron manganese developed by manufacturer B and label them as B. Take 20g of material B and divide it into two groups (10g of positive electrode material in each group). Mix each group of positive electrode material with 100ml of ultrapure water to obtain suspension 1 and suspension 2.

[0037] (2) Stir the mixture at 550 rpm for 10 min at room temperature using a magnetic stirrer to ensure that the surface of the positive electrode material can be in full contact with H2O. After the suspension 1 is left to stand for 30 min, test the pH of the supernatant. After the suspension 2 is transferred to a sealed container, it is left to stand at room temperature for 24 h and the pH of its supernatant is tested. The test results are shown in Table 1.

[0038] Example 3

[0039] This embodiment provides a method for determining the bulk structural stability of a sodium-ion battery cathode material, the method comprising the following steps:

[0040] (1) Select sodium nickel iron manganese oxide developed by manufacturer C and label it as C. Take 20g of C material and divide it into two groups (10g of positive electrode material in each group). Mix each group of positive electrode material with 100ml of ultrapure water to obtain suspension 1 and suspension 2.

[0041] (2) Stir the mixture at 550 rpm for 10 min at room temperature using a magnetic stirrer to ensure that the surface of the positive electrode material can be in full contact with H2O. After the suspension 1 is left to stand for 30 min, test the pH of the supernatant. After the suspension 2 is transferred to a sealed container, it is left to stand at room temperature for 24 h and the pH of its supernatant is tested. The test results are shown in Table 1.

[0042] Example 4

[0043] This embodiment provides a method for determining the bulk structural stability of a sodium-ion battery cathode material, the method comprising the following steps:

[0044] (1) Select sodium nickel iron manganese oxide developed by manufacturer A and label it A. Take 20g of material A and divide it into two groups (10g of positive electrode material in each group). Mix each group of positive electrode material with 100ml of ultrapure water to obtain suspension 1 and suspension 2.

[0045] (2) Stir the mixture at 550 rpm for 10 min at room temperature using a magnetic stirrer to ensure that the surface of the positive electrode material can be in full contact with H2O. After the suspension 1 is left to stand for 30 min, test the pH of the supernatant. After the suspension 2 is transferred to a sealed container, it is left to stand at room temperature for 8 h and the pH of its supernatant is tested. The test results are shown in Table 1.

[0046] Example 5

[0047] This embodiment provides a method for determining the bulk structural stability of a sodium-ion battery cathode material, the method comprising the following steps:

[0048] (1) Select sodium nickel iron manganese oxide developed by manufacturer A and label it A. Take 20g of material A and divide it into two groups (10g of positive electrode material in each group). Mix each group of positive electrode material with 100ml of ultrapure water to obtain suspension 1 and suspension 2.

[0049] (2) Stir the mixture at 550 rpm for 10 min at room temperature using a magnetic stirrer to ensure that the surface of the positive electrode material can be in full contact with H2O. After the suspension 1 is left to stand for 30 min, test the pH of the supernatant. After the suspension 2 is transferred to a sealed container, it is left to stand at room temperature for 16 h and the pH of its supernatant is tested. The test results are shown in Table 1.

[0050] Example 6

[0051] This embodiment provides a method for determining the bulk structural stability of a sodium-ion battery cathode material, the method comprising the following steps:

[0052] (1) Select sodium nickel iron manganese oxide developed by manufacturer A and label it A. Take 20g of material A and divide it into two groups (10g of positive electrode material in each group). Mix each group of positive electrode material with 100ml of ultrapure water to obtain suspension 1 and suspension 2.

[0053] (2) Stir the mixture at 550 rpm for 10 min at room temperature using a magnetic stirrer to ensure that the surface of the positive electrode material can be in full contact with H2O. After the suspension 1 is left to stand for 30 min, test the pH of the supernatant. After the suspension 2 is transferred to a sealed container, it is left to stand at room temperature for 32 h and the pH of its supernatant is tested. The test results are shown in Table 1.

[0054] Example 7

[0055] The only difference between this embodiment and Embodiment 1 is that the stirring time is 5 minutes, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0056] Performance testing:

[0057] The pH results of the supernatant of the suspensions described in Examples 1-7 are shown in Table 1:

[0058] Table 1

[0059]

[0060]

[0061] As shown in Table 1, based on Examples 1-3, the pH change of cathode material A before and after standing was minimal, indicating that after material A came into contact with water, the Na in the bulk phase... + The material with the least proton exchange exhibits the best bulk stability; while cathode material C shows the largest pH change before and after storage, indicating that C material has the worst bulk stability, which is detrimental to the performance and improvement of the cell after application. Cathode material B shows a moderate pH change, reflecting moderate bulk stability. Therefore, for these three materials, the order of bulk stability is A>B>C.

[0062] The pH changes of the supernatant in the suspensions of the three sodium-ion battery cathode materials described in Examples 1-3 are shown in the following figure. Figure 1 As shown, the three sodium-ion battery cathode materials described in Examples 1-3 were used to fabricate coin cells, and the cells were cycled for 50 cls under the same charge / discharge voltage and charge / discharge rate. The cycle life comparison chart of the coin cells is shown below. Figure 3 As shown.

[0063] The pH comparison diagram of the supernatant of suspension 2 in Examples 1 and 4-6 is shown below. Figure 2 As shown, a comparison between Examples 1 and Examples 4-6 reveals that the settling time in the method described in this invention affects the test results. If the test time is too short, the pH will be unstable and the test results will be inaccurate. If the test time is too long, the pH will no longer change.

[0064] A comparison of Examples 1 and 7 shows that the stirring time affects the test results of the method described in this invention. If the stirring time is too short, the water cannot completely wet the cathode material, resulting in deviations in the test results.

[0065] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for determining the bulk structural stability of a sodium-ion battery cathode material, characterized in that, The method includes the following steps: (1) The sodium-ion battery cathode material was divided into two groups and mixed with ultrapure water to obtain suspension 1 and suspension 2 respectively; (2) Stirring the suspension 1 and suspension 2 respectively, allowing suspension 1 to stand for one step and testing the pH of the supernatant, transferring suspension 2 to a sealed container and allowing it to stand for two steps, testing the pH of the supernatant, and determining the bulk structure stability of the sodium-ion battery cathode material based on the pH difference between suspension 1 and suspension 2. The stirring time in step (2) is 8~12 minutes; The two-step settling time in step (2) is 20~30 hours; The pH difference between suspension 1 and suspension 2 in step (2) is ≤1.1, indicating that the bulk structure stability of the sodium-ion battery cathode material is relatively high.

2. The method as described in claim 1, characterized in that, The sodium-ion battery cathode material mentioned in step (1) includes sodium-ion battery transition metal layered oxide cathode material.

3. The method as described in claim 2, characterized in that, The sodium-ion battery transition metal layered oxide cathode material includes one or more of sodium nickel iron manganese oxide, sodium nickel cobalt manganese oxide, sodium iron cobalt manganese oxide, and sodium nickel copper manganese oxide.

4. The method as described in claim 1, characterized in that, In step (1), the sodium-ion battery cathode material in suspension 1 and suspension 2 has the same mass concentration.

5. The method as described in claim 1, characterized in that, The mass concentration of sodium-ion battery cathode material in suspension 1 and suspension 2 is 50~150g / L.

6. The method as described in claim 1, characterized in that, The stirring speed in step (2) is 100~800 rpm.

7. The method as described in claim 1, characterized in that, The settling time in step (2) is 20~40 minutes.

8. The method as described in claim 1, characterized in that, The pH difference between suspension 1 and suspension 2 in step (2) is ≤0.5, indicating that the bulk structure stability of the sodium-ion battery cathode material is relatively high.

9. The method as described in claim 1, characterized in that, The method includes the following steps: (1) The sodium-ion battery cathode material was divided into two groups and mixed with ultrapure water to obtain suspension 1 and suspension 2 with the same mass concentration of 50~150g / L. (2) Stir suspension 1 and suspension 2 at 500-600 rpm for 8-12 min respectively. Let suspension 1 stand for 20-40 min and test the pH of the supernatant. Transfer suspension 2 to a sealed container and let it stand for 20-30 h. Test the pH of the supernatant. Determine the bulk structure stability of the sodium-ion battery cathode material based on the pH difference between suspension 1 and suspension 2.

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