Layered oxide cathode material for sodium-ion battery surface modified by high-voltage selenium-based sodium-containing composite coating and preparation method thereof

Abstract

The application discloses a high-voltage selenium-based sodium-containing composite coating surface modified sodium ion battery layered oxide positive electrode material and a preparation method thereof. In the high-voltage selenium-based sodium-containing composite coating surface modified sodium ion battery layered oxide positive electrode material, a selenium source reacts with residual alkali on the surface of a sodium ion battery layered oxide positive electrode material under high temperature, air or O2 atmosphere, the O2 concentration is 5%-95%, and a high-voltage selenium-based sodium-containing composite coating is formed on the surface of the particle. The high-voltage selenium-based sodium-containing composite coating is stably coated on the surface of the sodium ion battery layered oxide positive electrode material as a sodium ion reservoir under a high-voltage state. The preparation method is simple, easy to operate, low in cost and environment-friendly. The generated high-voltage selenium-based sodium-containing composite coating is stably coated on the surface of the sodium ion battery layered oxide positive electrode material as a sodium ion reservoir under a high-voltage state, and can improve the structural stability and cycle life of the sodium ion battery layered oxide positive electrode material.

Description

Technical Field

[0001] This invention relates to sodium-ion battery electrode material preparation technology, specifically a high-voltage selenium-based sodium-containing composite coating surface-modified layered oxide cathode material for sodium-ion batteries and its preparation method. Background Technology

[0002] With the limited supply of traditional fossil fuels, the new energy industry has begun to develop rapidly, and sodium-ion batteries have received increasing attention. Cathode materials are a key component of sodium-ion batteries, significantly impacting their performance. Therefore, developing cathode materials with high energy density, low cost, long cycle life, and air stability is crucial for the development of sodium-ion batteries. Currently, sodium-ion battery cathode materials mainly include four types: layered oxides, Prussian blue compounds, polyanionic compounds, and organic compounds. Among these, layered oxides and Prussian blue compounds have advantages in energy density and cost, especially layered oxide cathode materials, which have strong feasibility for mass production.

[0003] However, layered oxide cathode materials currently suffer from several major problems. First, there is the complex phase evolution process. Layered oxide cathode materials typically undergo complex phase transitions during charge and discharge. P2 phase materials undergo an irreversible P2→O2 phase transition at high potentials, while the phase transition of O3 phase materials is even more complex. This can lead to a decrease in battery energy density and cycle life to some extent. Second, there is the problem of air instability. Layered oxide cathode materials are very sensitive to air. When exposed to air, they are prone to absorbing moisture, which can cause deliquescence on the material surface, resulting in poor cycle performance and increased material transportation costs.

[0004] To address the defects of layered oxide cathode materials, current modification strategies mainly include elemental doping, surface coating, and P / O mixed phases. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a high-voltage selenium-based sodium-containing composite coating surface-modified sodium-ion battery layered oxide cathode material and its preparation method. This preparation method is simple to operate, low in cost, and environmentally friendly. The resulting high-voltage selenium-based sodium-containing composite coating acts as a sodium ion pool, stably coating the surface of the sodium-ion battery layered oxide cathode material under high voltage, thereby improving the structural stability and cycle life of the sodium-ion battery layered oxide cathode material.

[0006] The technical solution to achieve the objective of this invention is: A high-voltage selenium-based sodium-containing composite coating surface-modified sodium-ion battery layered oxide cathode material is disclosed. In this high-voltage selenium-based sodium-containing composite coating surface-modified sodium-ion battery layered oxide cathode material, a selenium source reacts with residual alkali on the surface of the sodium-ion battery layered oxide cathode material under high temperature and air or O2 (concentration 5%-95%) atmosphere to generate the high-voltage selenium-based sodium-containing composite coating surface-modified sodium-ion battery layered oxide cathode material. This high-voltage selenium-based sodium-containing composite coating stably coats the surface of the sodium-ion battery layered oxide cathode material as a sodium ion reservoir under high voltage. The mass ratio of the selenium source to the sodium-ion battery layered oxide cathode material is 1:50-200. The chemical formula of the sodium-ion battery layered oxide cathode material is NaNi. x Fe y Mn z O2, where 0.5≤m≤1, 0.2≤x≤0.4, 0.2≤y≤0.4, and 0.2≤z≤0.4.

[0007] The method for preparing the above-mentioned high-voltage selenium-based sodium-containing composite coating surface-modified layered oxide cathode material for sodium-ion batteries includes the following steps: 1) Weigh out nickel salt, iron salt, and manganese salt, and dissolve them separately in deionized water to prepare salt solutions with a concentration of 0.5-2 mol / L for each salt. The nickel salt, iron salt, and manganese salt are selected based on the chemical formula of NaNi, a layered oxide cathode material for sodium-ion batteries. x Fe y Mn z The molar ratio of Ni, Fe and Mn elements in O2 is determined by the following formula: 0.5≤m≤1, 0.2≤x≤0.4, 0.2≤y≤0.4, 0.2≤z≤0.4. 2) Prepare a mixed alkaline solution by dissolving alkali and ammonia in deionized water, wherein the concentration of alkali is 2-10 mol / L and the concentration of ammonia is 40%-80%; 3) Add the mixed alkaline solution obtained in step 2) into the reaction vessel using a peristaltic pump, and control the pH value between 9 and 12; 4) The nickel salt, iron salt and manganese salt solutions prepared in step 1) are added to the reaction vessel at a constant speed using a peristaltic pump. The pH value is between 9 and 12 and the temperature is between 40 and 60°C throughout the process. 5) After adding nickel salt, iron salt and manganese salt, let it stand and age for 3-12 hours, then filter the precipitate, wash the precipitate and dry it; 6) Mix the dried precipitate with sodium salt evenly, pre-calcine at 350-500℃ for 4-6 hours in air atmosphere, and then calcine at 800-950℃ for 14-20 hours to obtain the sodium-ion battery layered oxide cathode material, wherein the molar ratio of precipitate to sodium salt is between 1:1.03 and 1:1.05. 7) Dissolve the selenium source in ethanol, then add the sodium-ion battery layered oxide cathode material obtained in step 6), and evaporate it to dryness at 80-100℃ to form a gel; 8) The gel obtained in step 7) is vacuum dried and crushed at 80-120℃, and pre-calcined at 300℃-600℃ for 2-10 hours in air or O2 (concentration of 5%-95%) atmosphere to obtain a high-voltage selenium-based sodium-containing composite coating surface-modified sodium-ion battery layered oxide cathode material.

[0008] In step 1), the nickel salt is one or more of nickel sulfate, nickel nitrate and nickel acetate, the iron salt is one or more of ferric sulfate, ferric nitrate and ferric acetate, and the manganese salt is one or more of manganese sulfate, manganese nitrate and manganese acetate.

[0009] The alkali mentioned in step 2) is one or both of sodium hydroxide solution and potassium hydroxide solution, and the concentration is 2-10 mol / L, and the molar ratio of sodium hydroxide to ammonia is 2:1.

[0010] The sodium salt mentioned in step 6) is one or more of sodium hydroxide, sodium carbonate, and sodium acetate.

[0011] In step 6), the pre-firing process involves raising the temperature to 350-500℃ at a rate of 1-5℃ / min and holding it for 4-6 hours. Then, during calcination, the temperature is raised to 800-950℃ at a rate of 1-5℃ / min and held for 14-20 hours.

[0012] The selenium source mentioned in step 7) is one or more of selenium powder, selenium dioxide, sodium selenite, and sodium selenate.

[0013] In step 8), the preheating process involves raising the temperature to 300-600℃ at a rate of 1-5℃ / min and holding it at that temperature for 2-10 hours. The atmosphere is one or more of air or O2 (concentration of 5%-95%).

[0014] This preparation method is simple, easy to operate, low in cost, and environmentally friendly. The resulting high-voltage selenium-based sodium-containing composite coating acts as a sodium ion pool and stably coats the surface of the layered oxide cathode material of sodium-ion batteries under high voltage, thereby improving the structural stability and cycle life of the layered oxide cathode material of sodium-ion batteries. Attached Figure Description

[0015] Figure 1 The XRD patterns of the high-voltage selenium-based sodium-containing composite coating surface-modified sodium-ion battery layered oxide cathode material and the sodium-ion battery layered oxide cathode material prepared in the examples are shown below. Figure 2 The image shows a SEM image of the high-voltage selenium-based sodium-containing composite coating surface-modified sodium-ion battery layered oxide cathode material prepared in the examples. Figure 3 The image shows a SEM image of the layered oxide cathode material for the sodium-ion battery in the examples. Figure 4 The discharge cycle curves of the high-voltage selenium-based sodium-containing composite coating surface-modified sodium-ion battery layered oxide cathode material and the sodium-ion battery layered oxide cathode material prepared in the examples are shown at a current density of 1.0C. Detailed Implementation

[0016] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this is not intended to limit the scope of the invention. Example:

[0017] Example 1:

[0018] A method for preparing high-voltage selenium-based sodium-containing composite coating surface-modified layered oxide cathode material for sodium-ion batteries includes the following steps: 1) According to the chemical formula of the layered oxide cathode material of sodium-ion batteries, NaNi 0.4 Fe 0.2 Mn 0.4 The molar ratio of Ni:Fe:Mn = 0.4:0.2:0.4 shown in O2 was used to weigh out nickel salt, iron salt and manganese salt respectively, and dissolved in deionized water to prepare a salt solution with a concentration of 1 mol / L. 2) Prepare a mixed alkaline solution by dissolving NaOH solution and ammonia in deionized water. The concentration of NaOH solution is 1 mol / L and the concentration of ammonia is 40%. 3) Add the above mixed alkaline solution into the reaction vessel using a peristaltic pump, and control the pH value in the reaction vessel to 10; 4) Add the prepared nickel salt, iron salt and manganese salt solutions to the reaction vessel at a constant rate using a peristaltic pump, and control the pH value at 9 and the temperature at 60℃ throughout the process; 5) After the nickel salt, iron salt and manganese salt have been added, let it stand and age for 12 hours, then filter, wash and dry the precipitate; 6) Mix the precipitate and sodium salt evenly (the molar ratio of precipitate to sodium salt is 1:1.05), pre-calcine at 450°C for 5 hours in air atmosphere, and then calcine at 850°C for 15 hours to obtain the layered oxide cathode material for sodium-ion batteries. 7) Dissolve the selenium source in ethanol, add the prepared sodium-ion battery layered oxide cathode material, and slowly evaporate it at 80°C to form a gel; 8) The obtained gel was vacuum dried and crushed at 120°C, and then calcined at 500°C for 5 hours in air or O2 (concentration of 5%-95%) atmosphere to obtain a high-voltage selenium-based sodium-containing composite coating surface-modified sodium-ion battery layered oxide cathode material.

[0019] like Figure 1 As shown, from Figure 1 It can be seen that the sodium-ion battery layered oxide cathode material after surface modification with a high-voltage selenium-based sodium-containing composite coating is basically the same as the sodium-ion battery layered oxide cathode material before modification. In other words, the surface modification with the selenium-based sodium-containing composite coating did not alter the structure of the sodium-ion battery layered oxide cathode material. The SEM images of the high-voltage selenium-based sodium-containing composite coating-modified sodium-ion battery layered oxide cathode material and the sodium-ion battery layered oxide cathode material (before modification) obtained in this example are shown below. Figure 2 and Figure 3 As shown, by Figure 2 and Figure 3 The comparison shows that the selenium-based sodium-containing composite coating is uniformly coated on the surface of the layered oxide cathode material of sodium-ion batteries.

[0020] The high-voltage selenium-based sodium-containing composite coating surface-modified sodium-ion battery layered oxide positive electrode material (or sodium-ion battery layered oxide positive electrode material) prepared in this example was mixed with conductive carbon black Super P and binder PVDF in a mass ratio of 8:1:1. N-methylpyrrolidone was added and stirred until homogeneous. The resulting slurry was coated onto current collector aluminum foil and dried at 120℃ to obtain a positive electrode sheet. Using a sodium metal sheet as the negative electrode, glass fiber as the separator, and NaClO4 as the electrolyte, a CR2032 type button cell was assembled in an argon-filled glove box. The resulting cell was charged and discharged at a rate of 1.0C, and the resulting cycle curve is shown below. Figure 4 As shown, by Figure 4 It can be seen that the initial discharge specific capacity of the sodium-ion battery layered oxide cathode material with selenium-based sodium-containing composite coating surface modification prepared in this example is 106.7 mAh / g. After 200 cycles, its discharge specific capacity is 92.5 mAh / g, and the cycle retention rate is about 86.7%. In contrast, the battery made of sodium-ion battery layered oxide cathode material has an initial discharge specific capacity of 120.9 mAh / g. After 200 cycles, its discharge specific capacity is 61.6 mAh / g, and the cycle retention rate is only 50.9%. From the above results, it can be seen that the sodium-ion battery layered oxide cathode material with high-voltage selenium-based sodium-containing composite coating surface modification has a stable structure and good cycle stability.

[0021] Example 2:

[0022] A method for preparing high-voltage selenium-based sodium-containing composite coating surface-modified layered oxide cathode material for sodium-ion batteries includes the following steps: 1) According to the chemical formula of sodium-ion battery cathode material NaNi 0.4 Fe 0.2 Mn 0.4The molar ratio of Ni:Fe:Mn = 0.4:0.2:0.4 shown in O2 was used to weigh out nickel salt, iron salt and manganese salt respectively, and dissolved in deionized water to prepare a salt solution with a concentration of 1 mol / L. 2) Prepare a mixed alkaline solution by dissolving NaOH solution and ammonia in deionized water. The concentration of NaOH solution is 2 mol / L and the concentration of ammonia is 50%. 3) Add the above mixed alkaline solution into the reaction vessel using a peristaltic pump, and control the pH value in the reaction vessel to 10; 4) The prepared nickel salt, iron salt and manganese salt solutions were added to the reaction vessel at a constant rate using a peristaltic pump. The pH value was controlled at 9 and the temperature at 60℃ throughout the process. 5) After the nickel salt, iron salt and manganese salt have been added, let it stand and age for 10 hours, then filter, wash and dry the precipitate; 6) Mix the precipitate and sodium salt evenly (the molar ratio of precipitate to sodium salt is 1:1.05), pre-calcine at 500°C in air for 4 hours, and then calcine at 900°C for 13 hours to obtain the layered oxide cathode material for sodium-ion batteries. 7) Dissolve the selenium source in ethanol, add the prepared sodium-ion battery layered oxide cathode material, and slowly evaporate it at 80°C to form a gel; 8) The obtained gel was vacuum dried and crushed at 120°C, and then calcined at 450°C for 5 hours in air or O2 (concentration of 5%-95%) atmosphere to obtain a high-voltage selenium-based sodium-containing composite coating surface-modified sodium-ion battery layered oxide cathode material.

[0023] Example 3:

[0024] A method for preparing high-voltage selenium-based sodium-containing composite coating surface-modified layered oxide cathode material for sodium-ion batteries includes the following steps: 1) According to the chemical formula of sodium-ion battery cathode material NaNi 0.4 Fe 0.2 Mn 0.4 The molar ratio of Ni:Fe:Mn = 0.4:0.2:0.4 shown in O2 was used to weigh out nickel salt, iron salt and manganese salt respectively, and dissolved in deionized water to prepare a salt solution with a concentration of 1 mol / L. 2) Prepare a mixed alkaline solution by dissolving NaOH solution and ammonia in deionized water. The concentration of NaOH solution is 2 mol / L and the concentration of ammonia is 60%. 3) Add the above mixed alkaline solution into the reaction vessel using a peristaltic pump, and control the pH value in the reaction vessel to 10; 4) The prepared nickel salt, iron salt and manganese salt solutions are added to the reaction vessel at a constant rate using a peristaltic pump. The pH value is controlled at 10.5 and the temperature is controlled at 50℃ throughout the process. 5) After the nickel salt, iron salt and manganese salt have been added, let it stand and age for 10 hours, then filter, wash and dry the precipitate; 6) Mix the precipitate and sodium salt evenly (the molar ratio of precipitate to sodium salt is 1:1.05), pre-calcine at 550°C for 3 hours in air atmosphere, and then calcine at 950°C for 15 hours to obtain the layered oxide cathode material for sodium-ion batteries. 7) Dissolve the selenium source in ethanol, add the prepared sodium-ion battery layered oxide cathode material, and slowly evaporate it at 80°C to form a gel; 8) The obtained gel was vacuum dried and crushed at 120°C, and calcined at 400°C for 5 hours in air or O2 (concentration of 5%-95%) atmosphere to obtain a high-voltage selenium-based sodium-containing composite coating surface-modified sodium-ion battery layered oxide cathode material.

[0025] Example 4:

[0026] A method for preparing high-voltage selenium-based sodium-containing composite coating surface-modified layered oxide cathode material for sodium-ion batteries includes the following steps: 1) According to the chemical formula of sodium-ion battery cathode material NaNi 0.4 Fe 0.2 Mn 0.4 The molar ratio of Ni:Fe:Mn = 0.4:0.2:0.4 shown in O2 was used to weigh out nickel salt, iron salt and manganese salt respectively, and dissolved in deionized water to prepare a salt solution with a concentration of 1 mol / L. 2) Prepare a mixed alkaline solution by dissolving NaOH solution and ammonia in deionized water. The concentration of NaOH solution is 2 mol / L and the concentration of ammonia is 60%. 3) Add the above mixed alkaline solution into the reaction vessel using a peristaltic pump, and control the pH value in the reaction vessel to 10; 4) The prepared nickel salt, iron salt and manganese salt solutions are added to the reaction vessel at a constant rate using a peristaltic pump. The pH value is controlled at 10.5 and the temperature at 50℃ throughout the process. 5) After the nickel salt, iron salt and manganese salt have been added, let it stand and age for 12 hours, then filter, wash and dry the precipitate; 6) Mix the precipitate and sodium salt evenly (the molar ratio of precipitate to sodium salt is 1:1.05), pre-calcine at 450°C for 5 hours in air atmosphere, and then calcine at 950°C for 15 hours to obtain the layered oxide cathode material for sodium-ion batteries. 7) Dissolve the selenium source in ethanol, add the prepared sodium-ion battery layered oxide cathode material, and slowly evaporate it at 80°C to form a gel; 8) The obtained gel was vacuum dried and crushed at 120°C, and then calcined at 350°C for 5 hours in an air or O2 (concentration of 5%-95%) atmosphere to obtain a high-voltage selenium-based sodium-containing composite coating surface-modified sodium-ion battery layered oxide cathode material.

[0027] Example 5: A method for preparing high-voltage selenium-based sodium-containing composite coating surface-modified layered oxide cathode material for sodium-ion batteries includes the following steps: 1) According to the chemical formula of sodium-ion battery cathode material NaNi 0.4 Fe 0.2 Mn 0.4 The molar ratio of Ni:Fe:Mn = 0.4:0.2:0.4 shown in O2 was used to weigh out nickel salt, iron salt and manganese salt respectively, and dissolved in deionized water to prepare a salt solution with a concentration of 1 mol / L. 2) Prepare a mixed alkaline solution by dissolving NaOH solution and ammonia in deionized water. The concentration of NaOH solution is 2 mol / L and the concentration of ammonia is 60%. 3) Add the above mixed alkaline solution into the reaction vessel using a peristaltic pump, and control the pH value in the reaction vessel to 10; 4) Add the prepared nickel salt, iron salt and manganese salt solutions to the reaction vessel at a constant rate using a peristaltic pump, and control the pH value at 10 and the temperature at 40℃ throughout the process; 5) After the nickel salt, iron salt and manganese salt have been added, let it stand and age for 12 hours, then filter, wash and dry the precipitate; 6) Mix the precipitate and sodium salt evenly (the molar ratio of precipitate to sodium salt is 1:1.05), pre-calcine at 450°C in air for 6 hours, and then calcine at 950°C for 15 hours to obtain the layered oxide cathode material for sodium-ion batteries. 7) Dissolve the selenium source in ethanol, add the prepared sodium-ion battery layered oxide cathode material, and slowly evaporate it at 80°C to form a gel; 8) The obtained gel was vacuum dried and crushed at 120°C, and then calcined at 300°C for 6 hours in air or O2 (concentration of 5%-95%) atmosphere to obtain a high-voltage selenium-based sodium-containing composite coating surface-modified sodium-ion battery layered oxide cathode material.

Claims

1. A high-voltage selenium-based sodium-containing composite coating surface-modified layered oxide composite cathode material for sodium-ion batteries, characterized in that, In the high-voltage selenium-based sodium-containing composite coating surface modification of sodium-ion battery layered oxide cathode material, the selenium source reacts with residual alkali on the surface of the sodium-ion battery layered oxide cathode material under high temperature, air, or O2 atmosphere, with an O2 concentration of 5%-95%, forming a high-voltage selenium-based sodium-containing composite coating on the particle surface. This high-voltage selenium-based sodium-containing composite coating stably coats the surface of the sodium-ion battery layered oxide cathode material as a sodium ion pool under high voltage. The mass ratio of selenium source to sodium-ion battery layered oxide cathode material is 1:50-200. The chemical formula of the sodium-ion battery layered oxide cathode material is NaNi. x Fe y Mn z O2, where 0.2≤x≤0.4, 0.2≤y≤0.4, and 0.2≤z≤0.

4.

2. A method for preparing the high-voltage selenium-based sodium-containing composite coating surface-modified layered oxide cathode material for sodium-ion batteries as described in claim 1, characterized in that, Includes the following steps: 1) Weigh out nickel salt, iron salt, and manganese salt, and dissolve them separately in deionized water to prepare salt solutions with a concentration of 0.5-2 mol / L for each salt. The nickel salt, iron salt, and manganese salt are selected based on the chemical formula of NaNi, a layered oxide cathode material for sodium-ion batteries. x Fe y Mn z The molar ratio of Ni, Fe and Mn elements in O2 is determined by weighing, where 0.2≤x≤0.4, 0.2≤y≤0.4, and 0.2≤z≤0.

4. 2) Dissolve alkali and ammonia in deionized water to prepare a mixed alkali solution, wherein the concentration of alkali is 2-10 mol / L and the concentration of ammonia is 40%-80%; 3) Add the mixed alkaline solution obtained in step 2) into the reaction vessel using a peristaltic pump, and control the pH value between 9 and 12; 4) The nickel salt, iron salt and manganese salt solutions prepared in step 1) are added to the reaction vessel at a uniform rate using a peristaltic pump. The pH value is between 9 and 12 and the temperature is between 40 and 60°C throughout the process. 5) After adding nickel salt, iron salt and manganese salt, let it stand and age for 3-12 hours, then filter the precipitate, wash the precipitate and dry it; 6) Mix the dried precipitate with sodium salt evenly, pre-calcine in air at 350-500℃ for 4-6 hours, and then calcine at 800-950℃ for 14-20 hours to obtain the sodium-ion battery layered oxide cathode material, wherein the molar ratio of precipitate to sodium salt is between 1:1.03 and 1:1.

05. 7) Dissolve the selenium source in ethanol, then add the sodium-ion battery layered oxide cathode material obtained in step 6), and evaporate it to dryness at 80-100℃ to form a gel; 8) The gel obtained in step 7) is vacuum dried and crushed at 80-120℃, and calcined at 300℃-600℃ for 2-10 hours in air or O2 atmosphere, with an O2 concentration of 5%-95%, to obtain a high-voltage selenium-based sodium-containing composite coating surface-modified sodium-ion battery layered oxide cathode material.

3. The method according to claim 2, characterized in that, In step 1), the nickel salt is one or more of nickel sulfate, nickel nitrate and nickel acetate, the iron salt is one or more of ferric sulfate, ferric nitrate and ferric acetate, and the manganese salt is one or more of manganese sulfate, manganese nitrate and manganese acetate.

4. The method according to claim 2, characterized in that, The alkali mentioned in step 2) is one or both of sodium hydroxide solution and potassium hydroxide solution, and the concentration is 2-10 mol / L, and the molar ratio of sodium hydroxide to ammonia is 2:

1.

5. The method according to claim 2, characterized in that, The sodium salt mentioned in step 6) is one or more of sodium hydroxide, sodium carbonate, and sodium acetate.

6. The method according to claim 2, characterized in that, In step 6), the pre-firing process involves raising the temperature to 350-500℃ at a rate of 1-5℃ / min and holding it for 4-6 hours. Then, during calcination, the temperature is raised to 800-950℃ at a rate of 1-5℃ / min and held for 14-20 hours.

7. The method according to claim 2, characterized in that, The selenium source mentioned in step 7) is one or more of selenium powder, selenium dioxide, sodium selenite, and sodium selenate.

8. The method according to claim 2, characterized in that, In step 8), the preheating process involves heating the temperature to 300-600℃ at a rate of 1-5℃ / min and holding it at that temperature for 2-10 hours. The atmosphere is one or more of air or O2 atmospheres, with an O2 concentration of 5%-95%.

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