Preparation method of high-capacity and high-cycle-performance layered manganese dioxide cathode material

Abstract

This invention discloses a method for preparing a high-capacity, high-cycle-performance layered manganese dioxide cathode material. The method involves first immersing carbon cloth in a sodium permanganate solution, followed by a hydrothermal reaction to obtain a sample grown on the carbon cloth. Then, sodium hypophosphite is used as a phosphorus source for phosphating. Finally, electrochemical treatment yields a layered manganese dioxide material containing phosphorus in the bulk phase. This invention employs a simple method to prepare layered manganese dioxide doped with phosphorus in both the surface and bulk phases. The prepared layered manganese dioxide cathode material exhibits high capacity and long-cycle stability at a current density of 1 mA cm⁻¹. ‑2 At that time, the specific capacity was as high as 528 F g. ‑1 At a current density of 10 A g ‑1 It can still maintain 99% after 30,000 cycles.

Description

Technical Field

[0001] This invention belongs to the field of aqueous sodium-ion battery cathode materials, and relates to a method for preparing a high-capacity, high-cycle-performance layered manganese dioxide cathode material. Background Technology

[0002] Metal-ion batteries, such as lithium-ion batteries, are widely used in electric vehicles and portable electronic devices, but they suffer from low power density and safety issues. Aqueous sodium-ion batteries, as a promising energy storage device, have attracted widespread attention due to their high power density, environmental friendliness, and long lifespan.

[0003] Among aqueous sodium-ion battery cathode materials, manganese oxide has a promising application prospect as a cathode material for supercapacitors due to its abundant reserves and low price. Among them, layered manganese dioxide is a promising electrode material with the advantages of abundant resources, environmental friendliness, low cost, and good theoretical capacitance. However, there are two main problems: (1) The low conductivity and poor ion transport ability of layered manganese dioxide significantly hinder the charge transfer rate, and its active sites are insufficient, resulting in a "dead volume" that does not contribute to capacitance, thus providing low capacitance; (2) There are problems with poor structural stability related to phase transition and manganese dissolution, leading to severe structural degradation and rapid capacity decay during cycling. Therefore, it is very necessary to achieve high performance of layered manganese dioxide in supercapacitors, improve its inherent conductivity and ion diffusion ability, and solve the cycling problems.

[0004] Several strategies have been employed to improve the cycling stability of layered manganese dioxide, such as metal doping, interlayer structure manipulation, vacancy introduction, cation disordering, and structural disordering. However, there is still room for further improvement in the capacity and cycling performance of layered manganese dioxide. Reference 1 reports that phosphorus species (P) act as an active material, accelerating the phase evolution process from one-dimensional oxide to two-dimensional oxide and enhancing charge storage kinetics. However, when the current density is 1 mA cm⁻¹... -2 At that time, the specific capacity was only 198 F g. -1 (Wei Guo, Boosting charge storage in 1D manganese oxide-carbon composite by phosphorus-assisted structural modification for supercapacitor applications, 2020). Reference 2 reports an electrochemical method for preparing amorphous manganese phosphate materials [AMP, Na]. 1.8 Mn4O 1.4 The method of [PO4)3]. Current density is 1 A g. -1At that time, the specific capacity was displayed as 253.4 mAh g. -1 However, it only cycled 5,000 times when the capacity retention rate was 97% (Duo Yang, A Manganese Phosphate Cathode for Long-Life Aqueous Energy Storage, 2021). Summary of the Invention

[0005] To address the issues of low capacity and poor cycle life of existing layered manganese dioxide cathode materials, this invention provides a method for preparing high-capacity, high-cycle-performance layered manganese dioxide cathode materials.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing high-capacity, high-cycle-performance layered manganese dioxide cathode material includes the following steps:

[0008] (1) Dissolve sodium permanganate in water to form an aqueous solution of sodium permanganate, then add 37% concentrated hydrochloric acid and mix to obtain a homogeneous solution;

[0009] (2) Immerse the empty carbon cloth in a uniform solution, place it in a polytetrafluoroethylene reaction vessel, and react at 150-175℃ for 14-16 hours to obtain a sample grown on the carbon cloth.

[0010] (3) Wash and dry the sample grown on carbon cloth, place the sample and sodium hypophosphite in a ceramic boat, and then place them in the downstream and midstream of a tube furnace, respectively. Heat to 250-350℃ under an argon atmosphere and keep warm for 15-60 min. After the reaction is complete, cool to room temperature to obtain the initial product.

[0011] (4) The initial product was dissolved in sodium sulfate electrolyte at 2A g. -1 By cycling the current density for 50 cycles, a layered manganese dioxide material containing phosphorus was obtained.

[0012] Preferably, in step (1), the concentration of the sodium permanganate aqueous solution is 7.5 g / L, and the volume ratio of the sodium permanganate aqueous solution to concentrated hydrochloric acid is 4000:1.

[0013] Preferably, in step (3), the mass ratio of sodium hypophosphite to the sample grown on carbon cloth is 0.6 to 2:12, more preferably 1:12.

[0014] Preferably, in step (3), the heating rate is 2–5 °C / min. -1 .

[0015] Preferably, in step (3), the temperature is raised to 300°C and the holding time is 30 minutes.

[0016] Preferably, in step (4), the concentration of sodium sulfate in the sodium sulfate electrolyte is 1 mol / L. -1 .

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] (1) The present invention can obtain layered manganese dioxide doped with phosphorus by a simple method. Phosphorus is uniformly distributed in the layered manganese dioxide. P exists not only on the surface of the material, but also in the bulk phase.

[0019] (3) This invention uses sodium sulfate as the electrolyte. During the reaction, the phosphorus-containing layered manganese dioxide material has more active sites, improving conductivity and ion transport capacity. Simultaneously, it suppresses phase transitions and structural instability issues caused by manganese dissolution, thus enabling the prepared layered manganese dioxide cathode material to possess high capacity and long-cycle stability at a current density of 1 mA cm⁻¹. -2 At that time, the specific capacity was as high as 528 F g. -1 At a current density of 10 A g -1 After 30,000 cycles, it still maintains 99%. Attached Figure Description

[0020] Figure 1 The images shown are scanning electron microscope (SEM) images and EDS images of layered manganese dioxide doped with P element in Example 1.

[0021] Figure 2 This is an XPS image of the P 2p layered manganese dioxide doped with P element in Example 1.

[0022] Figure 3 The undoped layered manganese dioxide prepared in Comparative Example 1 and the doped layered manganese dioxide prepared in Examples 1-3 were scanned at a rate of 1 mA / cm². -2 The cyclic voltammetry curve below.

[0023] Figure 4 Layered manganese dioxide doped with P element prepared in Examples 1, 4, and 5 was scanned at a rate of 1 mA / cm². -2 The cyclic voltammetry curve below.

[0024] Figure 5 Layered manganese dioxide doped with P element prepared in Examples 1, 6, and 7 was scanned at a rate of 1 mA / cm². -2 The cyclic voltammetry curve below.

[0025] Figure 6 Layered manganese dioxide doped with P element in Example 1 was subjected to a current density of 10 Ag. -1 The cycle retention rate curve is shown below. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0027] Example 1

[0028] S1. Carbon cloth preparation: Commercial porous carbon cloth is pretreated in concentrated nitric acid at 90°C for 10 hours to remove surface impurities and increase hydrophilicity.

[0029] S2. Raw material preparation: First, weigh 0.3g of sodium permanganate and dissolve it in 40mL of deionized water. Stir at 300-500rpm for 30min, then add 10μL of 37% concentrated hydrochloric acid to obtain a well-mixed purple solution.

[0030] S3. Feeding reaction: Transfer the obtained homogeneous solution to a 50mL autoclave with a polytetrafluoroethylene liner and a stainless steel shell. Take a clean carbon cloth of 2cm×3cm and immerse it in the homogeneous solution. Soak it in the autoclave for 10min. Then heat the autoclave at 160℃ for 15h.

[0031] S4. Sample Phosphating: Wash and dry the sample obtained in S3. Place the resulting sample and 0.5g of sodium hypophosphite (the mass ratio of sodium hypophosphite to the sample grown on carbon cloth is 1:12) in separate ceramic boats, and place them downstream and midstream of a tube furnace. Then, under an Ar atmosphere, phosphate at 5℃ for 1 minute. -1 Heat to 300℃, hold for 30 minutes, then reduce temperature by 5℃ for 1 minute. -1 The flow rate decreases to room temperature, yielding the initial product.

[0032] S5. Preliminary Electrochemistry: The obtained initial product is subjected to an electrochemical reaction at a concentration of 1 mol / L. -1 In sodium sulfate electrolyte at 2A g -1 Cycling at a current density for 50 cycles yielded phosphorus-containing layered manganese dioxide.

[0033] Example 2

[0034] S1. Carbon cloth preparation: Commercial porous carbon cloth is pretreated in concentrated nitric acid at 90°C for 10 hours to remove surface impurities and increase hydrophilicity.

[0035] S2. Raw material preparation: First, weigh 0.3g of sodium permanganate and dissolve it in 40mL of deionized water. Stir at 300-500rpm for 30min, then add 10μL of 37% concentrated hydrochloric acid to obtain a well-mixed purple solution.

[0036] S3. Feeding reaction: Transfer the obtained homogeneous solution to a 50mL autoclave with a polytetrafluoroethylene liner and a stainless steel shell. Take a clean carbon cloth of 2cm×3cm and immerse it in the homogeneous solution. Soak it in the autoclave for 10min. Then heat the autoclave at 160℃ for 15h.

[0037] S4. Sample Phosphating: Wash and dry the sample obtained in S3. Place the obtained sample and 0.3g of sodium hypophosphite (the mass ratio of sodium hypophosphite to the sample grown on carbon cloth is 0.6:12) in ceramic boats, respectively, and place them downstream and midstream of a tube furnace. Then, under an Ar atmosphere, phosphate at 5℃ for 1 minute. -1 Heat to 300℃, hold for 30 minutes, then reduce temperature by 5℃ for 1 minute. -1 The flow rate decreases to room temperature, yielding the initial product.

[0038] S5. Preliminary Electrochemistry: The obtained initial product is subjected to an electrochemical reaction at a concentration of 1 mol / L. -1 In sodium sulfate electrolyte at 2A g -1 Cycling at a current density for 50 cycles yielded phosphorus-containing layered manganese dioxide.

[0039] Example 3

[0040] S1. Carbon cloth preparation: Commercial porous carbon cloth is pretreated in concentrated nitric acid at 90°C for 10 hours to remove surface impurities and increase hydrophilicity.

[0041] S2. Raw material preparation: First, weigh 0.3g of sodium permanganate and dissolve it in 40mL of deionized water. Stir at 300-500rpm for 30min, then add 10μL of 37% concentrated hydrochloric acid to obtain a well-mixed purple solution.

[0042] S3. Feeding reaction: Transfer the obtained homogeneous solution to a 50mL autoclave with a polytetrafluoroethylene liner and a stainless steel shell. Take a clean carbon cloth of 2cm×3cm and immerse it in the homogeneous solution. Soak it in the autoclave for 10min. Then heat the autoclave at 160℃ for 15h.

[0043] S4. Sample Phosphating: Wash and dry the sample obtained in S3. Place the resulting sample and 1g of sodium hypophosphite (the mass ratio of sodium hypophosphite to the sample grown on carbon cloth is 2:12) in separate ceramic boats, and place them downstream and midstream of a tube furnace. Then, under an Ar atmosphere, phosphate at 5℃ for 1 minute. -1 Heat to 300℃, hold for 30 minutes, then reduce temperature by 5℃ for 1 minute. -1 The flow rate decreases to room temperature, yielding the initial product.

[0044] S5. Preliminary Electrochemistry: The obtained initial product is subjected to an electrochemical reaction at a concentration of 1 mol / L. -1 In sodium sulfate electrolyte at 2A g -1Cycling at a current density for 50 cycles yielded phosphorus-containing layered manganese dioxide.

[0045] Example 4

[0046] S1. Carbon cloth preparation: Commercial porous carbon cloth is pretreated in concentrated nitric acid at 90°C for 10 hours to remove surface impurities and increase hydrophilicity.

[0047] S2. Raw material preparation: First, weigh 0.3g of sodium permanganate and dissolve it in 40mL of deionized water. Stir at 300-500rpm for 30min, then add 10μL of 37% concentrated hydrochloric acid to obtain a well-mixed purple solution.

[0048] S3. Feeding reaction: Transfer the obtained homogeneous solution to a 50mL autoclave with a polytetrafluoroethylene liner and a stainless steel shell. Take a clean carbon cloth of 2cm×3cm and immerse it in the homogeneous solution. Soak it in the autoclave for 10min. Then heat the autoclave at 160℃ for 15h.

[0049] S4. Sample Phosphating: Wash and dry the sample obtained in S3. Place the resulting sample and 0.5g of sodium hypophosphite (the mass ratio of sodium hypophosphite to the sample grown on carbon cloth is 1:12) in separate ceramic boats, and place them downstream and midstream of a tube furnace. Then, under an Ar atmosphere, phosphate at 5℃ for 1 minute. -1 Heat to 300℃, hold for 15 minutes, then reduce temperature by 5℃ for 1 minute. -1 The flow rate decreases to room temperature, yielding the initial product.

[0050] S5. Preliminary Electrochemistry: The obtained initial product is subjected to an electrochemical reaction at a concentration of 1 mol / L. -1 In sodium sulfate electrolyte at 2A g -1 Cycling at a current density for 50 cycles yielded phosphorus-containing layered manganese dioxide.

[0051] Example 5

[0052] S1. Carbon cloth preparation: Commercial porous carbon cloth is pretreated in concentrated nitric acid at 90°C for 10 hours to remove surface impurities and increase hydrophilicity.

[0053] S2. Raw material preparation: First, weigh 0.3g of sodium permanganate and dissolve it in 40mL of deionized water. Stir at 300-500rpm for 30min, then add 10μL of 37% concentrated hydrochloric acid to obtain a well-mixed purple solution.

[0054] S3. Feeding reaction: Transfer the obtained homogeneous solution to a 50mL autoclave with a polytetrafluoroethylene liner and a stainless steel shell. Take a clean carbon cloth of 2cm×3cm and immerse it in the homogeneous solution. Soak it in the autoclave for 10min. Then heat the autoclave at 160℃ for 15h.

[0055] S4. Sample Phosphating: Wash and dry the sample obtained in S3. Place the resulting sample and 0.5g of sodium hypophosphite (the mass ratio of sodium hypophosphite to the sample grown on carbon cloth is 1:12) in separate ceramic boats, and place them downstream and midstream of a tube furnace. Then, under an Ar atmosphere, phosphate at 5℃ for 1 minute. -1 Heat to 300℃, hold for 60 minutes, then reduce by 5℃ for 5 minutes. -1 The flow rate decreases to room temperature, yielding the initial product.

[0056] S5. Preliminary Electrochemistry: The obtained initial product is subjected to an electrochemical reaction at a concentration of 1 mol / L. -1 In sodium sulfate electrolyte at 2A g -1 Cycling at a current density for 50 cycles yielded phosphorus-containing layered manganese dioxide.

[0057] Example 6

[0058] S1. Carbon cloth preparation: Commercial porous carbon cloth is pretreated in concentrated nitric acid at 90°C for 10 hours to remove surface impurities and increase hydrophilicity.

[0059] S2. Raw material preparation: First, weigh 0.3g of sodium permanganate and dissolve it in 40mL of deionized water. Stir at 300-500rpm for 30min, then add 10μL of 37% concentrated hydrochloric acid to obtain a well-mixed purple solution.

[0060] S3. Feeding reaction: Transfer the obtained homogeneous solution to a 50mL autoclave with a polytetrafluoroethylene liner and a stainless steel shell. Take a clean carbon cloth of 2cm×3cm and immerse it in the homogeneous solution. Soak it in the autoclave for 10min. Then heat the autoclave at 160℃ for 15h.

[0061] S4. Sample Phosphating: Wash and dry the sample obtained in S3. Place the resulting sample and 0.5g of sodium hypophosphite (the mass ratio of sodium hypophosphite to the sample grown on carbon cloth is 1:12) in separate ceramic boats, and place them downstream and midstream of a tube furnace. Then, under an Ar atmosphere, phosphate at 5℃ for 1 minute. -1 Heat to 250℃, hold for 30 minutes, then reduce temperature by 5℃ for 1 minute. -1 The flow rate decreases to room temperature, yielding the initial product.

[0062] S5. Preliminary Electrochemistry: The obtained initial product is subjected to an electrochemical reaction at a concentration of 1 mol / L. -1 In sodium sulfate electrolyte at 2A g -1 Cycling at a current density for 50 cycles yielded phosphorus-containing layered manganese dioxide.

[0063] Example 7

[0064] S1. Carbon cloth preparation: Commercial porous carbon cloth is pretreated in concentrated nitric acid at 90°C for 10 hours to remove surface impurities and increase hydrophilicity.

[0065] S2. Raw material preparation: First, weigh 0.3g of sodium permanganate and dissolve it in 40mL of deionized water. Stir at 300-500rpm for 30min, then add 10μL of 37% concentrated hydrochloric acid to obtain a well-mixed purple solution.

[0066] S3. Feeding reaction: Transfer the obtained homogeneous solution to a 50mL autoclave with a polytetrafluoroethylene liner and a stainless steel shell. Take a clean carbon cloth of 2cm×3cm and immerse it in the homogeneous solution. Soak it in the autoclave for 10min. Then heat the autoclave at 160℃ for 15h.

[0067] S4. Sample Phosphating: Wash and dry the sample obtained in S3. Place the resulting sample and 0.5g of sodium hypophosphite (the mass ratio of sodium hypophosphite to the sample grown on carbon cloth is 1:12) in separate ceramic boats, and place them downstream and midstream of a tube furnace. Then, under an Ar atmosphere, phosphate at 5℃ for 1 minute. -1 Heat to 350℃, hold for 30 minutes, then reduce temperature by 5℃ for 1 minute. -1 The flow rate decreases to room temperature, yielding the initial product.

[0068] S5. Preliminary Electrochemistry: The obtained initial product is subjected to an electrochemical reaction at a concentration of 1 mol / L. -1 In sodium sulfate electrolyte at 2A g -1 Cycling at a current density for 50 cycles yielded phosphorus-containing layered manganese dioxide.

[0069] Comparative Example 1

[0070] S1. Carbon cloth preparation: Commercial porous carbon cloth is pretreated in concentrated nitric acid at 90°C for 10 hours to remove surface impurities and increase hydrophilicity.

[0071] S2. Raw material preparation: First, weigh 0.3g of sodium permanganate and dissolve it in 40mL of deionized water. Stir at 300-500rpm for 30min, then add 10μL of 37% concentrated hydrochloric acid to obtain a well-mixed purple solution.

[0072] S3. Feeding reaction: Transfer the obtained homogeneous solution to a 50mL autoclave with a polytetrafluoroethylene liner and a stainless steel shell. Take a clean carbon cloth of 2cm×3cm and immerse it in the purple homogeneous solution. Soak it in the autoclave for 10min. Then heat the autoclave at 160℃ for 15h.

[0073] S4. High-temperature treatment of samples: Wash and dry the sample obtained in S3, and then treat the sample at 5℃ for 5 minutes in an Ar-H2 atmosphere. -1Heat to 300℃, hold for 60 minutes, then reduce by 5℃ for 5 minutes. -1 The flow rate is reduced to room temperature, and the initial product is obtained.

[0074] S5. Preliminary Electrochemistry: The obtained initial product is subjected to an electrochemical reaction at a concentration of 1 mol / L. -1 In sodium sulfate electrolyte at 2A g -1 The current density was circulated for 100 cycles to obtain layered manganese dioxide.

[0075] Based on the above test results, the bulk-doped P-element layered manganese dioxide prepared by this invention exhibits high capacity and long cycle stability as a cathode material for aqueous sodium-ion batteries. Correspondingly, Figure 1 The electron microscope images show that the layered manganese dioxide has a one-dimensional nanowire morphology, and elements such as P are evenly distributed. Figure 2 XPS images of P 2p at different etching levels show that the bulk phase contains P. Figure 3 The graph shows the constant current charge-discharge of phosphorus-free layered manganese dioxide and layered manganese dioxide at a temperature of 300℃ and a holding time of 30 min, with sodium hypophosphite amounts of 0.3g, 0.5g, and 1g, respectively. It can be seen from the graph that when the sodium hypophosphite amount is 0.5g, the charge-discharge time is the longest and the capacity is the largest. Figure 4 The graph shows the constant current charge-discharge of layered manganese dioxide at a temperature of 300℃, a sodium hypophosphite content of 0.5g, and holding times of 15min, 30min, and 60min. It can be seen from the graph that the charge-discharge time is the longest and the capacity is the largest when the holding time is 30min. Figure 6 The graph shows the constant current charge-discharge of layered manganese dioxide at 30 min, 0.5 g of sodium hypophosphite, and temperatures of 250 °C, 300 °C, and 350 °C. It can be seen from the graph that the charge-discharge time is the longest and the capacity is the largest when the temperature is 300 min. Figure 6 Layered manganese dioxide at a current density of 10 Ag -1 The cycle retention curve below shows that after 30,000 cycles, the cycle retention rate is still around 99%. This indicates that the prepared bulk P-doped layered manganese dioxide has changed the problem of low capacity caused by low conductivity and poor ion transport ability, and has alleviated the problem of severe structural degradation and rapid capacity decay during cycling.

Claims

1. A method for preparing high-capacity, high-cycle-performance layered manganese dioxide cathode material, characterized in that, Includes the following steps: (1) Dissolve sodium permanganate in water to form an aqueous solution of sodium permanganate, then add 37% concentrated hydrochloric acid and mix to obtain a homogeneous solution; (2) Immerse the empty carbon cloth in a uniform solution, place it in a polytetrafluoroethylene reaction vessel, and react at 150-175℃ for 14-16 hours to obtain a sample grown on the carbon cloth. (3) Wash and dry the sample grown on carbon cloth, place the sample and sodium hypophosphite in a ceramic boat, and then place them in the downstream and midstream of a tube furnace, respectively. Heat to 250-350℃ under an argon atmosphere and keep warm for 15-60 min. After the reaction is complete, cool to room temperature to obtain the initial product. (4) The initial product was dissolved in sodium sulfate electrolyte at 2A g. -1 By cycling the current density for 50 cycles, a layered manganese dioxide material containing phosphorus was obtained.

2. The preparation method according to claim 1, characterized in that, In step (1), the concentration of sodium permanganate aqueous solution is 7.5 g / L, and the volume ratio of sodium permanganate aqueous solution to concentrated hydrochloric acid is 4000:

1.

3. The preparation method according to claim 1, characterized in that, In step (3), the mass ratio of sodium hypophosphite to the sample grown on carbon cloth is 0.6 to 2:

12.

4. The preparation method according to claim 1, characterized in that, In step (3), the mass ratio of sodium hypophosphite to the sample grown on carbon cloth is 1:

12.

5. The preparation method according to claim 1, characterized in that, In step (3), the heating rate is 2–5 °C / min. -1 .

6. The preparation method according to claim 1, characterized in that, In step (3), the temperature is raised to 300℃ and held for 30 minutes.

7. The preparation method according to claim 1, characterized in that, In step (4), the concentration of sodium sulfate in the sodium sulfate electrolyte is 1 mol / L. -1 .

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