Method for improving low-temperature rate and cycling stability of iodine battery through synergistic effect of metal monatomic doped positive electrode and anti-freezing electrolyte

Abstract

The invention discloses a method for manufacturing a polytetrafluoroethylene (PTFE) pole piece by doping onion carbon with iron monatomic, and remarkably improving the electrochemical stability and low-temperature performance of a battery in combination with a specific electrolyte. The preparation method comprises the following specific steps: firstly, pretreating an onion carbon material; treatment is carried out through the modes of iron precursor solution soaking, high-temperature annealing in the argon atmosphere and the like; finally, the monatomic iron is successfully loaded on the onion carbon. The obtained monatomic iron doped onion carbon is prepared into a PTFE pole piece through a PTFE adhesive, so that the electrochemical stability of the pole piece is remarkably improved. And then loading iodine onto the PTFE pole piece in a high-temperature and high-pressure manner. In addition, an electrolyte formed by mixing zinc perchlorate and acetonitrile is also prepared for the lithium ion battery, so that the battery shows excellent cycle stability without capacity fading in 1000 circles and excellent rate capability even in an extremely low-temperature environment of-40 DEG C.

Description

Technical Field

[0001] The invention patent relates to a method of making PTFE pole pieces by doping onion carbon with single iron atoms and combining it with a specific electrolyte to significantly improve the low temperature performance and electrochemical stability of the battery. It belongs to the field of electrochemical energy storage technology. Background Art

[0002] In the field of energy storage systems, lithium-ion batteries have become the preferred type of energy storage battery due to their significant high energy density and long life. However, it cannot be ignored that lithium-ion batteries have high costs and safety issues. The concerns caused by these problems have seriously limited their further promotion and application in large-scale energy storage systems. In contrast, aqueous zinc-based batteries, with their high safety and low cost advantages, provide new development opportunities for large-scale energy storage. Among the zinc-based battery series, rechargeable zinc-iodine batteries are particularly worthy of attention. They have many advantages and broad prospects: first, seawater contains abundant iodine resources, which provides a strong guarantee for the supply of raw materials for batteries; second, the battery has a high specific capacity and can store more electrical energy per unit mass or unit volume; third, its high discharge platform potential allows the battery to output a higher voltage during the discharge process, thereby providing stronger power support for external devices. In addition, the liquid phase conversion mechanism in the battery cathode gives the system excellent rate performance, which means that the battery can maintain a relatively stable and efficient power conversion efficiency at different charge and discharge rates.

[0003] The positive electrode material of zinc-iodine batteries directly determines their energy density, power density and electrochemical stability. Problems such as the dissolution of iodine intermediates and corrosion of zinc negative electrodes are particularly prominent. These problems lead to the loss of active substances during the charging and discharging process of the battery at room temperature and low temperature, the destruction of the internal structure of the battery, and the increase in the irreversibility of the electrode reaction. The rapid capacity decay at low temperatures has further limited the large-scale development of aqueous zinc-iodine batteries, making it impossible to operate normally under low temperature conditions and unable to fully meet the strict requirements of large-scale energy storage systems for high-performance batteries.

[0004] To solve the above problems, works such as Nano Research (2022): 1-8 and Advanced Materials, 2022, 34(23): 2201716 have conducted relevant research on low-temperature zinc-iodine batteries, including modifying the zinc-iodine positive electrode to optimize the electrochemical performance and improving the low-temperature resistance of the electrolyte. Summary of the invention

[0005] The purpose of the present invention is to make a PTFE pole piece by doping onion carbon with single iron atoms and combining it with a specific electrolyte to improve the low temperature performance and electrochemical stability of the battery.

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

[0007] Single iron atoms are doped onto onion carbon and the electrode is made in a PTFE self-supporting form, achieving a higher capacity in a low-temperature resistant electrolyte and maintaining good operation at high rate and high stability in an extremely low temperature environment.

[0008] The preparation steps are as follows:

[0009] The commercial onion carbon was soaked in ferric nitrate, annealed in an Ar atmosphere with the help of a tube furnace, soaked in concentrated hydrochloric acid to obtain onion carbon loaded with single atomic iron, and finally loaded with iodine active substances by high temperature hydrothermal. It was mixed with PTFE and Ketjen black, ground thoroughly, and then softened with isopropanol to prepare sheets. Finally, a zinc perchlorate acetonitrile electrolyte with a concentration of 1 mol / L was matched.

[0010] Preferably, the iron precursor solution is a ferric nitrate solution with a concentration of 0.05 mol / L, a soaking time of 48 hours, and a holding temperature of 40°C.

[0011] Preferably, the tubular furnace annealing time is 2 hours and the holding temperature is 1000°C.

[0012] Preferably, the concentration of the ferric nitrate precursor solution is 0 mol / L, 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, or 0.05 mol / L.

[0013] Preferably, the mass ratio of onion carbon to elemental iodine is 1:1 during high-temperature hydrothermal treatment.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] (1) Single-atom catalysts can be obtained using a simple thermal decomposition method.

[0016] (2) PTFE-type electrodes do not require a carbon substrate and have excellent stability.

[0017] (3) The positive electrode loaded with iodine active material does not need to be matched with an iodine-containing electrolyte.

[0018] (4) Maintain high capacity, high rate and high cycle stability at low temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a scanning transmission electron microscope (SEM) image of the onion carbon prepared in Example 1 after annealing and acid etching;

[0020] Figure 2 This is the EDS elemental spectrum of the onion carbon prepared in Example 1 after annealing and acid etching;

[0021] Figure 3 The low temperature rate performance diagram of the modified positive electrode made of iron-doped single-atom onion carbon and the original onion carbon positive electrode prepared in Example 1;

[0022] Figure 4 The constant current charge-discharge cycle diagram of the modified positive electrode made of iron-doped single-atom onion carbon and the original onion carbon positive electrode prepared in Example 1;

[0023] Figure 5 This is a constant current charge-discharge cycle diagram of the iron single atom doped onion carbon PTFE self-supporting electrode prepared in Example 1 at room temperature;

[0024] Figure 6 This is a constant current charge-discharge cycle diagram of the onion carbon slurry coated carbon cloth substrate electrode doped with iron single atom prepared in Example 6 at room temperature; DETAILED DESCRIPTION

[0025] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments:

[0026] Example 1

[0027] The first step: place the onion carbon in a 0.05 mol / L ferric nitrate solution and soak it at 40°C for 48 hours. After drying, anneal it at 1000°C in an argon atmosphere. Take out the carbon material powder and soak it in concentrated hydrochloric acid for 6 hours to expose the metal clusters. The onion carbon material is thus prepared.

[0028] Step 2: Put the iron-doped onion carbon and iodine into a high-temperature resistant glass jar at a mass ratio of 1:1, shake and mix well, place in a hydrothermal axe, and react at 120°C for 12 hours to obtain an onion carbon material loaded with iodine.

[0029] Step 3: Mix the onion carbon loaded with monatomic iron with PTFE and Ketjen black in a ratio of 8:1:1. After grinding, drip an appropriate amount of isopropanol solution into it to soften it, and press it into an electrode.

[0030] Step 4: Match the electrode with the configured 1 mol / L zinc perchlorate acetonitrile electrolyte and start the electrochemical cycle test.

[0031] Example 2

[0032] The first step: soak the onion carbon in deionized water at 40°C for 48 hours. After drying, anneal it at 1000°C in an argon atmosphere. Take out the carbon material powder and soak it in concentrated hydrochloric acid for 6 hours to expose the metal clusters. The onion carbon material is thus prepared.

[0033] Step 2: Put the iron-doped onion carbon and iodine into a high-temperature resistant glass jar at a mass ratio of 1:1, shake and mix well, place in a hydrothermal axe, and react at 120°C for 12 hours to obtain an onion carbon material loaded with iodine.

[0034] Step 3: Mix the onion carbon loaded with monatomic iron with PTFE and Ketjen black in a ratio of 8:1:1. After grinding, drip an appropriate amount of isopropanol solution into it to soften it, and press it into an electrode.

[0035] Step 4: Match the electrode with the configured 1 mol / L zinc perchlorate acetonitrile electrolyte and start the electrochemical cycle test.

[0036] Example 3

[0037] The first step: place the onion carbon in a 0.01 mol / L iron nitrate solution and soak it at 40°C for 48 hours. After drying, anneal it at 1000°C in an argon atmosphere. Take out the carbon material powder and soak it in concentrated hydrochloric acid for 6 hours to expose the metal clusters. The onion carbon material is thus prepared.

[0038] Step 2: Put the iron-doped onion carbon and iodine into a high-temperature resistant glass jar at a mass ratio of 1:1, shake and mix well, place in a hydrothermal axe, and react at 120°C for 12 hours to obtain an onion carbon material loaded with iodine.

[0039] Step 3: Mix the onion carbon loaded with monatomic iron with PTFE and Ketjen black in a ratio of 8:1:1. After grinding, drip an appropriate amount of isopropanol solution into it to soften it, and press it into an electrode.

[0040] Step 4: Match the electrode with the configured 1 mol / L zinc perchlorate acetonitrile electrolyte and start the electrochemical cycle test.

[0041] Example 4

[0042] The first step: place the onion carbon in a 0.02 mol / L iron nitrate solution and soak it at 40°C for 48 hours. After drying, anneal it at 1000°C in an argon atmosphere. Take out the carbon material powder and soak it in concentrated hydrochloric acid for 6 hours to expose the metal clusters. The onion carbon material is thus prepared.

[0043] Step 2: Put the iron-doped onion carbon and iodine into a high-temperature resistant glass jar at a mass ratio of 1:1, shake and mix well, place in a hydrothermal axe, and react at 120°C for 12 hours to obtain an onion carbon material loaded with iodine.

[0044] Step 3: Mix the onion carbon loaded with monatomic iron with PTFE and Ketjen black in a ratio of 8:1:1. After grinding, drip an appropriate amount of isopropanol solution into it to soften it, and press it into an electrode.

[0045] Step 4: Match the electrode with the configured 1 mol / L zinc perchlorate acetonitrile electrolyte and start the electrochemical cycle test.

[0046] Example 5

[0047] The first step: place the onion carbon in a 0.03 mol / L iron nitrate solution and soak it at 40°C for 48 hours. After drying, anneal it at 1000°C in an argon atmosphere. Take out the carbon material powder and soak it in concentrated hydrochloric acid for 6 hours to expose the metal clusters. The onion carbon material is thus prepared.

[0048] Step 2: Put the iron single atom doped onion carbon and iodine into a high temperature resistant glass jar with a mass ratio of 1:1, shake and mix well, put into a hydrothermal axe, and react at a high temperature of 120℃ for 12h to obtain the onion carbon material loaded with iodine.

[0049] Step 3: Mix the onion carbon loaded with monatomic iron with PTFE and Ketjen black in a ratio of 8:1:1. After grinding, drip an appropriate amount of isopropanol solution into it to soften it, and press it into an electrode.

[0050] Step 4: Match the electrode with the configured 1 mol / L zinc perchlorate acetonitrile electrolyte and start the electrochemical cycle test.

[0051] Example 6

[0052] The first step: place the onion carbon in a 0.05 mol / L ferric nitrate solution and soak it at 40°C for 48 hours. After drying, anneal it at 1000°C in an argon atmosphere. Take out the carbon material powder and soak it in concentrated hydrochloric acid for 6 hours to expose the metal clusters. The onion carbon material is thus prepared.

[0053] Step 2: Put the iron-atom-doped onion carbon and iodine into a high-temperature resistant glass jar at a mass ratio of 1:0.5, shake and mix well, place in a hydrothermal axe, and react at a high temperature of 120°C for 12 hours to obtain an onion carbon material loaded with iodine.

[0054] Step 3: Mix the onion carbon loaded with monatomic iron with PVDF and Ketjen black in a ratio of 8:1:1. After grinding, add an appropriate amount of ethylene glycol to grind into slurry. Apply the slurry on commercial carbon cloth to make it evenly thick. Dry it at 40°C to make it into an electrode.

[0055] Step 4: Match the electrode with the configured 1 mol / L zinc perchlorate acetonitrile electrolyte and start the electrochemical cycle test.

[0056] like Figure 1As shown in the figure, the onion carbon after annealing and acid etching has a porous structure, and the structure is observed to be loose, which is conducive to improving the adsorption capacity of the carbon structure for polyiodide ions. In addition, the acid etching does not destroy the overall structure of the onion carbon, and the adsorption characteristics of the onion carbon can still be maintained after annealing and acid etching.

[0057] like Figure 2 As shown in the figure, the modified onion carbon was analyzed using energy dispersive X-ray spectroscopy (EDX) to confirm the composition of metal elements. As can be seen from the figure, the iron element in the iron precursor solution is evenly attached to the surface of the onion carbon.

[0058] like Figure 3 As shown in the figure, under a constant temperature of -40°C, Example 1 shows good rate performance, and the discharge specific capacities at current densities of 2C, 5C, 10C, and 20C are 151, 148, 124, and 79 mAh g, respectively. -1 In contrast, the discharge capacity of Example 2 at the same current density was only 124, 98, 74, and 48 mAh g -1 The presence of single iron atoms greatly improves the charge and discharge rate and stability of the onion carbon cathode at low temperatures.

[0059] like Figure 4 As shown, under a constant temperature environment of -40℃, Example 1 exhibits good charge and discharge cycle stability. As can be seen from the figure, after 1000 charge and discharge cycles, the battery capacity retention rate is above 100%. The increase in discharge capacity is due to the extremely low temperature environment of the battery. The initial 100 cycles are the stage of active material activation, and the activation of iodine active materials will bring a certain capacity increase.

[0060] like Figure 5 , 6 As shown, under the constant temperature state, the modified group and the unmodified group ( Figure 5 ) Compared with Example 6, the electrode piece of carbon cloth coated with onion carbon slurry ( Figure 6 ) showed higher charge and discharge cycle stability. After 6000 cycles of constant current charge and discharge, the capacity of the PTFE self-supporting electrode was still maintained at 78%, while the capacity retention rate of the slurry-coated electrode was only 37.5% due to the peeling of the active material from the substrate during the charge and discharge process.

Claims

1. A method for improving the low-temperature rate and cycle stability of an iodine battery by synergistically acting with an iodine-loaded electrode and an antifreeze electrolyte, characterized in that: The following steps are involved: (1) Iron single atom doped onion carbon PTFE electrode First, the onion-like carbon material was pretreated with nitric acid, then immersed in ferric nitrate solution for 48 hours, and then the carbon powder was dried and annealed at high temperature in an argon atmosphere. After annealing, it was placed in concentrated hydrochloric acid for 6 hours to 14 hours to expose the onion layer and pore structure and remove metal clusters. (2) Onion carbon loaded with iodine active substances The onion carbon powder obtained in step (1) and the iodine element are placed in a high temperature resistant glass jar, shaken and mixed, and then placed in a hydrothermal axe and reacted at a high temperature of 120°C for 24 hours. (3) Making PTFE self-supporting electrode The powder is mixed with commercial PTFE solution and Ketjen black in a certain mass ratio, softened with isopropyl alcohol, and flat-pressed to make the final PTFE pole piece. (4) Preparation of a mixed electrolyte of octanol perchlorate and acetonitrile Weigh a certain amount of zinc perchlorate hexahydrate crystals, place them into a pure acetonitrile solution, and place them at room temperature in a sealed state to stir and dissolve them, thereby finally obtaining a zinc perchlorate-acetonitrile mixed solution.

2. The preparation method according to claim 1, characterized in that: In step (1), the concentration of the ferric nitrate solution needs to be 0.05 mol / L, the soaking time is 48 h, and the soaking temperature is 40°C.

3. The preparation method according to claim 1, characterized in that: In step (1), the high temperature annealing temperature is 1000° C. and the holding time is 2 h.

4. The preparation method according to claim 1, characterized in that: In step (1), the mixture of concentrated hydrochloric acid and onion carbon powder is placed in a temperature environment of 60° C. and reacted for 6 hours.

5. The preparation method according to claim 1, characterized in that: In step (2), the mass ratio of elemental iodine to onion carbon powder is 1:1, the high-temperature hydrothermal reaction temperature should be 120° C., and the hydrothermal time is 24 h.

6. The preparation method according to claim 1, characterized in that: In step (3), the concentration of PTFE solution is 60%, and the mass ratio of onion carbon, PTFE and Ketjen black is 8:1:

1. The concentration of isopropyl alcohol should be 99.9% or above.

7. The preparation method according to claim 1, characterized in that: The concentration of zinc perchlorate in step (4) should be 1 mol / L.

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