A sodium ion battery negative electrode FeS / C composite material and its preparation method and application

Abstract

The present invention discloses a sodium ion battery negative electrode FeS / C composite material and its preparation method and application, comprising the following steps: (1) mixing ferrous sulfate or ferrous sulfate heptahydrate with lignin, and adding water and stirring until uniformly dispersed; (2) heating the solution obtained in step (1) at 60-120°C, stirring and drying to obtain a mixed powder; (3) calcining the powder obtained in step (2) at 700-900°C under a protective atmosphere for 3-8 hours, washing, and drying to obtain the sodium ion battery negative electrode FeS / C composite material. The present invention does not add an additional vulcanizing agent, nor does it use H2 / Ar mixed gas as a reducing gas. Only industrial lignin is used as a carbon precursor. Nano-granular FeS / C material is obtained through a two-step process of one-pot stirring and drying and tubular furnace heat treatment. The process is simple, green, efficient, and low-cost.

Description

Technical Field

[0001] The present invention aims to provide a method for preparing a FeS / C composite material for a negative electrode of a sodium ion battery by using lignin as a carbon precursor and lignin-assisted reduction, which belongs to the field of high-value utilization of lignin and negative electrode materials for sodium ion batteries. Background Art

[0002] Benefiting from the low cost and geographical distribution of sodium resources, as well as the low price of sodium raw materials, sodium-ion batteries have become one of the best choices to replace lithium-ion batteries. Sodium can form a variety of compounds, which makes the electrode and electrolyte materials available for selection and research more abundant. + The standard electrode potential of Li / Na is + / Li is about 0.3V higher. Therefore, the operating voltage of sodium-ion batteries is relatively low, and the electrolyte is not easily decomposed under high voltage, which makes the battery safer and more stable. In addition to the above unique advantages of sodium-ion batteries, they also have a long cycle life and high capacity like lithium-ion batteries.

[0003] Among various anode materials, metal sulfides have attracted considerable attention due to their high theoretical specific capacity and easily controllable morphology. Iron-based sulfides, in particular, stand out due to their abundant resources, low cost, high theoretical specific capacity, and environmental friendliness. However, like many other metal sulfides, iron-based sulfides suffer from inherently low electrical conductivity, severe volume changes caused by the electrochemical reaction of large amounts of sodium, and the polysulfide shuttling effect.

[0004] In response to the above problems, researchers have proposed some methods to improve the sodium storage performance of FeS. There are mainly three solutions: (1) Structural design of FeS to construct a porous nanostructure, thereby exposing more active sites and providing a fast channel for ion transport and electron transfer. Jung Sang Cho et al. prepared porous FeS nanofibers with a large number of nanovoids by electrospinning and further sulfurization. However, changing the structure still cannot obtain a FeS material with good cycle stability. (2) Doping with heteroatoms. Chae Ryong Cho et al. synthesized an electrode material with FeS as the core, N-doped carbon and reduced graphene oxide (rGO) as the composite shell through a series of methods such as electrospinning, hydrothermal reaction and chemical vapor deposition. The capacity of the electrode material was 856 mAh g after 50 cycles at 0.5 A / g. –1 However, the synthesis process of this material is complicated and the steps are tedious, which is not conducive to industrial production. (3) Composite with carbon materials. Carbon-based materials are relatively stable and have a small volume change during the sodium ion insertion and extraction process. Composite with them is an effective method to improve sodium storage performance. For example, Kang et al. synthesized FeS-rGO composite materials by sulfurization treatment. -1The capacity after 50 cycles is 547 mAh g -1 However, it is obvious that this process has some disadvantages, such as cumbersome procedures and harsh reaction conditions, which inhibit the widespread use of rGO-modified materials.

[0005] Currently, the reported preparation process of FeS / C composite materials is complex and requires an additional sulfur source for vulcanization, which is not conducive to the environmental requirements of green and sustainable development. Lignin, the second most abundant biomass, is a biomass polymer with a three-dimensional network structure formed by three phenylpropane units interconnected by ether bonds and carbon-carbon bonds. It contains a rich variety of aromatic ring structures, aliphatic and aromatic hydroxyl groups, and quinone groups and other active groups. It is a by-product of the papermaking industry. However, due to the shortcomings of industrial lignin such as severe molecular aggregation and low reactivity, the current high-value utilization rate is less than 10%. To date, there are still no reports on the successful application of lignin in FeS negative electrode materials for sodium-ion batteries. Summary of the Invention

[0006] The invention uses lignin and ferrous sulfate heptahydrate as raw materials, adopts a stirring drying method and a tubular furnace heat treatment in two steps to obtain a sodium ion battery ferrous sulfide-based carbon composite material with high specific capacity and good cycle stability. The chemical composition of the ferrous sulfide-based carbon composite material is FeS / C.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A method for preparing a FeS / C composite material for a sodium ion battery negative electrode comprises the following steps:

[0009] (1) mixing ferrous sulfate or ferrous sulfate heptahydrate with lignin, and adding water and stirring until the mixture is uniformly dispersed; wherein the mass ratio of ferrous sulfate heptahydrate to lignin is (1-5):1;

[0010] (2) heating the solution obtained in step (1) at 60-120° C., stirring and drying to obtain a mixed powder;

[0011] (3) calcining the powder obtained in step (2) at 700-900° C. for 3-8 hours under a protective atmosphere, washing, and drying to obtain the FeS / C composite material for the negative electrode of the sodium ion battery.

[0012] Preferably, in step (1), the mass ratio of ferrous sulfate heptahydrate to lignin is 3±1:1.

[0013] Preferably, the concentration of lignin in water in step (1) is 0.01-0.1 g / mL.

[0014] Preferably, the drying temperature in step (2) is 80-100°C.

[0015] Preferably, the stirring time in step (2) is 24±6h.

[0016] Preferably, the carbonization temperature of step (3) is 800±100° C., and the calcination time is 6±1 h.

[0017] Preferably, the lignin in step (1) is one or both of sodium lignin sulfonate and ammonia-oxidized lignin.

[0018] Preferably, the protective atmosphere in step (3) is at least one of nitrogen, argon and helium.

[0019] Application of the FeS / C composite material for sodium ion battery negative electrode prepared by the above method in sodium ion batteries.

[0020] In step (1), ferrous sulfate provides S and Fe elements, and the hydroxyl functional groups rich in lignin react with Fe 2+ Lignin-coated ferrous sulfate nanospheres are formed in situ under chelation. This coating is crucial for the in-situ reduction to FeS during the subsequent calcination process. The amount of lignin added is crucial. Experiments have shown that without lignin, FeS cannot be obtained, resulting in only Fe₃O₄. Excessive lignin addition leads to increased gas release and foaming during pyrolysis, resulting in poor contact between the carbon layer and the material and significantly reducing the coating effect.

[0021] In step (3), during the pyrolysis of lignin, ferrous sulfate first turns into ferric oxide, then undergoes carbon thermal reduction to ferroferric oxide, and finally is reduced to FeS. At the same time, the lignin itself is transformed into a carbon material, which encapsulates the FeS, thereby inhibiting the volume expansion of the FeS during the charge and discharge process. The carbon-coated structure also successfully alleviates the polysulfide shuttle effect. Based on the thermal decomposition characteristics of FeSO4·7H2O itself, calcination at 700-900℃ is mainly adopted:

[0022] FeSO4·7H2O→FeSO4·4H2O+3H2O

[0023] FeSO4·4H2O→FeSO4·H2O+3H2O

[0024] FeSO4·H2O→FeSO4+H2O

[0025] 2FeSO4→Fe2O3+2SO2+1 / 2O2

[0026] During the carbonization process of lignin, pure FeS / C was prepared by in situ carbothermal reduction of FeSO4.

[0027] FeSO4·7H2O→FeSO4·4H2O+4H2O

[0028] FeSO4·4H2O→FeSO4·H2O+H2O

[0029] FeSO4·H2O→FeSO4+H2O

[0030] 2FeSO4→Fe2O3+2SO2+1 / 2O2

[0031] C+SO2→S n +CO2(CO)

[0032] Fe2O3+C→Fe3O4+CO(CO2)

[0033] Fe3O4+S n →Fe 1-x S+SO2

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) At the same temperature, the present invention neither adds an additional sulfurizing agent nor uses H2 / Ar mixed gas as a reducing gas. Only industrial lignin is used as a carbon precursor. Ferrous sulfate can be in situ reduced to FeS through two steps of one-pot stirring drying and tubular furnace heat treatment to prepare nano-granular FeS / C material. The process is simple, green and efficient, low-cost, and reduces the consumption of fossil energy, increases the safety of the experimental process, and is conducive to industrial application and high-value utilization of lignin.

[0036] (2) In the FeS / C composite material of the present invention, the hydroxyl functional groups rich in lignin and Fe 2+ Lignin-coated ferrous sulfate nanospheres are formed in situ under chelation, and then calcined at high temperature to produce carbon-coated ferrous sulfide. The carbon coating on the ferrous sulfide surface mitigates volume changes during charge and discharge, and inhibits polysulfide shuttling. The resulting material offers high capacity, excellent cycle stability, and a high specific surface area, meeting the current market demand for superior sodium-ion battery anodes.

[0037] (3) The iron sulfide in the composite material prepared by the present invention has a distinctly uniformly distributed nanosphere structure, coated with a carbon layer, which increases the specific surface area and facilitates ion and electron transport. At high current densities (20 A / g), it exhibits excellent rate performance and long-term cycling stability (capacity retention reaches 98% after 1000 cycles at 1 A / g). BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is the XRD pattern of the composite material prepared in Example 1 after calcination at 700-900°C.

[0039] Figure 2 The XRD patterns of the composite materials after calcination in Example 1 with lignin added (calcined at 800° C.) and in Comparative Example 1 without lignin added are shown.

[0040] Figure 3 1 is a SEM image of the FeS / C composite material prepared in Example 1; the left image is the sample morphology after stirring and drying, and the right image is the FeS / C nanosphere sample morphology obtained after calcination.

[0041] Figure 4 The FeS / C composite material prepared in Example 1 was assembled into a button cell at a current density of 0.1Ag. -1 The first charge and discharge curve at .

[0042] Figure 5 Graph showing the coulombic efficiency and rate performance of button cells assembled from the FeS / C composite material prepared in Example 1 at different current densities.

[0043] Figure 6 The FeS / C composite material prepared in Example 1 was assembled into a button cell at a current density of 1A. -1 Time cycle performance diagram.

[0044] Figure 7 XRD pattern of the FeS / C composite material prepared in Comparative Example 2.

[0045] Figure 8 This is the SEM image of the FeS / C composite material prepared in Comparative Example 2.

[0046] Figure 9 This is a graph showing the coulombic efficiency and rate performance of a button-type battery assembled with the FeS / C composite material prepared in Comparative Example 2 at different current densities.

[0047] Figure 10 The commercial FeS material in Example 5 is 1Ag -1 The long cycle performance diagram below. DETAILED DESCRIPTION

[0048] The present invention will be described in further detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto. For process parameters not specifically noted, conventional techniques may be used. The protective atmosphere in the examples is nitrogen.

[0049] Example 1: Effect of different calcination temperatures on the preparation of FeS / C composite materials

[0050] (1) Add 1 g of ammonia-oxidized lignin to 3 g of ferrous sulfate heptahydrate. Add 30 mL of ultrapure water and stir until the mixture is evenly dispersed.

[0051] (2) heating and stirring the solution obtained in step (1) at 100° C. for 24 hours to obtain a mixed powder;

[0052] (3) The powder obtained in step (2) was calcined at 800°C for 6 hours under a protective atmosphere, washed, and dried to obtain the FeS / C composite material for the negative electrode of the sodium ion battery. At the same time, control group experiments were carried out using 700°C, 750°C, and 900°C.

[0053] Example 2: Effects of different lignin types on the preparation and properties of FeS / C composite materials

[0054] (1) Add 1 g of sodium lignin sulfonate to 3 g of ferrous sulfate heptahydrate. Add 30 mL of ultrapure water and stir until the mixture is evenly dispersed.

[0055] (2) heating and stirring the solution obtained in step (1) at 100° C. for 24 hours to obtain a mixed powder;

[0056] (3) The powder obtained in step (2) is calcined at 800° C. for 6 h under a protective atmosphere, washed, and dried to obtain the FeS / C composite material for the sodium ion battery negative electrode.

[0057] Example 3: Effect of different lignin contents on the preparation and properties of FeS / C composite materials

[0058] (1) Add 3 g of ammonia-oxidized lignin to 3 g of ferrous sulfate heptahydrate. Add 30 mL of ultrapure water and stir until the mixture is evenly dispersed. 0.5 g of ammonia-oxidized lignin was used as a control group.

[0059] (2) heating and stirring the two solutions with different lignin contents obtained in step (1) at 100° C. for 24 hours to obtain mixed powders;

[0060] (3) The powder obtained in step (2) is calcined at 800° C. for 6 h under a protective atmosphere, washed, and dried to obtain the FeS / C composite material for the sodium ion battery negative electrode.

[0061] Example 4: Effect of different stirring temperatures on the preparation and properties of FeS / C composite materials

[0062] (1) Add 1 g of ammonia-oxidized lignin to 3 g of ferrous sulfate heptahydrate. Add 30 mL of ultrapure water and stir until the mixture is evenly dispersed.

[0063] (2) heating and stirring the solution obtained in step (1) at 60° C. and 80° C. for 24 hours to obtain a mixed powder;

[0064] (3) The powder obtained in step (2) is calcined at 800° C. for 6 h under a protective atmosphere, washed, and dried to obtain the FeS / C composite material for the sodium ion battery negative electrode.

[0065] Example 5: Effect of different calcination times on the synthesis and properties of the product FeS / C

[0066] (1) Add 1 g of ammonia-oxidized lignin to 3 g of ferrous sulfate heptahydrate. Add 30 mL of ultrapure water and stir until the mixture is evenly dispersed.

[0067] (2) heating and stirring the solution obtained in step (1) at 100° C. for 24 hours to obtain a mixed powder;

[0068] (3) The powder obtained in step (2) is calcined at 800° C. for 3 h under a protective atmosphere, washed, and dried to obtain the FeS / C composite material for the sodium ion battery negative electrode.

[0069] Comparative Example 1: Preparation of Fe3O4 material by calcination under inert gas without adding lignin

[0070] (1) 3 g of ferrous sulfate heptahydrate was calcined at 800 °C for 6 h under a protective atmosphere, washed, and dried to obtain Fe3O4 material without obtaining FeS.

[0071] Comparative Example 2: Preparation of FeS / C material by spray drying and calcination at 800°C for 6h

[0072] (1) Add 1 g of ammonia-oxidized lignin to 3 g of ferrous sulfate heptahydrate. Add 30 mL of ultrapure water and stir until the mixture is evenly dispersed.

[0073] (2) spray drying the solution obtained in step (1) (outlet temperature 100° C.) to obtain a mixed powder;

[0074] (3) The powder obtained in step (2) is calcined at 800° C. for 6 h under a protective atmosphere, washed, and dried to obtain the FeS / C composite material for the sodium ion battery negative electrode.

[0075] Comparative Example 3: Preparation of FeS / C composite material using glucose as carbon source

[0076] (1) Add 1 g of glucose to 3 g of ferrous sulfate heptahydrate. Add 30 mL of ultrapure water and stir until the mixture is evenly dispersed.

[0077] (2) heating and stirring the solution obtained in step (1) at 100° C. for 24 hours to obtain a mixed powder;

[0078] (3) The powder obtained in step (2) is calcined at 800° C. for 6 h under a protective atmosphere, washed, and dried to obtain the FeS / C composite material for the sodium ion battery negative electrode.

[0079] Comparative Example 4: Directly using FeS2 to prepare FeS / C material

[0080] (1) Add 1 g of ammonia-oxidized lignin to 3 g of ferrous disulfide. Add 30 mL of ultrapure water and stir until the mixture is evenly dispersed.

[0081] (2) spray drying the solution obtained in step (1) to obtain a mixed powder;

[0082] (3) The powder obtained in step (2) is calcined at 800° C. for 6 h under a protective atmosphere, washed, and dried to obtain the FeS / C composite material for the sodium ion battery negative electrode.

[0083] Comparative Example 5: Direct use of commercial FeS material

[0084] The morphology and size of the samples of the present invention were tested by field emission scanning electron microscopy (SEM, Hitach SU8220). The battery assembly adopts half-cell assembly, model CR2032. The composition of the negative electrode material is 70wt% active material, 15wt% carbon black, and 15wt% carboxymethyl cellulose (CMC), wherein the active material is the material prepared by the above-mentioned Examples 1-5 and Comparative Examples 1-5. Sodium sheet is used as the counter electrode, and the electrolyte is a mixed solution prepared by dissolving 1.0M sodium hexafluorophosphate in dimethyl ether. The entire assembly process of the sodium ion half-cell is completed in an argon-protected glove box. The test was carried out at 0.01V~3.0V using the Neware battery performance test system, and the long cycle stability test was carried out at a high current density of 1A / g.

[0085] The obtained materials were applied to the negative electrode materials of sodium ion batteries and electrochemical tests and material characterization were performed. The results are shown in Table 1 and Figure 1-6 .

[0086] Table 1

[0087]

[0088]

[0089] Table 1 shows that the FeS / C negative electrode material prepared in Example 1 has a -1 At a current density of 1.5, the initial capacity is 560 mAh g -1 , has a high initial capacity and good cycle stability, which is significantly better than similar materials. In addition, the cycle performance of all example samples is better than that of other comparative samples. This is mainly due to the effective coating of lignin carbon and the in-situ reduction of ferrous sulfate heptahydrate by lignin during pyrolysis, which makes the material have an initial coulombic efficiency of about 80% and excellent rate performance: the capacity is as high as 395mAh·g at a high current density of 20A / g. -1 ( Figure 5) and excellent cycling stability: Capacity retention reached 98% after 1000 cycles at a high current density of 1 A / g. Comparative Examples 2, 3, and 4 demonstrate that while FeS has a high specific capacity, it suffers from significant instability, and all of these comparative examples suffer from poor long-term cycling stability. Sodium lignin sulfonate and ammonia-oxidized lignin also assist in reduction, and coating FeS with lignin carbon enhances material stability, significantly improving the electrochemical performance of sodium-ion batteries.

[0090] In Table 1, Comparative Example 1 is the material obtained without adding lignin. Because no lignin was added, the final product was Fe3O4. After electrochemical testing, its initial coulombic efficiency was as low as 43%, and the capacity retention rate after 100 cycles at a high current density of 1A / g was only 31%, indicating that its volume expansion was large, resulting in the material being crushed and unable to be stably cycled for a long time. Comparative Example 2 did not use the stirring drying method but the spray drying method, and also obtained a carbon-coated ferrous sulfide composite material. Figure 7-9 It can be seen that the spray-dried FeS / C material not only has no advantage in morphology, showing larger particles, but more importantly, it also has no advantage in capacity, indicating that the stirring drying and carbon coating steps are indispensable for the preparation of FeS / C.

[0091] Figure 1 This is the XRD pattern of the composite material prepared in Example 1 of the present invention after calcination at 700-900°C. It can be seen that under the action of lignin, ferrous sulfate heptahydrate can be reduced to ferrous sulfide, among which the purest FeS XRD phase and the best electrochemical performance are obtained at 800°C.

[0092] Figure 2 1 is the XRD pattern of ferrous sulfate heptahydrate calcined at 800° C. with and without lignin in Example 1 of the present invention, proving the auxiliary reduction effect of lignin.

[0093] Figure 3 This is an SEM image of the composite material FeS / C in Example 1 of the present invention. It can be seen that the material is in the form of carbon-coated nanospheres, and the interior of the material is dispersed nanospheres. This morphology has a larger specific surface area, and the area in contact with the electrolyte will also become larger, and the sodium storage active sites will increase accordingly, thereby significantly improving the electrochemical performance of the material.

[0094] Figure 4 This is the first cycle specific capacity-voltage diagram of the composite material FeS / C in Example 1 of the present invention at a current density of 0.1 A / g. It can be seen that the initial coulombic efficiency is high and the capacity is high.

[0095] Figure 5This is a rate graph of the FeS / C composite material from Example 1 of the present invention at different current densities. It shows that even at a high current density of 20 A / g, it still maintains a capacity of approximately 380 mAh / g, demonstrating excellent stability. The capacity at the final return to 0.1 A / g does not decrease compared to the initial capacity and even shows an upward trend, demonstrating the composite material's good reversibility.

[0096] Figure 6 The FeS / C composite material prepared in Example 1 is assembled into a button cell at a maximum current density of 1A. -1 From the long cycle performance diagram, it can be seen that the material has good stability under the coating of the carbon layer, and the capacity is still 480mAh / g after 1000 cycles.

[0097] Figure 7 This is the XRD pattern of the composite material FeS / C prepared by spray drying in Comparative Example 2 of the present invention. It can be seen that FeS / C can also be prepared by spray drying.

[0098] Figure 8 This is an SEM image of the FeS / C composite material prepared in Comparative Example 2. It can be seen that the composite material prepared by spray drying has a larger particle size. Stirring and drying obtain 100 nm FeS, while spray drying obtains 2 μm FeS. The FeS prepared by spray drying does not have an advantage in morphology and is prone to greater volume expansion, resulting in poor battery cycle stability.

[0099] Figure 9 The figure shows the rate performance of button-type batteries assembled with the FeS / C composite material prepared in Comparative Example 2 at different current densities. Compared with the rate performance figure of Example 1, it can be seen that the spray drying method does not perform as well as the stirring drying method. This may be due to the fact that its particle size is much larger than that of the stirring drying method. Therefore, it can also be judged that the volume expansion of the material causes the capacity decay at high current density.

[0100] Figure 10 The commercial FeS in Example 5 is 1A g -1 The long-term cycling diagram at high current density shows that after the lignin carbon coating is lost, the material's cycling stability is poor and its capacity rapidly decays due to volume expansion during the sodium insertion and extraction process and the polysulfide shuttle effect. This further verifies the effective role of lignin carbon in mitigating volume expansion and the polysulfide shuttle effect.

[0101] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing a FeS / C composite material for a negative electrode of a sodium ion battery, characterized in that: The following steps are involved: (1) mixing ferrous sulfate or ferrous sulfate heptahydrate with lignin, and adding water and stirring until the mixture is uniformly dispersed; wherein the mass ratio of ferrous sulfate heptahydrate to lignin is (1-5):1; and the lignin is one or both of sodium lignin sulfonate and ammonia-oxidized lignin; (2) heating the solution obtained in step (1) at 80-120° C., stirring and drying to obtain a mixed powder; (3) The powder obtained in step (2) is calcined at 750-900° C. for 3-8 h under a protective atmosphere, washed, and dried to obtain the FeS / C composite material for the negative electrode of the sodium ion battery.

2. The preparation method according to claim 1, characterized in that In step (1), the mass ratio of ferrous sulfate heptahydrate to lignin is 3±1:

1.

3. The preparation method according to claim 2, characterized in that The drying temperature in step (2) is 80-100°C.

4. The preparation method according to claim 3, characterized in that The stirring time in step (2) is 24±6h.

5. The preparation method according to claim 1, 2, 3 or 4, characterized in that: The calcination temperature of step (3) is 800±50°C, and the calcination time is 6±1h.

6. The preparation method according to claim 5, characterized in that The protective atmosphere in step (3) is at least one of nitrogen, argon and helium.

7. A FeS / C composite material for a negative electrode of a sodium ion battery obtained by the method according to any one of claims 1 to 6.

8. Use of the FeS / C composite material for sodium ion battery negative electrode according to claim 7 in a sodium ion battery.

Images