Iron selenide / carbon composite material and preparation method and application thereof

Abstract

The invention discloses an iron selenide / carbon composite material and a preparation method and application thereof, and belongs to the technical field of battery electrode materials. According to the preparation method, the organic acid iron and the selenium powder are subjected to ball milling and uniform mixing and placed in the argon atmosphere for calcination treatment, and controllable preparation of the iron selenide / carbon composite materials with different selenylation degrees can be achieved through coordinated regulation and control of the molar ratio of the organic acid iron to the selenium powder and the calcination treatment temperature; the preparation method is simple and efficient in process, and the prepared iron selenide / carbon composite material is high in phase purity and has good electrochemical performance.

Description

Technical Field

[0001] The present invention specifically relates to an iron selenide / carbon composite material and a preparation method and application thereof, belonging to the technical field of battery electrode materials. Background Art

[0002] Iron selenide is an important negative electrode material for lithium-ion batteries and sodium-ion batteries. Due to its non-Faradaic capacitance storage effect of lithium / sodium, iron selenide has a discharge capacity far higher than its theoretical value and has good electrochemical performance. However, the electronegativity of selenium is relatively small, and it can be used as a negative one-valent Se2 2- ions and negative divalent Se 2- The stable presence of ions makes the chemical composition and crystal structure of iron selenide relatively complex. According to the degree of selenization, as the degree of selenization increases and the valence of the selenium ion decreases, iron selenide exists in the form of FeSe, Fe7Se8, Fe3Se4, and FeSe2, respectively. The corresponding crystal structure also changes from simple cubic FeSe and Fe7Se8 to monoclinic Fe3Se4 and pyrite FeSe2. These differences in the structure and composition of iron selenide will inevitably affect its electrochemical performance. Therefore, how to synthesize iron selenide with different degrees of selenization in a targeted and controllable manner has become an urgent problem to be solved.

[0003] At the same time, as a conversion electrode material, iron selenide also has obvious defects during the charge and discharge process: on the one hand, its volume is very easy to expand, causing the spatial structure of the electrode material to collapse; on the other hand, it is significantly affected by the "shuttle effect", which makes the battery face the problem of continuous capacity decay during the charge and discharge process. Currently, combining iron selenide with carbon to form an iron selenide / carbon composite material is an important strategy to improve the charge and discharge performance of iron selenide. The presence of soft carbon can buffer the volume change of iron selenide during the cycle, which is expected to achieve an improvement in the electrochemical performance of iron selenide. However, as disclosed in Chinese patents CN201910835861.4, CN201910164409.X, CN202110285441.0, CN202110388009.4, etc., iron source, carbon source and selenium source are basically synthesized into iron selenide carbon-based compounds by hydrothermal selenization or solid-phase reaction. These schemes often involve the use of more organic reagents or the synthesis of more complex precursors. The preparation process is cumbersome, and the synthesized product is only a single phase or a specific mixed phase of iron selenide. Due to the significant differences in the structure, composition and electrochemical properties of iron selenide with different degrees of selenization, the application of the preparation scheme of the above-mentioned iron selenide / carbon composite material has obvious limitations. Therefore, it is urgent to develop a method for preparing an iron selenide / carbon composite material with a simple process, good electrochemical properties and the ability to achieve different degrees of selenization. Summary of the Invention

[0004] In response to existing problems, the present invention provides an iron selenide / carbon composite material, a preparation method and application thereof; the present invention mixes organic acid iron and selenium powder by ball milling and calcines them under an argon atmosphere, and realizes the controllable preparation of iron selenide / carbon composite materials with different degrees of selenization through the coordinated regulation of the molar ratio of organic acid iron to selenium powder and the calcination temperature; the preparation method is simple and efficient, the obtained iron selenide / carbon composite material has high phase purity and good performance in electrochemical properties.

[0005] The technical solutions of the present invention are as follows:

[0006] The present invention provides an iron selenide / carbon composite material, wherein the iron selenide / carbon composite material can be represented by a chemical formula of Fe x Se y / C indicates that Fe x Se y stands for iron selenide, Fe x Se y It is a pure phase of FeSe, Fe7Se8, Fe3Se4, FeSe2 or a mixed phase of FeSe, Fe7Se8, Fe3Se4, FeSe2; the iron selenide / carbon composite material presents a three-dimensional block structure morphology formed by aggregation of nanoparticles and has good lithium / sodium ion transmission performance.

[0007] Preferably, the iron selenide of the iron selenide / carbon composite material is one of pure phase FeSe2, Fe3Se4, and Fe7Se8.

[0008] Preferably, the iron selenide of the iron selenide / carbon composite material is a mixed phase of FeSe2 and Fe3Se4 or a mixed phase of FeSe and Fe7Se8.

[0009] The present invention provides a method for preparing the above-mentioned iron selenide / carbon composite material. The method uses organic acid iron as an iron source and a carbon source, ball-mills the organic acid iron and selenium powder in a molar ratio of 1:(1.5-5) and mixes them evenly, and then calcines them at 400-700°C in an argon atmosphere to obtain the iron selenide / carbon composite material.

[0010] The degree of selenization of the iron selenide / carbon composite material obtained by the preparation method is simultaneously affected by the combined influence of the selenium powder concentration and the calcination temperature during the preparation process; by increasing the calcination temperature or reducing the selenium powder concentration, the degree of selenization of the iron selenide in the obtained iron selenide / carbon composite material can be gradually reduced, and the iron selenide presents a corresponding single phase according to the degree of selenization from high to low (in order of FeSe2, Fe3Se4, Fe7Se8, FeSe), or a mixed phase of two or more adjacent iron selenides with different degrees of selenization. By coordinating the feeding molar ratio of organic acid iron and selenium powder and the calcination temperature in the preparation method, the present invention can realize the controllable preparation of iron selenide / carbon composite materials with different degrees of selenization, and under the conditions of appropriate feeding ratio and calcination temperature, pure phase iron selenide / carbon composite materials with different degrees of selenization can be obtained.

[0011] Furthermore, the organic acid iron is one of ferric citrate, ferrocene, and ferric tartrate.

[0012] Furthermore, the specific steps of ball milling and mixing are: pouring organic acid iron and selenium powder into a ball mill jar, adding anhydrous ethanol and agate balls thereto, ball milling and mixing in a ball mill for at least 4 hours, and then drying and grinding the obtained mixture.

[0013] Furthermore, the organic acid iron and selenium powder are added in a molar ratio of 1:(3-5), the calcination temperature is set to one of 400° C., 500° C., 600° C. or 700° C., and the calcination time is 4 hours.

[0014] Furthermore, when the organic acid iron and selenium powder are added in a molar ratio of 1:(3-5) and the calcination temperature is 400° C., the obtained iron selenide / carbon composite material is pure phase FeSe2 / C.

[0015] Furthermore, when the organic acid iron and selenium powder are added in a molar ratio of 1:(3-5) and the calcination temperature is 500° C., the obtained iron selenide / carbon composite material is a mixed phase of FeSe2 / C and Fe3Se4 / C.

[0016] Furthermore, when the organic acid iron and selenium powder are added in a molar ratio of 1:(3-5) and the calcination temperature is 600° C., the obtained iron selenide / carbon composite material is a pure phase Fe3Se4 / C.

[0017] Furthermore, when the organic acid iron and selenium powder are added in a molar ratio of 1:(3-5) and the calcination temperature is 700° C., the obtained iron selenide / carbon composite material is a pure phase Fe7Se8 / C.

[0018] Furthermore, the organic acid iron and selenium powder are added in a molar ratio of 1:1.5, and the calcination temperature is 700° C. The obtained iron selenide / carbon composite material is a mixed phase of Fe7Se8 / C and FeSe / C.

[0019] The iron selenide / carbon composite material provided by the present invention can be used as a negative electrode material for lithium ion batteries or sodium ion batteries.

[0020] Different from the prior art, the present invention has the following beneficial effects:

[0021] 1. The present invention provides a new method for preparing an iron selenide / carbon composite material. The present invention uses organic acid iron as both an iron source and a carbon source for carbonization, mixes it with selenium powder by ball milling, and calcines it under an argon atmosphere to obtain an iron selenide / carbon composite material; when the molar ratio of organic acid iron to selenium powder is within the range of 1:(3-5), and the calcination temperature is 400°C, 600°C, and 700°C, respectively, the formed iron selenide / carbon composite materials are pure phase FeSe2 / C, Fe3Se4 / C, and Fe7Se8 / C materials, respectively. When the molar ratio of organic acid iron to selenium powder is 1:1.5 and the calcination temperature is 700°C, a FeSe / C material with a low degree of selenization appears in the formed iron selenide / carbon composite material; the present invention can achieve controllable preparation of iron selenide / carbon composite materials with different degrees of selenization through coordinated regulation of the feed ratio of ferric citrate and selenium powder and the calcination treatment temperature; the preparation method has a simple process, readily available raw materials, and does not require multi-step operations. By simply changing the preparation process conditions, the directional preparation of high-phase-purity iron selenide / carbon composite materials with different degrees of selenization can be achieved.

[0022] 2. The present invention synthesizes an iron selenide / carbon composite material in situ by a solid-phase method. By combining iron selenide with carbon, the problems of spatial structure collapse and capacity attenuation of single iron selenide during the charge and discharge process are effectively solved. The presence of soft carbon can buffer the volume change during the cycle and effectively improve the electrochemical performance of the material. The iron selenide / carbon composite material prepared by the present invention presents a three-dimensional block structure morphology formed by the aggregation of nanoparticles. The nanoparticles can provide a shorter lithium ion transmission path, and the three-dimensional structure can provide a stable framework, which is more conducive to structural stability. Thanks to the above characteristics, the iron selenide / carbon composite material can be used as a high-performance negative electrode material in the battery field. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 1 is the XRD spectrum of the iron selenide / carbon composite material of Examples 1 to 4.

[0024] Figure 2 The XRD comparison diagrams of the composite materials prepared in Examples 1 to 13 under different feed ratios of ferric citrate to selenium powder and calcination treatment temperatures are shown.

[0025] Figure 3The thermogravimetric (TG) analysis test and thermogravimetric differential curve (DTG) diagram of the reaction raw materials of Example 1 (ferric citrate and selenium powder in a molar ratio of 1:3) under a nitrogen atmosphere are shown.

[0026] Figure 4 This is the XPS spectrum of 400-FeSe in Example 1.

[0027] Figure 5 SEM images of 400-FeSe and 600-FeSe, where (a, b) are 400-FeSe and (c, d) are 600-FeSe.

[0028] Figure 6 SEM images of 500-FeSe and 700-FeSe, where (a, b) are 500-FeSe and (c, d) are 700-FeSe.

[0029] Figure 7 (ad) EDS images of 400-FeSe, 500-FeSe, 600-FeSe, and 700-FeSe, respectively.

[0030] Figure 8 These are the charge and discharge performance test curves of 400-FeSe, 500-FeSe, 600-FeSe, and 700-FeSe as lithium battery negative electrode materials for the 2nd and 3rd cycles and the 98th and 99th cycles.

[0031] Figure 9 The charge and discharge performance of 400-FeSe, 500-FeSe, 600-FeSe, and 700-FeSe as negative electrode materials for sodium ion batteries at the 2nd and 3rd cycles and the 98th and 99th cycles.

[0032] Figure 10 The 400-FeSe of Example 1 was subjected to different scanning rates (0.4-1 mV s -1 ) under cyclic voltammetry test results.

[0033] Figure 11 The battery rate performance of 400-FeSe and 600-FeSe at different current rates. DETAILED DESCRIPTION

[0034] The present invention will be further described below in conjunction with the accompanying drawings and preferred embodiments. The given embodiments are only for illustrating the present invention, rather than for limiting the scope of the present invention.

[0035] Unless otherwise specified, the materials, reagents, etc. used in the following examples can be obtained from commercial sources; the methods in the following examples are conventional methods unless otherwise specified.

[0036] Example 1

[0037] Example 1 provides a method for preparing an iron selenide / carbon composite material, comprising the following steps:

[0038] S1. Weigh 3.3503 g of ferric citrate as the iron and carbon sources, pour the ferric citrate and selenium powder into a ball mill according to a specific molar ratio, add about 6 mL of anhydrous ethanol and about 15 g of agate balls (mixed sizes) into the jar, tightly seal the jar and place it in a ball mill, and ball mill for 4 h; then place the resulting sample in an 80°C oven to dry to obtain a mixed phase;

[0039] S2. Pour the mixed phase obtained in step S1 into a clean and dry quartz ark and shake it slightly to make it evenly distributed in the ark. Use a furnace hook to slowly place it into the middle heating zone of the tubular furnace. After the installation is completed, open the argon bottle and exhaust it at a large flow rate for 30 minutes. Then adjust the airflow size between 20 and 30 mL / min. After the airflow stabilizes, heat it to the preset calcination treatment temperature at a rate of 5°C / min, and calcinate for 4 hours. After calcination, wait for the sample to cool, grind and crush it to obtain the iron selenide / carbon composite material.

[0040] The difference between Examples 2 to 13 and Example 1 is that the molar ratio of ferric citrate to selenium powder in step S1 and the preset calcination temperature in step S2 are different. The molar ratio of ferric citrate to selenium powder, the calcination temperature and the iron selenide phase of the obtained iron selenide / carbon composite material of the above examples are shown in Table 1. Table 1 The molar ratio of ferric citrate to selenium powder, the calcination temperature and the iron selenide phase of the obtained iron selenide / carbon composite material of each example

[0041]

[0042] In Examples 1 to 4, the iron / selenium ratio was controlled to be 1:3, and only the calcination temperature was changed. Figure 1 3. XRD comparison diagram of the iron selenide / carbon composite material prepared in Examples 1 to 4 of the present invention.

[0043] like Figure 1 As shown in (a), the calcination temperature of Example 1 is 400°C, and the obtained iron selenide / carbon composite material is FeSe2 / C. The diffraction peak of the sample is consistent with the standard colorimetric card of FeSe2 (JCPDS NO: 97-004-2115), and it has diffraction peaks of all crystal planes of FeSe2. It can be seen that the iron selenide of the composite material is a pure phase FeSe2 of the orthorhombic crystal system.

[0044] like Figure 1As shown in (b), the calcination temperature treatment temperature of Example 2 is 500°C, and the obtained iron selenide / carbon composite material is a mixed phase composite material of FeSe2 / C and Fe3Se4 / C. The diffraction peak of the sample is consistent with the standard colorimetric card of FeSe2 (JCPDS NO: 97-004-2115) and Fe3Se4 (JCPDS NO: 97-001-5043), and has the crystal plane diffraction peaks of FeSe2 and Fe3Se4. The iron selenide of the composite material is a mixed phase of FeSe2 and Fe3Se4.

[0045] like Figure 1 As shown in (c), the calcination temperature of Example 3 is 600°C, and the obtained iron selenide / carbon composite material is Fe3Se4 / C. The diffraction peak of the sample is consistent with the standard colorimetric card of Fe3Se4 (JCPDS NO:97-001-5043), and it has diffraction peaks of all crystal planes of Fe3Se4. It can be seen that the iron selenide of the composite material is a pure phase Fe3Se4 of the monoclinic system.

[0046] like Figure 1 As shown in (d), the calcination temperature of Example 4 is 700°C, and the obtained iron selenide / carbon composite material is Fe7Se8 / C. The diffraction peak of the sample is consistent with the standard colorimetric card of Fe7Se8 (JCPDS NO:97-000-8048), and it has diffraction peaks of all crystal planes of Fe7Se8. The iron selenide of this material is a pure phase Fe7Se8 of the hexagonal system.

[0047] Figure 2 The XRD comparison diagrams of the composite materials prepared under different feeding molar ratios of ferric citrate and selenium powder and calcination treatment temperatures (the samples in the figure are named according to their corresponding feeding molar ratios and calcination treatment temperatures).

[0048] Combine Figure 2 From the experimental results of (a) to (d), we can find that: when the molar ratio of ferric citrate to selenium powder is higher than 1:3, when the calcination temperature is 400℃, the reaction process is mainly dominated by chemical kinetics, and the iron selenide of the obtained iron selenide / carbon composite material tends to form stable FeSe2; when the calcination temperature rises to 500℃, due to the Se -1 Ions begin to undergo disproportionation reaction, and some lose e - The electrons are converted into selenium and escape (orange-red powder can be seen at both ends of the quartz tube during the experiment), and part of them are converted into low-valent Se 2- ions, forming FeSe2 / C and Fe3Se4 / C mixed phase composite materials, from Figure 2(b) It can be seen that the peak corresponding to FeSe2 is stronger than that of Fe3Se4 at this time, indicating that Se should still be mainly in the form of -1 valence; when the calcination temperature reaches 600℃, the disproportionation reaction continues to strengthen, and a pure phase Fe3Se4 / C composite material is generated. When the calcination temperature reaches 700℃, Se mainly exists in the form of -2 valence, generating Fe7Se8 / C composite material.

[0049] When the molar ratio of ferric citrate to selenium powder is below 1:3, the reaction process is influenced by both the calcination temperature and the selenium concentration. At a molar ratio of 1:1.5, at 400°C, the low selenium content prevents the formation of highly selenized FeSe2 / C, favoring a low-selenization product (Fe3Se4 / C) with poor crystallinity. However, when the iron-selenium ratio rises to 1:2, the crystallinity of the Fe3Se4 / C product improves due to the increased selenium content. When the iron-selenium ratio rises further to 1:3, the limited influence of selenium content in the system is reduced, and the product becomes primarily highly selenized FeSe2 / C. Similar trends are observed at other calcination temperatures, such as 500°C, 600°C, and 700°C. When the calcination temperature reaches 700℃, under the conditions of satisfying thermodynamic formation conditions and sufficient raw material selenium (the molar ratio of ferric citrate to selenium powder is higher than 1:3), the product in the system is mainly Fe7Se8 / C. However, under the condition of insufficient selenium content (the molar ratio of ferric citrate to selenium powder is lower than 1:3), the reaction tends to produce iron selenide FeSe with lower selenization degree. The iron selenide phase of the obtained iron selenide / carbon composite material shows a mixed phase of Fe7Se8 and FeSe, which is clearly shown in the XRD spectrum ( Figure 2 (d)).

[0050] Therefore, based on the above results, it can be concluded that the degree of selenization of the iron selenide / carbon composite is influenced by both the selenium powder concentration and the calcination temperature. When the ratio of ferric citrate to selenium powder is higher than 1:3, the calcination temperature is the dominant factor affecting the reaction. As the calcination temperature gradually increases, the degree of selenization of the iron selenide in the resulting iron selenide / carbon composite decreases, and the iron selenide exhibits single phases such as FeSe2, Fe3Se4, and Fe7Se8, or mixed phases of two adjacent degrees of selenization. Preferably, when the feed ratio of ferric citrate to selenium powder is in the range of 1:(3-5) and the calcination temperature is one of 400°C, 600°C, and 700°C, pure phases of FeSe2, Fe3Se4, and Fe7Se8 can be obtained. In the temperature range between these temperatures, a mixed phase of two iron selenides of adjacent temperatures is obtained; and when the feed ratio of ferric citrate to selenium powder is lower than 1:3 and greater than 1:1.5, the reaction product is affected by both the selenium content and the calcination temperature, tending to generate an iron selenide / carbon composite material with a low degree of selenization; preferably, when the feed ratio of ferric citrate to selenium powder is as low as 1:1.5 and the calcination temperature is 700°C, a FeSe / C material with a low degree of selenization appears in the formed iron selenide / carbon composite material; the present invention realizes the controllable preparation of iron selenide / carbon composite materials with different degrees of selenization through the coordinated regulation of the feed ratio of ferric citrate and selenium powder and the calcination temperature.

[0051] like Figure 3 As shown, the present invention selected the reaction materials of Example 1 (ferric citrate and selenium powder in a molar ratio of 1:3) and conducted thermogravimetric (TG) analysis under a nitrogen atmosphere, and a thermogravimetric differential (DTG) curve was plotted. The DTG curve shows four significant weight loss peaks near 189°C, 342°C, 574°C, and 788°C, and four distinct weight loss intervals within the TG curve (weight loss rates of 16.56%, 24.07%, 8.14%, and 7.93%, respectively). In the first weight loss range (before 200℃), it is mainly considered to be caused by the volatilization of the adsorbed water and crystal water of the ferric citrate in the raw material. In the second weight loss range (200℃ to 400℃), a slight increase in weight was found at around 200℃ to 300℃, which may be due to the thermal decomposition of hydroxyl groups in ferric citrate. With the formation of Fe2O3 and pyrolytic carbon, SeO2 was also produced. Then (300℃ to 400℃), as the reaction temperature increased, Se began to sublime rapidly and combined with Fe to form FeSe2. In this process, the weight decreased significantly due to the large amount of Se sublimation. At (400℃ to 500℃), due to the large amount of Se sublimation loss mentioned above, the Se in FeSe2 was mainly lost. -1The ions begin to undergo disproportionation reaction and develop towards the direction of generating products with lower degree of selenization, but are limited by thermodynamics, so only a small amount of FeSe2 begins to transform into Fe3Se4 (with Figure 1 (b) The peak corresponding to FeSe2 is more intense than that of Fe3Se4); in the third weight loss zone (500℃ to 600℃) and the fourth weight loss zone (600℃ to 800℃), due to the continuous increase in reaction temperature, Se -1 The ions undergo continuous disproportionation reactions, losing e electrons to escape into elemental selenium and continuously developing into products with low degrees of selenization. The final product is Fe2O3, with a reaction residue percentage of 39.89%. Its weight changes only slightly as the pyrolysis temperature reaches 800°C and increases to 1000°C, indicating that the pyrolysis reaction is essentially complete at around 800°C. The thermal analysis curves reveal the possible temperatures at which different degrees of selenization form, which are generally consistent with the material synthesis conditions. This further confirms that the preparation method of the iron selenide / carbon composite material provided by the present invention can achieve the controllable preparation of iron selenide / carbon composite materials with different degrees of selenization by regulating the feed ratio of ferric citrate and selenium powder and the calcination temperature.

[0052] Performance Testing

[0053] In order to elaborate on the present invention in detail, the present invention selects the iron selenide / carbon composite materials prepared at different calcination temperatures provided in the above Examples 1 to 4 for structural characterization, and performs performance tests on them as negative electrode materials for lithium-ion batteries and sodium-ion batteries, respectively. The results are shown below. Among them, the samples of Examples 1 to 4 are named 400-FeSe, 500-FeSe, 600-FeSe, and 700-FeSe according to the calcination treatment temperatures in the examples.

[0054] (1) Structural characterization

[0055] Figure 4 is the XPS spectrum of 400-FeSe in Example 1; the full XPS spectrum is as follows Figure 4 As shown in (a), Se 3d, C 1s, O 1s, and Fe 2p peaks are clearly observed, and there are also a large number of Se Auger peaks. The high-resolution XPS spectrum of C is shown in Figure 4 As shown in (b), the main peak of C1s is located at 284.8eV, which corresponds to the C-C bond between sp2 hybridized carbon atoms; and the peak at 287.42eV should be the C=O bond produced by the oxidation of O2 in the air and the surface of the material. Oxidation peaks can also be observed in the high-resolution spectra of subsequent elements. The high-resolution XPS spectrum of Fe is shown in Figure 2. Figure 4 As shown in (c), due to the high spin of Fe ions, two pairs of asymmetric split peaks are split, namely Fe 2+ (2p 3 / 2Located at 709.28eV, 2p 1 / 2 Located at 717.73eV), Fe 3+ (2p 3 / 2 Located at 710.08eV, 2p 1 / 2 Located at 723.43eV). Due to the influence of O2 on the surface of the material, an Fe2O3 oxidation peak is formed at 711.13eV, which is similar to the Figure 4 (d) The spin splitting of Se 3d in the Se spectrum shown 3 / 2 (55.56 eV) and 3d 5 / 2 (56.41eV), and in the high-resolution image of Se, oxidized SeO can be seen at 58.88eV. x The results show that the chemical valence of the material is basically consistent with the XRD experimental analysis.

[0056] Figures 5-6 The SEM images of 400-FeSe, 500-FeSe, 600-FeSe, and 700-FeSe of Examples 1 to 4, respectively, can well reflect the morphology of FeSe2 / C pure phase, FeSe2 / C and Fe3Se4 / C mixed phase, Fe3Se4 / C pure phase, and Fe7Se8 / C pure phase composite materials; the composite materials with different degrees of selenization present a three-dimensional block structure morphology formed by aggregation of nanoparticles. The nanoparticles can provide a shorter lithium ion transmission path, and the three-dimensional structure can provide a stable framework, which is more conducive to structural stability; with the continuous deepening of the Se disproportionation reaction and the increase of the reaction temperature, the crystal particles of the composite materials formed in Examples 1 to 4 continue to decrease as a whole. Due to recrystallization between the precursors, the original large particles become agglomerated small particles, the agglomeration phenomenon is more significant, and the formed agglomerated particles have high crystallinity, and the corresponding XRD diffraction pattern is clearer and the peak is stronger.

[0057] Figure 7 (ad) are EDS images of 400-FeSe, 500-FeSe, 600-FeSe, and 700-FeSe, respectively. The presence of Fe, Se, and C elements can be observed from the figures, and iron and selenium elements are evenly distributed. The Fe / Se ratio in the detection data continues to decrease, which is consistent with the continuous decrease in the degree of selenization in the synthetic material.

[0058] (2) Electrochemical performance test

[0059] Figure 8 The charge-discharge performance test curves of 400-FeSe, 500-FeSe, 600-FeSe, and 700-FeSe as lithium battery negative electrode materials for the 2nd and 3rd cycles and the 98th and 99th cycles are shown in Figure 2. The results show that the specific capacity of 400-FeSe in the 2nd and 3rd cycles is 711.7 mAh g-1 and 701.3mAh·g -1 By the 98th and 99th cycles, the specific capacity dropped to 261.7 mAh g -1 and 264.6 mAh g -1 As the calcination temperature of the samples increased, the samples calcined below 600°C showed a continuous upward trend (500-FeSe: 701.4 mAh·g in the second and third cycles). -1 and 700.6mAh·g -1 , 395mAh·g at 98th and 99th cycles -1 and 394.1mAh·g -1 600-FeSe: 745.6 mAh g in the second and third cycles -1 and 735.9mAh·g -1 At the 98th and 99th cycles, 643.8 mAh g -1 and 639.9mAh·g -1 ), but after the calcination temperature was raised to above 600 °C, the specific capacity of the sample showed a significant attenuation (the 2nd and 3rd cycles of 700-FeSe were 671.7 mAh g -1 and 642.7mAh·g -1 At the 98th and 99th cycles, 62.9 mAh g -1 and 62.1mAh·g -1 ), this is because the introduction of Se is beneficial to the interfacial lithium energy storage of the material, thereby improving the capacity, but too high a sintering temperature will induce an increase in the size of the material, which is not conducive to capacity improvement, so 600-FeSe has the highest capacity.

[0060] Figure 9 The charge-discharge performance of 400-FeSe, 500-FeSe, 600-FeSe, and 700-FeSe as negative electrode materials for sodium ion batteries at the 2nd and 3rd cycles and the 98th and 99th cycles. 500-FeSe has the best performance: at the 2nd and 3rd cycles, the specific capacities are 360.87 and 35.9 mAh g, respectively. -1 and 352.1 735.9 mAh g -1 By the 98th and 99th cycles, the specific capacity dropped to 243.97735.9 mAh g -1 and 240.8 735.9 mAh g -1 .

[0061] Figure 10 The 400-FeSe of Example 1 was subjected to different scanning rates (0.4-1 mV s -1) shows that the material has good kinetic data and its capacity contribution mainly comes from the non-Faradaic capacitance contribution of the material. Due to its high selenium content, the non-Faradaic capacitance contribution is relatively large.

[0062] Figure 11 The battery rate performance of 400-FeSe and 600-FeSe at different current rates can be seen. When the current ratio is 1:2:4:8 (400-FeSe composite material at 0.2Ag -1 , 0.4Ag -1 , 0.8Ag -1 and 1.6Ag -1 When the discharge capacity is 652.1mAh·g -1 、656.5mAh·g -1 、606.9mAh·g -1 , 443.6mAh·g -1 ;600-FeSe composite material in 0.2Ag -1 , 0.4Ag -1 , 0.8Ag -1 and 1.6Ag -1 When the discharge capacity is 783.4 mAh g -1 , 717.1mAh·g -1 , 589.9mAh·g -1 , 426.4mAh·g -1 ), the capacity of the 600-FeSe composite material in the first half of the test (at low current) is better than that of the 400-FeSe composite material.

[0063] In summary, the present invention uses organic acid iron as the iron source and carbon source, and successfully prepares an iron selenide / carbon composite material by a solid phase method in a tubular furnace filled with argon as a protective atmosphere. In the above embodiment, ferric citrate can also be replaced with other organic acid irons such as ferrocene and ferric tartaric acid, and an iron selenide / carbon composite material with similar performance can also be obtained; the iron selenide / carbon composite material prepared by the preparation method provided by the present invention has good performance as a negative electrode material for lithium ion batteries, among which FeSe2 / C and Fe3Se4 / C perform best. The present invention realizes the controllable preparation of iron selenide / carbon composite materials with different degrees of selenization by coordinated regulation of the feed ratio of ferric citrate and selenium powder and the calcination treatment temperature in the preparation step; the above embodiments of the present invention are only examples for clearly illustrating the present invention, and are not limitations on the embodiments of the present invention. For ordinary technicians in the field, other different forms of changes or modifications can be made on the basis of the above description. It is impossible to enumerate all the embodiments here. It is obvious that all the technical solutions of the present invention are extended.

Claims

1. A method for preparing an iron selenide / carbon composite material, characterized in that: The organic acid iron and selenium powder are ball-milled and mixed in a molar ratio of 1:(1.5-5), and the mixture is calcined at 400-700° C. under an argon atmosphere to obtain the iron selenide / carbon composite material.

2. The method for preparing the iron selenide / carbon composite material according to claim 1, wherein The organic acid iron is one of ferric citrate, ferrocene and ferric tartrate.

3. The method for preparing the iron selenide / carbon composite material according to claim 1, wherein: The specific steps of ball milling and mixing are as follows: pouring organic acid iron and selenium powder into a ball mill jar, adding anhydrous ethanol and agate balls thereto, ball milling and mixing in a ball mill for at least 4 hours, and then drying and crushing the obtained mixture.

4. The method for preparing the iron selenide / carbon composite material according to claim 1, wherein: The organic acid iron and selenium powder are added in a molar ratio of 1:(3-5), the calcination temperature is one of 400° C., 500° C., 600° C. and 700° C., and the calcination time is 4 hours.

5. The method for preparing the iron selenide / carbon composite material according to claim 1, wherein: The organic acid iron and selenium powder are added in a molar ratio of 1:1.5, the calcination temperature is 700° C., and the holding time is 4 hours.

6. An iron selenide / carbon composite material, characterized in that The iron selenide / carbon composite material is prepared by the preparation method of the iron selenide / carbon composite material according to any one of claims 1 to 4.

7. The iron selenide / carbon composite material according to claim 6, characterized in that The iron selenide / carbon composite material is represented by the chemical formula Fe x Se y / C indicates that it presents a three-dimensional bulk structure morphology formed by the aggregation of nanoparticles, among which Fe x Se y stands for iron selenide, Fe x Se y It is a pure phase of FeSe, Fe7Se8, Fe3Se4, FeSe2 or a mixed phase of FeSe, Fe7Se8, Fe3Se4, FeSe2.

8. The iron selenide / carbon composite material according to claim 6, characterized in that The iron selenide of the iron selenide / carbon composite material is one of pure phase FeSe2, Fe3Se4, and Fe7Se8.

9. The iron selenide / carbon composite material according to claim 6, characterized in that The iron selenide of the iron selenide / carbon composite material is a mixed phase of FeSe2 and Fe3Se4 or a mixed phase of FeSe and Fe7Se8.

10. Use the iron selenide / carbon composite material according to claims 6 to 9 as a negative electrode material for a lithium ion battery or a sodium ion battery.

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