Preparation method of coal gangue-based red phosphorus-doped C / SiO x composite lithium battery anode material

Abstract

The present invention discloses a preparation method of a coal gangue-based red phosphorus-doped C / SiO x composite lithium battery anode material, belonging to the technical field of battery materials. In the present invention, coal gangue is used as a raw material, and after being soaked in acid solution, metal impurity-removed coal gangue is obtained. After being soaked in hot alkali, silicon-removed coal gangue is obtained. Then, after being activated by acid solution, a hierarchical porous C / SiO x composite material is obtained. Finally, a coal gangue-based red phosphorus-doped C / SiO x composite lithium battery anode material is prepared by the evaporation condensation method. The coal gangue-based red phosphorus-doped C / SiO x composite lithium battery anode material prepared by the present invention has both a relatively high reversible specific capacity, a relatively low electrode reaction resistance, good rate performance, excellent cycle stability and a relatively high initial Coulomb efficiency. At the same time, all the waste liquids generated in the preparation process of the present invention can be used to synthesize nitrogen-phosphorus-potassium compound fertilizers, and the whole process has zero emissions and zero pollution, which conforms to the development concept of green environmental protection.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and particularly relates to a preparation method of a coal gangue-based red phosphorus-doped C / SiO x composite lithium battery anode material. Background Technique

[0002] Coal gangue is a solid waste generated during coal mining and washing processes, and its output accounts for about 18% of the annual coal output. With the increasing annual coal output, the annual discharge of coal gangue is also increasing continuously. At present, the main utilization methods of coal gangue are: coal gangue power generation, production of building materials products, roadbed paving, land reclamation, treatment of subsidence areas, and underground filling for coal replacement, etc. The technology of underground filling and replacement of coal with coal gangue realizes that coal gangue does not rise to the surface and does not occupy land. However, affected by factors such as transportation, market environment, and power generation installed capacity limitations, the comprehensive utilization rate of coal gangue in some areas is not high, and a large amount of coal gangue is stacked in the open air, occupying a large amount of land area and causing waste of resources.

[0003] Coal gangue is mainly composed of elements such as C (28.92%), H, O, N, S, etc. and inorganic minerals. The inorganic components are mainly Al 2 O 3 (22.76%) and SiO 2 (34.16%). After coal gangue is treated by acid soaking to remove metal oxides, the main components of the obtained solid residue are amorphous carbon and silicon dioxide. Among them, the three elements of C, Si, and O are evenly distributed, and no complex carbon coating process is required. Utilizing these inherent characteristics of acid-treated coal gangue, porous C / SiO x composite materials are prepared in-situ. Using the obtained porous C / SiO x composite materials as the anode of lithium-ion batteries is an effective method for synthesizing high-performance SiO x anode materials.

[0004] C / SiO x composite materials synthesized by chemical reagents or in-situ synthesis of biomass all have high reversible specific capacity, low electrode reaction resistance, good rate performance, and excellent cycle stability. However, the first Coulombic efficiency of these materials is less than 60%. The first Coulombic efficiency of the anode material directly affects the capacity of the cathode material and the overall design of the battery; the low first Coulombic efficiency is one of the main reasons why C / SiO x materials cannot be widely used. The main reasons for the low first Coulombic efficiency of C / SiO x materials are three: ① During the first lithium intercalation process of C / SiO x materials, the Li 4 SiO 4 and Li 2 O consumed by the formation of inert components+ The more, the lower the initial Coulombic efficiency; ② For bulk non-porous C / SiO x materials, due to the existence of irreversible lithium storage sites, after the first lithiation, part of the Li + is difficult to be de-lithiated, resulting in a lower initial Coulombic efficiency; ③ During the first lithiation process, a solid electrolyte interface (SEI) film is formed on the surface of the C / SiO x material, which consumes part of the Li + , increasing the irreversible capacity of the first charge-discharge and reducing the initial Coulombic efficiency of the electrode material. Therefore, how to prepare an electrode material that has a high reversible specific capacity, a low electrode reaction resistance, good rate performance, excellent cycle stability, and at the same time has a high initial Coulombic efficiency is a technical problem that needs to be solved urgently at present. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention provides a method for preparing a red phosphorus-doped C / SiO x composite lithium battery anode material with a high initial Coulombic efficiency by using widely existing coal gangue solid waste through a simple process. The prepared coal gangue-based red phosphorus-doped C / SiO x composite lithium battery anode material has both a high reversible specific capacity, a low electrode reaction resistance, good rate performance, excellent cycle stability, and a high initial Coulombic efficiency.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] One of the objects of the present invention is to provide a preparation method of a coal gangue-based red phosphorus-doped C / SiO x composite lithium battery anode material. Using coal gangue as a raw material, it is successively subjected to acid solution soaking, hot alkali soaking, and acid solution activation treatment, and then red phosphorus is used to prepare the coal gangue-based red phosphorus-doped C / SiO x composite lithium battery anode material by evaporation condensation method.

[0008] Further, it includes the following steps:

[0009] (1) Crush the coal gangue, soak it in acid solution to obtain metal impurity-removed coal gangue, soak it in hot alkali to obtain silicon-removed coal gangue, and then activate it with acid solution to obtain hierarchical porous C / SiO x composite material;

[0010] (2) Place red phosphorus at the bottom of a porcelain boat, and spread the hierarchical porous C / SiO x composite material obtained in step (1) above red phosphorus. The hierarchical porous C / SiO xThe mass ratio of the composite material to red phosphorus is 1:1 to 3; the porcelain boat is placed in a quartz tube and heated to 550 °C at a heating rate of 5 °C / min in a nitrogen atmosphere and left standing for 8 h, then cooled to 260 °C and held for 20 h, and after further cooling to room temperature, it is washed 2 to 3 times with CS 2 and absolute ethanol, and then dried in a vacuum drying oven at 60 °C for 12 h to obtain a coal gangue-based red phosphorus-doped C / SiO x (RP@C / SiO x ) composite lithium battery anode material, where 0 < x < 2.

[0011] Furthermore, the particle size requirement for the crushing in step (1) is to pass through a 100-200 mesh sieve; the acid solution soaking is to soak the coal gangue in a 0.5-2 mol / L nitric acid solution for 24-48 h.

[0012] Furthermore, the mass-volume ratio of the coal gangue to the nitric acid solution is 1 g:4-7 mL; after the acid solution soaking is completed, filtration is carried out, and then the filter residue is washed with distilled water until neutral and dried to obtain coal gangue with metal impurities removed and acid-containing washing waste liquid.

[0013] Furthermore, the hot alkali soaking in step (1) is to mix the coal gangue with metal impurities removed with KOH and place it in deionized water, and soak it at 70 °C for 24 h.

[0014] Furthermore, the mass ratio of the coal gangue with metal impurities removed to KOH is 1:2; after the hot alkali soaking is completed, filtration is carried out, and then the filter residue is washed with distilled water until neutral and dried to obtain silicon-removed coal gangue and alkali-containing washing waste liquid.

[0015] Furthermore, the acid solution activation in step (1) is to soak the silicon-removed coal gangue in concentrated phosphoric acid for 48 h, dry it and then put it into a tube furnace with nitrogen as the protective gas for carbonization activation, and then wash it with distilled water and nitric acid to remove the activator to obtain a hierarchical porous C / SiO x composite material and washing waste liquid.

[0016] Furthermore, the mass ratio of the silicon-removed coal gangue to concentrated phosphoric acid is 1:4; the carbonization activation is carried out at 600 °C for 2 h.

[0017] Furthermore, for the waste liquid generated after washing with CS 2 and absolute ethanol in step (2), its alcohol and CS 2 are removed by distillation, and then it is mixed with the acid-containing washing waste liquid, alkali-containing washing waste liquid and washing waste liquid generated by acid solution activation in step (1) until neutral, and distilled to obtain a nitrogen-phosphorus-potassium compound fertilizer; the distilled alcohol solution and CS 2 can be recycled for use in step (2), and the distilled water can be recycled for each step.

[0018] The second object of the present invention is to provide a coal gangue-based red phosphorus-doped C / SiO x composite lithium battery anode material prepared by the preparation method described above.

[0019] The third object of the present invention is to provide an application of the coal gangue-based red phosphorus-doped C / SiO x composite lithium battery anode material in the preparation of lithium ion batteries.

[0020] Advantages of the present invention:

[0021] In the present invention, coal gangue is soaked in nitric acid solution to remove metal impurities, and then the acid-treated coal gangue is soaked by alkali heating to remove part of silicon dioxide and aluminum oxide in the acid-soaked coal gangue, and its silicon dioxide content is controlled to obtain desilicated coal gangue with controllable silicon dioxide content. Then, the desilicated coal gangue is activated with concentrated H 3 PO 4 to prepare a hierarchical porous C / SiO x composite lithium battery anode material, which is a hierarchical porous material composed of macropores, mesopores and micropores, has a relatively thin pore wall, can form an interconnected porous network structure, avoid the generation of irreversible lithium intercalation sites, and can improve the initial Coulomb efficiency of the material to a certain extent.

[0022] The hierarchical porous C / SiO x composite material and red phosphorus of the present invention are used to prepare a coal gangue-based red phosphorus-doped C / SiO x composite lithium battery anode material. During the preparation process, red phosphorus penetrates into the surface and inner pore walls of the porous C / SiO x , and forms P-O bonds and P-C bonds with the C skeleton, which is beneficial to the formation of a dense thin solid electrolyte interface layer. SiO x in the hierarchical porous C / SiO x composite material reacts with red phosphorus at high temperature to generate SiP 2 and SiP 2 O 7 . SiP 2 O 7 has a cubic structure, with SiO 6 octahedrons at the corners and P 2 O 7 at the edges. This structure can provide many proton bonding positions and transport paths, which is beneficial to have more Li + storage positions and high electronic conductivity under anhydrous conditions. SiP 2 has a three-dimensional cubic crystal structure, which is beneficial to the diffusion and accommodation of Li + . SiP 2 reacts with Li + to generate Li 13 Si4 and Li 3 P, which are reversible phases. Therefore, irreversible products such as Li x O and Li 2 O and Li 4 SiO 4 during the lithiation process of the electrode are avoided, thus effectively improving its initial Coulombic efficiency. In addition, the porous C structure can not only shorten the transmission channel of Li + , but also relieve the mechanical stress generated by the volume expansion and contraction of Li + during the insertion / extraction process.

[0023] By controlling the penetration amount of red phosphorus, optimizing the pore structure of the material, the residual amount of SiO x , the P-O bonds and P-C bonds on the material surface, the present invention improves the initial Coulombic efficiency without affecting other electrochemical properties. The coal gangue-based red phosphorus-doped C / SiO x composite lithium battery anode material prepared by the present invention has both a high reversible specific capacity, a low electrode reaction resistance, good rate performance, excellent cycle stability and a high initial Coulombic efficiency. At the same time, all the waste liquids generated in the preparation process of the present invention can be used to synthesize nitrogen, phosphorus and potassium compound fertilizers, and the whole process is zero-emission and zero-pollution, which conforms to the development concept of green environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0025] Figure 1 are the morphology diagrams of Example 1 and Comparative Example 1; among them, a and b are the scanning electron microscope images of Comparative Example 1; c and d are the scanning electron microscope images of Example 1, e is the energy spectrum diagram of C, O, P and Si, f is the high-resolution electron microscope (HRTEM) image, and g and h are the corresponding selected area electron diffraction (SAED) patterns of Example 1;

[0026] Figure 2 are the physical property detection diagrams of the samples of Examples 1-3 and Comparative Example 1; among them, a is the X-ray diffraction spectrum, b is the Raman spectrum, c is the nitrogen adsorption / desorption isotherm, and d is the pore size distribution;

[0027] Figure 3Performance detection diagrams of the samples of Examples 1-3 and Comparative Example 1; a is the cycling performance at a current density of 0.1 A / g for 100 cycles; b is the coulombic efficiency for the first three cycles at a current density of 0.1 A / g; c is the rate performance; d is the Nyquist plot after 140 cycles;

[0028] Figure 4 For the preparation process of the coal gangue-based red phosphorus-doped C / SiO x composite lithium battery anode material. Detailed implementation manners

[0029] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below in conjunction with the embodiments.

[0030] Example 1

[0031] (1) Crush the coal gangue and pass it through a 150-mesh sieve, soak it in a 1 mol / L nitric acid solution for 36 h, the mass-volume ratio of the coal gangue to the nitric acid solution is 1 g:5 mL. After the acid solution soaking is completed, filter it, and then wash the filter residue with distilled water until it is neutral and dry to obtain coal gangue with metal impurities removed;

[0032] (2) Mix the coal gangue with removed metal impurities and KOH in a mass ratio of 1:2, and place it in deionized water, soak it at 70 °C for 24 h. After the hot alkali soaking is completed, filter it, and then wash the filter residue with distilled water until it is neutral and dry to obtain coal gangue with silicon removed;

[0033] (3) Soak the coal gangue with silicon removed in concentrated phosphoric acid for 48 h, the mass ratio of the coal gangue with silicon removed to the concentrated phosphoric acid is 1:4. After drying, put it into a tubular furnace with nitrogen as the protective gas, carbonize and activate it at 600 °C for 2 h, and then wash it with distilled water and nitric acid to obtain a hierarchical porous C / SiO x composite material;

[0034] (4) Place the red phosphorus at the bottom of the porcelain boat, spread the hierarchical porous C / SiO x composite material obtained in step (3) above the red phosphorus, the mass ratio of the hierarchical porous C / SiO x composite material to the red phosphorus is 1:1.5; put the porcelain boat into the quartz tube, heat it to 550 °C at a heating rate of 5 °C / min in a nitrogen atmosphere, keep it standing for 8 h, then cool it to 260 °C and keep it warm for 20 h. After continuing to cool to room temperature, wash it with CS 2 and absolute ethanol, and then dry it at 60 °C for 12 h to obtain a coal gangue-based red phosphorus-doped C / SiO x composite lithium battery anode material. Note: The obtained sample is named S3 / 2.

[0035] Example 2

[0036] (1) Crush the coal gangue through a 100-mesh sieve, soak it in a 0.5 mol / L nitric acid solution for 24 h, with the mass-volume ratio of coal gangue to nitric acid solution being 1 g:4 mL. After the acid solution soaking is completed, filter it, and then wash the filter residue with distilled water until neutral and dry to obtain coal gangue with metal impurities removed.

[0037] (2) Mix the coal gangue with metal impurities removed and KOH in a mass ratio of 1:2, place them in deionized water, soak at 70 °C for 24 h. After the hot alkali soaking is completed, filter it, and then wash the filter residue with distilled water until neutral and dry to obtain coal gangue with silicon removed.

[0038] (3) Soak the coal gangue with silicon removed in concentrated phosphoric acid for 48 h, with the mass ratio of coal gangue with silicon removed to concentrated phosphoric acid being 1:4. After drying, put it into a tube furnace with nitrogen as the protective gas, carbonize and activate at 600 °C for 2 h, and then wash with distilled water and nitric acid to obtain hierarchical porous C / SiO x Composite material;

[0039] (4) Place red phosphorus at the bottom of a porcelain boat, spread the hierarchical porous C / SiO x Composite material obtained in step (3) above red phosphorus, with the mass ratio of hierarchical porous C / SiO x Composite material to red phosphorus being 1:1; put the porcelain boat into a quartz tube, heat it in a nitrogen atmosphere at a heating rate of 5 °C / min to 550 °C, let it stand for 8 h, then cool to 260 °C and keep it warm for 20 h. After continuing to cool to room temperature, wash with CS 2 And absolute ethanol, and then dry at 60 °C for 12 h to obtain a coal gangue-based red phosphorus-doped C / SiO x Composite lithium battery anode material. Note: The obtained sample is named S1 / 1.

[0040] Example 3

[0041] (1) Crush the coal gangue through a 200-mesh sieve, soak it in a 2 mol / L nitric acid solution for 48 h, with the mass-volume ratio of coal gangue to nitric acid solution being 1 g:7 mL. After the acid solution soaking is completed, filter it, and then wash the filter residue with distilled water until neutral and dry to obtain coal gangue with metal impurities removed.

[0042] (2) Mix the coal gangue with metal impurities removed and KOH in a mass ratio of 1:2, place them in deionized water, soak at 70 °C for 24 h. After the hot alkali soaking is completed, filter it, and then wash the filter residue with distilled water until neutral and dry to obtain coal gangue with silicon removed.

[0043] (3) Soak the coal gangue with silicon removed in concentrated phosphoric acid for 48 h, with the mass ratio of coal gangue with silicon removed to concentrated phosphoric acid being 1:4. After drying, put it into a tube furnace with nitrogen as the protective gas, carbonize and activate at 600 °C for 2 h, and then wash with distilled water and nitric acid to obtain hierarchical porous C / SiOx Composite material;

[0044] (4) Place red phosphorus at the bottom of the porcelain boat, and lay the hierarchical porous C / SiO x composite material from step (3) above the red phosphorus. The mass ratio of the hierarchical porous C / SiO x composite material to red phosphorus is 1:2; place the porcelain boat into a quartz tube, heat it to 550 °C at a heating rate of 5 °C / min in a nitrogen atmosphere, keep it standing for 8 h, then cool it to 260 °C and keep it warm for 20 h. After continuing to cool to room temperature, wash it with CS 2 and absolute ethanol, and then dry it at 60 °C for 12 h to obtain a coal gangue-based red phosphorus-doped C / SiO x composite lithium battery anode material. Note: The obtained sample is named S1 / 2.

[0045] Comparative Example 1

[0046] Same as Example 1, except that red phosphorus is not added. Note: The obtained hierarchical porous C / SiO x composite material sample is named CRH.

[0047] Figure 1 are the morphology diagrams of Example 1 and Comparative Example 1; among them, a and b are the scanning electron microscope images of Comparative Example 1; c and d are the scanning electron microscope images of Example 1, e is the energy spectrum diagram of C, O, P and Si, f is the high-resolution electron microscope (HRTEM) image, and g and h are the corresponding selected area electron diffraction (SAED) patterns of Example 1;

[0048] The electrode materials before and after modification are both black blocks with irregular shapes ( Figure 1 a and 1c). The hierarchical porous C / SiO x composite material has distinct edges and corners, clear contours, and no flocculants on the surface ( Figure 1 a). In addition, the hierarchical porous C / SiO x composite material has a hierarchical pore structure with a relatively thin pore wall, which indicates that when the desilicated coal gangue is activated and carbonized with H 3 PO 4 a hierarchical porous C / SiO structure can be obtained ( x ( Figure 1 b). After embedding red phosphorus (RP), flocs appear on the surface of S3 / 2, with blurred edges and corners ( Figure 1 c). The micropores and mesopores on the surface of S3 / 2 disappear, and red phosphorus with a diameter of dozens of nanometers adheres to the surface, resulting in poor surface conductivity ( Figure 1 d). Elemental analysis shows that the elements C, O, P and Si are evenly distributed in S3 / 2 ( Figure 1 e), proving that red phosphorus has successfully and evenly adhered to the surface and inner pore walls of S3 / 2. FromFigure 1 From the HRTEM image of f, it can be seen that the lattice fringes in the crystalline region are consistent with those of pure red phosphorus (004) and (012), SiP 2 (211) and (111), and SiP 2 O 7 (211) and (111), which is consistent with the test results of X-ray diffraction. In addition, the corresponding SAED pattern with diffraction spots ( Figure 1 g) was also detected, which can be attributed to the (012) and (104) planes of red phosphorus, SiP 2 of (211) and (311) planes, and SiP 2 O 7 of (211) and (111) planes, further confirming the presence of pure red phosphorus, SiP 2 and SiP 2 O 7 in sample S3 / 2. In addition, there are no obvious bright spots in the SEAD pattern of the amorphous region ( Figure 1 h), indicating that the C / SiO x skeleton is amorphous.

[0049] Table 1 Element contents of samples in Examples 1-3 and Comparative Example 1.

[0050]

[0051] Table 2 Pore structure parameters of samples in Examples 1-3 and Comparative Example 1.

[0052]

[0053]

[0054] Figure 2 are the performance detection diagrams of samples in Examples 1-3 and Comparative Example 1; among them, a is the X-ray diffraction spectrum, b is the Raman spectrum, c is the nitrogen adsorption / desorption isotherm, and d is the pore size distribution;

[0055] The phase composition of the samples was analyzed using an X-ray diffractometer ( Figure 2 a). There is a common overlapping broad peak at 23°, which confirms the presence of amorphous C and amorphous SiO x . In addition, there are two weak peaks at 15° and 34°, which belong to the diffraction peaks of red phosphorus. In addition, the four peaks located at 2θ = 23.0°, 26.4°, 30.1° and 54.9° can be attributed to the (600), (630), (722) and (420) crystal planes of SiP 2 O 7 with relatively high conductivity. The two peaks at 2θ = 35.1° and 38.6° correspond to SiP 2The (210) and (211) crystal planes, which have a cubic crystal structure and a three-dimensional skeleton, facilitate the diffusion of Li + and electrons. All of these indicate that during the red phosphorus infiltration process, silicon dioxide nanoparticles react with red phosphorus to form SiP 2 O 7 and SiP 2 substances. In addition, no diffraction peaks of any other impurities were detected.

[0056] To characterize the C skeletons of red phosphorus-doped C / SiO x and hierarchical porous C / SiO x , Raman scattering spectroscopy tests were carried out ( Figure 2 b). An obvious D band is located at about 1334.8 cm -1 −1, which belongs to the edges and disordered C in the carbon structure. In addition, a visible G band at about 1607.5 cm -1 −1 is attributed to the ordered sp2-hybridized C. The intensity ratio of I D / I G represents the degree of disorder of the graphite structure. The I x / I D / I G of all red phosphorus-doped C / SiO x samples are all greater than the I D / I G of hierarchical porous C / SiO x , and increases with the increase of red phosphorus, indicating that the addition of red phosphorus increases the degree of defects and the distance between the C layer skeletons. The high degree of disorder of the red phosphorus-doped C / SiO x samples is not only suitable for the insertion and extraction of Li + , but also suitable for the diffusion of Li + .

[0057] As shown in Figure 2 c, all red phosphorus-doped C / SiO x and hierarchical porous C / SiO x samples have type-IV curves and related H3-type hysteresis loops, which not only indicate that capillary condensation occurs in their mesopores, but also the coexistence of mesopores and micropores. The presence of mesopores and micropores is conducive to the rapid diffusion of ions, provides a buffer layer to adapt to the volume change inside the carbonaceous materials, and contributes to the structural stability. In addition, the presence of micropores also helps to form red phosphorus-doped C / SiO x samples with a high specific surface area, which provides a sufficient electrode / electrolyte interface for the accumulation of Li + or charges. During the infiltration of red phosphorus into porous C / SiO x , red phosphorus is deposited on the inner walls of the pores of porous C / SiO x , and a small amount reacts with the C skeleton and silicon dioxide. With the increase of red phosphorus, the deposition on porous C / SiOx The more red phosphorus on the inner wall, the corresponding red phosphorus-doped C / SiO x The porosity of the sample is smaller (Table 1). Therefore, for the red phosphorus-doped C / SiO x The specific surface area of the sample gradually decreases with the addition of red phosphorus (Table 2). In addition, with the increase in the amount of red phosphorus, more micropores and mesopores are blocked. Therefore, for the red phosphorus-doped C / SiO x The average pore size of the sample gradually increases with the increase in red phosphorus (Table 2 and Figure 2 d).

[0058] Figure 3 Performance detection diagrams for the samples of Examples 1-3 and Comparative Example 1; a is the cycling performance at a current density of 0.1 A / g for 100 cycles; b is the first three Coulombic efficiencies at a current density of 0.1 A / g; c is the rate performance; d is the Nyquist curve after 140 cycles;

[0059] Porous C / SiO x The electrode has good cycling stability ( Figure 3 a), indicating that the C skeleton of the porous C / SiO x relieves the volume expansion of the SiO x nanoparticles and maintains the structural stability of the material during cycling. Compared with the porous C / SiO x , the reversible capacity of the red phosphorus-doped C / SiO x electrode is significantly improved. In addition, then with the increase in red phosphorus, the reversible specific capacity of these red phosphorus-doped C / SiO x electrodes first increases and then decreases ( Figure 3 a). After 3 cycles, the discharge capacity of the S3 / 2 electrode can reach 1304.9 mA / g at 0.1 A / g and remains at 1147.4 mA / g after 100 cycles, with a capacity retention rate of 87.9%. This data is significantly higher than that of the other two red phosphorus-doped C / SiO x electrodes. There are several reasons for these phenomena: First, after red phosphorus penetrates into the inner wall of the pores of the porous C / SiO x , it is connected to the C skeleton through P-C and P-O bonds. The infiltrated red phosphorus also reacts with the surface of the silica particles to form SiP 2 O 7 and SiP 2 . When these reactions reach their limits, the excess red phosphorus deposits in the channels of the porous C / SiO x . Moreover, with the increase in the amount of red phosphorus used, more and more residual red phosphorus will be present. As is well known, the theoretical specific capacity of red phosphorus is as high as 2596 mAh / g. Therefore, for the red phosphorus-doped C / SiO xThe specific capacity of the electrode should increase with the increase in the remaining amount of red phosphorus. Secondly, with the increase in red phosphorus, the more red phosphorus deposited on the inner wall of porous C / SiO x the smaller the porosity of the corresponding red phosphorus-doped C / SiO x sample. As mentioned above, the high specific surface area provides sufficient electrode / electrolyte interface for the accumulation of ions or charges. Therefore, the specific capacity of the red phosphorus-doped C / SiO x electrode should decrease with the decrease in its specific surface area. Finally, the introduction of red phosphorus generates more defects in the C skeleton of red phosphorus-doped C / SiO x resulting in more Li + storage sites. Therefore, with the increase in the degree of defects in red phosphorus-doped C / SiO x the number of Li + storage sites increases. In summary, these three factors have a synergistic effect on the specific capacity of the red phosphorus-doped C / SiO x electrode. Therefore, among all the composite samples, S3 / 2 has the largest reversible specific capacity.

[0060] The initial discharge specific capacity and charge specific capacity of the S3 / 2 electrode are 2375.6 and 1749.9 mAh / g respectively. Therefore, the first Coulombic efficiency of the S3 / 2 electrode is approximately 73.6% ( Figure 3 b). The Coulombic efficiency of the S3 / 2 electrode in the first three cycles is greater than that of the other three electrodes ( Figure 3 b). On the one hand, the generated SiP 2 O 7 and SiP 2 as reversible phases are beneficial to reducing the content of SiOx, thereby reducing the generation of irreversible substances Li 2 O and Li 4 SiO 4 during the first charge-discharge process, effectively improving its first Coulombic efficiency. On the other hand, the P-O bonds on the surface and inner pore walls of red phosphorus-doped C / SiO x change the morphology and composition of the solid electrolyte interface film, which is beneficial to the formation of a thin and dense solid electrolyte interface film. Therefore, with the increase in red phosphorus, the formation amounts of SiP 2 O 7 and SiP 2 on the surface of SiO x and the number of P-O bonds connected to the C skeleton increase, and thus the first Coulombic efficiency of the red phosphorus-doped C / SiO x electrode increases. However, when the formation reactions of these substances reach the limit, the remaining red phosphorus deposits on the inner pore walls of the red phosphorus-doped C / SiO x sample, covering the P-O bonds. Therefore, in red phosphorus-doped C / SiO xA thick and porous solid electrolyte film has formed on the inner wall of the electrode, which will affect their initial Coulombic efficiency. In summary, red phosphorus-doped C / SiO x The initial Coulombic efficiency of the electrode first increases and then decreases with the increase of red phosphorus.

[0061] Figure 3 c compared the rate performance of red phosphorus-doped C / SiO x and porous C / SiO x electrodes. At each current density, the reversible capacity of the red phosphorus-doped C / SiO x electrode is greater than that of the porous C / SiO x electrode, and shows a trend of first increasing and then decreasing with the increase of the red phosphorus ratio, which is consistent with the results of the cycling performance test. Among them, the S3 / 2 electrode has the largest reversible capacity, and the reversible specific capacities at 0.1 A / g, 0.2 A / g, 0.4 A / g, 0.8 A / g, 1.0 A / g, 1.2 A / g, and 1.6 A / g are 1360.4, 1107.1, 1016.1, 916.7, 876.1, 809.1, and 699.5 mAh / g respectively. When the current density is increased by 16 times, the capacity retention rate can still reach 52.1%. When the current density is restored from 1.6 A / g to 0.1 A / g, the reversible specific capacity of S3 / 2 is basically restored, showing excellent rate performance.

[0062] The electrochemical behavior of the synthesized red phosphorus-doped C / SiO x and porous C / SiO x electrodes was further studied by impedance experiments ( Figure 3 d). The semicircle in the high-frequency region represents the charge transfer resistance (Rct) at the electrode / electrolyte interface, and the oblique line in the low-frequency region represents the Warburg impedance (Zw) during the Li + diffusion process. With the increase of red phosphorus, the semicircle diameters of these electrodes first decrease and then increase, and the S3 / 2 electrode has the smallest Rct value. The smaller Rct value indicates that the P-O bond in the C skeleton may contribute to the formation of a thin and dense solid electrolyte film during cycling, resulting in a smaller Rct. On the other hand, the generated SiP 2 O 7 also plays an important role in improving the conductivity. Therefore, with the increase of red phosphorus, the conductivity of the red phosphorus-doped C / SiO x electrode should gradually increase. However, the small pore volume of the red phosphorus-doped C / SiO x composite material is not conducive to the diffusion of Li + and electrons. Therefore, the conductivity of the red phosphorus-doped C / SiO x electrode first increases and then decreases with the increase of red phosphorus.

[0063] The embodiments described above are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the spirit of the present invention's design, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A preparation method of a coal gangue-based red phosphorus-doped C / SiO x composite lithium battery anode material It is characterized in that Using coal gangue as raw material, successively carry out acid solution soaking, hot alkali soaking and acid solution activation treatment, and then prepare coal gangue-based red phosphorus-doped C / SiO by evaporation condensation method with red phosphorus x Composite lithium battery anode material; it includes the following steps: (1) Crush the coal gangue, soak it in acid solution to obtain coal gangue with metal impurities removed, soak it in hot alkali to obtain coal gangue with silicon removed, and then activate it with acid solution to obtain hierarchical porous C / SiO x composite material; (2) Place red phosphorus at the bottom of the container, and lay the hierarchical porous C / SiO x composite material from step (1) above the red phosphorus. The mass ratio of the hierarchical porous C / SiO x composite material to red phosphorus is 1:1 to 3; heat the container in a nitrogen atmosphere at a heating rate of 5 °C / min to 550 °C, let it stand for 8 h, then cool it to 260 °C and keep it warm for 20 h. After continuing to cool to room temperature, wash it with CS 2 and absolute ethanol, and then dry it at 60 °C for 12 h to obtain a coal gangue-based red phosphorus-doped C / SiO x composite lithium battery anode material. During the preparation process, red phosphorus penetrates into the surface and inner wall of the pores of the porous C / SiO x to form P-O bonds and P-C bonds by connecting with the C skeleton. SiO x reacts with red phosphorus at high temperature to generate SiP 2 and SiP 2 O 7 ; In step (1), the particle size requirement of the pulverization is to pass through a 100-200 mesh sieve; the acid solution soaking is to soak the coal gangue in a 0.5-2 mol / L nitric acid solution for 24-48 h; the mass-volume ratio of the coal gangue to the nitric acid solution is 1 g: 4-7 mL; after the acid solution soaking is completed, filtration is carried out, and then the filter residue is washed with distilled water until neutral and dried to obtain coal gangue with metal impurities removed; In step (1), the hot alkali soaking is to mix the coal gangue with metal impurities removed with KOH, place it in deionized water, and soak it at 70 °C for 24 h; the mass ratio of the coal gangue with metal impurities removed to KOH is 1:2; after the hot alkali soaking is completed, filtration is carried out, and then the filter residue is washed with distilled water until neutral and dried to obtain coal gangue with silicon removed; The acid activation in step (1) is to soak the silicon-removed coal gangue in concentrated phosphoric acid for 48 h, dry it, put it into a tube furnace with nitrogen as the protective gas for carbonization activation, and then wash it with distilled water and nitric acid to obtain a hierarchical porous C / SiO x composite material; the mass ratio of the coal gangue with silicon removed to concentrated phosphoric acid is 1:4; the carbonization activation is carried out at 600 °C for 2 h.

2. A coal gangue-based red phosphorus-doped C / SiO composite lithium battery anode material prepared by the preparation method according to claim 1 x ​ 3. Application of the coal gangue-based red phosphorus-doped C / SiO x composite lithium battery anode material in the preparation of lithium-ion batteries.

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