Iron / nitrogen co-doped silicon monoxide composite negative electrode material and preparation method thereof

Abstract

The invention relates to the technical field of lithium ion battery negative electrode materials, and discloses an iron / nitrogen co-doped silicon monoxide composite negative electrode material and a preparation method thereof.The method comprises the steps that in an alkaline buffer solution, dopamine is subjected to a self-polymerization reaction on the surfaces of silicon monoxide particles and is synchronously coordinated with iron salt, and the iron / nitrogen co-doped silicon monoxide composite negative electrode material is obtained; the preparation method comprises the following steps: firstly, preparing a polydopamine-iron (SiOx-coated PDA-Fe) precursor by using a hydrothermal method to form a uniform SiOx-coated polydopamine-iron (SiOx-coated PDA-Fe) precursor, then, carrying out two-step heat treatment on the precursor in an inert atmosphere to synchronously realize iron-catalyzed carbon layer graphitization and silicon monoxide disproportionation reaction, and finally, carrying out acid pickling to obtain a target product. According to the preparation method, through the precise process of step-by-step heat treatment, the coating layer is stably carbonized firstly, then material activation and conductive network construction are synchronously completed, a unique core-shell structure and a point-line-surface three-dimensional conductive buffer network are formed, the prepared material has high first efficiency, excellent rate capability and ultra-long cycle life, the process is efficient, and the preparation method is suitable for industrial production. The method is suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the technical field of lithium-ion battery anode materials, specifically relating to an iron / nitrogen co-doped silicon suboxide composite anode material and its preparation method. Background Technology

[0002] Silicon suboxide, as a lithium-ion battery anode material, has a theoretical capacity far exceeding that of traditional graphite, and its volume expansion is less than that of pure silicon, making it considered one of the most promising next-generation high-capacity anode materials. However, the commercial application of silicon suboxide is mainly limited by two inherent bottlenecks: First, its intrinsic electronic and ionic conductivity is extremely low, resulting in sluggish electrode reaction kinetics and poor rate performance; second, it undergoes huge volume changes during charge and discharge, and repeated volume expansion and contraction easily lead to the pulverization of active materials, continuous cracking and reconstruction of the solid electrolyte interface, ultimately causing electrode structure collapse and a sharp decline in capacity.

[0003] To overcome the above-mentioned shortcomings, existing technologies have researched and adopted various modification strategies, such as carbon coating on SiO₂. x Coating the surface with an amorphous carbon layer can improve conductivity to some extent and buffer the volume effect; however, the carbon layer formed by mechanical mixing or impregnation reacts with SiO₂. x The matrix bonding is weak, and the electrical conductivity of amorphous carbon itself is limited. Disproportionation treatment under a high-temperature inert atmosphere affects SiO₂. x Heat treatment is used to disproportionate the silicon suboxide into a stable structure where nano-silicon clusters are uniformly dispersed in a SiO2 matrix. This structure effectively mitigates volume changes, but the SiO2 generated on the surface after disproportionation leads to low conductivity and irreversible material formation during the first charge-discharge cycle. Application publication number CN116207221A describes nitrogen-doped carbon coating of silicon suboxide surface using chitosan. Then, a mixed alkaline solution is used to etch the composite material to form a porous structure. Finally, it is further composited and coated with carbon materials such as graphite. Materials prepared using this method have high capacity and high initial efficiency, but require secondary composite coating, making the process relatively complex. Application publication number CN120674465A describes ball milling silicon suboxide material mixed with dopant material, then adding an organic nitrogen source and ball milling again. The ball-milled mixture is calcined, crushed, and sieved, and finally reacted with a mixed gas to generate a composite material. This method significantly improves the conductivity of silicon suboxide material, but it does not address the problem of SiO2 formation during disproportionation at its source.

[0004] In summary, existing technologies mostly involve simple physical superposition of the aforementioned modification methods, such as carbon coating followed by gas-phase nitrogen doping, or doping followed by coating. This multi-step, non-integrated process suffers from problems such as cumbersome procedures, high energy consumption, and weak interfacial bonding between components. Therefore, developing a method that can suppress SiO2 formation at the reaction source and achieve strong coupling and synergistic effects between functional components, thereby improving structural stability and conductivity, has become a pressing technical challenge in this field. Summary of the Invention

[0005] This invention provides an iron / nitrogen co-doped silicon suboxide composite anode material and its preparation method, in order to solve the problems of poor conductivity, severe volume expansion during cycling, and insufficient material structural stability of silicon suboxide as anode material in lithium-ion batteries in the prior art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing an iron / nitrogen co-doped silicon suboxide composite anode material, comprising the following steps: S1: Precursor construction: Silica powder was added to an alkaline buffer solution to form a suspension. Dopamine and iron salts were dissolved in water and added to the suspension. The mixture was then heated and stirred to form an iron-polydopamine coating on the silica surface. After filtration and drying, SiO2 was obtained. x @PDA-Fe precursor; S2: Low-temperature carbonization. The precursor obtained in step S1 is placed in a reactor, and the reactor temperature is controlled to rise to the first stage heat treatment temperature under an inert atmosphere to carbonize polydopamine. S3: High-temperature reaction. Under an inert atmosphere, the reactor is heated to the second-stage heat treatment temperature to simultaneously achieve the disproportionation reaction of silicon suboxide and the graphitization of carbon layers catalyzed by iron nanoparticles. S4: Pickling, pickling the product from step S3 to remove exposed metallic iron nanoparticles from the material surface. S5: Collect the solid by centrifugation of the acid washing product, wash it with deionized water until neutral, and finally vacuum dry and cool to obtain iron / nitrogen co-doped silicon suboxide composite anode material.

[0007] The inventors added silica powder to an alkaline buffer solution to form a suspension. They utilized the self-polymerization reaction of dopamine on the surface of the silica particles, simultaneously coordinating with iron salts to form a uniform SiO₂. x @Polydopamine-Iron (SiO) xThe precursor (@PDA-Fe) uses polydopamine to provide carbon and nitrogen sources, while simultaneously achieving molecular-level uniform mixing and fixation of iron and nitrogen elements. Under an inert atmosphere, the precursor obtained in step S1 undergoes a first-stage heat treatment to achieve preliminary carbonization and stabilization of polydopamine, forming a stable framework structure. Then, under an inert atmosphere, the intermediate product after step S2 undergoes a second-stage heat treatment to simultaneously achieve disproportionation reaction of silicon suboxide and graphitization of carbon layers catalyzed by iron nanoparticles. This forms an iron / nitrogen co-doped silicon suboxide composite anode material structure with a core composed of nano-silicon clusters generated by the disproportionation reaction and a silicon oxide matrix, surrounded by a nitrogen-doped carbon layer. Furthermore, graphitized carbon fibers or carbon nanotubes generated by iron nanoparticles are grown in situ in the carbon layer of the structure, forming a three-dimensional conductive network. This structure effectively enhances the conductivity and structural stability of the material, improving the cycle performance and rate performance of lithium-ion batteries.

[0008] Preferably, in step S2, the heat treatment heating rate is 2-10℃ / min, the calcination temperature is 400-700℃, and the calcination time is 0.5-3h.

[0009] In step S2, a heating rate of 2–10 °C / min and low-temperature carbonization at 400–700 °C have the following advantages: a moderate heating rate facilitates the orderly pyrolysis of polydopamine molecular chains, avoiding carbon skeleton breakage or structural inhomogeneity due to excessively rapid heating; within this temperature range, polydopamine can gradually remove oxygen- and nitrogen-containing functional groups and undergo cross-linking carbonization, forming an amorphous carbon skeleton with suitable pore structure and mechanical strength. This carbon skeleton can not only firmly fix Fe and N elements to SiO x The surface also provides stable structural support for the subsequent high-temperature disproportionation reaction and catalytic graphitization, thereby ensuring the integrity of the conductive network and the electrochemical stability of the final composite material.

[0010] Preferably, in step S3, the heat treatment heating rate is 2–10 °C / min, the calcination temperature is 900–1200 °C, and the calcination time is 0.5–5 h. This calcination temperature range is beneficial for SiO₂. x The silicon particles are fully transformed into uniformly dispersed nano-silicon clusters and SiO2 matrix, avoiding silicon particle agglomeration and improving structural stability. The simultaneous disproportionation and graphitization processes enable the silicon clusters, graphitized carbon, and nitrogen-doped carbon layers to be tightly combined, forming a "point-line-plane" conductive buffer system, which improves the material's conductivity and structural toughness.

[0011] Preferably, the pickling uses one or more of hydrochloric acid, acetic acid or nitric acid, with a concentration of 0.1M to 0.5M, a reaction temperature of 25 to 90°C, and a reaction time of 0.5 to 5 hours.

[0012] The acid exhibits moderate reactivity in the concentration range of 0.1M to 0.5M, effectively dissolving exposed metallic iron nanoparticles while showing no significant corrosion to iron particles encased in a carbon layer or those with a core-shell structure, thus achieving selective cleaning. Trace amounts of residual acid radicals, such as Cl-, remain after acid washing. - NO3 - CH3COO - Plasma can be completely removed by washing with water, avoiding its negative impact on electrolyte stability and battery cycle performance; in addition, acid is inexpensive, widely available, and has mild processing conditions, making it suitable for large-scale industrial applications.

[0013] Preferably, after adding silicon suboxide powder in step S1, the suspension is ultrasonically treated for 25-35 minutes. Ultrasonic dispersion of the silicon suboxide powder forms a uniform suspension, which is beneficial for the formation of uniform SiO₂. x @Polydopamine-Iron (SiO) x @PDA-Fe) precursor.

[0014] Preferably, the iron salt is one or more of ferric chloride, ferric nitrate or ferric sulfate, ferric ammonium citrate, and ferric nitrate nonahydrate.

[0015] Preferably, the amount of iron salt added is based on 3% to 8% of the mass of silicon dioxide, and the amount of dopamine added is 30% to 70% of the mass of silicon dioxide.

[0016] Within this dosage range, dopamine can form a carbon coating layer of suitable thickness. If the carbon layer is too thin, the buffering effect is insufficient; if it is too thick, it affects ion transport. Combined with iron catalysis, this carbon layer can be partially converted into graphitized carbon, forming a composite shell of "flexible amorphous carbon and highly conductive graphitized carbon," balancing conductivity and mechanical buffering functions. At this ratio, the sufficient carbon source and appropriate iron catalyst work synergistically, enabling the graphitized carbon fibers / tubes (wires) generated after high-temperature treatment to fully connect with the disproportionated silicon nanoclusters (dots), forming a complete three-dimensional conductive buffer network with the outer nitrogen-doped carbon matrix (surface), significantly improving the material's structural integrity and charge transport efficiency.

[0017] Preferably, the temperature of the stirring reaction process in step S1 is 20~80℃, and the reaction time is 0.5~3h.

[0018] Preferably, in step S5, vacuum drying is performed at 75~85°C.

[0019] To achieve the above objectives, this solution also provides a method for preparing iron / nitrogen co-doped silicon suboxide composite anode materials using the above method.

[0020] To achieve the above objectives, this solution also provides a lithium-ion battery anode material prepared from the aforementioned iron / nitrogen co-doped silicon suboxide composite anode material.

[0021] To achieve the above objectives, this solution also provides the application of the aforementioned iron / nitrogen co-doped silicon suboxide composite anode material in lithium-ion batteries.

[0022] The beneficial effects of this plan are: By using a solution method to fully mix iron atoms and dopamine to form a coordination complex, molecular-level uniform mixing and fixation of iron and nitrogen elements is achieved during the precursor construction stage. The amount of iron salt and dopamine can be precisely controlled, ensuring the uniformity and stability of the active components in the final product and avoiding the inhomogeneity and agglomeration problems of traditional doping methods.

[0023] A multi-stage heat treatment strategy of "low-temperature carbonization - high-temperature reaction - low-temperature calcination" is adopted. Low-temperature carbonization causes the organic carbon source to initially decompose and cross-link, forming an amorphous carbon skeleton, and fixing Fe and N elements in SiO. x The surface and vicinity of the particles ensure pre-stabilization of the carbon framework. During the high-temperature reaction, SiO₂... x A disproportionation reaction occurs, forming nano-silicon clusters. Simultaneously, the active carbon generated during the low-temperature carbonization stage inhibits the formation of the insulating phase SiO2 at high temperatures, thus avoiding affecting the conductivity of the silicon suboxide material. In this invention, the two key transformations of disproportionation and catalytic graphitization can be completed simultaneously in one high-temperature reaction step, improving the efficiency of material production and realizing the controllable preparation of high-capacity, long-life, and highly conductive composite anode materials.

[0024] The product was washed with dilute acid to remove some of the exposed, uncoated Fe nanoparticles, thus preventing their catalytic decomposition of the electrolyte. Meanwhile, the internal Fe particles were retained due to the protection of the carbon layer, allowing them to continue to perform their electron transport function.

[0025] 4) The iron / nitrogen co-doped silicon suboxide composite anode material of the present invention forms a core-shell structure with disproportionated silicon suboxide as the core and nitrogen-doped carbon and catalytic graphitized carbon as the shell. The three-dimensional network composed of graphitized carbon fibers / tubes greatly improves conductivity. The flexible nitrogen-doped carbon matrix and the robust graphitized carbon work together to provide excellent buffer space for the volume expansion of silicon, thereby ensuring the structural integrity of the electrode.

[0026] 5) The anode material prepared by the present invention exhibits high initial coulombic efficiency, excellent rate performance and ultra-long cycle life, and its overall performance is significantly better than that of silicon suboxide materials modified by traditional methods.

[0027] 6) In the preparation method of this invention, the coating layer is first stabilized and carbonized, and then the material activation and conductive network construction are completed simultaneously, forming a unique core-shell structure and a three-dimensional conductive buffer network of "point-line-surface". A core-shell structure with nitrogen-doped carbon and catalytic graphitized carbon as the shell can be achieved in one coating. Compared with the traditional method, the coating process steps are reduced, the material production efficiency is higher, the process is simpler, and it is suitable for large-scale production. Attached Figure Description

[0028] Figure 1 This is a scanning electron microscope (SEM) image of the silicon suboxide anode material of Example 1 of the present invention.

[0029] Figure 2 This is the first coulombic efficiency test result of the silicon suboxide anode material in Example 1 of the present invention. Detailed Implementation

[0030] The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they should be performed in accordance with the techniques or conditions described in the literature in the field, or in accordance with the product manual.

[0031] In the following embodiments, all instruments and equipment used, unless otherwise specified, are conventional products that can be purchased through legitimate channels. Unless otherwise stated, all methods described are conventional methods, and all raw materials are available from publicly available commercial sources.

[0032] Example 1: A method for preparing an iron / nitrogen co-doped silicon suboxide composite anode material includes the following steps: S1: Precursor construction: Silica powder was added to an alkaline buffer solution to form a suspension. Dopamine and iron salts were dissolved in water and added to the suspension. The mixture was then heated and stirred to form an iron-polydopamine coating on the silica surface. After filtration and drying, SiO2 was obtained. x @PDA-Fe precursor.

[0033] The amount of iron salt added is based on 3% to 8% of the mass of silicon suboxide, and the amount of dopamine added is 30% to 70% of the mass of silicon suboxide. The amounts of silicon suboxide powder, iron salt, and dopamine added in this scheme can be adjusted adaptively.

[0034] In this step, the temperature during the stirring reaction is 20~80℃, and the reaction time is 0.5~3h.

[0035] In this embodiment, 1.0 g of silica powder was added to 200 mL of Tris-hydrochloric acid buffer solution (pH=8.5) and sonicated at 300 W for 30 minutes to fully disperse it and form a uniform suspension. Subsequently, 0.5 g of dopamine hydrochloride and 0.1 g of ferric chloride were dissolved together in 20 mL of deionized water to allow iron atoms and dopamine to fully mix and form a coordination complex, thereby achieving uniform mixing and fixation of iron and nitrogen elements at the molecular level.

[0036] This mixture was then quickly poured into the aforementioned silica-substrate suspension. The mixture was mechanically stirred at 300 rpm for 2 hours in a 40°C water bath, utilizing the self-polymerization of dopamine on the surface of the silica-substrate particles and simultaneous coordination with iron salts to form uniform SiO₂. x @Polydopamine-Iron (SiO) x @PDA-Fe) precursor.

[0037] After the reaction was complete, the solid product was collected by vacuum filtration, washed three times with deionized water, and dried in a vacuum drying oven at 80°C for 12 hours to obtain black SiO₂. x @PDA-Fe precursor powder.

[0038] S2: Low-temperature carbonization. The precursor obtained in step S1 is placed in a reactor, and the reactor temperature is controlled to rise to the first stage heat treatment temperature under an inert atmosphere to carbonize the polydopamine.

[0039] In this step, the heat treatment heating rate is 2-10℃ / min, the calcination temperature is 400-700℃, and the calcination time is 0.5-3h.

[0040] In this embodiment, the precursor powder obtained above is placed in a tube furnace and heated from room temperature to 600°C at a heating rate of 5°C / min under argon atmosphere protection. The temperature is then maintained at this temperature for 1 hour to achieve preliminary carbonization and stabilization of polydopamine, forming a stable skeleton structure.

[0041] S3: High-temperature reaction. Under an inert atmosphere, the reactor is heated to the second-stage heat treatment temperature to simultaneously achieve the disproportionation reaction of silicon suboxide and the graphitization of carbon layers catalyzed by iron nanoparticles.

[0042] In this step, the heat treatment heating rate is 2-10℃ / min, the calcination temperature is 900-1200℃, and the calcination time is 0.5-5h.

[0043] In this embodiment, after calcination in step S2, the temperature is increased from room temperature to 1000°C at a rate of 5°C / min, and then held at this temperature for 2 hours. During this process, the silicon suboxide core undergoes a disproportionation reaction to generate nano-silicon clusters and a silica matrix. Simultaneously, iron species are reduced to nano-iron particles and catalyze the graphitization transformation of the polydopamine carbon layer. In this process, the carbon generated during low-temperature carbonization is used to reduce SiO2 to SiO through a gasification reaction during high-temperature heat treatment, suppressing the formation of disproportionated SiO2 and ensuring the electrical conductivity of the silicon suboxide material.

[0044] S4: Pickling, the product of step S3 is pickled to remove exposed metallic iron nanoparticles from the material surface.

[0045] In this embodiment, the product after high-temperature reaction was dispersed in 100 mL of 0.3 M dilute hydrochloric acid solution and stirred for 2 hours in a 60°C water bath to remove exposed, uncoated metallic iron nanoparticles from the material surface.

[0046] S5: After the reaction is complete, the solid is collected by centrifugation, washed with deionized water until neutral, and finally vacuum dried at 80°C to obtain the final iron / nitrogen co-doped silicon suboxide composite anode material, as detailed below. Figure 1 As shown.

[0047] In addition to the drying temperature mentioned above, this step can also be performed within the temperature range of 75~85℃.

[0048] The iron / nitrogen co-doped silicon suboxide composite anode material prepared above was used to fabricate lithium-ion batteries, and the results were tested to obtain data on coulombic efficiency, excellent rate performance, and ultra-long cycle life. The specific testing method included: mixing the iron / nitrogen co-doped silicon suboxide composite anode material, SP (superconducting carbon black), CMC (sodium carboxymethyl cellulose), and SBR (styrene-butadiene rubber latex) in a weight ratio of 8:1:0.5:0.5; adjusting the doctor blade slit to 100 μm for coating; and compacting to a density of 1.2 g / cm³. 3 The cells were rolled to produce coin cells for testing. The test was performed in the following cycle: rate discharge, rest, constant voltage discharge, rest, rate charge, and rest. After 200 cycles, the test was completed. The initial coulombic efficiency of the sample was 76.95%. The initial coulombic efficiency test data for the sample are as follows: Figure 2 As shown.

[0049] In this scheme, 11 additional lithium-ion batteries were prepared using the above method, and the test data are shown in the table below: Battery test result data table Battery number First charge specific capacity (mAh / g) First discharge specific capacity (mAh / g) First-time Coulomb efficiency (%) 1 1312.14 1705.18 76.95 2 1405.79 1737.04 80.93 3 1335.26 1755.76 76.05 4 1370.72 1759.14 77.92 5 1375.22 1759.94 78.14 6 1311.47 1752.84 74.82 7 1291.33 1752.38 73.69 8 1320.98 1746.86 75.62 9 1376.50 1768.14 77.85 10 1345.21 1751.58 76.8 11 1418.55 1753.68 80.89 12 1286.49 1682.34 76.47 As shown in the table above, the material presented in this invention exhibits high reversible specific capacity in the first cycle, with an average first-cycle coulombic efficiency exceeding 77%, combining high energy density with good interfacial stability. The data is concentrated and reproducible, indicating mature material structure design and preparation process, possessing excellent comprehensive electrochemical performance and industrialization potential. The iron / nitrogen co-doped silicon suboxide composite anode material with a core-shell structure—using disproportionated silicon suboxide as the core and nitrogen-doped carbon and catalytic graphitized carbon as the shell—prepared by the method of this invention exhibits high first-cycle coulombic efficiency, excellent rate performance, and ultra-long cycle life, with comprehensive performance significantly superior to silicon suboxide materials modified by traditional methods.

[0050] In this scheme, the iron salt can also be one or more of ferric chloride, ferric nitrate or ferric sulfate, ferric ammonium citrate, and ferric nitrate nonahydrate.

[0051] In this scheme, the acid used for pickling can be one or more of hydrochloric acid, acetic acid, or nitric acid.

[0052] The above descriptions are merely embodiments of the present invention. Commonly known structures, properties, and reactant ratios are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. For example, simply adjusting the parameter selection within or near a specified parameter range should also be considered within the scope of protection of the present invention, and these will not affect the effectiveness of the invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing an iron / nitrogen co-doped silicon monoxide composite negative electrode material, characterized in that, The method comprises the following steps: S1: precursor construction, adding silicon monoxide powder to the alkaline buffer solution to form a suspension, dissolving dopamine and iron salt in water and adding to the suspension, then heating and stirring to form an iron-polydopamine coating layer on the surface of silicon monoxide, and after filtering and drying, obtaining SiO x @PDA-Fe precursor; S2: low-temperature carbonization, the precursor obtained in step S1 is placed in a reactor, the reactor is controlled to be heated to a first-stage heat treatment temperature under an inert atmosphere, and polydopamine is carbonized; S3: high-temperature reaction, the reactor is controlled to continue to be heated to a second-stage heat treatment temperature under an inert atmosphere, and a disproportionation reaction of silicon monoxide and graphitization of a carbon layer catalyzed by iron nanoparticles are simultaneously achieved; S4: acid washing, the product of step S3 is subjected to acid washing to remove exposed iron nanoparticles on the surface of the material; S5: the acid-washed product is collected by centrifugal separation, washed with deionized water until neutral, and finally vacuum dried, to obtain an iron / nitrogen co-doped silicon monoxide composite negative electrode material after cooling.

2. The method of claim 1, wherein, In the step S2, the heat treatment heating rate is 2-10℃ / min, the calcination temperature is 400-700℃, and the calcination time is 0.5-3h.

3. The method of claim 1, wherein, In the step S3, the heat treatment heating rate is 2-10℃ / min, the calcination temperature is 900-1200℃, and the calcination time is 0.5-5h.

4. The method of claim 1, wherein, In the step S4, the acid washing uses one or more of hydrochloric acid, acetic acid or nitric acid, the concentration is 0.1M-0.5M, the reaction temperature is 25-90℃, and the reaction time is 0.5-5h.

5. The method of claim 1, wherein, In the step S1, after the addition of the silicon monoxide powder, the suspension is subjected to ultrasonic treatment for 25-35min.

6. The method of claim 1, wherein, The iron salt is one or more of ferric chloride, ferric nitrate or ferric sulfate, ferric ammonium citrate, and ferric nitrate nine hydrate.

7. The method of claim 1, wherein, The amount of the iron salt added is 3%-8% of iron based on the mass of the silicon monoxide, and the amount of the dopamine added is 30%-70% of the mass of the silicon monoxide.

8. The method of claim 1, wherein, In the step S1, the reaction process temperature is 20-80℃, and the reaction time is 0.5-3h.

9. The method of claim 1, wherein, In the step S5, the vacuum drying is performed at 75-85℃.

10. An iron / nitrogen co-doped silicon monoxide composite negative electrode material, characterized in that, Prepared by the method of any one of claims 1-9.

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