Negative electrode material, preparation method thereof and secondary battery
By constructing a gradient silicon content on the outer side of the core and a nanocomposite shell structure in the silicon-oxygen anode material, combined with multi-stage heating and rapid cooling processes, the problems of low initial coulombic efficiency and capacity reduction in silicon-oxygen anode materials were solved, achieving high-efficiency electrochemical performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-05
- Publication Date
- 2026-03-31
AI Technical Summary
Existing silicon-oxygen anode materials exhibit low initial coulombic efficiency and significant capacity degradation during the first electrochemical cycle. Traditional pre-lithiation and pre-magnesiation processes are costly or have limited effectiveness.
It adopts a core-outer gradient silicon content design and a nanocomposite shell structure. The core is composed of silicon elements increasing from 25% to 85%, and the shell is composed of nano-silicon matrix and magnesium silicate. A stable core-shell structure is formed through multi-stage heating and rapid cooling processes, combined with an inorganic salt coating layer.
It significantly improves initial coulombic efficiency, maintains high specific capacity, enhances cycle stability, and reduces irreversible capacity loss and lithium consumption.
Smart Images
Figure CN121769067A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of electrochemical energy storage, specifically to a negative electrode material and its preparation method, and a secondary battery. Background Technology
[0002] Silicon-oxygen anode materials are usually prepared by gas-phase method to produce silicon suboxide precursor materials, and then silicon-oxygen anode materials are obtained by carbon coating. In order to improve the first efficiency of silicon-oxygen anode materials, existing technologies often use lithium hydride doping or magnesium metal doping to improve the first efficiency.
[0003] Pre-lithiation of silicon-oxygen anode materials can significantly improve their initial coulombic efficiency, but the process cost is high and the capacity is severely reduced. Traditional pre-magnesiation of silicon-oxygen anode materials can improve their initial coulombic efficiency, but the specific capacity is severely reduced and the improvement in initial efficiency is only small. Summary of the Invention
[0004] In view of this, this application provides a negative electrode material and a method for preparing the same, to solve at least one of the aforementioned technical problems. Furthermore, this application also provides a secondary battery.
[0005] In a first aspect, this application provides a negative electrode material comprising a core and a shell formed on the outside of the core. The core comprises a composite of nano-silicon and silicon oxide, and the mass fraction of silicon increases from 25% to 38% to 70% to 85% from the outside of the core to the center of the core. The shell is formed on the outside of the core, and the shell comprises a nano-silicon matrix and a nanocomposite dispersed in the nano-silicon matrix, the nanocomposite comprising magnesium oxide and magnesium silicate.
[0006] Based on the first aspect, in some possible implementations, based on the negative electrode material, the ratio of the thickness of the shell to the diameter of the core is 1:1.5 to 1:2.5.
[0007] Based on the first aspect, in some possible implementations, the mass ratio of the magnesium oxide to the magnesium silicate is 0.1 to 0.6.
[0008] Based on the first aspect, in some possible implementations, the negative electrode material also includes an inorganic salt coating layer, the material of which includes... One or more of them.
[0009] Secondly, this application provides a method for preparing a negative electrode material, the method comprising: mixing silicon oxide, a magnesium source and an alcohol-soluble salt to obtain a composite; The complex was subjected to a multi-stage heating process followed by a cooling process to obtain the first intermediate. The multi-stage heating process includes first heating to 400-450℃ at a rate of 1-3℃ / min under an inert atmosphere and holding for 30 minutes, then heating to 490℃ at a rate of 3-5℃ / min and holding for 45 minutes, then heating to 510℃ at a rate of 3-5℃ / min and holding for 45 minutes, then starting the furnace rotation system and heating to 530-550℃ at a rate of 1-3℃ / min and holding for 240-360 minutes, and then heating to 600℃ at a rate of 8-10℃ / min and holding for 30 minutes; the cooling process includes using gas atomization rapid cooling technology to cool to 500℃ at a cooling rate of not less than 1000℃ / s and holding for 60 minutes.
[0010] Remove the alcohol-soluble salt from the first intermediate to obtain the second intermediate; The second intermediate is coated with an inorganic salt to obtain the negative electrode material.
[0011] Based on the second aspect, in some possible implementations, a magnesium source and silicon suboxide are mixed under inert gas conditions to obtain a premix, wherein the mass ratio of the magnesium source to the silicon suboxide is 0.2-0.5. The composite was prepared by ball milling an alcohol-soluble salt and a premix under an inert atmosphere, wherein the mass ratio of the alcohol-soluble salt to the premix was 0.1-0.3.
[0012] Based on the second aspect, in some possible implementations, the second intermediate is crushed and ground, the second intermediate and inorganic salt are dispersed in pure water, and the negative electrode material is obtained by spray pyrolysis using a spray dryer.
[0013] Based on the second aspect, in some possible implementations, the crushing and grinding particle size range is 1~15μm, and the mass ratio of the second intermediate to the inorganic salt is 1:0.005~1:0.01.
[0014] Based on the second aspect, in some possible implementations, the step "removing the alcohol-soluble salt from the first intermediate" includes: dispersing the first intermediate in anhydrous ethanol, centrifuging and filtering, and then drying under vacuum to obtain the second intermediate.
[0015] Based on the second aspect, in some possible implementations, a heat preservation process is further included after the multi-stage heating process and before the cooling process. The heat preservation process includes: cooling to 500°C under an inert atmosphere and holding at that temperature for at least 60 minutes. Thirdly, this application provides a secondary battery comprising the aforementioned negative electrode material.
[0016] In the anode material provided in this application, a gradient structure with gradually increasing silicon content from the outside to the inside is constructed in the core region. This reduces the intensity of side reactions between the low-silicon content region on the outer side of the core and the electrolyte during the initial lithium insertion process, thereby mitigating the loss of active lithium caused by irreversible reactions on the surface. Meanwhile, maintaining a high silicon content in the core center provides sufficient reversible capacity without sacrificing specific capacity due to an overall reduction in silicon content. Simultaneously, by forming a shell layer on the outer side of the core composed of a nano-silicon matrix and a magnesium oxide / magnesium silicate nanocomposite, the magnesium silicate provides a stable chemical interface during lithium insertion / extraction, reducing continuous lithium consumption caused by interface decomposition. The presence of magnesium oxide further enhances the structural stability of the shell layer, ensuring its relative integrity during silicon volume changes and reducing repeated breakage and reconstruction of the solid electrolyte interface. Therefore, this core-shell structure maintains high specific capacity while significantly reducing irreversible capacity loss, improving initial coulombic efficiency, and enhancing cycle stability. Attached Figure Description
[0017] Figure 1 This is a schematic diagram of the silicon-oxygen anode material structure designed for this invention.
[0018] Figure 2 and Figure 3 Electron micrographs of the silicon-oxygen anode material prepared in Example 1 at different magnifications.
[0019] Figure 4 and Figure 5 Electron micrographs of the silicon-oxygen anode material prepared in Example 6 at different magnifications.
[0020] Figure 6 and Figure 7 Electron micrographs of the silicon-oxygen anode material prepared for Comparative Example 1 at different magnifications.
[0021] Figure 8 The electrochemical performance data are for Examples 1-7 and Comparative Examples 1-3.
[0022] Explanation of main component symbols Anode material 100 Kernel 10 Nano Silicon 11 Silicon Oxide 11 Shell 20 Nano-silicon substrate 30 Magnesium oxide 31 Magnesium Silicate 32 Inorganic salt coating layer 40 The following detailed description, in conjunction with the accompanying drawings, will further illustrate this application. Detailed Implementation
[0023] The embodiments of this application are described in detail below. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application; it should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; where there is no conflict, the implementation methods and features of the implementation methods of this application can be combined with each other; many specific details are set forth in the following description to provide a full understanding of this application, and the described implementation methods are only a part of the implementation methods of this application, and not all of the implementation methods.
[0024] Among related technologies, silicon-oxygen anode materials (SiOx) have attracted much attention in the industry due to their high lithium diffusion coefficient, high specific capacity, good fast-charging performance, and suitable operating potential. However, SiOx anode materials form lithium oxide and lithium silicate during the first electrochemical cycle, which leads to a decrease in the first coulombic efficiency of the anode material, limiting the application of SiOx anode materials in the field of rechargeable batteries. Currently, the industrial production of silicon-oxygen anode materials usually adopts pre-lithiation and pre-magnesiation processes to improve the first efficiency of SiOx anode materials.
[0025] There are three types of SiOx pre-lithiation processes: electrochemical pre-lithiation, chemical pre-lithiation, and physical pre-lithiation. Electrochemical pre-lithiation mainly controls the pre-lithiation process by changing the current and voltage. Liquid-phase chemical pre-lithiation often uses lithium-containing reagents with strong reducing power to transfer active lithium ions to SiOx through redox reactions. A typical physical pre-lithiation process involves redox reactions between lithium metal and reduced lithium compounds and SiOx materials to pre-form lithium silicate and lithium oxide. These methods can significantly improve the first coulombic efficiency of SiOx anode materials, but their further industrial application is limited by problems such as complex processes, high equipment requirements, high production costs, and the significant reduction in specific capacity due to pre-lithiation.
[0026] The pre-magnesification process reduces SiOx using magnesium and magnesium compounds, improving the material's initial coulombic efficiency. Compared to the pre-lithiation process, pre-magnesification is simpler, uses lower-priced raw materials, and requires less sophisticated equipment, highlighting its industrialization potential. However, pre-magnesification also reduces the specific capacity of SiOx materials, and the large amount of heat released during the process promotes disproportionation in SiOx, affecting the material's electrochemical cycling performance.
[0027] In summary, pre-lithiation of existing silicon-oxygen anode materials can significantly improve their initial coulombic efficiency, but the process cost is high and the capacity is severely reduced. Traditional pre-magnesiation processes for silicon-oxygen anode materials can improve their initial coulombic efficiency, but the specific capacity is severely reduced, and the improvement in initial efficiency is only small.
[0028] Based on this, embodiments of this application construct a core-shell heterostructure with an elemental gradient core and a pinned composite shell, thereby significantly improving the first coulombic efficiency while maintaining the high specific capacity of the silicon-oxygen anode.
[0029] Based on this, please see Figure 1 One embodiment of this application provides a negative electrode material 100, including a core 10 and a shell 20 formed on the outside of the core 10. The core 10 includes a composite of nano-silicon 11 and silicon oxide 12. Based on the total mass of the core, the mass fraction of silicon increases from 25%~38% to 70%~85% from the outside of the core 10 to the center of the core. The shell 20 includes a nano-silicon matrix 30 and a nanocomposite dispersed in the nano-silicon matrix 30. The nanocomposite includes magnesium oxide 31 and magnesium silicate 32.
[0030] In the negative electrode material 100 provided in this application, a nanocomposite of magnesium oxide 31 and magnesium silicate 32 is introduced into the shell layer 20. The high reactivity of magnesium oxide 31 is used to in-situ modify the SiOx surface, resulting in the formation of a stable magnesium silicate 32 layer on its surface. Magnesium silicate 32 can effectively reduce the consumption of active lithium during subsequent electrochemical cycles. Specifically: Regarding the shell 20, magnesium silicate 32 and nano-silicon jointly construct a shell 20 with flexible support capabilities. This shell 20 not only possesses moderate mechanical flexibility, providing buffering and pinning stability when the volume of silicon-oxygen materials changes, but also maintains a stable electron and ion transport interface during cycling, thereby ensuring the integrity of the core layer structure and interface. This helps to suppress the capacity decay problem caused by the generation of a large amount of inactive magnesium silicate 32 in traditional pre-magnesification processes.
[0031] Regarding the core 10, the core 10 of the anode material 100 adopts a gradient transition design from a high silicon content region to a low silicon content region. This transition design helps to reduce the intensity of side reactions during the initial lithium intercalation process, making the volume change of the anode material 100 more controllable during cycling, significantly reducing the number of cracks in the shell 20, effectively reducing the repeated rupture and reconstruction of the solid-electrolyte interphase (SEI) film, reducing irreversible lithium consumption, and thus further improving the initial coulombic efficiency and cycle stability of the material.
[0032] In some implementations, the ratio of the thickness of the shell 20 to the diameter of the core 10 is 1:1.5 to 1:2.5. The thickness of the shell 20 can specifically be 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 100nm, or any value within the range of any two of the above values; correspondingly, the diameter of the core 10 can be 30nm, 45nm, 60nm, 75nm, 90nm, 110nm, 130nm, 150nm, or any value within the range of any two of the above values. Constructing a core-shell structure within these value ranges allows the shell 20 to possess appropriate flexibility and support capabilities, thereby effectively absorbing volume changes in the core 10 during lithium insertion / extraction processes and reducing cracking and interface damage of the shell 20 caused by stress concentration. The aforementioned size matching also enables the nano-silicon matrix 30 and the nanocomposite in the shell 20 to maintain a stable dispersion distribution, reducing the inability to form a complete mechanical buffer network due to an excessively thin shell 20, and also reducing the reduction in the specific capacity of the material due to an excessively thick shell 20. The core-shell structure constructed within this size range is beneficial for maintaining the continuity of electron and ion transport paths, improving the material's initial coulombic efficiency, and significantly improving cycling stability.
[0033] In some implementations, the nanocomposite exhibits an irregular elongated structure, with dimensions ranging from 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, and 100 nm, or any value within any two of these ranges. The size of the nanocomposite refers to its characteristic length along its longest direction, or the average particle size measured from the equivalent major axis under irregular morphology. Within these size ranges, the nanocomposite can form a relatively uniform dispersed arrangement within the shell 20, constructing spatial pinning points between the nano-silicon substrates 30, thereby limiting the structural displacement and tensile deformation of the shell 20 during cycling to a certain extent. Smaller nanocomposite sizes are more conducive to maintaining the compactness of the shell 20, while larger nanocomposite sizes may provide a certain mechanical constraint, allowing the shell 20 to maintain its morphological integrity when absorbing the expansion stress of the core 10. Adjusting the size of the nanocomposite within the above-mentioned range helps to balance the flexible buffering effect of the shell 20 with the stability of the electrochemical interface, thereby improving the first coulombic efficiency and cycle performance of the anode material 100.
[0034] In some embodiments, the mass ratio of magnesium oxide 31 to magnesium silicate 32 in the shell 20 can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, or any value within the range of any two of the above values. Within this mass ratio range, magnesium oxide 31 can moderately participate in surface modification and transform into magnesium silicate 32 during heat treatment, and its participation amount is generally not enough to cause significant loss of active silicon in the core 10 or the shell 20. Under lower mass ratio conditions, the magnesium silicate 32 generated in the shell 20 helps to improve structural compactness; a higher mass ratio may enhance the mechanical support capacity of the shell 20, enabling the shell 20 to better cope with the local stress caused by the expansion of the core 10. Adjusting the ratio of the two within the above mass ratio range can obtain a composite shell 20 with a more stable structure and better interface continuity, while taking into account specific capacity and initial coulombic efficiency to a certain extent, and also helping to improve the performance retention of the material during cycling.
[0035] In some embodiments, the core-shell structure exhibits a distinct interface with a near-spherical morphology. The sphericity can be 0.8, 0.85, 0.88, 0.9, 0.92, 0.95, 0.98, 1, or any value within the range of any two of the above values. Sphericity refers to the degree to which the outer contour of the core 10 closely approximates an ideal sphere in geometric shape, and can be measured by a sphericity coefficient (calculated from the ratio of the diameter of the smallest circumscribed sphere to the diameter of the largest inscribed sphere, or the equivalent sphere parameters after three-dimensional reconstruction). A core-shell interface with sphericity within the above range can achieve a more uniform stress distribution in three dimensions, making it less prone to high stress concentration in localized areas when the core 10 undergoes volume changes due to lithium insertion / extraction, thereby reducing the possibility of interface fracture. Higher sphericity conditions are more conducive to the formation of a more stable SEI film; moderately lower sphericity may enhance the mechanical interlocking between the shell 20 and the core 10. Controlling the sphericity within the above-mentioned range helps maintain the long-term stability of the core-shell interface, thereby improving the material's performance in terms of cycling performance and rate capability.
[0036] In the negative electrode material 100 provided in this application, an inorganic salt coating layer 40 is uniformly distributed on the surface of the negative electrode material 100. This coating layer, as an ion conduction layer, can provide a stable interfacial ion migration channel during electrochemical cycling and reduce lithium loss caused by repeated rupture of the solid electrolyte interphase (SEI) film. Specifically, the material of the inorganic salt coating layer 40 includes... One or more of these inorganic salts. These inorganic salts all have high ionic conductivity and good thermal stability, and can form a continuous and dense ion-conducting network on the particle surface, improving the interfacial lithium-ion migration rate, while suppressing the problem of insufficient electron conduction caused by the magnesia reaction products, thereby further improving the rate performance and cycle stability of the material.
[0037] An embodiment of this application also provides a method for preparing a negative electrode material, including the following steps: Step 1: Mix silicon oxide, magnesium source, and alcohol-soluble salt to obtain a complex; In this embodiment, step one specifically includes: mixing a magnesium source and silicon suboxide under inert gas conditions to obtain a premix, wherein the mass ratio of magnesium source to silicon suboxide is 0.2-0.5. Subsequently, ball milling an alcohol-soluble salt with the premix under inert atmosphere conditions to prepare a composite, wherein the mass ratio of alcohol-soluble salt to premix is 0.1-0.3. The alcohol-soluble salt in the composite not only has a certain thermal conductivity, but can also absorb the reaction heat at the interface between the magnesium source and silicon suboxide and undergo local melting, thereby forming an ion-conducting film, providing a favorable environment for the diffusion and migration of magnesium atoms, and reducing the excessive accumulation of interfacial heat. Specifically, the alcohol-soluble salt includes one or more of zinc chloride, cobalt chloride, ferric chloride, calcium chloride, potassium bromide, sodium acetate, and sodium ethoxide.
[0038] Step 2: After subjecting the complex to multi-stage heating, a cooling process is performed to obtain the first intermediate.
[0039] In this embodiment, the multi-stage heating process includes: Uniform heating stage: Under inert atmosphere conditions, the temperature is increased to 400-450℃ at a heating rate of 1-3℃ / min to ensure the uniformity of the temperature field in the furnace cavity before the reaction and to ensure that the components of the composite obtain a uniform temperature.
[0040] Second-stage preheating: Keep warm at 400-450℃ in an inert atmosphere for about 30 minutes to promote further uniformity of internal temperature of the material and improve the activity of the reaction interface.
[0041] Three-stage pre-reaction: Under an inert atmosphere, the temperature is increased to approximately 490°C at a rate of 3-5°C / min and held for about 45 minutes. During this stage, the magnesium source and silicon suboxide undergo a slow reaction at the interface. The highly reactive small-particle magnesium source reacts preferentially to form the initial shell structure of nano-silicon and magnesium oxide. At the same time, due to the relatively low temperature, the release of reaction heat is slow, inhibiting undesirable disproportionation of silicon suboxide.
[0042] The fourth pre-reaction stage involves heating the material to approximately 510°C under an inert atmosphere at a rate of 3-5°C / min, and then holding it at that temperature for about 45 minutes. Similar to the aforementioned pre-reaction stage, this stage allows the relatively less reactive magnesium source to react further with silicon suboxide under a higher thermodynamic driving force, while maintaining a relatively mild heat release.
[0043] Five-stage dynamic calcination: The furnace rotation system is activated, and the temperature is raised to 530-550℃ at a rate of 1-3℃ / min under an inert atmosphere, and held for 240-360min. During this stage, the thermodynamic driving force is significantly enhanced, and the magnesium source continues to react with silicon suboxide. The rotation system keeps the material moving, enhancing the interfacial contact between the magnesium source and silicon suboxide, while also helping to remove the heat of reaction in a timely manner, avoiding local temperature rises that could cause the system to run away from its temperature.
[0044] Six-stage high-temperature dynamic calcination: Under an inert atmosphere, the temperature is increased to approximately 600°C at a rate of 8-10°C / min and held for about 30 minutes to provide the reaction system with a high thermodynamic driving force. In this stage, the magnesium source rapidly reacts with silicon suboxide to form magnesium oxide, which further forms inactive magnesium silicate on its surface, thus forming a nanocomposite structure of magnesium oxide and magnesium silicate. However, since most of the magnesium source has been consumed in the preceding stages, only a portion of the magnesium oxide is further converted into inactive magnesium silicate in this stage, thereby avoiding the consumption of a large amount of active silicon material.
[0045] In this embodiment, step two also includes a heat preservation treatment. After the sixth stage of high temperature dynamic reduction, the heat preservation treatment includes: cooling to 500°C under inert atmosphere conditions and holding at that temperature for at least 60 minutes to further release the internal stress generated during the reaction process and stabilize the material structure.
[0046] In this embodiment, the cooling process includes: using rapid cooling to cool the reaction system to room temperature, suppressing element segregation during slow cooling, and ensuring the uniformity of the nanocomposite structure in the SiOx shell.
[0047] The multi-stage heating process described above ensures a uniform magnesium thermoelectric reaction, while preventing excessively high temperatures that could lead to undesirable disproportionation of silicon suboxide and suppressing the formation of large amounts of inactive magnesium silicates. Furthermore, the reduction reaction of the outer silicon suboxide layer consumes a large number of oxygen atoms, creating a radial gradient distribution of oxygen and silicon elements in the core, which helps reduce volume expansion during subsequent electrochemical cycling. (During the entire reaction between SiOx and magnesium, magnesium diffuses and migrates into SiOx and reacts with it to form Si and MgO. During this process, Mg combines with O, causing O in the core to migrate towards the shell (from the core center outwards). This O migration process creates a silicon gradient distribution.) Step 3: Remove the alcohol-soluble salt from the first intermediate to obtain the second intermediate; In this embodiment, step three includes: dispersing the first intermediate in anhydrous ethanol, fully dissociating it by ultrasonic stirring, then centrifuging and filtering, and drying under vacuum conditions to obtain the second intermediate. This step effectively removes alcohol-soluble salts from the reaction system and prevents the material from oxidizing in an aqueous environment.
[0048] Step 4: Coat the second intermediate with inorganic salts to obtain the negative electrode material.
[0049] In this embodiment, step four specifically includes: first, crushing and grinding the second intermediate to control its particle size within the range of 1-15 micrometers. Then, dispersing the second intermediate and inorganic salt in pure water at a mass ratio of 1:0.005-1:0.01, and performing spray pyrolysis using a spray drying device, causing the inorganic salt to form a coating layer on the material surface. The inorganic salt can be... One or more of the following. Through the spray pyrolysis process, a coating layer with good ion conductivity can be reconstructed on the material surface to improve the electrical conductivity that may be caused by the magnesia reaction products.
[0050] One embodiment of this application also provides a secondary battery comprising the aforementioned negative electrode material. The secondary battery of this application exhibits good discharge capacity, initial coulombic efficiency, and cycle stability.
[0051] In some embodiments, the secondary battery includes a casing, an electrode assembly, and an electrolyte. Both the electrode assembly and the electrolyte are located within the casing. The casing can be a packaging bag encapsulated with a film (such as an aluminum-plastic film), for example, a pouch battery. In other embodiments, it can also be a steel-cased battery, an aluminum-cased battery, etc. The electrode assembly includes electrode sheets and a separator. The electrode sheets include a positive electrode sheet and a negative electrode sheet, and the separator is used to separate the positive and negative electrode sheets and can be disposed between the positive and negative electrode sheets. In some embodiments, the electrode assembly can be a stacked structure, for example, it is formed by alternately stacking a positive electrode sheet, a separator, and a negative electrode sheet. In other embodiments, the electrode assembly can also be a wound structure, for example, it is formed by sequentially stacking and then winding a positive electrode sheet, a separator, and a negative electrode sheet. The negative electrode sheet includes a negative current collector and a negative electrode material active layer disposed on at least one surface of the negative current collector. The negative electrode material active layer includes the aforementioned negative electrode material.
[0052] The present application's solution will be explained below with reference to embodiments. Those skilled in the art will understand that the following examples are for illustrative purposes only and should not be construed as limiting the present application. Unless otherwise stated, reagents, software, and instruments involved in the following embodiments that are not specifically mentioned are all conventional commercially available products or open-source materials.
[0053] Example 1 S1: Raw material premix: Weigh 10 kg of silica powder (SiOx) and 2.5 kg of magnesium powder, and mix them thoroughly in an atmosphere mixer under argon atmosphere to obtain a premix; S2: High-energy composite: Weigh 1.25Kg of calcium chloride and composite it through a high-energy ball mill to obtain a composite material. The composite process is as follows: ball-to-material ratio is 15:1, rotation speed is 800r / min, and ball milling time is 420min. S3: The composite is loaded into a graphite crucible and transferred to a rotary kiln for a multi-stage heating reaction under an inert atmosphere. a) Uniform heating in one stage: Under inert atmosphere conditions, the temperature is increased to 450℃ at a heating rate of 2℃ / min; b) Second-stage preheating: Hold at 450℃ in an inert atmosphere for 30 minutes; c) Three-stage pre-reaction: Under inert atmosphere, the temperature is increased to 490℃ at a rate of 4℃ / min and held for 45min; d) Four-stage pre-reaction: Under inert atmosphere, the temperature is increased to 510℃ at a rate of 4℃ / min and held for 45min; e) Five-stage dynamic calcination: Start the furnace cavity rotation system, raise the temperature to 530℃ at a rate of 1℃ / min under inert atmosphere, and hold for 240min; f) Six-stage high-temperature dynamic calcination: Under inert atmosphere conditions, the temperature is increased to 600℃ at a rate of 8℃ / min and held for 30min; g) Seven-stage cooling calcination: Cool to 500℃ under inert atmosphere and hold for 60 min; S4: Stop the furnace cavity ventilation and furnace cavity rotation system, and use gas atomization rapid cooling process to obtain the first intermediate; S5: The first intermediate in S4 is stirred and washed in 25L of anhydrous ethanol, centrifuged and filtered, and then dried in a vacuum oven to obtain the second intermediate. S6: Crush and grind the second intermediate from S5, weigh 10 kg of the second intermediate and 0.1 kg of inorganic salt, disperse them in 30 L of anhydrous water, and then perform spray pyrolysis using a spray dryer to obtain the negative electrode material. Please refer to [link to relevant documentation]. Figure 2 and Figure 3 .
[0054] Examples 2-6 In this embodiment, except for the process parameters in Table 1, the rest are the same as in Embodiment 1.
[0055] Table 1 In the above embodiments, the six-stage and seven-stage reaction steps in step S3 were not performed in implementation 6.
[0056] Example 7 In this embodiment, except for the process parameters in Table 2, the rest are the same as in Embodiment 1.
[0057] Table 2 Compared with Example 1, in Example 7, step S4 is a slow cooling treatment with the furnace.
[0058] Comparative Example 1 S1. Weigh 10 kg of silica powder (SiOx) and 2.5 kg of magnesium powder, and mix them thoroughly in an argon atmosphere using an atmosphere mixer to obtain a uniform mixture. S2: The mixture is heated to the reaction temperature of 600℃ in an argon atmosphere using an electric resistance furnace and held for 240 min. S3: After the heat preservation is completed, the furnace is cooled to room temperature to obtain a bulk anode material precursor. Then, the particle size is adjusted to 5μm (median particle size) by crushing and grinding to obtain a powder anode material precursor.
[0059] S4: The powder anode material precursor is heated in a rotary furnace under an argon atmosphere. After the temperature reaches 900°C, methane gas (flow rate 0.4L / min) is introduced into the furnace cavity and held for 100 minutes. After cooling in the furnace, the material is discharged. S5: The particle size of the material treated in S4 is adjusted to 5μm (median particle size) to obtain the negative electrode material. Please refer to [link to relevant documentation]. Figure 6 and Figure 7 .
[0060] Comparative Example 2 S1: Weigh 10 kg of silica fume (SiOx), 2.5 kg of magnesium powder, and 1.5 kg of sodium chloride. Mix them thoroughly in an argon atmosphere using an atmosphere mixer to obtain a uniform mixture of SiOx / Mg / NaCl. S2: The SiOx / Mg / NaCl mixture was heated to the reaction temperature of 700℃ and held in an argon atmosphere using a resistance furnace; S3: After the heat preservation is completed, the material is cooled to room temperature in the furnace to obtain a bulk anode material precursor. Then, it is crushed and washed with water. The material is then dried, crushed and ground to adjust the particle size to 5μm (median particle size) to obtain a powder anode material precursor.
[0061] S4: The powder anode material precursor is heated in a rotary furnace under an argon atmosphere. After the temperature reaches 900°C, methane gas (flow rate 0.4L / min) is introduced into the furnace cavity and held for 100 minutes. After cooling in the furnace, the material is discharged. S5: The particle size of the material after S4 treatment is adjusted to 5μm (median particle size) to obtain the negative electrode material.
[0062] Comparative Example 3 S1. Weigh 10 kg of carbon-coated silica powder (SiOx) and 2.5 kg of magnesium powder, and mix them thoroughly in an atmosphere mixer under an argon atmosphere to obtain a uniform SiOx / Mg mixture. S2: The SiOx / Mg mixture was heated to the reaction temperature of 550℃ and held in an argon atmosphere using a resistance furnace; S3: After the heat preservation is completed, the material is cooled to room temperature in the furnace and then crushed and ground to adjust the particle size to 5μm (median particle size) to obtain the negative electrode material.
[0063] Half-cell tests were performed on the silicon-oxygen anode materials prepared in Examples 1-7 and Comparative Examples 1-3, and the electrochemical performance data were statistically analyzed, as shown in Table 3.
[0064] Table 3 A comprehensive comparison of Examples 1-7 shows that the initial coulombic efficiency of the anode material synthesized using the method provided in this application can reach 90%. (1) The charge capacity can reach 1500mAh g-1: the capacity retention rate after 300 electrochemical cycles is 80~88%.
[0065] (2) Comparative analysis of Examples 1-5 shows that the anode materials synthesized in Examples 2 and 3 have lower initial coulombic efficiencies. This is because the amount of magnesium source added is small, resulting in a low degree of reduction of silicon suboxide, and there is still a lot of silicon in the oxidized state, which limits the improvement of initial coulombic efficiency. Similarly, the initial coulombic efficiencies of Examples 4 and 5 have increased significantly but have not reached 90%, mainly due to insufficient magnesium source addition.
[0066] (3) Comparing Examples 2, 3, 4 and 5 respectively, it can be found that compared with Examples 2 and 3, the capacity and efficiency of the anode materials synthesized in Examples 4 and 5 are not significantly different, but the cycle capacity retention rate is lower. This is because the increase in the temperature of the fifth stage reaction leads to an increase in the rate of magnesium thermal reaction, and the heat released accumulates, causing the nano-silicon to disproportionate and grow, exhibiting more obvious volume expansion during electrochemical cycling, which affects the cycle performance. Comparing Examples 1 and 6, it can be found that the anode material synthesized in Example 6 has a high initial coulombic efficiency of 90%, but its charging capacity and cycle capacity retention rate are lower. Example 6 did not use the six-stage high-temperature reaction and the seven-stage cooling calcination, resulting in the anode material shell nanostructure consisting of a large amount of magnesium oxide existing alone, which affects the lithium insertion / extraction ability of the shell active material. At the same time, this structure cannot form a stable dispersed network of nanocomposite, reducing the structural stability of the material.
[0067] (4) Please see Figure 1 , Figure 4 and Figure 5It can be observed that the negative electrode material prepared in Example 1 formed a continuous and uniform magnesium oxide / magnesium silicate composite shell structure, and the nanocomposite inside the shell was diffusely distributed with complete interface and uniform stress. However, in Example 6, due to the absence of a cooling calcination step, obvious interparticle cracks and local agglomeration appeared inside the shell, and the nanocomposite structure was discontinuous, making it difficult to form an effective pinning network.
[0068] A comparative analysis of Examples 1 and 7 shows that the initial coulombic efficiency of the anode material synthesized in Example 7 is consistent with that in Example 1, but its capacity and capacity retention are lower. Example 7 did not undergo rapid cooling; instead, it employed a furnace cooling process. During the prolonged cooling process, the nanocomposite structure of the shell and the silicon oxide active material formed a large amount of inert silicates, damaging the original shell and nanocomposite structures and reducing the material's capacity and capacity retention. Furthermore, the slow cooling treatment provided a longer segregation time for elements in the anode material, leading to localized elemental agglomeration within the material and reducing its structural uniformity.
[0069] Please see Figure 8 Compared with Example 1, the anode materials synthesized in Comparative Examples 1, 2 and 3 have poorer overall electrochemical performance, mainly manifested in low initial coulombic efficiency and low capacity retention.
[0070] Please see Figure 6 and Figure 7 Although the anode material synthesized in Comparative Example 1 achieved an initial coulombic efficiency of 86%, the large amount of heat released during the magnesian reaction was not effectively controlled, causing disproportionation and promoting silicon grain growth, which reduced the material's capacity and capacity retention. Comparative Example 2 controlled the magnesian reaction of the anode material by adding a large amount of metal salt, but the large amount of magnesium oxide generated by the reaction reduced the material's initial efficiency.
[0071] Comparative Examples 1 and 2 underwent high-temperature methane coating after the magnesium thermal reaction, which improved the surface conductivity of the negative electrode material. However, the coating process easily led to material disproportionation, which to some extent affected the cycling performance of the material and reduced the capacity retention rate.
[0072] Comparative Example 3 used carbon-coated silicon suboxide as a raw material. During the magnesothermic reaction, the carbon layer slowed down the reaction to some extent, allowing the heat to be released slowly. However, heat still accumulated in the reaction system, causing silicon grains to grow and affecting the capacity retention of the material. In addition, the carbon layer was prone to peeling off during the reaction, encapsulating the magnesium source, which reduced the degree of reaction of the anode material and affected the first coulombic efficiency of the material to some extent.
[0073] In summary, the silicon suboxide modification method provided by this invention significantly improves the initial coulombic efficiency of the anode material while maintaining high specific capacity and cycle performance, thereby improving the overall electrochemical performance of the anode material.
[0074] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.
Claims
1. A negative electrode material, characterized in that, The negative electrode material includes: The core comprises a composite of nano-silicon and silicon oxide, and the mass fraction of silicon increases from 25% to 38% to 70% to 85% from the outer side to the center of the core. A shell is formed on the outside of the core. The shell includes a nano-silicon matrix and a nanocomposite dispersed in the nano-silicon matrix. The nanocomposite includes magnesium oxide and magnesium silicate.
2. The negative electrode material as described in claim 1, characterized in that, The ratio of the thickness of the shell to the diameter of the core is 1:1.5 to 1:2.
5.
3. The negative electrode material as described in claim 1, characterized in that, The nanocomposite has an irregular elongated structure with a size of 20~100 nm.
4. The negative electrode material as described in claim 1, characterized in that, The mass ratio of magnesium oxide to magnesium silicate is 0.1 to 0.
6.
5. A method for preparing a negative electrode material, characterized in that, Including the following steps: A complex was obtained by mixing silicon oxide, a magnesium source, and an alcohol-soluble salt. The complex was subjected to a multi-stage heating process followed by a cooling process to obtain the first intermediate. The multi-stage heating process includes: Increase the temperature to 400-450℃ at a rate of 1-3℃ / min, and then hold for 30 minutes; Heat to 490℃ at a rate of 3-5℃ / min and hold for 45 minutes. Heat to 510℃ at a rate of 3-5℃ / min and hold for 45 minutes; Increase the temperature to 530-550℃ at a rate of 1-3℃ / min and hold for 240-360 minutes; The cooling process includes: The gas atomization rapid cooling technology is adopted, with a cooling rate ≥1000℃ / S; Remove the alcohol-soluble salt from the first intermediate to obtain the second intermediate; The second intermediate is coated with an inorganic salt to obtain the negative electrode material.
6. The preparation method according to claim 5, characterized in that, Including the following steps: A premix is obtained by mixing a magnesium source with silicon suboxide under inert gas conditions, wherein the mass ratio of the magnesium source to the silicon suboxide is 0.2-0.
5. The composite was prepared by ball milling an alcohol-soluble salt and a premix under an inert atmosphere, wherein the mass ratio of the alcohol-soluble salt to the premix was 0.1-0.
3.
7. The preparation method according to claim 6, characterized in that, Including the following steps: The second intermediate is crushed and ground, and the second intermediate and inorganic salt are dispersed in pure water and then sprayed pyrolyzed using a spray dryer to obtain the negative electrode material.
8. The preparation method according to claim 7, characterized in that, The particle size range for crushing and grinding is 1~15μm, and the mass ratio of the second intermediate to the inorganic salt is 1:0.005~1:0.
01.
9. The preparation method according to claim 5, characterized in that, The inorganic salt package One or more of them.
10. The preparation method according to claim 5, characterized in that, The step "removing the alcohol-soluble salt from the first intermediate" includes: The first intermediate was dispersed in anhydrous ethanol, centrifuged and filtered, and then dried under vacuum to obtain the second intermediate.
11. The preparation method according to claim 5, characterized in that, The process includes a heat preservation process after the multi-stage heating process and before the cooling process, which includes cooling to 500°C under an inert atmosphere and holding the temperature for at least 60 minutes.
12. A secondary battery, characterized in that, The secondary battery includes the negative electrode material as described in any one of claims 1-4.