Porous negative electrode active material and method for producing the same

Abstract

The present application provides a porous negative electrode active material and a manufacturing method thereof, wherein the porous negative electrode active material includes a first structure including a silicon element having a valence of 0 to 4 and a metal doping element, wherein the mass percentage of the silicon element is 40% or more and the mass percentage of the metal doping element is 1% to 15%, the first structure includes a porous structure including micropores having a pore size of less than 2 nm and mesopores having a pore size of 2 nm to 50 nm, and the first structure further includes silicon crystal grains having a size of 10 nm or less; an adsorption / desorption curve of the porous negative electrode active material has a hysteresis loop, a relative pressure corresponding to the hysteresis loop is 0.4 to 1, and an adsorption amount is 5 cm 3 / g~25cm 3 The porous negative active material of the technical solution of the present application can improve the fast charging ability and cycle performance of the battery, and can also reduce the expansion of the battery during cycling.

Description

[Technical Field]

[0001] The present application relates to the field of lithium ion batteries, and in particular to porous negative electrode active materials and methods for making the same. [Background technology]

[0002] Although silicon-based materials have significant advantages in lithium storage capacity, their rate performance currently falls short of that of conventional graphite anodes in high-pressure dense systems. Therefore, there remains a need to improve the dynamic performance of silicon-based materials to meet the ever-increasing demand for rapid charging of batteries. To improve the fast charging capability of batteries, it has been proposed to design a tunnel structure in the anode material, which can improve the fast charging capability of the battery, but accelerates the cycle life of the battery.In addition, in conventional technologies, when manufacturing porous anode materials, silicon oxide is often used to obtain a porous structure through acid treatment, but this has problems such as strong acid corrosion resistance, high cost, a significant decrease in volume density after pore formation, and poor cycle performance, making large-scale application difficult. Summary of the Invention

[0003] The present application provides a porous negative electrode active material and a manufacturing method thereof, which allows the negative electrode material to have good pore features, improves the fast charging ability and cycling performance of the battery, and reduces the battery swelling during cycling. One aspect of the present application provides a porous negative electrode active material, the porous negative electrode active material comprising a first structure including a silicon element having a valence of 0 to 4 and a metal doping element, wherein the mass percentage of the silicon element is 40% or more and the mass percentage of the metal doping element is 1% to 15%, the first structure including a porous structure including micropores having a pore size of less than 2 nm and mesopores having a pore size of 2 nm to 50 nm, the first structure further including silicon crystal grains having a size of 10 nm or less, the porous negative electrode active material having a hysteresis loop in an adsorption / desorption curve, a relative pressure corresponding to the hysteresis loop being 0.4 to 1, and an adsorption amount of 5 cm 3 / g~25cm 3 / g. In an embodiment of the present application, in the first structure, 0≦m Si(4価) / m Si(0価) ≦1, wherein m Si(4価) is the mass of tetravalent silicon, and m Si(0価) is the mass of silicon with a valence of zero. In an embodiment of the present application, the metal doping element comprises at least one of Li, Na, Ge, Mg, Ca, Al and Be. In an embodiment of the present application, the porous negative electrode active material further includes a second structure coated on a surface of the first structure, the second structure including at least one of amorphous carbon and graphitized carbon, and the mass ratio of carbon element to the total mass of the second structure is 80% or more. In an embodiment of the present application, the thickness of the second structure is 0 nm to 40 nm, and the average particle size of the porous negative electrode active material is 0.1 μm to 18 μm. Another aspect of the present application further provides a method for producing a porous negative electrode active material, the method including: providing a mixture containing elemental silicon, a tetravalent oxidation state of silicon, and a metal doping element, wherein the mass percentage of the silicon element is 40% or more and the mass percentage of the metal doping element is 1% to 15%; melting the mixture and cooling it to room temperature at a cooling rate of 20°C / min or more to obtain a first structure, the first structure including silicon element with a valence of 0 to 4 and the metal doping element; the first structure including a porous structure including micropores with a pore size of less than 2 nm and mesopores with a pore size of 2 nm to 50 nm; and the first structure further including silicon crystal grains with a size of 10 nm or less; and the porous negative electrode active material has an adsorption / desorption curve with a hysteresis loop, a relative pressure corresponding to the hysteresis loop is 0.4 to 1, and an adsorption amount is 5 cm 3 / g~25cm 3 / g. In an embodiment of the present application, in the first structure, 0≦m Si(4価) / m Si(0価) ≦1, wherein m Si(4価)is the mass of tetravalent silicon, and m Si(0価) is the mass of silicon with a valence of zero. In an embodiment of the present application, the metal doping element comprises at least one of Li, Na, Ge, Mg, Ca, Al and Be. In an embodiment of the present application, the method for manufacturing the porous negative electrode active material further includes applying a second structure to a surface of the first structure, the second structure including at least one of amorphous carbon and graphitized carbon, and a mass ratio of carbon element to the total mass of the second structure being 80% or more. The present application further provides another method for producing a porous negative electrode active material, the method including: providing a mixture containing elemental silicon, a tetravalent oxidation state of silicon, and a metal doping element, wherein the mass percentage of the silicon element is 40% or more and the mass percentage of the metal doping element is 1% to 15%; heating the mixture to a first temperature and cooling the mixture to a second temperature at a predetermined vacuum level, wherein the temperature difference between the first temperature and the second temperature is 300°C or more; and obtaining a first structure, the first structure including a silicon element with a valence of zero to tetravalent and the metal doping element; the first structure including a porous structure including micropores with a pore size of less than 2 nm and mesopores with a pore size of 2 nm to 50 nm; and the first structure further including silicon crystal grains with a size of 10 nm or less; and the adsorption / desorption curve of the porous negative electrode active material has a hysteresis loop, the relative pressure corresponding to the hysteresis loop is 0.4 to 1, and the adsorption amount is 5 cm 3 / g~25cm 3 / g. In an embodiment of the present application, the first temperature is 1000°C to 1400°C, the second temperature is 400°C to 900°C, and the predetermined vacuum degree is 10 -3 Pa~10 2 It is Pa. In an embodiment of the present application, in the first structure, 0≦m Si(4価) / m Si(0価) ≦1, wherein m Si(4価) is the mass of tetravalent silicon, and m Si(0価) is the mass of silicon with a valence of zero. In an embodiment of the present application, the metal doping element comprises at least one of Li, Na, Ge, Mg, Ca, Al and Be. In an embodiment of the present application, the method for manufacturing the porous negative electrode active material further includes applying a second structure to a surface of the first structure, the second structure including at least one of amorphous carbon and graphitized carbon, and a mass ratio of carbon element to the total mass of the second structure being 80% or more. The porous negative electrode active material of the technical solution of the present application comprises a first structure, which includes both micropores and mesopores, wherein the micropores increase the diffusion paths and are advantageous for improving the rate, and the mesopores can mitigate the deterioration of cycle performance due to volume expansion and are advantageous for cycle stability. In addition, the first structure further comprises silicon crystal grains, the size of which is 10 nm or less. Therefore, when the porous negative electrode active material is used in a negative electrode, the kinetic performance of lithium combination is better, which in turn improves the fast charging capability and cycle performance of the battery. In the method for manufacturing a porous negative electrode active material of the technical solution of the present application, the raw materials include elemental silicon, tetravalent oxidation state of silicon, and metal doping element, wherein the mass percentage of the silicon element is 40% or more, and the mass percentage of the metal doping element is 1%-15%. Together with adjusting the manufacturing process, the manufactured porous negative electrode active material has good pore features, thereby improving the fast charging ability and cycle performance of the battery and reducing the battery swelling during cycling. [Brief explanation of the drawings]

[0004] The following drawings describe in detail exemplary embodiments disclosed in the present application, where the same reference numerals represent similar structures in the several views of the drawings. As will be understood by those skilled in the art, these embodiments are non-limiting exemplary embodiments, and the drawings are merely used for illustration and explanation, and are not intended to limit the scope of the present application, and other forms of embodiments can similarly achieve the objectives of the invention of the present application. It should be understood that the drawings are not drawn to scale. [Figure 1] 2 is a pore size distribution diagram of the negative electrode active materials prepared in Example 1, Example 2, and Comparative Example 1 of the present application. [Figure 2] 1 shows adsorption / desorption curves of the negative electrode active materials prepared in Example 1, Example 2, and Comparative Example 1 of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0005] The following description provides specific application scenarios and requirements of the present application to enable those skilled in the art to make and use the content of the present application. Various modifications to the disclosed embodiments will be apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present application. Thus, the present application is not intended to be limited to the embodiments shown, but is accorded the widest scope consistent with the claims.

[0006] The technical solution of the present invention will be described in detail below with reference to the embodiments and drawings. An embodiment of the present application provides a porous negative electrode active material, the porous negative electrode active material having a first structure including silicon element having a valence of 0 to 4 and a metal doping element. The presence of the metal doping element allows the entire material to exhibit electrical neutrality. The metal doping element may include at least one of Li, Na, Mg, Ca, Al, and Be. The metal doping element may exist in an atomic or ionic state in the porous negative electrode active material, such as Mg or Al, or may combine with an element having electron-accepting ability to form a metal oxide or metal salt, such as MgO, Na2O, CaO, Na3PO4, or MgSO3. The metal doping element may also combine with silicon element having a valence of 0 to 4 to form a silicate, such as MgSiO3, CaSiO3, Li2SiO3, or Na2SiO3. In addition, the silicate formed by combining the metal doping element with silicon element having a valence of 0 to 4 can form a tunnel structure during deposition. The doping amount of the metal doping element is closely related to the battery's first-cycle Coulombic efficiency, cycle performance, and gram capacity. The higher the doping amount of the metal doping element, the higher the battery's first-cycle Coulombic efficiency. However, the battery's cycle performance tends to increase and then decrease. As the doping amount of the metal doping element increases, the amount of active lithium that can be absorbed per unit mass decreases. Therefore, by controlling the doping amount of the metal doping element, it is possible to change the characteristics of the porous negative electrode active material under high-temperature storage conditions after absorbing active lithium, and also to improve the battery's cycle performance and first-cycle Coulombic efficiency. Furthermore, during research and development, it was found that the doping amount of the metal doping element affects the silicate deposition morphology, and that when the mass percentage of the doping element is 1% to 15%, the silicate deposition morphology has good pore structure characteristics.

[0007] In an embodiment of the present application, the mass ratio of the silicon element to the total mass of the first structure is 40% or more, and 0≦mSi(4価) / m Si(0価) is less than or equal to 1, where the m Si(4価) is the mass of the tetravalent silicon element, and m Si(0価) is the mass of the zero-valent silicon element. The silicon element with a valence of 0 to 4 may be silicon existing in a single state, silicon oxide SiOx (0 < x ≤ 2), and silicate. The general formula of the silicate is RySiO3, where 1 ≤ y ≤ 2 and R is the doping element described above. The contents of the silicon element and the metal doping element can be realized by adjusting the relative contents among the silicon single substance, silicon oxide, and silicate contained in the first structure. The first structure includes a porous structure containing micropores and mesopores. Here, due to the existence of the micropores, the negative electrode material has many diffusion paths, which is advantageous for improving the rate. On the other hand, the mesopores can mitigate the attenuation of the cycle performance due to volume expansion, which is advantageous for cycle stability. The pore diameter of the micropores is less than 2 nm. For example, the pore diameter of the micropores is 0.2 nm, 0.5 nm, 0.8 nm, 1 nm, 1.5 nm, etc. The pore diameter of the mesopores is 2 nm to 50 nm. For example, the pore diameter of the mesopores is 2 nm, 5 nm, 10 nm, 15 nm, 20 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, etc. The first structure further includes silicon crystallites with a size of 10 nm or less. The silicon crystallites with a small size have good kinetic performance in the combination with lithium, so they can endow the negative electrode material with good rapid charging ability and cycle performance.

[0008] Since the first structure has a porous structure, there is a hysteresis loop in the adsorption and desorption curve of the porous negative electrode active material. The relative pressure corresponding to the hysteresis loop is 0.4 to 1, and the adsorption amount is 5 cm 3 / g to 25 cm 3 / g, and when the hysteresis loop in the adsorption / desorption curve of a porous negative electrode active material is within this range, it exhibits good cycle performance and fast charge capability when applied to a battery. This is because the porous negative electrode active material has a tunnel structure, which is favorable for lithium ion diffusion and electrolyte impregnation, and the solid electrolyte interlayer (SEI) structure formed is stable, preventing battery failure during cycling. Furthermore, the multiple lithium ion diffusion paths are favorable for improving fast charge characteristics. If the adsorption amount is too small, i.e., the pore volume is small, the diffusion paths become insufficient, affecting kinetics. If the adsorption amount is too large, i.e., the pore volume is too large, excessive electrolyte decomposition occurs, increasing resistance, resulting in poor fast charge performance and rapid cycle decay.

[0009] The porous negative electrode active material has a high specific surface area due to the presence of a porous structure, and the specific surface area of ​​the porous negative electrode active material in the examples of the present application is 2 m 2 / g~15m 2 / g.

[0010] In some embodiments, the porous negative electrode active material further includes a second structure coated on the surface of the first structure, the second structure including at least one of amorphous carbon and graphitized carbon, and the mass ratio of carbon element to the total mass of the second structure is 80% or more. The thickness of the second structure is, for example, 0 nm to 40 nm, and the average particle size of the porous negative electrode active material is 0.1 μm to 18 μm. When the thickness of the second structure is 0 nm, i.e., the porous negative electrode active material includes only the first structure, the second structure can improve the conductive performance of the porous negative electrode active material.

[0011] In some embodiments, the second structure may be a single-layer structure, for example, a single-layer structure including amorphous carbon, a single-layer structure including graphitized carbon, or a single-layer structure including both amorphous carbon and graphitized carbon. In other embodiments, the second structure may be a multi-layer structure, for example, including an amorphous carbon layer and a graphitized carbon layer, and the number and application order of the amorphous carbon layer and the graphitized carbon layer are not limited. The "application" described in the examples of the present application may be a partial application or a complete application, and the degree of application varies depending on the manufacturing process of the porous negative electrode active material.

[0012] An embodiment of the present application further provides a method for manufacturing a porous negative electrode active material, including: Step S1: Providing a mixture containing elemental silicon, silicon in a tetravalent oxidation state, and a metal doping element, wherein the metal doping element includes at least one of Li, Na, Ge, Mg, Ca, Al, and Be. The elemental silicon may be, for example, polysilicon, the tetravalent oxidation state of silicon may be, for example, silica, and the silica-containing material may be, for example, quartz. The tetravalent oxidation state of silicon may also be a silicate, for example, a compound having the general formula RySiO3, where 1≦y≦2, and R is a main group element of Groups I, II, or III, such as Li, Na, Mg, or Ca.

[0013] The metal doping element may be derived from an elemental metal, a metal oxide, a metal hydroxide, or a metal salt, such as elemental Mg, elemental Li, elemental Ca, elemental Ge, MgO, Na2O, CaO, Na3PO4, MgSO3, LiOH, Li2CO3, MgCO3, MgSiO3, CaSiO3, Li2SiO3, or Na2SiO3. In some embodiments of the present application, the source materials forming the first mixture include elemental silicon, silica, and elemental Mg, in other embodiments of the present application, the source materials include elemental silicon, silica, and magnesium oxide, and in further embodiments of the present application, the source materials include elemental silicon, silica, and lithium hydroxide.

[0014] In the mixture, the mass percentage of the silicon element is 40% or more, and the mass percentage of the metal doping element is 1% to 15%, and in the formed first structure, 0≦m Si(4価) / m Si(0価) The composition ratio of each raw material is controlled so that m≦1. Si(4価) is the mass of tetravalent silicon, and m Si(0価) is the mass of silicon with a valence of zero.

[0015] Step S2: The mixture is melted and cooled to room temperature to obtain a first structure. In some embodiments, the mixture may be heated to a molten state under the protection of a non-oxidizing gas, which may be an inert gas such as helium gas, neon gas, or argon gas. The temperature at which the mixture is heated to a molten state is not limited and may be determined according to the actual situation. It should be noted that the formed first structure includes a porous structure, which includes both micropores with a pore size of less than 2 nm and mesopores with a pore size of 2 nm to 50 nm. The first structure also includes silicon crystal grains with a size of 10 nm or less. The adsorption / desorption curve of the produced porous negative electrode active material has a hysteresis loop, and the relative pressure corresponding to the hysteresis loop is 0.4 to 1, and the adsorption capacity is 5 m / s. 3 / g~25m 3 / g, the cooling rate must be strictly controlled and must be 20°C / min or more, so that the porous negative electrode active material obtained by the preparation method according to the examples of the present application has good pore features, which can effectively improve the fast charging ability and cycle performance of the battery, and reduce the expansion of the battery during cycling.

[0016] In some embodiments of the present application, the method for manufacturing the porous negative electrode active material further includes applying a second structure to a surface of the first structure, the second structure including at least one of amorphous carbon and graphitized carbon, and a mass ratio of carbon element to a total mass of the second structure being 80% or more. The method for forming the second structure may include decomposing a carbon source substance in a non-oxidizing atmosphere to obtain a decomposition product, the decomposition product corresponding to a Raman spectrum Id / Ig<0.5 and an electrical conductivity >10 2 S·m -1 wherein the carbon source material comprises one or more of a gaseous carbon source material, a vaporized carbon source material, and an atomized carbon source material, the gaseous carbon source material comprises hydrocarbons that are gaseous at room temperature and aldehydes that are gaseous at room temperature, the gaseous carbon source material comprises methane, ethane, ethylene, acetylene, propane, and propylene, the vaporized carbon source material is a carbonaceous material that is liquid at room temperature and gaseous at a temperature higher than room temperature but lower than the temperature of the pre-decomposition region, and the vaporized carbon source material comprises n-hexane, ethanol, and benzene. The atomized carbon source material is a material that does not easily evaporate when heated but can be formed into small droplets using an atomizer, for example, a material that is liquid when the temperature is lower than that of a pre-decomposition region. The atomized carbon source material includes polyethylene and polypropylene, and the decomposition product is vapor-deposited and reacted with the powdered first structure to form an amorphous carbon coating layer, a graphitized carbon coating layer, or a composite layer including an amorphous carbon coating layer and a graphitized carbon coating layer on the surface of the powdered first structure.

[0017] When the vapor deposition reaction occurs, a nitrogen-containing substance may be passed through the coating material, and the nitrogen-containing substance may include at least one of NH3, melamine, acetonitrile, aniline, and butylamine. By passing the nitrogen-containing substance through the coating material, an amorphous carbon coating layer and / or a graphitized carbon coating layer doped with nitrogen atoms can be obtained. The amorphous carbon coating layer and / or the graphitized carbon coating layer doped with nitrogen atoms further improves the conductivity of the material, thereby reducing the internal resistance of the battery and ensuring the large current charge / discharge capability of the battery.

[0018] In the method for producing a porous negative electrode active material described in the examples of the present application, the relative blending ratio of silicon element and doping element in the mixture is controlled, and the molten mixture is cooled to room temperature at a cooling rate of 20°C / min or more, whereby the obtained first structure has a porous structure including micropores with a pore size of less than 2 nm and mesopores with a pore size of 2 nm to 50 nm, and the first structure also includes silicon crystal grains with a size of 10 nm or less, which can effectively improve the fast charging capability and cycle performance of the battery and reduce battery swelling during cycling. The porous negative electrode active material formed by the manufacturing method described in the examples of the present application has a hysteresis loop in its adsorption / desorption curve, and the relative pressure corresponding to the hysteresis loop is 0.4 to 1, and the adsorption amount is 5 m 3 / g~25m 3 / g.

[0019] The embodiments of the present application further provide another method for manufacturing a porous negative electrode active material, which includes: Step S1: Providing a mixture containing elemental silicon, silicon in the tetravalent oxidation state, and a metal doping element. The elemental silicon may be, for example, polysilicon, the tetravalent oxidation state of silicon may be, for example, silica, and the silica-containing material may be, for example, quartz. The tetravalent oxidation state of silicon may also be a silicate, for example, a compound having the general formula RySiO3, where 1≦y≦2, and R is a main group element of Groups I, II, or III, such as Li, Na, Mg, or Ca.

[0020] The metal doping element includes at least one of Li, Na, Ge, Mg, Ca, Al, and Be, and may be derived from an elemental metal, a metal oxide, a metal hydroxide, or a metal salt, such as elemental Mg, elemental Li, elemental Ca, elemental Ge, MgO, Na2O, CaO, Na3PO4, MgSO3, LiOH, Li2CO3, MgCO3, MgSiO3, CaSiO3, Li2SiO3, or Na2SiO3. In some embodiments of the present application, source materials forming the first mixture include elemental silicon, silica, and elemental Mg. In other embodiments of the present application, the source materials include elemental silicon, silica, and magnesium oxide. In further embodiments of the present application, the source materials include elemental silicon, silica, and lithium hydroxide. In the mixture, the mass percentage of the silicon element is 40% or more, and the mass percentage of the metal doping element is 1%-15%, and in the formed first structure, 0≦m Si(4価) / m Si(0価) The composition ratio of each raw material is controlled so that m≦1. Si(4価) is the mass of tetravalent silicon, and m Si(0価) is the mass of silicon with a valence of zero.

[0021] Step S2: The mixture is heated to a first temperature and cooled to a second temperature under a predetermined vacuum, with the temperature difference between the first temperature and the second temperature being 300°C or more, to obtain a first structure. The process of heating the mixture to the first temperature may be performed under non-oxidizing gas protection, and the non-oxidizing gas is an inert gas such as helium gas, neon gas, or argon gas. By controlling the temperature difference between the first temperature and the second temperature to be 300°C or more, the formed first structure has good pore features, including both micropores with a pore size of less than 2 nm and mesopores with a pore size of 2 nm to 50 nm, and further including silicon crystal grains with a size of 10 nm or less. The adsorption / desorption curve of the produced porous negative electrode active material has a hysteresis loop, and the relative pressure corresponding to the hysteresis loop is 0.4 to 1, and the adsorption amount is 5 m / s or more. 3 / g~25cm 3 / g.

[0022] In some embodiments of the present application, the first temperature is 1000°C to 1400°C, the second temperature is 400°C to 900°C, and the predetermined vacuum degree is 10 -3 Pa~10 2 It is Pa. In some embodiments of the present application, the method for manufacturing the porous negative electrode active material further includes coating a second structure on a surface of the first structure, the second structure including at least one of amorphous carbon and graphitized carbon, and the mass ratio of carbon element to the total mass of the second structure is 80% or more. The method for forming the second structure may refer to the above content, and the description will be omitted here.

[0023] Example 1 A mixture is provided that includes elemental silicon, silica, and elemental Mg, wherein the weight percent of elemental silicon is 45% and the weight percent of elemental magnesium is 10%. The mixture was heated to a molten state under argon gas protection, and then cooled to room temperature at a cooling rate of 20°C / min to obtain the first structure. The first structure was then powdered, and an 8 nm amorphous carbon coating layer and a graphitized carbon coating layer were deposited on the surface of the powder. The performance parameters of the porous negative electrode active material thus formed are shown in Table 1.

[0024] Examples 2 to 5 For a specific process description, see Example 1, and for specific process data and performance parameters of the formed porous negative electrode active material, see Table 1.

[0025] Comparative Example 1 For a specific process description, see Example 1, and for specific process data and performance parameters of the formed porous negative electrode active material, see Table 1.

[0026] Example 6 A mixture is provided that includes elemental silicon, silica, and elemental magnesium, wherein the weight percent of elemental silicon is 43% and the weight percent of elemental magnesium is 10%. The mixture was heated to a first temperature under argon gas protection and a vacuum of 10 -1 Pa, and the mixture was cooled to a second temperature to obtain a first structure, the first temperature being 1000°C to 1400°C, the second temperature being 400°C to 900°C, and the temperature difference between the first temperature and the second temperature being controlled to 300°C. The first structure was then powdered, and an 8 nm amorphous carbon coating layer and a graphitized carbon coating layer were deposited on the surface of the powder. The performance parameters of the porous negative electrode active material thus formed are shown in Table 2.

[0027] Examples 7 to 10 For a specific process description, see Example 6, and for specific process data and performance parameters of the formed porous negative electrode active material, see Table 2.

[0028] Comparative Example 2 For a specific process description, see Example 6, and for specific process data and performance parameters of the formed porous negative electrode active material, see Table 2.

[0029] The negative electrode active materials obtained in Examples 1 to 10 and Comparative Examples 1 and 2 were tested as follows: (1) A Micromeritics ASAP2020 was used as a testing device to obtain pore size distribution diagrams and adsorption / desorption curves for Example 1, Example 2, and Comparative Example 1, as shown in Figures 1 and 2. The testing method was as follows: The software version was V3.04H, the adsorption medium was N2, the vacuum degassing pretreatment temperature was 150°C, the pretreatment time was 1 hour, the sample mass was 0.3±0.05 g, and the BJH model was used, corrected by Faas, and Halsey: t=3.54*[-5 / ln(P / P o )] ^0.333 The pore size range was 0.1 nm to 300.0000 nm, the adsorbate characteristic factor k was 0.95300 nm, the density conversion factor was 0.0015468, and the open area ratio at both ends was 0.00. Based on the pore size distribution range obtained by desorption using the BJH model, the average pore size was automatically calculated, and the results are shown in Tables 1 and 2. A pore size distribution diagram was obtained based on the dV / dlog(w) pore volume of desorption using the BJH model. (2) The negative electrode active materials prepared in Examples 1 to 10 and Comparative Examples 1 and 2, PAA (polypropylene acid adhesive), and SP (conductive carbon black) were mixed in a mass ratio of 80:10:10, and 1 mol / L LiPF was used as an electrolyte. The mixture was applied to a button battery (model number CR2430) and the following electrochemical performance tests were carried out at 25°C: Cycle performance test: Discharge to 10mV at a constant current of 0.1C, let stand for 10 minutes, continue discharging to 5mV at a constant current of 0.02C, let stand for 10 minutes, and then charge to 1.5V at a constant current of 0.1C. Subsequent cycles were performed in this manner, and the test results are shown in Table 1 and Table 2. Rate charge test: First, discharge to 10mV at a constant current of 0.1C, leave for 10 minutes, then continue to discharge to 5mV at a constant current of 0.02C, leave for 10 minutes, then charge to 1.5V at a constant current of 0.1C, continue to discharge to 5mV at a constant current of 0.2C, record the 0.2C capacity, then charge to 1.5V at a constant current of 0.1C, then discharge to 5mV at 0.5C, 1.5C, 3.0C respectively, and charge to 1.5V at 0.1C, and compare the capacity ratios of 0.5C / 1.5C / 3.0C / 0.2C, the test results are shown in Table 1 and Table 2. Rate discharge test: First, discharge to 10mV at a constant current of 0.1C, let stand for 10 minutes, then continue to discharge to 5mV at a constant current of 0.02C, let stand for 10 minutes, then charge to 1.5V at a constant current of 0.2C, then uniformly discharge to 5mV at 0.1C, and then charge to 1.5V at 0.5C, 1.5C, and 3.0C respectively, and compare the capacity ratios of 0.5C / 1.5C / 3.0C / 0.2C. The test results are shown in Table 1 and Table 2.

[0030] As can be seen from Figures 1 and 2, the pore volumes of Examples 1 and 2 are within the optimum range, while Comparative Example 1 has almost no micropores due to the slow cooling rate, and the average mesopore diameter is 43 nm, which is much larger than those of Examples 1 and 2. Therefore, the rate charge / discharge and capacity retention rate after 50 cycles of Comparative Example 1 are significantly lower than those of Examples 1 and 2.

[0031] Combining Tables 1 and 2, it can be seen that the porous negative electrode active materials obtained by the manufacturing methods of the examples of the present application all have micropores and mesopores with appropriate pore sizes and silicon crystal grains with a size of less than 10 nm. When the obtained porous negative electrode active materials are used as negative electrode materials for lithium batteries, they have good fast charging ability and cycle performance, and can significantly reduce the expansion rate of the battery. [Table 1] [Table 2]

[0032] Finally, it should be understood that the embodiments of the application disclosed herein are merely illustrative of the principles of the embodiments of the application. Other modified embodiments are also within the scope of the application. Therefore, the embodiments disclosed in the application are merely examples and are not limiting. Those skilled in the art can implement the application of the application using alternative configurations based on the embodiments of the application. Therefore, the embodiments of the application are not limited to those exactly described in the application.

Claims

1. A porous negative electrode active material, a first structure comprising silicon element with a valence of 0 to 4 and a metal doping element, wherein the mass percentage of the silicon element is 40% or more and the mass percentage of the metal doping element is 1% to 15%; the first structure comprises a porous structure including micropores having a pore size of less than 2 nm and mesopores having a pore size of 2 nm to 45 nm; the first structure further includes silicon grains having a size of 10 nm or less; the adsorption / desorption curve of the porous negative electrode active material has a hysteresis loop, and the relative pressure corresponding to the hysteresis loop is 0.4 to 1; The porous negative electrode active material, wherein the metal doping element includes at least one of Ge and Mg.

2. In the first structure, 0≦m Ｓｉ（４価） / m Ｓｉ（０価） ≦1, wherein the m Ｓｉ（４価） is the mass of tetravalent silicon, and m Ｓｉ（０価） 2. The porous negative electrode active material according to claim 1, wherein is the mass of silicon element with a valence of zero.

3. 2. The porous negative electrode active material according to claim 1, further comprising a second structure on a surface of the first structure, the second structure comprising at least one of amorphous carbon and graphitized carbon, and a mass ratio of carbon element to a total mass of the second structure being 80% or more.

4. 4. The porous negative electrode active material according to claim 3, wherein the thickness of the second structure is 40 nm or less, and the average particle size of the porous negative electrode active material is 0.1 μm to 18 μm.

5. A method for producing a porous negative electrode active material, providing a mixture comprising elemental silicon, a tetravalent oxidation state of silicon, and a metal doping element, wherein the mass percentage of the silicon element is 40% or more and the mass percentage of the metal doping element is between 1% and 15%; melting the mixture and cooling it to room temperature at a cooling rate of 20°C / min or more to obtain a first structure; the first structure includes a silicon element with a valence of zero to four and a metal doping element; the first structure comprises a porous structure including micropores having a pore size of less than 2 nm and mesopores having a pore size of 2 nm to 45 nm; the first structure further includes silicon grains having a size of 10 nm or less; the adsorption / desorption curve of the porous negative electrode active material has a hysteresis loop, and the relative pressure corresponding to the hysteresis loop is 0.4 to 1; The method of claim 1, wherein the metal doping element comprises at least one of Ge and Mg.

6. In the first structure, 0≦m Ｓｉ（４価） / m Ｓｉ（０価） ≦1, wherein the m Ｓｉ（４価） is the mass of tetravalent silicon, and m Ｓｉ（０価） The method for producing a porous negative electrode active material according to claim 5, wherein is the mass of silicon element with a valence of zero.

7. 6. The method for producing a porous negative electrode active material according to claim 5, further comprising depositing a second structure on a surface of the first structure, the second structure comprising at least one of amorphous carbon and graphitized carbon, and a mass ratio of carbon element to a total mass of the second structure being 80% or more.

8. A method for producing a porous negative electrode active material, providing a mixture comprising elemental silicon, a tetravalent oxidation state of silicon, and a metal doping element, wherein the mass percentage of the silicon element is 40% or more and the mass percentage of the metal doping element is between 1% and 15%; heating the mixture to a first temperature and cooling the mixture to a second temperature at a predetermined vacuum level, the temperature difference between the first temperature and the second temperature being 300° C. or more, to obtain a first structure; the first structure includes a silicon element with a valence of zero to four and a metal doping element; the first structure comprises a porous structure including micropores having a pore size of less than 2 nm and mesopores having a pore size of 2 nm to 45 nm; the first structure further includes silicon grains having a size of 10 nm or less; the adsorption / desorption curve of the porous negative electrode active material has a hysteresis loop, and the relative pressure corresponding to the hysteresis loop is 0.4 to 1; the first temperature is 1000°C to 1400°C, the second temperature is 400°C to 900°C, and the predetermined degree of vacuum is 10 -3 Pa to 10 2 Pa; The method of claim 1, wherein the metal doping element comprises at least one of Ge and Mg.

9. In the first structure, 0≦m Ｓｉ（４価） / m Ｓｉ（０価） ≦1, wherein the m Ｓｉ（４価） is the mass of tetravalent silicon, and m Ｓｉ（０価） The method for producing a porous negative electrode active material according to claim 8, wherein is the mass of silicon element with a valence of zero.

10. 9. The method for producing a porous negative electrode active material according to claim 8, further comprising depositing a second structure on a surface of the first structure, the second structure comprising at least one of amorphous carbon and graphitized carbon, and a mass ratio of carbon element to a total mass of the second structure being 80% or more.

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