Silicon-based negative electrode active material, secondary battery and electric device

Abstract

The present application provides a silicon-based negative electrode active material that includes an alkali metal element-containing silicate and contains both S and Mg elements.

Description

[Technical Field]

[0001] The present application relates to the technical field of batteries, and in particular to silicon-based negative electrode active materials, secondary batteries, and electrical devices. [Background technology]

[0002] In recent years, as the application range of secondary batteries continues to expand, secondary batteries are widely used in many fields, such as energy storage power supply systems for hydroelectric power, thermal power, wind power, and solar power plants, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace.

[0003] Silicon-based materials have attracted widespread attention in the industry due to their high capacity, and their electrochemical performance is also highly demanded, so there is still a need in the field for silicon-based negative electrode active materials with better performance. Summary of the Invention

[0004] In view of the above problems, the present application provides a novel silicon-based negative electrode active material, a secondary battery, and an electric device, which are each described below.

[0005] In a first aspect, the present application provides a silicon-based negative electrode active material that includes an alkali metal element-containing silicate and contains both an S element and an Mg element.

[0006] In the above solution, the silicon-based negative electrode active material contains a combination of sulfur and magnesium, and this particular combination improves the cycle capacity retention of the silicon-based negative electrode active material. The combination of sulfur and magnesium produces an unexpected synergistic effect, and the technical effect achieved by this combination is significantly greater than the simple sum of the effects of using each element separately. Without being limited to the following theory, the lithium-sulfur compound formed by sulfur and lithium can mitigate particle expansion and improve material stability, effectively improving the cycle performance of the battery. Mg can form magnesium aluminum silicate with silicon-oxygen materials, effectively improving the initial coulombic efficiency of the battery.

[0007] In some embodiments, the content of the S element is greater than the content of the Mg element, and within the above ratio range, the S element and the Mg element exhibit an unexpected synergistic effect, further improving the cycle capacity retention rate of the battery.

[0008] In some embodiments, the mass ratio of the S element to the Mg element is 1.3:1 or more, and optionally 2.2:1 to 10:1. By using the negative electrode active material according to the above embodiments in a battery, the battery has an improved cycle capacity retention rate.

[0009] In some embodiments, the content of the S element is 50 ppm or more, and preferably 500 ppm to 1500 ppm. By using the negative electrode active material according to the above embodiments in a battery, the battery has an improved cycle capacity retention rate.

[0010] In some embodiments, the content of the Mg element is 500 ppm or less, and preferably 50 ppm to 300 ppm. By using the negative electrode active material according to the above embodiments in a battery, the battery has further improved initial coulombic efficiency.

[0011] In some embodiments, the volume average particle diameter D v50 is 4 μm to 10 μm. By using the negative electrode active material according to the above method in a battery, the battery has a further improved cycle capacity retention rate.

[0012] In some embodiments, the specific surface area of ​​the silicon-based negative electrode active material is 3 m 2 / g or less, and selectively 1m 2 / g~2m 2 By using the negative electrode active material according to the above method in a battery, the battery has a further improved cycle capacity retention rate.

[0013] In some embodiments, the silicon-based negative electrode active material has a powder volume resistivity of 3 Ω cm or less, and optionally 0.5 Ω cm to 1.5 Ω cm, at a pressure of 4 MPa. By using the negative electrode active material according to the above embodiments in a battery, the battery has an improved cycle capacity retention rate.

[0014] In some embodiments, the silicon-based negative electrode active material has a compaction density of 1.4 to 1.8 g / cm at a pressure of 49000 N. 3 and selectively 1.5 to 1.7 g / cm 3 By using the negative electrode active material according to the above scheme in a battery, the battery has a further improved capacity.

[0015] In some embodiments, the alkali metal element-containing silicate comprises a lithium-containing silicate, and the lithium-containing silicate has an XRD diffraction peak half width of 0.5° or more, and optionally 1.1° to 1.8°. By using the above-mentioned negative electrode active material in a battery, the battery has an improved cycle capacity retention rate.

[0016] In some embodiments, the alkali metal element-containing silicate comprises a lithium-containing silicate, and the lithium-containing silicate has a crystallite size of 10 nm or less, preferably 2 nm to 6 nm. By using the above-mentioned negative electrode active material in a battery, the battery has an improved cycle capacity retention rate.

[0017] In some embodiments, at least a portion of the surface of the silicon-based negative electrode active material has a coating layer.

[0018] In a second aspect, the present application provides a method for producing any one of the silicon-based negative electrode active materials described above, Providing a raw material containing Si element, O element, S element and Mg element; heating the source material to form a vapor by vapor deposition, and then cooling the vapor to form a deposit; pulverizing the sediment to obtain a pulverized product; and reacting the previous product with an alkali metal source to obtain an alkali metal-containing product.

[0019] In some embodiments, the method for producing a silicon-based negative electrode active material includes: The method further includes subjecting the alkali metallization product to a coating treatment to obtain a product having a coating layer.

[0020] In some embodiments, the temperature of the raw material is 1100 to 1550°C when the raw material is heated to form steam.

[0021] In some embodiments, the cooling temperature for cooling the vapor to form the deposit is 800-1050°C.

[0022] In a third aspect, the present application provides a secondary battery including a negative electrode containing any one of the silicon-based negative electrode active materials described above.

[0023] In a fourth aspect, the present application provides an electrical device comprising any one of the secondary batteries described above.

[0024] Beneficial effects One or more embodiments of the present application have one or more of the following beneficial effects:

[0025] (1) The combination of S and Mg elements produces an unexpected synergistic effect, and the technical effect achieved by the combination of the two is significantly greater than the simple sum of the effects achieved when used separately. (2) Batteries using silicon-based negative electrode active materials have improved first coulombic efficiency. (3) Batteries using silicon-based negative electrode active materials have improved cycle capacity retention. (4) Batteries that use silicon-based negative electrode active materials have high energy density. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a schematic diagram of a secondary battery according to an embodiment of the present application. [Figure 2] FIG. 2 is an exploded view of the secondary battery shown in FIG. 1 according to the embodiment of the present application. [Figure 3] 1 is a schematic diagram of a battery module according to an embodiment of the present application; [Figure 4] 1 is a schematic diagram of a battery pack according to an embodiment of the present application. [Figure 5] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present application. [Figure 6] 1 is a schematic diagram of an electrical device in which a secondary battery according to an embodiment of the present application is used as a power source; DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, embodiments specifically disclosing the silicon-based negative electrode active material and its manufacturing method, positive electrode sheet, negative electrode sheet, secondary battery, battery module, battery pack, and device of the present application will be described in detail with appropriate reference to the drawings. However, unnecessary detailed description may be omitted. For example, detailed description of well-known matters may be omitted, and redundant description of substantially the same structure may be omitted. This is to avoid unnecessary redundancy in the following description so as to facilitate understanding by those skilled in the art. Furthermore, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application, and are not intended to limit the scope of the claims.

[0028] The "ranges" disclosed in this application are defined by a lower limit and an upper limit. A given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits define the boundaries of that particular range. Such defined ranges may or may not include the endpoints, and may be arbitrarily combined; that is, any lower limit and any upper limit may be combined to form a single range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that the ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if 1 and 2 are listed as the minimum range values ​​and 3, 4, and 5 are listed as the maximum range values, the ranges of 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5 are all contemplated. In this application, unless otherwise specified, a numerical range of "a to b" represents a shorthand notation for any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0 to 5" means that all real numbers between "0 and 5" have already been enumerated herein, and "0 to 5" is merely a shorthand notation for combinations of these numbers. Note that when a parameter is described as an integer ≧2, this is equivalent to disclosing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0029] Unless otherwise specified, all embodiments and optional embodiments in this application can be combined with each other to form new technical solutions.

[0030] Unless otherwise specified, all steps in this application may be performed in order or randomly, preferably in order. For example, the method including steps (a) and (b) means that the method may include steps (a) and (b) performed in order, or may include steps (b) and (a) performed in order. For example, the method may further include step (c), meaning that step (c) can be added to the method in any order; for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), or may be other cases.

[0031] Unless otherwise specified, expressions such as "comprise" and "comprises" referred to in this application may be open-ended or closed-ended. For example, expressions such as "comprise" and "comprises" may indicate that the invention may further include or include other components not listed, or may include or include only the listed components.

[0032] Unless otherwise specified, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following conditions satisfy the condition "A or B": A is true (or exists) but B is false (or does not exist); A is false (or does not exist) but B is true (or exists); or A and B are both true (or exist).

[0033] In this specification, ppm (parts per million) means parts per million, provided that when ppm is used to describe the content of S element or Mg element, it means parts per million of the mass of S element or Mg element in the silicon-based negative electrode active material relative to the mass of the silicon-based negative electrode active material.

[0034] [Secondary battery] Secondary batteries, also known as rechargeable batteries or storage batteries, refer to batteries that can be used continuously after being discharged by activating the active material through charging.

[0035] Typically, a secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. During charging and discharging, active ions (e.g., sodium ions) are inserted and removed between the positive and negative electrode sheets. The separator is located between the positive and negative electrode sheets and primarily serves to prevent short circuits between the positive and negative electrodes while allowing the active ions to pass through. The electrolyte is located between the positive and negative electrode sheets and primarily serves to conduct the active ions.

[0036] An example of a secondary battery is a lithium-ion battery. A lithium-ion battery is mainly composed of a positive electrode, a negative electrode, a separator, and an electrolyte. The positive and negative electrodes are separated by a separator to prevent short circuits, and the electrolyte is impregnated into the positive and negative electrodes to ensure ionic conduction. When charging, Li + Li is released from the positive electrode, passes through the separator via the electrolyte, and is inserted into the negative electrode, causing the positive electrode to be in a high-potential sodium-deficient state and the negative electrode to be in a low-potential sodium-rich state. + Li+ is released from the negative electrode, passes through the separator via the electrolyte, and is inserted into the positive electrode material, returning the positive electrode to a sodium-rich state. To maintain charge balance, an equal number of electrons are transferred through an external circuit during charging and discharging, moving between the positive and negative electrodes along with Li+, resulting in oxidation and reduction reactions at the positive and negative electrodes, respectively. Lithium ions can reversibly move between the positive and negative electrodes in the electrolyte, and both the positive and negative electrodes are composed of insertion-type materials that allow reversible insertion and desorption of lithium ions.

[0037] The secondary battery is, for example, a sodium ion battery. A sodium ion battery is mainly composed of a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode and the negative electrode are separated by a separator to prevent short circuits, and the electrolyte is impregnated into the positive electrode and the negative electrode to ensure ionic conduction. During charging, Na + is released from the positive electrode, passes through the separator via the electrolyte, and is inserted into the negative electrode, causing the positive electrode to be in a high-potential sodium-deficient state and the negative electrode to be in a low-potential sodium-rich state. + The sodium ions are released from the negative electrode, pass through the separator via the electrolyte, and are inserted into the positive electrode material, returning the positive electrode to a sodium-rich state. To maintain charge balance, the same number of electrons are transferred through an external circuit during charging and discharging, moving between the positive and negative electrodes along with Na+, resulting in oxidation and reduction reactions at the positive and negative electrodes, respectively. Sodium ions can reversibly move between the positive and negative electrodes in the electrolyte, and both the positive and negative electrodes are composed of an insertion-type material that allows reversible insertion and desorption of sodium ions.

[0038] [Negative electrode sheet] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.

[0039] The negative electrode active material of the present application is a silicon-based negative electrode active material that includes an alkali metal element-containing silicate and also contains both S and Mg elements.

[0040] In the above solution, the silicon-based negative electrode active material contains a combination of sulfur and magnesium, and this particular combination improves the cycle capacity retention of the silicon-based negative electrode active material. The combination of sulfur and magnesium produces an unexpected synergistic effect, and the technical effect achieved by this combination is significantly greater than the simple sum of the effects of using each element separately. Without being limited to the following theory, the lithium-sulfur compound formed by sulfur and lithium can mitigate particle expansion and improve material stability, effectively improving the cycle performance of the battery. Mg can form magnesium aluminum silicate with silicon-oxygen materials, effectively improving the initial coulombic efficiency of the battery.

[0041] In some embodiments, the alkali metal element includes one or more of Li, Na, and K. Optionally, the alkali metal element includes Li. In these embodiments, the battery has improved first cycle efficiency and cycle capacity retention.

[0042] In some embodiments, the alkali metal element-containing silicate comprises a lithium-containing silicate, and the lithium-containing silicate has an XRD diffraction peak half width of 0.5° or more, preferably 1.1° to 1.8°. In the above embodiments, the battery has improved initial coulombic efficiency and cycle capacity retention.

[0043] In some embodiments, the alkali metal silicate comprises a lithium silicate, and the lithium silicate has a crystallite size of 10 nm or less, preferably 2 nm to 6 nm. In the above embodiments, the battery has improved initial coulombic efficiency and cycle capacity retention.

[0044] In some embodiments, the lithium-containing silicate includes at least one of Li2Si2O5 and Li2SiO3, and optionally, the lithium-containing silicate includes Li2SiO3.

[0045] In some embodiments, the S and Mg elements grow in the silicon-based negative electrode active material, for example, during a vapor phase growth process of the silicon-based negative electrode active material. In some embodiments, the S and Mg elements grow in the silicon-based negative electrode active material when vapor-deposited together with the silicon-based negative electrode active material.

[0046] In some embodiments, the silicon in the silicon-based negative electrode active material may be present in the form of multiple silicon phases, including crystalline silicon, and the silicon phases may be dispersed and uniformly distributed in the matrix.

[0047] In some embodiments, the silicon-based negative electrode active material further includes at least one of silicon crystal grains and silicon-oxygen material crystal grains.

[0048] In some embodiments, the silicon-based negative electrode active material has a greater S content than Mg content, and within the above ratio range, S and Mg exhibit an unexpected synergistic effect, resulting in improved initial coulombic efficiency and cycle capacity retention.

[0049] In some embodiments, the silicon-based negative electrode active material has a mass ratio of S to Mg of at least 1.3:1. Within this ratio range, S and Mg exhibit an unexpected synergistic effect, resulting in improved cycle capacity retention in the battery.

[0050] In some embodiments, the silicon-based negative electrode active material has a mass ratio of S to Mg of 1.3:1 to 25:1. Within this ratio range, S and Mg exhibit an unexpected synergistic effect, resulting in improved initial coulombic efficiency and cycle capacity retention.

[0051] In some embodiments, the silicon-based negative electrode active material has a mass ratio of S to Mg of 1.3:1 to 20:1. Within this ratio range, S and Mg exhibit an unexpected synergistic effect, resulting in improved initial coulombic efficiency and cycle capacity retention.

[0052] In some embodiments, the silicon-based negative electrode active material has a mass ratio of S to Mg of 1.3:1 to 15:1. Within this ratio range, S and Mg exhibit an unexpected synergistic effect, resulting in improved initial coulombic efficiency and cycle capacity retention.

[0053] In some embodiments, the silicon-based negative electrode active material has a mass ratio of S to Mg of 2.2:1 to 10:1. Within this ratio range, S and Mg exhibit an unexpected synergistic effect, resulting in improved initial coulombic efficiency and cycle capacity retention.

[0054] In some embodiments, the mass ratio of S to Mg in the silicon-based negative electrode active material may be 30:1 or less, 20:1 or less, 15:1 or less, 14:1 or less, 13:1 or less, 12:1 or less, or 10:1 or less. In some embodiments, the mass ratio of S to Mg in the silicon-based negative electrode active material may be 1.1:1 or more, 2:1 or more, 3:1 or more, 4:1 or more, 5:1 or more, or 6:1 or more. The mass ratio of S to Mg may be within any of the upper and lower limits described above. Within the above ratio range, S and Mg exhibit an unexpected synergistic effect, resulting in improved initial coulombic efficiency and cycle capacity retention.

[0055] In some embodiments, the mass ratio of S element to Mg element in the silicon-based negative electrode active material may be 1 to 7:1, 2 to 7:1, 3 to 7:1, 1 to 8:1, 2 to 8:1, 3 to 8:1, 4 to 8:1, 1 to 10:1, 2 to 10:1, 4 to 10:1, 6 to 10:1, 1 to 15:1, 2 to 15:1, 4 to 15:1, 6 to 15:1, 1 to 20:1, 2 to 20:1, 4 to 20:1, 6 to 20:1, 1 to 25:1, 2 to 25:1, 4 to 25:1, or 6 to 25:1.

[0056] In some embodiments, the silicon-based negative electrode active material contains 50 ppm or more of S. Within this range, S and Mg exhibit an unexpected synergistic effect, resulting in improved cycle capacity retention.

[0057] In some embodiments, the content of S in the silicon-based negative electrode active material is 50 ppm to 1500 ppm, which allows the battery to have improved first cycle efficiency and cycle capacity retention. Within this content range, S and Mg exhibit an unexpected synergistic effect, allowing the battery to have improved cycle capacity retention.

[0058] In some embodiments, the content of S in the silicon-based negative electrode active material is 100 ppm to 1400 ppm, which allows the battery to have improved first cycle efficiency and cycle capacity retention. Within this content range, S and Mg exhibit an unexpected synergistic effect, allowing the battery to have improved cycle capacity retention.

[0059] In some embodiments, the upper limit of the S element content in the silicon-based negative electrode active material may be any one selected from 1500 ppm, 1400 ppm, 1300 ppm, 500 ppm, 400 ppm, 300 ppm, and 200 ppm, and the lower limit of the S element content may be any one selected from 300 ppm, 200 ppm, 150 ppm, 100 ppm, 80 ppm, and 50 ppm. That is, the S element content range may be any one of the upper and lower limits described above. Within the above content ranges, S and Mg exhibit an unexpected synergistic effect, resulting in improved cycle capacity retention of the battery.

[0060] In some embodiments, the content of S element in the silicon-based negative electrode active material is optionally 500 to 1000 ppm, 500 to 1200 ppm, 500 to 1500 ppm, 800 to 1000 ppm, 800 to 1200 ppm, 800 to 1500 ppm, 1000 to 1200 ppm, or 1000 to 1500 ppm.

[0061] In some embodiments, the content of Mg element in the silicon-based negative electrode active material is 500 ppm or less, so that the battery has improved initial coulombic efficiency.

[0062] In some embodiments, the content of Mg element in the silicon-based negative electrode active material is 50 ppm to 300 ppm, which allows the battery to have a further improved initial coulombic efficiency.

[0063] In some embodiments, the content of Mg element in the silicon-based negative electrode active material is 100 ppm to 300 ppm, which allows the battery to have a further improved initial coulombic efficiency.

[0064] In some embodiments, the upper limit of the Mg content in the silicon-based negative electrode active material may be any one selected from 800 ppm, 600 ppm, 500 ppm, 400 ppm, 300 ppm, 200 ppm, 100 ppm, 80 ppm, and 60 ppm, and the lower limit of the Mg content may be any one selected from 10 ppm, 30 ppm, 50 ppm, 70 ppm, and 100 ppm. That is, the range of the Mg content may be any one of the upper and lower limits described above. Within the above content ranges, the battery exhibits improved initial coulombic efficiency.

[0065] In some embodiments, the content of Mg element in the silicon-based negative electrode active material is optionally 50 ppm to 100 ppm, 50 ppm to 150 ppm, 50 ppm to 200 ppm, 200 ppm to 250 ppm, 50 ppm to 300 ppm, 50 ppm to 350 ppm, 50 ppm to 400 ppm, 50 ppm to 450 ppm, 50 ppm to 500 ppm, 100 ppm to 150 ppm, 100 ppm to 200 ppm, 200 ppm to 250 ppm, 100 ppm to 300 ppm, 100 ppm to 350 ppm, 100 ppm to 400 ppm, 100 ppm to 450 ppm, or 100 ppm to 500 ppm. Within the above content ranges, the battery has improved initial coulombic efficiency.

[0066] In some embodiments, the volume average particle diameter D v 50 is 4 μm to 10 μm, and optionally 5 μm to 8 μm. In the above solution, the battery has a further improved cycle capacity retention rate.

[0067] In some embodiments, the volume average particle diameter D v The average particle diameter D is preferably 4 μm or more, and more preferably 5 μm or more, to reduce the consumption of active ions in the film formation at the negative electrode and to reduce the side reaction of the electrolyte at the negative electrode, thereby reducing the irreversible capacity of the secondary battery and improving the cycle performance of the secondary battery. It can also reduce the amount of binder added to the negative electrode sheet, which helps to improve the energy density of the secondary battery. v 50 is preferably 10 μm or less, more preferably 8 μm or less, thereby shortening the migration path of active ions and electrons within the material particles and increasing the migration speed of ions and electrons, thereby improving the dynamic performance of the secondary battery and helping to prevent the silicon-based negative electrode active material from exploding during charging and discharging, further improving the cycle performance of the secondary battery.

[0068] In some embodiments, the specific surface area of ​​the silicon-based negative electrode active material is 3 m 2 / g or less, and selectively 1m 2 / g~2m 2 / g. In the above method, the battery has a further improved cycle capacity retention rate.

[0069] In some embodiments, the specific surface area of ​​the silicon-based negative electrode active material is 1 m 2 / g~2m 2 / g. The specific surface area is optionally 1 m 2 / g or more, the surface of the material particles can have many active sites, which effectively improves the electrochemical performance of the silicon-based negative electrode active material and meets the requirements for the dynamic performance of secondary batteries. 2 / g or less helps to reduce side reactions of the electrolyte at the negative electrode, reduces the consumption of active ions in the film formation at the negative electrode, reduces the irreversible capacity of the secondary battery, and further improves the cycle performance of the secondary battery.

[0070] In some embodiments, the silicon-based negative electrode active material has a powder volume resistivity of 3 Ω·cm or less, and optionally 0.5 Ω·cm to 1.5 Ω·cm, at a pressure of 4 MPa. In these embodiments, the battery has an improved cycle life.

[0071] In some embodiments, the powder volume resistivity of the silicon-based negative electrode active material at a pressure of 4 MPa is 3 Ω cm or less, more preferably 1.5 Ω cm or less. When the powder volume resistivity of the silicon-based negative electrode active material is within the above range, it is possible to reduce the obstruction of electron movement within the particles, which helps to improve the dynamic performance of the silicon-based negative electrode active material, helps to reduce the polarization phenomenon of the negative electrode, and improve the cycle life of the secondary battery.

[0072] In some embodiments, the silicon-based negative electrode active material has a compaction density of 1.4 to 1.8 g / cm at a pressure of 49000 N. 3 and selectively 1.5 to 1.7 g / cm 3 In the above solution, the battery has a further improved energy density.

[0073] In some embodiments, the silicon-based negative electrode material contains Si and O, and the molar ratio of O to Si is greater than 0 and less than 2, preferably 0.2-1.8:1, more preferably 0.3-1.7:1, more preferably 0.4-1.6:1, more preferably 0.6-1.5:1, more preferably 0.7-1.4:1, more preferably 0.8-1.3:1, more preferably 0.9-1.2:1, and more preferably 1.0-1.1:1.

[0074] In some embodiments, at least a portion of the surface of the silicon-based negative electrode active material has a coating layer.

[0075] In some embodiments, the coating layer material may include one or more of a polymer, a carbon material, a metal material, and a metal compound. For example, the coating layer may include one or more of a polymer coating layer, a carbon coating layer, and a metal compound coating layer. Optionally, the polymer may be one or more selected from polyaniline, polyacetylene, polystyrene, polyacrylonitrile, polyvinyl chloride, and polyethylene. Optionally, the carbon material may include one or more of graphite, mesocarbon microbeads (MCMB), hydrocarbon-based compound pyrolytic carbon, hard carbon, and soft carbon, where graphite may be one or more of natural graphite and artificial graphite. Optionally, the metal compound may include one or more of Ti5Si3, Al2O3, and TiO2. The coating layer may further mitigate the volume expansion effect of the silicon-based negative electrode active material and improve the cycle life of the material. At the same time, the coating layer further protects the silicon-based negative electrode active material, suppresses side reactions of the electrolyte on the material surface, and protects the material surface from erosion by the electrolyte, allowing the silicon-based negative electrode active material to exhibit high capacity and further improving the cycle life of the battery.

[0076] In a second aspect, the present application provides a method for producing any one of the silicon-based negative electrode active materials described above, Providing a raw material containing Si element, O element, S element and Mg element; heating the source material to form a vapor by vapor deposition, and then cooling the vapor to form a deposit; pulverizing the sediment to obtain a pulverized product; and reacting the previous product with an alkali metal source to obtain an alkali metal-containing product.

[0077] In some embodiments, the method for producing a silicon-based negative electrode active material includes: The method further includes subjecting the alkali metallization product to a coating treatment to obtain a product having a coating layer.

[0078] In some embodiments, the Si element in the raw material may be derived from elemental silicon and silicon oxide, and the O element in the raw material may be derived from silicon oxide. Here, the elemental silicon includes, for example, metallic silicon. The silicon oxide includes, for example, one or more of silicon monoxide (SiO) and silicon dioxide (SiO2). The purity of the elemental silicon is, for example, 3N or more, 4N or more, 5N or more, or 6N or more.

[0079] In some embodiments, the S element in the raw material may be derived from the S element contained in elemental silicon or silicon oxide itself, or may be derived from a sulfur source added to the raw material.

[0080] In some embodiments, the Mg element in the raw material may be derived from elemental silicon or silicon oxide itself, or may be derived from a magnesium source added to the raw material.

[0081] In some embodiments, the alkali metal element in the raw material may be derived from the alkali metal element contained in elemental silicon or silicon oxide itself, or may be derived from an alkali metal source added to the raw material.

[0082] In some embodiments, the feedstock contains a sulfur source, and at least a portion of the S element in the feedstock is derived from the sulfur source. The sulfur source may be one or more selected from high-sulfur coke, elemental sulfur, metal sulfides, sulfates, and polysulfides.

[0083] In some embodiments, the raw material contains a magnesium source. At least a portion of the Mg element in the raw material is derived from the magnesium source. The magnesium source may be one or more selected from metallic magnesium, magnesium alloys, and magnesium compounds. Here, the magnesium compound may be one or more selected from magnesium oxide, magnesium sulfide, magnesium carbonate, magnesium hydroxide, magnesium acetate, magnesium oxalate, magnesium nitrate, and magnesium sulfate.

[0084] In some embodiments, the alkali metal source may be one or more selected from an alkali metal element, an alkali metal alloy, and an alkali metal compound, wherein the alkali metal compound may be one or more selected from an alkali metal oxide, an alkali metal sulfide, an alkali metal carbonate, an alkali metal hydroxide, an alkali metal acetate, an alkali metal oxalate, an alkali metal nitrate, and an alkali metal sulfate.

[0085] In some embodiments, the raw material containing the elements Si, O, S, and Mg includes elemental silicon, silicon dioxide, a sulfur source, and a magnesium source.

[0086] In some embodiments, the content of element S in the negative electrode active material is adjusted by adjusting the type and amount of sulfur source in the raw materials.

[0087] In some embodiments, the content of elemental Mg in the negative electrode active material is adjusted by adjusting the type and amount of magnesium source in the raw materials.

[0088] In some embodiments, the content of the S element in the negative electrode active material is adjusted by one or more means, such as mixing silicon oxide powders or metal silicon powders with different S element contents, and adjusting the type and amount of the sulfur source.

[0089] In some embodiments, the content of Mg element in the negative electrode active material is adjusted by one or more means, such as mixing silicon oxide powders or metal silicon powders with different Mg element contents, and adjusting the type and amount of magnesium source.

[0090] In some embodiments, the heating of the feedstock to form the vapor is carried out in an inert atmosphere at atmospheric or reduced pressure.

[0091] In some embodiments, the cooling of the vapor to form the deposit is carried out in an inert atmosphere at atmospheric or reduced pressure.

[0092] In the above manufacturing method, the inert atmosphere may be a nitrogen atmosphere, an argon atmosphere, a helium atmosphere, etc. Optionally, the absolute pressure of the inert atmosphere is normal pressure (1 standard atmosphere) or reduced pressure (less than 1 standard atmosphere). Optionally, the absolute pressure of the inert atmosphere is 10 Pa to 950 Pa, more preferably 20 Pa to 100 Pa.

[0093] In some embodiments, by reducing the pressure (i.e., increasing the degree of vacuum) within the above-mentioned pressure range of the inert atmosphere, the contents of S and Mg in the final silicon-based negative electrode active material can be increased accordingly.

[0094] In some embodiments, the temperature of the raw material is 1100 to 1550°C when the raw material is heated to form steam.

[0095] In some embodiments, the cooling temperature for cooling the vapor to form the deposit is 800-1050°C.

[0096] In some embodiments, the cooling temperature during the vapor-cooling process to form the deposit can be adjusted to achieve a suitable crystal structure. Alternatively, the cooling temperature can be set to 850°C to 1050°C, which helps achieve good crystallite size and suitable crystallinity in the silicon-based negative electrode active material and ensures high battery cycle performance. If the cooling temperature is lower than 800°C, the deposit will be severely pulverized, and the crystallite size of the material will become too large, affecting the battery cycle performance. If the cooling temperature is higher than 1050°C, the deposition efficiency of the vapor mixture will be low, and further deposition may not be possible.

[0097] In some embodiments, by increasing the temperature within the above heating temperature range, the contents of S and Mg in the final silicon-based negative electrode active material can be increased accordingly.

[0098] In some embodiments, within the above pressure range of the inert atmosphere, the pressure can be reduced, i.e., the degree of vacuum can be increased, thereby correspondingly increasing the contents of S and Mg elements in the final silicon-based negative electrode active material.

[0099] In some embodiments, the operation of crushing the sediment is carried out to obtain a predetermined volume average particle size (D v 50) and specific surface area parameters, and subjecting the sediment to coarse crushing, fine grinding, and classification to obtain a product that meets the predetermined parameters. In some embodiments, the sediment can be crushed and classified using any method or device known in the art, such as a grinder, an integrated airflow crusher, and classifier.

[0100] In some embodiments, the method for preparing a silicon-based negative electrode active material further includes a step of coating the alkali metallization product to obtain a product having a coating layer.

[0101] In some embodiments, the coating layer material may include one or more of a polymer, a carbon material, a metal material, and a metal compound. For example, the coating layer may include one or more of a polymer coating layer, a carbon coating layer, and a metal compound coating layer. Optionally, the polymer may be one or more selected from polyaniline, polyacetylene, polystyrene, polyacrylonitrile, polyvinyl chloride, and polyethylene. Optionally, the carbon material may include one or more of graphite, mesocarbon microbeads (MCMB), hydrocarbon-based compound pyrolytic carbon, hard carbon, and soft carbon, where graphite may be one or more of natural graphite and artificial graphite. Optionally, the metal compound may include one or more of Ti5Si3, Al2O3, and TiO2. The coating layer may further mitigate the volume expansion effect of the silicon-based negative electrode active material, thereby improving the cycle life of the material. At the same time, the coating layer further protects the silicon-based negative electrode active material, suppresses side reactions of the electrolyte on the material surface, and protects the material surface from erosion by the electrolyte, allowing the silicon-based negative electrode active material to exhibit high capacity and further improving the cycle life of the battery.

[0102] In some embodiments, a liquid-phase coating method is used to coat the surface of the silicon-based negative electrode active material to form a coating layer, for example, by dissolving a polymer in a solvent and thoroughly mixing it with silicon-based negative electrode active material particles to homogeneously mix them, and then evaporating and removing the solvent, so that the polymer uniformly coats the surface of the silicon-based negative electrode active material particles.

[0103] In some embodiments, a coating layer is formed on the surface of the silicon-based negative electrode active material by chemical vapor deposition, for example, by introducing a hydrocarbon compound gas into a reactor containing the silicon-based negative electrode active material and performing heat treatment in an inert atmosphere to carbonize the hydrocarbon compound and form a coating layer that coats the surface of the silicon-based negative electrode active material, thereby obtaining a silicon-based negative electrode active material whose surface is coated with the coating layer.

[0104] In some embodiments, the coating process includes a carbon coating process, which optionally includes placing the pulverized product in a chamber containing a carbon source gas, heating the pulverized product to 700-1000°C, and maintaining the temperature for 1-6 hours.

[0105] In some embodiments, the coating process includes a carbon coating process, which optionally includes placing the pulverized product in a chamber containing a carbon source gas, heating the pulverized product to 800-900°C, and maintaining the temperature for 2-5 hours.

[0106] In some embodiments, the alkali metal source may be one or more of an alkali metal, an alkali metal hydroxide, an alkali metal carbonate, an alkali metal nitrate, an alkali metal amide, or an alkali metal hydride.

[0107] In some embodiments, the alkali metal source may be one or more of metallic lithium, lithium hydroxide, lithium carbonate, lithium nitrate, lithium amide, and lithium hydride.

[0108] For example, the negative electrode current collector has two surfaces facing each other in the thickness direction thereof, and the negative electrode film layer is provided on either one or both of the two facing surfaces of the negative electrode current collector.

[0109] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, the metal foil may be a copper foil. The composite current collector may include a polymeric substrate layer and a metal layer formed on at least one surface of the polymeric substrate. The composite current collector may be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy) on a polymeric substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0110] In some embodiments, the negative electrode film layer may include silicon-based negative electrode active materials known in the art other than those described herein, and those skilled in the art can select the material based on their actual needs. Examples include, but are not limited to, one or more of artificial graphite, natural graphite, hard carbon, soft carbon, other silicon-based materials, and tin-based materials. The other silicon-based materials may include one or more of silicon elemental, silicon-oxygen complexes other than those described herein, silicon-carbon complexes, silicon-nitrogen complexes, and silicon alloys. The tin-based materials may include one or more of tin elemental, tin-oxygen compounds, and tin alloys. All of these materials are commercially available.

[0111] In some embodiments, the negative electrode membrane layer optionally further includes a binder. For example, the binder may be at least one selected from styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0112] In some embodiments, the negative electrode film layer optionally further includes a conductive agent, for example, at least one selected from superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0113] In some embodiments, the negative electrode membrane layer optionally further comprises other auxiliary agents, such as a thickener (e.g., carboxymethylcellulose sodium (CMC-Na)).

[0114] In some embodiments, the negative electrode sheet can be manufactured as follows: The components for manufacturing the negative electrode sheet described above, such as the silicon-based negative electrode active material, the conductive agent, the binder, and any other components, are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry, which is then coated onto a negative electrode current collector, followed by baking, cold pressing, and other processes to obtain a negative electrode sheet.

[0115] [Positive electrode sheet] In some embodiments, the positive electrode sheet generally includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer including a positive electrode active material.

[0116] For example, the positive electrode current collector has two surfaces facing each other in the thickness direction thereof, and the positive electrode film layer is provided on either one or both of the two facing surfaces of the positive electrode current collector.

[0117] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, the metal foil may be aluminum foil. The composite current collector may include a polymeric substrate layer and a metal layer formed on at least one surface of the polymeric substrate layer. The composite current collector may be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy) on a polymeric substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0118] In some embodiments, the positive electrode membrane layer optionally further includes a binder. For example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0119] In some embodiments, the positive electrode film layer optionally further comprises a conductive agent, for example, the conductive agent may comprise at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0120] In some embodiments, the positive electrode sheet can be manufactured as follows: The components for manufacturing the positive electrode sheet described above, such as the positive electrode active material, conductive agent, binder, and any other components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry, which is then coated onto a positive electrode current collector, followed by baking, cold pressing, and other processes to obtain the positive electrode sheet.

[0121] [Cathode active material] In some embodiments, the positive electrode active material can be any positive electrode active material for secondary batteries known in the art.

[0122] For example, the positive electrode active material may include at least one material selected from the group consisting of lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and modified compounds thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include lithium cobalt oxide (e.g., LiCoO), lithium nickel oxide (e.g., LiNiO), lithium manganese oxide (e.g., LiMnO, LiMnO), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (e.g., LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM 333 (can also be abbreviated as LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM 523 (can also be abbreviated as LiNi 0.5 Co 0.25 Mn 0.25 O2(NCM 211 (can also be abbreviated as LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM 622 (can also be abbreviated as LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM 811 Lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05Examples of the lithium-containing phosphate having an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (e.g., LiFePO4 (which may also be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (e.g., LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

[0123] [Electrolyte] The electrolyte serves to conduct ions between the positive electrode sheet and the negative electrode sheet. In the present application, the type of electrolyte is not specifically limited and can be selected as needed. For example, the electrolyte may be liquid, gel-like, or all solid.

[0124] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0125] In some embodiments, the electrolyte salt is selected from sodium perchlorate, sodium hexafluorophosphate, sodium tetrafluoroborate, and sodium hexafluoroarsenate.

[0126] In some embodiments, the solvent may be at least one selected from ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0127] In some embodiments, the electrolyte solution optionally further includes additives. For example, the additives may include a negative electrode film-forming additive, a positive electrode film-forming additive, or may further include additives that can improve specific performance of the battery, such as an additive that improves the overcharge performance of the battery or an additive that improves the high-temperature or low-temperature performance of the battery.

[0128] [Separator] In some embodiments, the secondary battery further includes a separator. In the present application, the type of separator is not particularly limited, and any separator with a known porous structure having good chemical stability and mechanical stability can be selected.

[0129] In some embodiments, the separator may be made of at least one material selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film, and is not particularly limited. When the separator is a multilayer composite film, the materials of the layers may be the same or different, and are not particularly limited.

[0130] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly by a winding process or a lamination process.

[0131] In some embodiments, the secondary battery may include an exterior body that can be used to package the electrode assembly and electrolyte.

[0132] In some embodiments, the exterior of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, or a steel case. The exterior of the secondary battery may be a soft pack, such as a bag-type soft pack. The soft pack may be made of plastic, such as polypropylene, polybutylene terephthalate, or polybutylene succinate.

[0133] In the present application, the shape of the secondary battery is not particularly limited, and may be cylindrical, rectangular, or any other shape. For example, Fig. 1 shows a secondary battery 5 having a rectangular structure as an example.

[0134] In some embodiments, referring to FIG. 2 , the exterior body may include a case 51 and a cover plate 53. Here, the case 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and side plates surround the case 51 to form a receiving cavity. The case 51 has an opening communicating with the receiving cavity, and the cover plate 53 can cover the opening to seal the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrode assembly 52 is impregnated with an electrolyte. The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and can be selected by those skilled in the art according to specific actual needs.

[0135] In some embodiments, the secondary batteries are assembled into a battery module, and the number of secondary batteries included in the battery module may be one or more, and the specific number can be selected by those skilled in the art depending on the application and capacity of the battery module.

[0136] Fig. 3 shows an example of a battery module 4. Referring to Fig. 3, in the battery module 4, the plurality of secondary batteries 5 may be arranged in order along the length of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 may be fixed by fastening members.

[0137] Optionally, the battery module 4 may further include a housing having an accommodating space, and the plurality of secondary batteries 5 are accommodated in the accommodating space.

[0138] In some embodiments, the above battery modules are further assembled into a battery pack, and the number of battery modules included in the battery pack may be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0139] 4 and 5 show an example of a battery pack 1. Referring to FIGS. 4 and 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 provided in the battery box. The battery box includes an upper box 2 and a lower box 3, and the upper box 2 is covered by the lower box 3 to form a sealed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

[0140] The present application also provides an electric device including at least one of the secondary batteries, battery modules, or battery packs provided herein. The secondary battery, battery module, or battery pack may be used as a power source for the electric device or as an energy storage unit for the electric device. The electric device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), trains, ships, satellites, energy storage systems, etc.

[0141] The electrical device can be selected from a secondary battery, a battery module, or a battery pack depending on the needs of the use.

[0142] 6 shows an example of an electric device, such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, which can use a battery pack or a battery module to meet the high power and high energy density requirements of secondary batteries.

[0143] Examples of the present application are described below. The examples described below are illustrative and are intended only to interpret the present application, and should not be understood as limiting the present application. If specific techniques or conditions are not specified in the examples, they will be carried out in accordance with the techniques or conditions described in the literature in this field or the product instructions. Reagents or equipment used without a specified manufacturer are all ordinary products that can be purchased commercially.

[0144] 1. Method for manufacturing silicon-based negative electrode active material 1.1 Overview In the specific embodiment below, a method for producing a negative electrode active material is outlined as follows.

[0145] 1) Vapor containing Si, O, S and Mg elements was provided and cooled to obtain a deposit. 2) The sediment was pulverized to obtain a pulverized product. 3) The pulverized product was subjected to a carbon coating treatment to obtain a carbon-coated product. 4) The carbon-coated product was subjected to a lithiation reaction with a lithium source, and the product was recovered to obtain a negative electrode active material.

[0146] 1.2 Details In the following specific embodiment, the method for producing the negative electrode active material will be described in detail as follows.

[0147] 1) Depending on the contents of S and Mg in the target product, a raw material composition containing elemental silicon, silicon oxide, a sulfur source (high-sulfur coke containing 2.5 wt% S), and a magnesium source (metallic magnesium) was provided. 2) In a helium atmosphere at an absolute pressure of 30 Pa, the raw material composition was heated to 1300°C by vapor phase growth to form vapor, and the vapor was cooled to 950°C to form a deposit. 3) The sediment was collected and crushed into powder. 4) The powder was placed in the reaction chamber of a vapor deposition device to which a mixture of carbon source gas (20% by volume of acetylene) and nitrogen gas was introduced, heated to 750°C, and held for 2 hours to obtain a carbon-coated product. 5) The carbon-coated product was mixed with a lithium source (lithium amide) in a mass ratio of 100:30, heated to 650°C, and kept at that temperature for 2 hours to carry out a lithiation reaction. The product was then recovered to obtain a negative electrode active material.

[0148] In the above-described manufacturing method, the contents of the sulfur source and magnesium source in the raw material mixture can be adaptively adjusted according to the composition of the target product, thereby obtaining negative electrode active materials with various S and Mg contents. It should be understood that, due to the influence of the purity of elemental silicon and silicon dioxide, some elemental silicon and silicon dioxide already contain a certain amount of elemental S and Mg. In this case, it is necessary to adaptively adjust the contents of the sulfur source and magnesium source in the raw material mixture according to the components and composition of the target product sample.

[0149] According to the above method, a plurality of negative electrode active material samples (hereinafter simply referred to as samples) having different S element contents and Mg element contents were manufactured and obtained. Details are as shown in Table 1. The examples shown in Table 1 include Examples 1 to 11 (E1 to E12) and Comparative Examples 1 to 3 (D1 to D3).

[0150] In the above-described manufacturing method, the contents of the alkali metal source, sulfur source, and magnesium source in the raw material mixture can be adaptively adjusted according to the composition of the target product, thereby obtaining silicon-based negative electrode active materials with various S and Mg contents. It should be understood that, due to the influence of the purity of elemental silicon and silicon dioxide, some elemental silicon and silicon dioxide already contain a certain amount of elemental S and Mg. In this case, it is necessary to adaptively adjust the contents of the sulfur source and magnesium source in the raw material mixture according to the components and composition of the target product sample.

[0151] According to the above method, a plurality of silicon-based negative electrode active material samples (hereinafter simply referred to as samples) having different S element contents and Mg element contents were produced and obtained. These samples have the following properties.

[0152] 1) The silicon-based negative electrode active material was a silicon-based negative electrode active material having a carbon coating layer, and the content of the carbon coating layer was 4.2±1%, with the remainder being the silicon-based negative electrode active material. 2) The molar ratio of O element to Si element in the silicon-based negative electrode active material was 1±0.1:1. 3) Based on 100% silicon-based negative electrode active material, the Li element content was 7.3±0.5%. 4) The content of S element was as shown in Table 1, based on 100% silicon-based negative electrode active material. 5) The content of Mg element was as shown in Table 1, based on 100% silicon-based negative electrode active material. 6) The volume average particle diameter Dv50 of the silicon-based negative electrode active material was 6.5±0.5 μm. 7) The specific surface area of ​​the silicon-based negative electrode active material is 1.6±0.25m 2 / g. 8) The powder volume resistivity of the silicon-based negative electrode active material was 1±0.1 Ω·cm at a pressure of 4 MPa. 9) The compaction density of silicon-based negative electrode active material at a pressure of 49,000 N is 1.6 ± 0.1 g / cm 3 It was. 10) The silicon-based negative electrode active material contained Li2SiO3, and the half-width of the XRD diffraction peak of Li2SiO3 was 1.6°±0.2°, and the crystallite size was 4±2 nm.

[0153] Table 1 shows silicon-based negative electrode active material samples with different S element contents and Mg element contents.

[0154] Button battery manufacturing (1) Preparation of negative electrode sheet: The silicon-based negative electrode active material prepared above, the conductive agent Super-P (conductive carbon black), and the binder PAA (polyacrylic acid) were mixed in a mass ratio of 85:5:10 in an appropriate amount of deionized water with sufficient stirring to form a uniform negative electrode slurry. The negative electrode slurry was coated onto the surface of the copper foil of the negative electrode current collector, dried, and cold-pressed to obtain a negative electrode sheet. (2) Counter electrode: metallic lithium sheet. (3) Separator: Polyethylene (PE) film. (4) Preparation of electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, and then LiPF6 was uniformly dissolved in the above solution to obtain an electrolyte. Fluoroethylene carbonate (FEC) was added, and the concentration of LiPF6 was 1 mol / L, and the mass proportion of FEC in the electrolyte was 6%. (5) Manufacture of button-type battery: The above-mentioned negative electrode sheet, separator, and counter electrode, which is a metallic lithium sheet, were laminated in this order, and the above-mentioned electrolyte solution was added to obtain a button-type battery.

[0155] II. Analysis and detection methods 2.1 Elemental analysis (e.g., S, Mg, Si, and alkali metal elements) The content of elements has a meaning known in the art and may be measured by a method known in the art. The silicon-based negative electrode active material is decomposed according to EPA-3052-1996 "Microwave Acid Decomposition Method for Silicates," and the content of the target element is measured using an ICAP-7000 inductively coupled plasma optical emission spectrometer (ICP-OES) from Thermo Fisher Scientific in the United States in accordance with EPA 6010D-2014 "Inductively Coupled Plasma Atomic Emission Spectroscopy." The specific measurement method is as follows: 0.5 g of a silicon-based negative electrode active material sample is microwave-decomposed using 10 mL of nitric acid and 10 mL of hydrofluoric acid. The decomposition is then transferred to a 50 mL volumetric flask and the volume is measured. The content of the target element is then measured using an ICAP-7000 ICP-OES.

[0156] 2.2 Elemental analysis (oxygen element, carbon element) The content of elements has a meaning known in the art and may be measured by a method known in the art. The content of carbon element in the silicon-based negative electrode active material may be measured with reference to GB / T 20123-2006 / ISO 15350:2000, and the testing equipment may be an HCS-140 type infrared carbon / sulfur analyzer.

[0157] The oxygen element content can be determined by referring to JY / T 017-1996 General Rules for Analysis Methods of Elemental Analysis Instruments, and the test equipment can be Elementar's rapid OXY cube oxygen elemental analyzer.

[0158] 2.3 Volume resistivity The volume resistivity of a material has a meaning known in the art and can be measured by instruments and methods known in the art. For example, the powder volume resistivity of the silicon-based negative electrode active material of the present application at a pressure of 4 MPa can be measured by a four-point probe method. The measurement method includes placing the silicon-based negative electrode active material powder of the present application on a sample stage, applying a pressure of 4 MPa to the powder with a press, and after the pressure has stabilized, reading the powder volume resistivity of the silicon-based negative electrode active material at a pressure of 4 MPa with a resistivity meter.

[0159] 2.4 Compaction The compaction degree of a material has a meaning known in the art and can be measured by instruments and methods known in the art, for example, by referring to the GB / T24533-2009 standard and using an electronic pressure tester such as the UTM7305 electronic pressure tester. A sample of about 1 g is precisely weighed to measure a material having a base area of ​​1.327 cm. 2The specimen is placed in a mold, and a pressure device is used to apply a pressure of 49,000 N to the specimen, and the specimen is held under this pressure for 30 seconds, after which the pressure is released. Then, the height of the specimen is measured, and the degree of compaction of the material can be obtained by the formula ρ = m / (1.327 × h), where ρ represents the degree of compaction of the material, m represents the mass of the specimen, and h represents the height of the specimen after a pressure of 49,000 N has been applied, held under this pressure for 30 seconds, and then the pressure is released.

[0160] 2.4 Powder particle size analysis Material D v 10. D v 50, D v 90 has a meaning known in the art and can be measured using methods known in the art, for example, see GB / T 19077-2016 standard, and can be measured using a laser particle size analyzer (e.g., Malvern Master Size 3000).

[0161] D v 10. D v 50, D v 90 are physically defined as the particle diameters corresponding to the cumulative volume distribution percentages of the silicon-based negative electrode active material when they are 10%, 50%, and 90%, respectively.

[0162] 2.5 Specific surface area analysis The specific surface area of ​​a material has a meaning known in the art and can be measured using instruments and methods known in the art, for example, by referring to GB / T 19587-2017, the standard for measuring the specific surface area of ​​solids by gas adsorption BET method, measuring using a specific surface area analysis measurement method by nitrogen adsorption, and calculating using the BET (Brunauer Emmett Teller) method, where the specific surface area analysis measurement by nitrogen adsorption may be performed using a Tri Star II 3020 specific surface area and pore analysis measurement device manufactured by Micromeritics, USA.

[0163] 2.6 Battery performance measurement (1) Initial coulombic efficiency and cycle capacity retention rate At 25°C and atmospheric pressure, the button battery was discharged at a constant current of 0.1C to 0.005V, then discharged at a constant current of 0.04C to 0.005V, and then allowed to stand for 5 minutes. The discharge capacity, i.e., the first lithium insertion capacity, was recorded. The battery was then charged at a constant current of 0.1C to 1.5V and allowed to stand for 5 minutes. This constituted one charge-discharge cycle, and the charge capacity, i.e., the first lithium extraction capacity, was recorded. The button battery was subjected to 30 charge-discharge cycles according to the above method, and the lithium extraction capacity was recorded for each cycle.

[0164] First coulomb efficiency (%) = First lithium desorption capacity / First lithium insertion capacity × 100% Cycle capacity retention rate (%) = 30th lithium desorption capacity / 1st lithium desorption capacity × 100%

[0165] [Table 1]

[0166] 3. Results and Discussion Table 1 shows the components and compositions of the raw materials for silicon-based negative electrode active materials in several examples of the present application, the contents and content ratios of S and Mg elements in the silicon-based negative electrode active material products, and the performance of batteries using the above silicon-based negative electrode active materials as negative electrode active materials. Each of these is discussed below.

[0167] (1) Composition of raw materials The raw material silicon element used for the samples (E1 to E15) was metallic silicon 1 (Si≧98.5 wt%, S=50 ppm, Mg=10 ppm).

[0168] The raw silicon element used for the samples (D1 to D3) was metallic silicon 2 (Si≧98.5 wt %, containing neither S nor Mg).

[0169] As can be seen from Table 1, the S element and Mg element in the silicon-based negative electrode active material may be of various origins. a) The S element in the silicon-based negative electrode active material may be derived from the raw material, metallic silicon. b) The Mg element in the silicon-based negative electrode active material may be derived from the raw material, metallic silicon. c) The S element in the silicon-based negative electrode active material may be derived from an additional sulfur source. d) The Mg element in the silicon-based negative electrode active material may be derived from an additional magnesium source.

[0170] Those skilled in the art can adaptively adjust the contents of S and Mg in the raw materials depending on the target chemical components of the silicon-based negative electrode active material to ultimately obtain a silicon-based negative electrode active material having the target chemical components. When it is necessary to increase or decrease the S content in the target silicon-based negative electrode active material, metal silicon (or silicon oxide) with a higher or lower S content may be used, or the amount of sulfur source added to the raw materials may be increased or decreased. When it is necessary to increase or decrease the Mg content in the target silicon-based negative electrode active material, metal silicon (or silicon oxide) with a higher or lower Mg content may be used, or the amount of magnesium source added to the raw materials may be increased or decreased.

[0171] (2) Synergistic effect of Mg and S The experimental data in Table 1 demonstrate that the combination of S and Mg in the negative electrode active material of the present application provides an unexpected synergistic effect. Example E1 and Comparative Examples D1, D2, and D3 are analyzed in detail below.

[0172] The silicon-based negative electrode active material of Comparative Example D3 did not contain S or Mg, and its IC+CR value was 152.0%. The silicon-based negative electrode active material of Comparative Example D1 contained 1000 ppm of S but no Mg, and its IC+CR value was 161.2%, a slight increase of 9.2% compared to D3. The silicon-based negative electrode active material of Comparative Example D2 contained 150 ppm of Mg but no S, and its IC+CR value was 154.9%, a slight increase of 2.9% compared to D3.

[0173] The silicon-based negative electrode active material of Example E1 contains both 1500 ppm of S element and 150 ppm of Mg element, and its IC + CR value is 176.0%, which is an increase of 24.0% compared to D1, and the increase is much greater than the simple sum of the performance improvements due to the addition of S or Mg alone (i.e., 9.2% + 2.9% = 12.1%). Therefore, the above experimental evidence demonstrates that the combination of S and Mg indeed brings about an unexpected synergistic effect.

[0174] (3) S / Mg weight ratio in silicon-based negative electrode active materials The experimental data in Table 1 further demonstrate that when the S / Mg weight ratio is greater than 1, the performance of the negative electrode active material is significantly improved. In Example E15, the S / Mg weight ratio was 0.5:1 (<1), and the IC+CR value of the negative electrode active material was only 162.3%. In Examples E1 to E14, the S / Mg weight ratio was 1.1:1 to 24:1 (>1), and the IC+CR values ​​of the negative electrode active materials were 165.2% to 176.0%, superior to Example E15. These experimental data demonstrate that when the S content in the silicon-based negative electrode active material is greater than the Mg content, the silicon-based negative electrode active material exhibits more significant improvements in initial coulombic efficiency and cycle capacity retention.

[0175] (4) S / Mg ratio in silicon-based negative electrode active materials As shown in Examples E1 to E14, when the S / Mg content ratio was 1.1:1 to 24:1, the IC+CR value of the negative electrode active material was 165.2% to 176.0%, and further improved initial coulombic efficiency and cycle capacity retention rate were observed.

[0176] As shown in Examples E1 to E10, when the S / Mg content ratio was 1.1:1 to 10:1, the IC+CR value of the negative electrode active material was 171.4% to 176.0%, and further improved initial coulombic efficiency and cycle capacity retention rate were observed.

[0177] (5) Content of S element and Mg element in silicon-based negative electrode active material As shown in Examples E1 to E15, the content of S element in the silicon-based negative electrode active material was 50 ppm or more, for example, 500 ppm to 1500 ppm, and the negative electrode active material showed improved performance in terms of improved initial coulombic efficiency and cycle capacity retention rate.

[0178] As shown in Examples E1 to E15, the content of Mg element in the silicon-based negative electrode active material was 500 ppm or less, for example, 50 ppm to 300 ppm. The negative electrode active material showed improved performance in terms of improved initial coulombic efficiency and cycle capacity retention rate.

[0179] The above experimental data showed that when silicon-based negative electrode active materials contain only Mg or S alone, only one of the initial coulombic efficiency and cycle capacity retention rate is usually improved, and the improvement is not significant. When silicon-based negative electrode active materials contain a combination of S and Mg, the negative electrode active materials show improvements in both the initial coulombic efficiency and cycle capacity retention rate, with particularly significant improvements, indicating that the S and Mg elements provide an unexpected synergistic effect.

[0180] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and all embodiments that have substantially the same technical ideas and provide the same functions and effects within the scope of the technical solution of the present application are included in the technical scope of the present application. Furthermore, various modifications that can be conceived by a person skilled in the art to the embodiments and other forms formed by combining some of the components of the embodiments are also included in the scope of the present application, as long as they do not deviate from the gist of the present application. [Explanation of symbols]

[0181] 1 battery pack 2 Upper Box 3 Lower Box 4 Battery Module 5 Secondary battery 51 cases 52 Electrode assembly 53 Top cover assembly

Claims

1. A silicon-based negative electrode active material includes an alkali metal element-containing silicate and also contains both an S element and an Mg element.

2. The silicon-based negative electrode active material according to claim 1 , wherein the content of the S element is greater than the content of the Mg element.

3. 3. The silicon-based negative electrode active material according to claim 1, wherein the mass ratio of the S element to the Mg element is 1.3:1 or more, and optionally 2.2:1 to 10:

1.

4. 4. The silicon-based negative electrode active material according to claim 1, wherein the content of the S element is 50 ppm or more, and optionally 500 ppm to 1500 ppm.

5. 5. The silicon-based negative electrode active material according to claim 1, wherein the content of the Mg element is 500 ppm or less, and optionally 50 ppm to 300 ppm.

6. (1) The volume average particle diameter D of the silicon-based negative electrode active material ｖ 50 is between 4 μm and 10 μm, and optionally between 5 μm and 8 μm; (2) The specific surface area of ​​the silicon-based negative electrode active material is 3 m ２ / g or less, and optionally 1m ２ / g to 2m ２ / g, and (3) The silicon-based negative electrode active material has a powder volume resistivity of 3 Ω cm or less at a pressure of 4 MPa, and optionally 0.5 Ω cm to 1.5 Ω cm; (4) The silicon-based negative electrode active material has a compaction density of 1.4 to 1.8 g / cm at a pressure of 49,000 N. ３ and optionally 1.5 to 1.7 g / cm ３ That is, (5) The alkali metal element-containing silicate includes a lithium-containing silicate, and optionally, the lithium-containing silicate is Li ２ Si ２ O ５ , Li ２ SiO ３ and (6) The alkali metal element-containing silicate contains a lithium-containing silicate, and the half width of the XRD diffraction peak of the lithium-containing silicate is 0.5° or more, and optionally 1.1° to 1.8°; (7) The alkali metal element-containing silicate contains a lithium-containing silicate, and the crystallite size of the lithium-containing silicate is 10 nm or less, and optionally 2 nm to 6 nm; The silicon-based negative electrode active material according to any one of claims 1 to 5, having one or more of the following characteristics:

7. 7. The silicon-based negative electrode active material according to claim 1, which has a coating layer on at least a portion of its surface.

8. A method for producing a silicon-based negative electrode active material according to any one of claims 1 to 7, Providing a raw material containing Si, O, S and Mg elements; heating the source material to form a vapor by vapor deposition, and then cooling the vapor to form a deposit; pulverizing the sediment to obtain a pulverized product; and reacting the previous product with an alkali metal source to obtain an alkali metal-containing product.

9. Coating the alkali metallized product to obtain a product having a coating layer The method of claim 8 further comprising:

10. (1) In the operation of heating the raw material to form steam, the heating temperature is 1100 to 1550°C; (2) In the operation of cooling the vapor to form a deposit, the cooling temperature is 800 to 1050°C; 10. The method according to any one of claims 8 to 9, characterized in that it has one or more of the following characteristics:

11. A secondary battery comprising a negative electrode containing the silicon-based negative electrode active material according to any one of claims 1 to 7.

12. An electrical device comprising the secondary battery of claim 11.

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