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

Abstract

The present application provides a silicon-based negative electrode active material that contains an alkaline earth metal element-containing silicate and also contains K and P 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, the range of applications of secondary batteries has expanded, and they are now widely used in a variety of fields, including power storage systems for hydroelectric, thermal, wind, and solar power plants, as well as power tools, electric bicycles, electric motorcycles, electric automobiles, military equipment, and aerospace.

[0003] Silicon-based materials are considered promising silicon-based negative electrode active materials for secondary batteries due to their high energy density. As secondary batteries have made great advances, higher requirements are being placed on their electrochemical performance. Therefore, there is still a need in this field for silicon-based negative electrode active materials with higher performance. Summary of the Invention

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

[0005] In a first aspect, the present application provides a silicon-based negative electrode active material that includes an alkaline earth metal element-containing silicate and simultaneously contains K and P elements.

[0006] In the above embodiment, the silicon-based negative electrode active material contains a combination of K and P elements, and this specific combination improves the cycle performance and rate performance of the silicon-based negative electrode active material. The combination of K and P results in an unexpected synergistic effect, and the technical effect achieved by combining the two elements is significantly superior to the simple addition of each element. Without being limited by the following theory, the K element can form an oxygen-containing silicon-based material and a silicate structure, while preventing rapid expansion of silicon crystal grains and mitigating volume expansion during cycling, effectively improving cycle performance. The P element can effectively lower the ion diffusion barrier and increase the diffusion coefficient of lithium ions in the bulk phase, which is beneficial to improving the rate performance of the battery. Therefore, by using the silicon-based negative electrode active material of the present application, secondary batteries can achieve both high cycle performance and rate performance.

[0007] In some embodiments, the content of the K element is greater than the content of the P element. Within the above ratio range, the K element and the P element exert a synergistic effect that is unexpected, significantly improving the cycle performance and rate performance of the silicon-based negative electrode active material.

[0008] In some embodiments, the mass ratio of the K element to the P element is 7:1 or more, and optionally 9:1 to 15:1. In the above embodiment, the silicon-based negative electrode active material has improved cycle performance and rate performance.

[0009] In some embodiments, the content of the K element is 600 ppm or more, and optionally 800 ppm to 1500 ppm. In the above embodiment, the silicon-based negative electrode active material has improved cycle performance and rate performance.

[0010] In some embodiments, the content of the P element is 500 ppm or less, and optionally 50 ppm to 200 ppm.In the above embodiment, the silicon-based negative electrode active material has improved cycle performance and rate performance.

[0011] In some embodiments, the volume average particle diameter D of the silicon-based negative electrode active material v 50 is 4 μm to 10 μm, and optionally 5 μm to 8 μm. In the above embodiment, the silicon-based negative electrode active material has improved cycle performance and rate performance.

[0012] In some embodiments, the specific surface area of ​​the silicon-based negative electrode active material is 6 m 2 / g or less, and optionally 2m 2 / g~5m 2 In the above embodiment, the silicon-based negative electrode active material has improved cycle performance and rate performance.

[0013] In some embodiments, the silicon-based negative electrode active material has a powder volume resistivity of 6 Ω·cm or less, and optionally 0.5 Ω·cm to 4.5 Ω·cm, at a pressure of 4 MPa. In the above embodiments, the silicon-based negative electrode active material has improved cycle performance and rate performance.

[0014] In some embodiments, the press density of the silicon-based negative electrode active material at a pressure of 49000 N is 1.4 to 1.8 g / cm 3 and optionally 1.5 to 1.7 g / cm 3 In the above embodiment, the silicon-based negative electrode active material has improved energy density.

[0015] In some embodiments, the alkaline earth metal element-containing silicate includes a magnesium-containing silicate, and the magnesium-containing silicate has an XRD diffraction peak half-width of 0.65° or less, and optionally 0.40° to 0.60°. In the above embodiment, the silicon-based negative electrode active material has improved cycle performance and rate performance.

[0016] In some embodiments, the alkaline earth metal element-containing silicate includes a magnesium-containing silicate, and the magnesium-containing silicate has a crystal grain size of 12 nm or more, and optionally 13 nm to 20 nm. In the above embodiment, the silicon-based negative electrode active material has improved cycle performance and rate performance.

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

[0018] In a second aspect, the present application provides: Providing a raw material containing Si element, O element, K element, P element and alkaline earth metal element; a vapor deposition method is employed, in which the source material is heated to form a vapor, and then the vapor is cooled to form a deposit; and pulverizing the deposited material to obtain a pulverized product.

[0019] In some embodiments, the method for preparing a silicon-based negative electrode active material includes: The method further includes performing a coating process on the pulverized product to obtain a product with a coating layer.

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

[0021] In some embodiments, in the step of cooling the vapor to form a deposit, the cooling temperature is 700 to 900°C.

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

[0023] In a fourth aspect, the present application provides an electrical device including the secondary battery according to any one of the above claims. [Effects of the Invention]

[0024] One or more embodiments of the present application may have one or more of the following beneficial effects: (1) The K and P elements have a synergistic effect beyond expectations, and the technical effect achieved by combining the two is significantly superior to the simple addition of the two elements. (2) Silicon-based anode active materials have improved cycle performance; (3) Silicon-based negative electrode active materials have improved rate performance; (4) Silicon-based negative electrode active materials have high energy density. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a schematic diagram of a secondary battery according to one embodiment of the present application. [Figure 2] FIG. 2 is an exploded view of the secondary battery shown in FIG. 1 according to one embodiment of the present application. [Figure 3] 1 is a schematic diagram of a battery module according to one embodiment of the present application. [Figure 4] 1 is a schematic diagram of a battery pack according to one embodiment of the present application. [Figure 5] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to one embodiment of the present application. [Figure 6] 1 is a schematic diagram of an electrical device using a secondary battery according to one embodiment of the present application as a power source. [Explanation of symbols]

[0026] 1···Battery pack, 2···Upper box, 3···Lower box, 4···Battery module, 5···Secondary battery, 51···Housing, 52···Electrode assembly, 53···Top cover assembly. DETAILED DESCRIPTION OF THE INVENTION

[0027] With proper reference to the detailed description of the drawings below, embodiments of the present application, including a silicon-based negative electrode active material and a manufacturing method thereof, a positive electrode sheet, a negative electrode sheet, a secondary battery, a battery module, a battery pack, and an apparatus, are specifically disclosed. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of actually identical structures may be omitted. This is to avoid unnecessarily lengthening the following description and 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 subject matter described in the claims.

[0028] The "ranges" disclosed herein are defined in the form of lower and upper limits, and a given range is defined by selecting one lower limit and one upper limit, with the selected lower and upper limits defining the boundaries of that particular range. Such defined ranges may or may not include the endpoints, and may be arbitrarily combined; i.e., any lower limit may be combined with any upper limit to form a single range. For example, if ranges of 60 to 120 and 80 to 110 are recited for a particular parameter, it is understood that the ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if minimum range values ​​of 1 and 2 are recited and maximum range values ​​of 3, 4, and 5 are recited, 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 specification, unless otherwise specified, a numerical range "a to b" is shorthand 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" indicates that all real numbers between "0 and 5" are listed in this document, and "0 to 5" is merely a shorthand representation of these numerical combinations. Furthermore, expressing that a parameter is an integer of 2 or greater is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0029] Unless otherwise specified, all embodiments and preferred embodiments of the present application may be combined with each other to form new technical aspects.

[0030] Unless otherwise specified, all steps herein may be performed in sequence or randomly, with sequence being preferred. For example, if a method includes steps (a) and (b), this means that the method may include steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, the method mentioned above may further include step (c), indicating that step (c) may 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), etc.

[0031] Unless otherwise specified, the terms "comprise" and "include" used herein may refer to an open or closed system. For example, the terms "comprise" and "include" may indicate that the composition further includes or includes other components not listed, or that the composition only includes or includes the listed components.

[0032] Unless otherwise stated, 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 one of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), or A and B are both true (or exist).

[0033] In this paper, ppm (parts per million) means parts per million. However, when ppm is used to describe the content of K or P, it means the mass of K or P in the silicon-based negative electrode active material as a percentage of the mass of the silicon-based negative electrode active material.

[0034] [Secondary battery] A secondary battery is also called a rechargeable battery or storage battery, and refers to a battery that can be continuously used by activating the active material through charging after discharging the battery.

[0035] Typically, a secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. During the charge and discharge process of the battery, active ions (e.g., sodium ions) are inserted and removed between the positive electrode sheet and the negative electrode sheet. The separator is located between the positive electrode sheet and the negative electrode sheet 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 electrode sheet and the negative electrode sheet and primarily serves to conduct the active ions.

[0036] An example of a secondary battery is a lithium-ion battery. The lithium-ion battery mainly consists 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 impregnates the positive and negative electrodes to ensure ionic conduction. During charging, Li + Li+ is released from the positive electrode and inserted into the negative electrode through the electrolyte and separator, placing the positive electrode in a high-potential, sodium-deficient state and the negative electrode in a low-potential, sodium-rich state. The discharge process is the reverse: Li+ is released from the negative electrode and inserted into the positive electrode material through the electrolyte and separator, restoring the positive electrode to a sodium-rich state. To maintain charge balance, the same number of electrons are transferred through an external circuit during the charge and discharge processes, 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 constructed of insertion-type materials that allow reversible insertion and desorption of lithium ions.

[0037] The secondary battery is, for example, a sodium ion battery. The sodium ion battery mainly comprises 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 impregnates the positive and negative electrodes to ensure ionic conduction. During charging, Na +Na+ is released from the positive electrode and inserted into the negative electrode through the electrolyte and separator, placing the positive electrode in a high-potential, sodium-deficient state and the negative electrode in a low-potential, sodium-rich state. The discharge process is the opposite: Na+ is released from the negative electrode and inserted into the positive electrode material through the electrolyte and separator, restoring the positive electrode to a sodium-rich state. To maintain charge balance, the same number of electrons are transferred through an external circuit during the charge and discharge processes, transferring 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 constructed of insertion-type materials that allow 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 invention is a silicon-based negative electrode active material that contains an alkaline earth metal element-containing silicate and also contains K and P elements simultaneously.

[0040] In the above embodiment, the silicon-based negative electrode active material contains a combination of K and P elements, and this specific combination improves the cycle performance and rate performance of the silicon-based negative electrode active material. The combination of K and P results in an unexpected synergistic effect, and the technical effect achieved by combining the two elements is significantly superior to the simple addition of each element. Without being limited by the following theory, the K element can form a silicate structure with the oxygen-containing silicon-based material, effectively reducing lithium ion consumption and effectively improving cycle performance, while the P element can effectively lower the ion diffusion barrier and increase the diffusion coefficient of lithium ions in the bulk phase, which is advantageous for improving the rate performance of the battery. Therefore, by using the silicon-based negative electrode active material of the present application, secondary batteries can achieve both high cycle performance and rate performance.

[0041] In some embodiments, the silicon in the silicon-based negative electrode active material may exist in a plurality of silicon phases, including crystalline silicon. Specifically, the silicon phases may be uniformly distributed and embedded / embedded in a matrix containing the silicon-based negative electrode active material. In other words, the silicon phases may be dispersed and uniformly distributed in the matrix.

[0042] In some embodiments, the alkaline earth metal element includes one or more of Mg, Be, Ca, and Ba. In these embodiments, the silicon-based negative electrode active materials all exhibit improved cycle performance and rate performance.

[0043] In some embodiments, the alkaline earth metal element includes Mg. In the above embodiments, the silicon-based negative electrode active materials all exhibit further improved cycle performance and rate performance.

[0044] In some embodiments, the alkaline earth metal element-containing silicate includes a magnesium-containing silicate, and the magnesium-containing silicate has an XRD diffraction peak half-width of 0.65° or less, and optionally 0.40° to 0.60°. In the above embodiment, the silicon-based negative electrode active material has further improved cycle performance and rate performance.

[0045] In some embodiments, the alkaline earth metal element-containing silicate includes a magnesium-containing silicate, and the magnesium-containing silicate has a crystal grain size of 12 nm or more, and optionally 13 nm to 20 nm. In the above embodiment, the silicon-based negative electrode active material has further improved cycle performance and rate performance.

[0046] In some embodiments, the silicon-based negative electrode active material contains at least one of silicon crystal grains and silicone material crystal grains.

[0047] In some embodiments, the K and P elements grow in the silicon-based negative electrode active material, for example, during vapor deposition of the silicon-based negative electrode active material. In some embodiments, the K and P elements grow in the silicon-based negative electrode active material when vapor deposited together with the silicon-based negative electrode active material.

[0048] In some embodiments, the content of the K element in the silicon-based negative electrode active material is greater than the content of the P element. Within the above ratio range, the K element and the P element exert an unexpected synergistic effect, which further significantly improves the cycle performance and rate performance of the silicon-based negative electrode active material.

[0049] In some embodiments, the silicon-based negative electrode active material has a mass ratio of K to P of 7:1 or more (e.g., 7.7:1 or more). Within this ratio range, the K and P elements exert an unexpected synergistic effect, further significantly improving the cycle performance and rate performance of the negative electrode active material.

[0050] In some embodiments, the silicon-based negative electrode active material has a mass ratio of K to P of 7:1 to 15:1 (e.g., 7.7:1 to 14.1:1). Within this ratio range, the K and P elements exert an unexpected synergistic effect, further significantly improving the cycle performance and rate performance of the negative electrode active material.

[0051] In some embodiments, the silicon-based negative electrode active material has a mass ratio of K to P of 10:1 to 14:1 (e.g., 10.3:1 to 13.8:1). Within this ratio range, the K and P elements exert an unexpected synergistic effect, further significantly improving the cycle performance and rate performance of the negative electrode active material.

[0052] In some embodiments, the silicon-based negative electrode active material has a mass ratio of K to P of 12:1 to 13:1. Within this ratio range, the K and P elements exert an unexpected synergistic effect, further significantly improving the cycle performance and rate performance of the negative electrode active material.

[0053] In some embodiments, the mass ratio of the K element to the P element in the silicon-based negative electrode active material may be 20:1 or less, 15:1 or less, 14:1 or less, 13:1 or less, or 12:1 or less. In some embodiments, the mass ratio of the K element to the P element in the silicon-based negative electrode active material may be 2:1 or more, 3:1 or more, 4:1 or more, 5:1 or more, 6:1 or more, 7:1 or more, or 8:1 or more. The mass ratio of the K element to the P element may be within any of the upper and lower limits described above. Within the above ratio range, the K element and the P element exert a synergistic effect that is greater than expected, further significantly improving the cycle performance and rate performance of the negative electrode active material.

[0054] In some embodiments, the mass ratio of the K element to the P element may be 13-14:1, optionally 12-14:1, optionally 11-14:1, optionally 10-14:1, optionally 9-14:1, optionally 9-15:1, optionally 8-15:1, optionally 7-15:1, optionally 6-15:1, optionally 5-15:1, optionally 4-15:1, optionally 3-15:1, optionally 2-15:1, or optionally 1-15:1.

[0055] In some embodiments, the content of K in the silicon-based negative electrode active material is 600 ppm or more. Within this content range, K and P exert a synergistic effect beyond expectations, significantly improving the cycle performance and rate performance of the negative electrode active material.

[0056] In some embodiments, the content of K in the silicon-based negative electrode active material is 800 ppm to 1500 ppm. This leads to improved cycle performance and rate performance of the negative electrode active material. Within this content range, K and P exert a synergistic effect beyond expectations, further improving the cycle performance and rate performance of the negative electrode active material.

[0057] In some embodiments, the content of K in the silicon-based negative electrode active material is 1000 ppm to 1500 ppm. This leads to improved cycle performance and rate performance of the negative electrode active material. Within this content range, K and P exert a synergistic effect beyond expectations, further improving the cycle performance and rate performance of the negative electrode active material.

[0058] In some embodiments, the content of K in the silicon-based negative electrode active material is 1100 ppm to 1400 ppm. This leads to improved cycle performance and rate performance of the negative electrode active material. Within this content range, K and P exert a synergistic effect beyond expectations, further improving the cycle performance and rate performance of the negative electrode active material.

[0059] In some embodiments, the content of K in the silicon-based negative electrode active material is 1100 ppm to 1300 ppm. This leads to improved cycle performance and rate performance of the negative electrode active material. Within this content range, K and P exert a synergistic effect beyond expectations, further improving the cycle performance and rate performance of the negative electrode active material.

[0060] In some embodiments, the silicon-based negative electrode active material contains 1200 ppm to 1300 ppm of K. This provides improved cycle performance and rate performance. Within this range, K and P exert a synergistic effect beyond expectations, significantly improving the cycle performance and rate performance of the negative electrode active material.

[0061] In some embodiments, the upper limit of the K element content in the silicon-based negative electrode active material may be any one of 1500 ppm, 1400 ppm, 1300 ppm, and 1200 ppm, and the lower limit of the K element content may be any one of 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, and 1100 ppm. That is, the K element content may be within any of the upper and lower limit values ​​described above. Within the above content ranges, the K element and the P element exert a synergistic effect beyond expectations, significantly improving the cycle performance and rate performance of the negative electrode active material.

[0062] In some embodiments, the content of K element in the silicon-based negative electrode active material is 1200 to 1300 ppm, optionally 1100 to 1300 ppm, optionally 1200 to 1400 ppm, optionally 1100 to 1400 ppm, optionally 1000 to 1400 ppm, optionally 1000 to 1500 ppm, or optionally 800 to 1500 ppm.

[0063] In some embodiments, the silicon-based negative electrode active material contains 500 ppm or less of P, which provides improved cycle performance and rate performance.

[0064] In some embodiments, the silicon-based negative electrode active material contains 50 ppm to 200 ppm of P, which provides improved cycle performance and rate performance.

[0065] In some embodiments, the silicon-based negative electrode active material contains 75 to 150 ppm of P, which provides improved cycle performance and rate performance.

[0066] In some embodiments, the silicon-based negative electrode active material contains 75 to 100 ppm of P, which provides improved cycle performance and rate performance.

[0067] In some embodiments, the silicon-based negative electrode active material contains 80 ppm to 95 ppm of P, which provides improved cycle performance and rate performance.

[0068] In some embodiments, the upper limit of the P content in the silicon-based negative electrode active material may be any one of 200 ppm, 190 ppm, 170 ppm, 150 ppm, and 130 ppm, and the lower limit of the P content may be any one of 30 ppm, 40 ppm, 50 ppm, 60 ppm, 70 ppm, 80 ppm, 90 ppm, and 100 ppm. That is, the P content range may be any one of the upper and lower limits. Within the above content range, the K and P elements exert a synergistic effect beyond expectations, significantly improving the cycle performance and rate performance of the negative electrode active material.

[0069] In some embodiments, the content of the P element in the silicon-based negative electrode active material is 90 to 100 ppm, optionally 80 to 100 ppm, optionally 80 to 110 ppm, optionally 80 to 120 ppm, optionally 70 to 120 ppm, optionally 70 to 130 ppm, optionally 70 to 140 ppm, optionally 70 to 150 ppm, optionally 70 to 160 ppm, optionally 70 to 170 ppm, optionally 70 to 180 ppm, optionally 70 to 180 ppm, optionally 70 to 190 ppm, optionally 70 to 200 ppm, optionally 60 to 200 ppm, or optionally 50 to 200 ppm.

[0070] In some embodiments, the volume average particle diameter D of the silicon-based negative electrode active material v50 is 4 μm to 10 μm, and optionally 5 μm to 8 μm. In the above embodiment, the silicon-based negative electrode active material has improved cycle performance and rate performance.

[0071] In some embodiments, the volume average particle diameter D of the silicon-based negative electrode active material v The average particle size D is preferably 4 μm or more, and more preferably 5 μm or more, which reduces the consumption of active ions in the negative electrode by film formation and reduces 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. The amount of adhesive added to the negative electrode sheet can also be reduced, which is advantageous for increasing the energy density of the secondary battery. v 50 is preferably 10 μm or less, more preferably 8 μm or less, which shortens the migration path of active ions and electrons in the material particles, increases the migration rate of ions and electrons, improves the dynamic performance of the secondary battery, prevents breakage of the silicon-based negative electrode active material during the charge / discharge process, and is also advantageous in improving the cycle performance of the secondary battery.

[0072] In some embodiments, the specific surface area of ​​the silicon-based negative electrode active material is 6 m 2 / g or less, and optionally 2m 2 / g~5m 2 In the above embodiment, the silicon-based negative electrode active material has further improved cycle performance and rate performance.

[0073] In some embodiments, the specific surface area of ​​the silicon-based negative electrode active material is 2 m 2 / g~6m 2 / g. The specific surface area is preferably 2m 2 / g or more, the active sites on the surface of the material particles can be increased, the electrochemical performance of the silicon-based negative electrode active material can be effectively improved, and the dynamic performance requirements of the secondary battery can be met. 2 / g or less is advantageous in reducing side reactions of the electrolyte at the negative electrode, and reducing the consumption of active ions in the film formation at the negative electrode can reduce the irreversible capacity of the secondary battery and improve the cycle performance of the secondary battery.

[0074] In some embodiments, the silicon-based negative electrode active material has a powder volume resistivity of 6 Ω·cm or less, and optionally 0.5 Ω·cm to 4.5 Ω·cm, at a pressure of 4 MPa. In the above embodiments, the silicon-based negative electrode active material has further improved rate performance.

[0075] In some embodiments, the powder volume resistivity of the silicon-based negative electrode active material at a pressure of 4 MPa is 6 Ω cm or less, more preferably 4.5 Ω cm or less. When the powder volume resistivity of the silicon-based negative electrode active material is within this range, inhibition of electron movement within particles can be reduced, which is advantageous for improving the dynamic performance of the silicon-based negative electrode active material.

[0076] In some embodiments, the press density of the silicon-based negative electrode active material at a pressure of 49000 N is 1.4 to 1.8 g / cm 3 and optionally 1.5 to 1.7 g / cm 3 In the above embodiment, the battery further has improved energy density.

[0077] 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, and optionally ranges from 0.2 to 1.8:1, more preferably from 0.3 to 1.7:1, even more preferably from 0.4 to 1.6:1, even more preferably from 0.6 to 1.5:1, even more preferably from 0.7 to 1.4:1, even more preferably from 0.8 to 1.3:1, even more preferably from 0.9 to 1.2:1, and even more preferably from 1.0 to 1.1:1.

[0078] In some embodiments, the silicon-based negative electrode active material has a coating layer on at least a portion of its surface.

[0079] 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 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 extending the cycle life of the material. On the other hand, 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, thereby further extending the cycle life of the battery.

[0080] In a second aspect, the present application provides: Providing a raw material containing Si element, O element, K element, P element and alkaline earth metal element; a vapor deposition method is employed, in which the source material is heated to form a vapor, and then the vapor is cooled to form a deposit; and pulverizing the deposited material to obtain a pulverized product.

[0081] In some embodiments, the method for preparing a silicon-based negative electrode active material includes: The method further includes performing a coating process on the pulverized product to obtain a product with a coating layer.

[0082] 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, elemental silicon includes, for example, metallic silicon. Silicon oxide includes, for example, one or more of silicon monoxide (SiO) and silicon dioxide (SiO2). The purity of elemental silicon is, for example, 3N or more, 4N or more, 5N or more, or 6N or more.

[0083] In some embodiments, the K element in the raw material may come from the K element contained in elemental silicon or silicon oxide itself, or from a potassium source added to the raw material.

[0084] In some embodiments, the P element in the raw material may come from the P element contained in elemental silicon or silicon oxide itself, or from a phosphorus source added to the raw material.

[0085] In some embodiments, the alkaline earth metal element in the feedstock may come from the alkaline earth metal element contained in elemental silicon or silicon oxide itself, or from an alkaline earth metal source added to the feedstock.

[0086] In some embodiments, the potassium source may be one or more selected from potassium oxide, potassium hydroxide, potassium chloride, and potassium silicate.

[0087] In some embodiments, the phosphorus source may be one or more selected from elemental phosphorus, phosphorus oxides, and phosphates.

[0088] In some embodiments, the alkaline earth metal source can be one or more selected from an alkaline earth metal, an alkaline earth metal alloy, and an alkaline earth metal compound, wherein the alkaline earth metal compound can be one or more selected from an alkaline earth metal oxide, an alkaline earth metal sulfide, an alkaline earth metal carbonate, an alkaline earth metal hydroxide, an alkaline earth metal acetate, an alkaline earth metal oxalate, an alkaline earth metal nitrate, and an alkaline earth metal sulfate.

[0089] In some embodiments, the source material containing the elements Si, O, K, P, and alkaline earth metal comprises elemental silicon, silicon dioxide, a potassium source, a phosphorus source, and an alkaline earth metal source.

[0090] In some embodiments, the content of element K in the negative electrode active material is adjusted by adjusting the type and amount of the potassium source in the raw materials.

[0091] In some embodiments, the content of P 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 P contents, and adjusting the type and amount of the phosphorus source.

[0092] In some embodiments, the act of heating the feedstock to form a vapor is carried out in an inert atmosphere at atmospheric or reduced pressure.

[0093] In some embodiments, the cooling of the vapor to form a deposit is carried out in an inert atmosphere at atmospheric or reduced pressure.

[0094] In the above preparation method, the inert atmosphere may be a nitrogen gas atmosphere, an argon gas atmosphere, a helium gas atmosphere, etc. Optionally, the absolute pressure of the inert atmosphere is normal pressure (one standard atmospheric pressure) or reduced pressure (less than one standard atmospheric pressure). Optionally, the absolute pressure of the inert atmosphere is 10 Pa to 950 Pa, more preferably 20 Pa to 100 Pa.

[0095] In some embodiments, by decreasing the pressure (i.e., increasing the degree of vacuum) within the above inert atmosphere pressure range, the contents of the K element and the P element in the final silicon-based negative electrode active material can be correspondingly increased.

[0096] In some embodiments, in the step of heating the raw material to form steam, the heating temperature is 1100 to 1550°C.

[0097] In some embodiments, in the step of cooling the vapor to form a deposit, the cooling temperature is 700 to 900°C.

[0098] In some embodiments, the cooling temperature during the cooling of the vapor to form the deposit can be adjusted to allow the deposit to have a suitable crystalline structure. Optionally, the cooling temperature is 850°C to 1050°C, which allows the silicon-based negative electrode active material to have a good crystallite size and suitable crystallinity, advantageously resulting in high cycle performance and high cycle performance. If the cooling temperature is lower than 800°C, the crystallinity of the material may be too low, which may affect the cycle performance of the material. If the cooling temperature is higher than 1050°C, the crystallite size of the material may be too large, which may affect the cycle performance of the material.

[0099] In some embodiments, within the above heating temperature range, increasing the temperature can correspondingly increase the contents of K and P elements in the final silicon-based negative electrode active material.

[0100] In some embodiments, within the above-mentioned range of inert atmosphere pressure, by decreasing the pressure, i.e., increasing the degree of vacuum, the contents of K and P elements in the final silicon-based negative electrode active material can be correspondingly increased.

[0101] In some embodiments, the operation of crushing the deposit comprises subjecting the deposit to a coarse crushing-fine crushing-sorting process based on the volume average particle size (Dv50) and specific surface area parameters of the predetermined product to obtain a product that meets the predetermined parameters. In some embodiments, the crushing and sorting process may be performed on the deposit using any method and equipment known in the art, such as a grinder or an airflow crushing-sorting combination machine.

[0102] In some embodiments, the method for preparing a silicon-based negative electrode active material further includes performing a coating treatment on the pulverized product to obtain a product with a coating layer.

[0103] 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 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 extending the cycle life of the material. On the other hand, 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, thereby further extending the cycle life of the battery.

[0104] 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, a polymer is dissolved in a solvent, and the polymer is thoroughly mixed with the silicon-based negative electrode active material particles by stirring, and then the solvent is evaporated to remove the polymer, thereby uniformly coating the surface of the silicon-based negative electrode active material particles.

[0105] 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, a hydrocarbon compound gas is introduced into a reactor containing the silicon-based negative electrode active material, and heat treatment is performed 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 having a coating layer on its surface.

[0106] In some embodiments, the coating treatment includes a carbon coating treatment, which optionally includes placing the pulverized product in a chamber containing a carbon source gas, heating the pulverized product to 700 to 1000°C, and maintaining the temperature for 1 to 6 hours.

[0107] In some embodiments, the coating treatment includes a carbon coating treatment. Optionally, the carbon coating treatment includes placing the pulverized product in a chamber containing a carbon source gas, heating it to 800 to 900°C, and maintaining the temperature for 2 to 5 hours.

[0108] In some embodiments, the alkaline earth metal source can be one or more of an alkaline earth metal, an alkaline earth metal hydroxide, an alkaline earth metal carbonate, an alkaline earth metal nitrate, an alkaline earth metal amide, or an alkaline earth metal hydride.

[0109] In some embodiments, the alkaline earth metal source can be one or more of magnesium metal, magnesium hydroxide, magnesium carbonate, magnesium nitrate, magnesium amino, magnesium hydride.

[0110] For example, the negative electrode current collector has two surfaces opposing each other in the thickness direction thereof, and the negative electrode film layer is provided on any one or both of the two opposing surfaces of the negative electrode current collector.

[0111] In some embodiments, the negative electrode current collector may be a metal foil strip or a composite current collector. For example, the metal foil strip may be a copper foil. The composite current collector may include a polymeric base 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)).

[0112] In some embodiments, the negative electrode film layer may include silicon-based negative electrode active materials other than those disclosed herein that are known in the art and may be selected by those skilled in the art based on 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 elemental silicon, silicone composites other than those disclosed herein, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based materials may include one or more of elemental tin, stannic acid compounds, and tin alloys. All of these materials are commercially available.

[0113] In some embodiments, the negative electrode membrane layer may further include an adhesive, which 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).

[0114] In some embodiments, the negative electrode film layer may further include a conductive agent, for example, at least one selected from the group consisting of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0115] In some embodiments, the negative electrode membrane layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethylcellulose (CMC-Na)).

[0116] In some embodiments, the negative electrode sheet may be prepared as follows: The components for preparing the negative electrode sheet, such as the silicon-based negative electrode active material, conductive agent, adhesive, and any other components, are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry, which is then applied to a negative electrode current collector, and the negative electrode sheet can be obtained after steps such as drying and cold pressing.

[0117] [Positive electrode sheet] In some embodiments, the positive electrode sheet typically includes a positive electrode current collector and a positive electrode membrane layer provided on at least one surface of the positive electrode current collector, the positive electrode membrane layer including a positive electrode active material.

[0118] For example, the positive electrode current collector has two surfaces opposing each other in the thickness direction thereof, and the positive electrode film layer is provided on any one or both of the two opposing surfaces of the positive electrode current collector.

[0119] In some embodiments, the positive electrode current collector may be a metal foil strip or a composite current collector. For example, aluminum foil may be used as the metal foil strip. The composite current collector may include a polymeric material base layer and a metal layer formed on at least one surface of the polymeric material base 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0120] In some embodiments, the positive electrode membrane layer may further include an adhesive. For example, the adhesive 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.

[0121] In some embodiments, the positive electrode film layer may further include a conductive agent, such as superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0122] In some embodiments, the positive electrode sheet may be prepared as follows: The components for preparing the positive electrode sheet, such as the positive electrode active material, conductive agent, adhesive, and any other components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry, which is then applied to a positive electrode current collector, followed by drying, cold pressing, and other steps to obtain a positive electrode sheet.

[0123] [Cathode active material] In some embodiments, the positive electrode active material may be a positive electrode active material used in secondary batteries that is well known in the art.

[0124] For example, the positive electrode active material may include at least one of a lithium-containing phosphate having an olivine structure, a lithium transition metal oxide, and a modified compound of each. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery positive electrode active material may also be used. These positive electrode active materials may be used alone or in combination of two or more. Here, 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 (may be abbreviated as "LiNi") 0.5 Co 0.2 Mn 0.3 O2(NCM 523 (may be abbreviated as "LiNi") 0.5 Co 0.25 Mn 0.25 O2(NCM 211 (may be abbreviated as "LiNi") 0.6 Co 0.2 Mn 0.2 O2(NCM 622 (may 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 0.0502) and modified compounds thereof, but is not limited thereto. Examples 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 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.

[0125] [Electrolyte] The electrolyte acts to conduct ions between the positive electrode sheet and the negative electrode sheet. The present application does not specifically limit the type of electrolyte, and it may be selected according to needs. For example, the electrolyte may be in a liquid state, a gel state, or a completely solid state.

[0126] In some embodiments, the electrolyte is in a liquid state and includes an electrolyte salt and a solvent.

[0127] In some embodiments, the electrolyte salt is selected from sodium perchlorate, sodium hexafluorophosphate, sodium tetrafluoroborate, and sodium hexafluoroarsenate.

[0128] 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.

[0129] In some embodiments, the electrolyte solution may further include additives. For example, the additives may include a negative electrode film-forming additive, a positive electrode film-forming additive, or an additive capable of improving a part of the 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.

[0130] [Separator] In some embodiments, the secondary battery further includes a separator. The present application does not particularly limit the type of separator, and any well-known porous separator having good chemical stability and mechanical stability may be selected.

[0131] 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 thin film or a multi-layer composite thin film, and is not particularly limited. When the separator is a multi-layer composite thin film, the materials of the layers may be the same or different, and are not particularly limited.

[0132] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be fabricated into an electrode assembly by a winding process or a lamination process.

[0133] In some embodiments, the secondary battery may include an exterior body, which may be used to seal the electrode assembly and the electrolyte.

[0134] In some embodiments, the exterior of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The exterior of the secondary battery may be a flexible package, such as a bag-type flexible package. The flexible package may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0135] The present application does not particularly limit the shape of the secondary battery, and it may be cylindrical, rectangular, or any other shape. For example, Figure 1 shows an exemplary secondary battery 5 with a rectangular structure.

[0136] In some embodiments, referring to FIG. 2 , the exterior body may include a housing 51 and a cover plate 53. Here, the housing 51 may include a bottom plate and side plates connected to the bottom plate, which together form a surrounding chamber. The housing 51 has an opening communicating with the chamber, and the cover plate 53 may be installed to cover the opening to close the chamber. The positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is sealed within the chamber. 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 may be selected by those skilled in the art according to specific actual needs.

[0137] In some embodiments, the secondary batteries may be 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 may be selected by those skilled in the art according to the application and capacity of the battery module.

[0138] Fig. 3 shows an example of a battery module 4. Referring to Fig. 3, in the battery module 4, a plurality of secondary batteries 5 may be arranged sequentially 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 fasteners.

[0139] Optionally, the battery module 4 may further include an outer shell having an accommodating space, and the plurality of secondary batteries 5 are accommodated in the accommodating space.

[0140] In some embodiments, the battery modules may be further assembled into a battery pack, and the battery pack may include one or more battery modules, the specific number of which may be selected by those skilled in the art according to the application and capacity of the battery pack.

[0141] 4 and 5 show an example battery pack 1. Referring to FIGS. 4 and 5, the battery pack 1 may include a battery case and a plurality of battery modules 4 provided in the battery case. The battery case includes an upper case 2 and a lower case 3, and the upper case 2 can be attached to the lower case 3 as a lid to form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery case in any desired configuration.

[0142] The present application also provides an electric device including at least one of the secondary battery, battery module, or battery pack according to the present application. The secondary battery, battery module, or battery pack may be used as a power source for the electric device or as a power 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.), electric trains, ships, satellites, and power storage systems.

[0143] The electrical device may be selected as a secondary battery, a battery module, or a battery pack according to its usage needs.

[0144] 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. To meet the high power and high energy density needs of the secondary battery of the electric device, a battery pack or a battery module may be employed.

[0145] 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, the techniques or conditions will be those described in literature in the field or in accordance with the product instructions. If the manufacturer of the reagents or equipment used is not specified, they are all common commercially available products.

[0146] 1. Preparation method of silicon-based negative electrode active material 1.1 Overview In the following specific embodiment, the method for preparing the silicon-based negative electrode active material is outlined as follows. 1) Providing a vapor containing Si, O, K, P, and Mg elements, and cooling the vapor to obtain a deposit. 2) crushing the deposit to obtain a crushed product; 3) The pulverized product is subjected to a carbon coating treatment to obtain a carbon-coated product.

[0147] 1.2 Details In the following specific embodiment, a detailed description of the preparation method of the silicon-based negative electrode active material is as follows. 1) providing a raw material composition including elemental silicon, silicon oxide, a potassium source (K2CO3), a phosphorus source (PO5), and an Mg source (metallic magnesium) according to the contents of Si, O, K, P, and Mg elements in a target product; 2) In a helium gas atmosphere having an absolute pressure of 30 Pa, the raw material composition is heated to 1300°C by vapor deposition to form a vapor, and then the vapor is cooled to 900°C to form a deposit; 3) collecting the deposit and grinding it into a powder; 4) The powder is placed in a reaction chamber of a vapor deposition apparatus, and a mixture of a carbon source gas (acetylene) and nitrogen gas with a ratio of 20% by volume is passed through the reaction chamber, and the reaction chamber is heated to 750°C and maintained at this temperature for 2 hours to obtain a carbon-coated product. 5) The carbon-coated product and the lithium source (lithium aminated) are mixed 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 is then collected to obtain the negative electrode active material.

[0148] In the above preparation method, silicon-based negative electrode active materials with various K and P contents can be obtained simply by appropriately adjusting the contents of the alkaline earth metal source, potassium source, and phosphorus source in the raw material mixture based on the composition of the target product. However, it should be understood that, depending on the purity of the silicon element and silicon dioxide, if some silicon element and silicon dioxide already contain a certain amount of K and P, it is necessary to appropriately adjust the contents of the potassium source and phosphorus source in the raw material mixture according to the component composition of the target product sample.

[0149] According to the above method, a plurality of silicon-based negative electrode active material samples (hereinafter simply referred to as samples) are obtained, and these samples have different contents of K and P. These samples have the following properties. 1) The silicon-based negative electrode active material is a silicon-based negative electrode active material having a carbon coating layer, wherein the content of the carbon coating layer is 4.2±1%, and the remainder is 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 is 1±0.1:1, 3) Based on 100% silicon-based negative electrode active material, the content of Mg element is 7±0.5%. 4) Based on 100% silicon-based negative electrode active material, the K content is as shown in Table 1. 5) Based on 100% silicon-based negative electrode active material, the P content is as shown in Table 1. 6) The volume average particle size Dv50 of the silicon-based negative electrode active material is 6.0±1 μm. 7) The specific surface area of ​​the silicon-based negative electrode active material is 5±0.25m 2 / g. 8) The powder volume resistivity of the silicon-based negative electrode active material at a pressure of 4 MPa is 4.2±0.25 Ω·cm. 9) The pressed density of silicon-based negative electrode active material at a pressure of 49,000 N is 1.6±0.1 g / cm 3 is 10) The silicon-based negative electrode active material contains MgSiO3, and the MgSiO3 has an XRD diffraction peak half-peak width of 0.5°±0.1° and a crystal grain size of 16±1 nm.

[0150] Table 1 shows silicon-based negative electrode active material samples with different K and P contents.

[0151] Preparation of coin cell batteries (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 adhesive PAA (polyacrylic acid) are thoroughly mixed and stirred in a mass ratio of 85:5:10 in an appropriate amount of deionized water to form a uniform negative electrode slurry. The negative electrode slurry is then applied to the surface of a negative electrode current collector copper foil, dried, and cold-pressed to obtain a negative electrode sheet. (2) Counter electrode: metallic lithium sheet. (3) Separator: polyethylene (PE) thin film. (4) Preparation of electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1, and then LiPF6 is uniformly dissolved in the above solution to obtain an electrolyte, and fluoroethylene carbonate (FEC) is added, where the concentration of LiPF6 is 1 mol / L and the mass proportion of FEC in the electrolyte is 6%. (5) Preparation of coin-shaped battery: The above negative electrode sheet, separator, and metallic lithium sheet counter electrode are stacked in this order, and the above electrolyte solution is added to obtain a coin-shaped battery.

[0152] II. Analysis and detection methods 2.1. Elemental analysis (e.g., K, P, Si, and alkaline earth metal elements) The elemental content has a meaning well known in the art and can be measured using methods well known in the art. Silicon-based negative electrode active materials can be decomposed in accordance with EPA-3052-1996, "Microwave-Assisted Acid Decomposition Method for Silicates," and then the content of the target elements can be measured using a Thermo Fisher Scientific ICAP-7000 type inductively coupled plasma optical emission spectrometer (ICP-OES) 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 elements is then measured using an ICAP-7000 type ICP-OES.

[0153] 2.2. Elemental analysis (oxygen element, carbon element) The element content has a meaning known in the art and may be measured by a method known in the art. The carbon element content in the silicon-based negative electrode active material may be measured in accordance with GB / T 20123-2006 / ISO 15350:2000, and the measuring instrument may be an HCS-140 type infrared carbon-sulfur analyzer.

[0154] The content of oxygen element can be determined by referring to JY / T 017-1996 General Rules for Elemental Analyzer Methods, and the measuring instrument can be Elementar's rapid OXY cube oxygen elemental analyzer.

[0155] 2.3. Volume resistivity The volume resistivity of a material has a meaning well known in the art, and may be measured using instruments and methods well known in the art. For example, a four-point probe method may be employed to measure the powder volume resistivity of the silicon-based negative electrode active material of the present application at a pressure of 4 MPa. 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 using 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 using a resistivity meter.

[0156] 2.4 Press Density The pressed density of a material has a meaning known in the art and may be measured using instruments and methods known in the art, for example, referring to the GB / T24533-2009 standard, and may be measured using an electronic pressure tester such as a UTM7305 type electronic pressure tester. A sample of about 1 g is precisely weighed, and the base area is 1.327 cm. 2 The sample is placed in a mold, and a pressure device is used to apply a pressure of 49,000 N to the sample, and this pressure is maintained for 30 seconds before the pressure is released. After that, the height of the sample is measured, and the pressed density of the material can be obtained by the formula ρ = m / (1.327 × h), where ρ is the pressed density of the material, m is the mass of the sample, and h is the height of the sample after a pressure of 49,000 N is applied, maintained for 30 seconds, and then the pressure is released.

[0157] 2.4, Powder particle size analysis The Dv10, Dv50 and Dv90 of a material have meanings known in the art and may be measured by methods known in the art, for example, see standard GB / T 19077-2016, and may be measured using a laser particle size analyzer (e.g., Malvern Master Size 3000).

[0158] The physical definitions of Dv10, Dv50, and Dv90 are the particle sizes corresponding to the percentages of cumulative volume distribution of the silicon-based negative electrode active material reaching 10%, 50%, and 90%, respectively.

[0159] 2.5. Specific surface area analysis The specific surface area of ​​a material has a meaning well known in the art and may be measured using instruments and methods well known in the art, for example, by measuring the specific surface area by nitrogen gas adsorption analysis in accordance with GB / T 19587-2017 Standard for Measuring the Specific Surface Area of ​​Solid Materials by Gas Adsorption BET Method, and calculating using the Brunauer Emmett Teller (BET) method. Here, the nitrogen gas adsorption specific surface area may be measured using a Tri Star II 3020 type specific surface area pore size analyzer manufactured by Micromeritics, USA.

[0160] 2.6. Battery performance measurement (1) Cycle performance At 25°C and under normal pressure, a coin battery is discharged at a constant current of 0.1C to 0.005V, then discharged at a constant current of 0.04C to 0.005V, and allowed to rest for 5 minutes. The discharge capacity at this point, i.e., the lithium insertion capacity for the first cycle, is recorded. It is then charged at a constant current of 0.1C to 1.5V, and allowed to rest for 5 minutes. This constitutes one cycle of charge-discharge, and the charge capacity at this point, i.e., the lithium desorption capacity for the first cycle, is recorded. The coin battery is subjected to 30 cycle charge-discharge measurements according to the above method, and the lithium desorption capacity for each cycle is recorded. Cycle capacity retention rate (%) = Reversible lithium desorption capacity at 1st cycle / Reversible lithium desorption capacity at 500th cycle × 100%

[0161] (2) 4C discharge rate measurement At 25°C and normal pressure, the coin cell 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. It was then charged at a constant current of 0.1C to 1.5V, and then allowed to stand for 5 minutes. This constitutes one cycle of charge-discharge. Using the same flow, change the charge / discharge current and charge / discharge at currents of 0.1C, 0.33C, 1C, 2C, and 4C, respectively, and record the discharge capacity after 10 cycles at each current. 4C discharge capacity retention rate (%) = 4C lithium desorption capacity average value / 0.1C lithium desorption capacity average value × 100%

[0162] [Table 1]

[0163] 3. Results and Discussion Table 1 shows the ingredients and compositions of the raw materials for silicon-based negative electrode active materials in several examples of the present application, the contents and weight ratios of K and P in the silicon-based negative electrode active material products, and the battery performance based on using the silicon-based negative electrode active materials as the silicon-based negative electrode active materials. Each of these will be discussed below.

[0164] (1) Composition of raw materials The raw silicon element used for the samples (E1 to E14) was metallic silicon 1 (Si≧99 wt%, K=100 ppm, P=30 ppm).

[0165] The raw silicon element used for the samples (D1 to D3) was metallic silicon 2 (Si≧99.9 wt%, containing neither K nor P).

[0166] As can be seen from Table 2, the K element and the P element in the silicon-based negative electrode active material may be derived from a variety of sources. a) The K element in the silicon-based negative electrode active material may be derived from raw material metal silicon, b) The P element in the silicon-based negative electrode active material may be derived from raw material metal silicon, c) The K element in the silicon-based negative electrode active material may be derived from an added potassium source; d) The P element in the silicon-based negative electrode active material may be derived from an added phosphorus source.

[0167] Those skilled in the art can adaptively adjust the contents of P and K in the raw materials based on the target chemical composition of the silicon-based negative electrode active material to ultimately obtain a negative electrode active material having the target chemical composition. If the K content in the target negative electrode active material needs to be increased or decreased, a silicon metal (or silicon oxide) with a higher or lower K content may be used, or the amount of potassium source added to the raw materials may be increased or decreased. If the P content in the target negative electrode active material needs to be increased or decreased, a silicon metal (or silicon oxide) with a higher or lower P content may be used, or the amount of phosphorus source added to the raw materials may be increased or decreased.

[0168] (2) Synergistic effects of K and P elements Below, Comparative Examples D1, D2, and D3 will be analyzed in detail in connection with Example E2. The silicon oxide composite of Comparative Example D3 does not contain K or P, and its 4C capacity retention value is 41.0%. The silicon oxide composite of Comparative Example D1 contains 1200 ppm of K but does not contain P, and its 4C capacity retention value is 46.1%, an increase of only 12% compared to D3. The silicon oxide composite of Comparative Example D2 contains 90 ppm of P but does not contain K, and its 4C capacity retention value is 45.5%, an increase of only 11% compared to D3. In Example E2, the silicon oxide composite simultaneously contained 1249 ppm of K and 90 ppm of P, and its 4C capacity retention value was 57%, a 39% increase compared to D3, which is far greater than the simple addition of performance improvements due to the single addition of K or P (i.e., 12% + 11% = 33%). Therefore, the above experimental evidence clearly demonstrated the unexpected synergistic effect brought about by the combination of K and P.

[0169] (3) K / P weight ratio in silicon oxide composites The experimental data in Table 1 demonstrate that when the weight ratio of K / P is greater than 1, the performance of the negative electrode active material is significantly improved.

[0170] In Example E14, the K / P weight ratio was 0.8:1 (<1), and the negative electrode active material had a 4C capacity retention value of 48.8% and a cycle performance of 78.6%. In Examples E1 to E13, the K / P weight ratio was 7.7:1 to 14.8:1 (greater than 1), and the negative electrode active materials had 4C capacity retention values ​​of 50% to 67% and capacity retention rates of 73% to 78%, which were superior to Example E14.

[0171] The above experimental data demonstrate that when the K content in the silicon oxide composite is greater than the P content, the silicon oxide composite exhibits more significant improvements in cycle performance and rate performance.

[0172] (4) K / P ratio in silicon oxide composites As shown in Examples E4 to E13, when the weight ratio of K / P is 7.7:1 to 14.8:1, the negative electrode active material has a 4C capacity retention value of 50% to 67%, which further shows improved cycle performance and rate performance.

[0173] As shown in Examples E9 to E11, when the weight ratio of K / P is 9.2:1 to 10.3:1, the negative electrode active material has a 4C capacity retention value of 64.5% to 67.4%, which further shows improved cycle performance and rate performance.

[0174] (5) Contents of K and P elements in silicon oxide composites As shown in Examples E1 to E14, when the content of K element in the silicon oxide composite is 600 ppm or more, for example, 800 ppm to 1500 ppm, the negative electrode active material exhibits improved cycle performance and rate performance.

[0175] As shown in Examples E1 to E14, the content of P element in the silicon oxide composite is 1000 ppm or less, for example, 50 ppm to 1000 ppm, and the negative electrode active material exhibits improved cycle performance and rate performance.

[0176] As shown in Examples E1 to E13, when the content of K element in the silicon oxide composite is 1000 ppm or more, for example, 1000 ppm to 1500 ppm, the negative electrode active material exhibits improved cycle performance and rate performance.

[0177] As shown in Examples E1 to E13, the content of P element in the silicon oxide composite is 500 ppm or less, for example, 50 ppm to 200 ppm, and the negative electrode active material exhibits improved cycle performance and rate performance.

[0178] The above experimental data demonstrate that when the silicon oxide composite contains only P or K alone, only one of the cycle performance and rate performance is improved, and the improvement is not significant. When the silicon oxide composite contains a combination of K and P, the negative electrode active material exhibits both improved cycle performance and rate performance, with particularly significant improvement, which demonstrates the unexpected synergistic effect of K and P.

[0179] The present application is not limited to the above-described embodiments. The above-described embodiments are merely illustrative, and any embodiment that has substantially the same configuration as the technical concept and achieves the same effects within the scope of the technical aspects of the present application is included within the technical scope of the present application. Furthermore, various modifications that a person skilled in the art could conceive of to the embodiments, or other forms constructed by combining some of the components of the embodiments, are also included within the scope of the present application, as long as they do not deviate from the gist of the present application.

Claims

1. The silicate contains an alkaline earth metal element and simultaneously contains a K element and a P element. Silicon-based negative electrode active material.

2. The content of the K element is greater than the content of the P element. The silicon-based negative electrode active material according to claim 1 .

3. The mass ratio of the K element to the P element is 7:1 or more, and optionally 9:1 to 15:1; The silicon-based negative electrode active material according to any one of claims 1 to 2.

4. The content of the K element is 600 ppm or more, and optionally 800 ppm to 1500 ppm. The silicon-based negative electrode active material according to any one of claims 1 to 3.

5. The content of the P element is 500 ppm or less, and optionally 50 ppm to 200 ppm. The silicon-based negative electrode active material according to any one of claims 1 to 4.

6. (1) Volume average particle size D ｖ 50 is between 4 μm and 10 μm, optionally between 5 μm and 8 μm; (2) The specific surface area is 6 m ２ / g or less, and optionally 2m ２ / g to 5m ２ / g, (3) The powder volume resistivity at a pressure of 4 MPa is 6 Ω cm or less, and optionally 0.5 Ω cm to 4.5 Ω cm; (4) The press density at a pressure of 49,000 N is 1.4 to 1.8 g / cm ３ and optionally 1.5 to 1.7 g / cm ３ That is, (5) The alkaline earth metal element-containing silicate includes a magnesium-containing silicate, and the half-peak width of the XRD diffraction peak of the magnesium-containing silicate is 0.65° or less, and optionally 0.40° to 0.60°; (6) The alkaline earth metal element-containing silicate comprises a magnesium-containing silicate, and the magnesium-containing silicate has one or more characteristics of having a crystal grain size of 12 nm or more, and optionally 13 nm to 20 nm. The silicon-based negative electrode active material according to any one of claims 1 to 5.

7. At least a portion of the surface has a coating layer. The silicon-based negative electrode active material according to any one of claims 1 to 6.

8. Providing a raw material containing Si, O, K, P, and an alkaline earth metal element; employing a vapor phase deposition method, heating the source material to form a vapor, and then cooling the vapor to form a deposit; - grinding the deposit and obtaining a grinding product, A method for preparing the silicon-based negative electrode active material according to any one of claims 1 to 7.

9. Further comprising performing a coating process on the pulverized product to obtain a product having a coating layer; The method of claim 8.

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 700 to 900°C. The method according to any one of claims 8 to 9.

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

12. The secondary battery according to claim 11, Electrical equipment.

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