Lithium secondary battery, negative active material, method for manufacturing the same, and electric device

Abstract

This application discloses a lithium secondary battery, a negative electrode active material, its preparation method, and an electrical device, relating to the field of secondary batteries. The lithium secondary battery includes a positive electrode, an electrolyte, and a negative electrode. The negative electrode includes a silicon-carbon material, which comprises carbon material, silicon material distributed within the carbon material, and lithium-containing substances. The carbon material also includes oxygen, which forms C-O groups and C=O groups with the carbon material. The amount of substance of the C-O groups is n1, and the amount of substance of the C=O groups is n2, where n2 / (n1+n2)×100% = 55%-65%. The lithium secondary battery proposed in this application has excellent initial efficiency and cycle performance.

Description

Technical Field

[0001] This application belongs to the field of secondary batteries, specifically relating to a lithium secondary battery, a negative electrode active material and its preparation method, and electrical equipment. Background Technology

[0002] Lithium-ion batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace and many other fields.

[0003] As lithium-ion batteries continue to expand into power and energy storage applications, the demand for high-energy-density batteries is increasing. Silicon-based materials theoretically possess a specific capacity of 3580 mAh / g at room temperature, along with advantages such as low delithiation potential and environmental friendliness, effectively improving battery energy density and meeting market demands. They have become one of the mainstream anode materials. However, during charge and discharge, the volume expansion and contraction of silicon-carbon anode active materials cause instability in the surface SEI (Solid Electrolyte Interphase), leading to continuous cracking and growth. This results in low first-cycle coulombic efficiency and poor cycle performance for silicon-based materials. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides a lithium secondary battery, which aims to improve the first efficiency of the lithium secondary battery, so as to improve the cycle performance of the lithium secondary battery.

[0005] To achieve the above objectives, the first aspect of this application proposes a lithium secondary battery, which includes a positive electrode, an electrolyte, and a negative electrode. The negative electrode includes a silicon-carbon material, which comprises carbon material, silicon material, and lithium-containing substances distributed within the carbon material. The carbon material also includes oxygen, which forms CO groups and C=O groups with the carbon material. The amount of substance of the CO groups is n1, the amount of substance of the C=O groups is n2, and n2 / (n1+n2)×100%=55%-65%.

[0006] The present application at least includes the beneficial effects described below: In the lithium secondary battery of the present application, by controlling the ratio of C-O groups and C=O groups, compared with the existing silicon-carbon materials, the content of C=O groups is reduced. Since the C=O groups are irreversible to active lithium (the C=O bond has strong polarity, and in a lithium-containing electrochemical system, it is prone to irreversible chemical reactions with lithium ions, thereby consuming active lithium), the defects of the negative electrode active material are less, improving the initial efficiency and cycle performance of the silicon-carbon material; and a lithium-containing substance is provided for the silicon material. During the charge and discharge process of the battery, it is beneficial for lithium ions to be released and participate in the formation of the SEI film, reducing the loss of active lithium at the positive electrode during the formation of the SEI film, achieving a lithium compensation effect, and thus significantly improving the initial Coulomb efficiency and cycle performance of the lithium secondary battery.

[0007] In some embodiments, n1 / (n1 + n2)×100% = 35% - 45%. Thus, the initial efficiency of the lithium secondary battery can be improved to enhance the cycle performance of the lithium secondary battery.

[0008] In some embodiments, based on the total mass of the carbon material, the mass proportion of the oxygen element is 0.2% - 3.5%. Thus, the initial efficiency of the lithium secondary battery can be improved to enhance the cycle performance of the lithium secondary battery.

[0009] In some embodiments, based on the total mass of the carbon material, the mass proportion of the oxygen element is 0.3% - 1.5%. Thus, the initial efficiency of the lithium secondary battery can be improved to enhance the cycle performance of the lithium secondary battery.

[0010] In some embodiments, in the dQ / dV charge curve of the silicon-carbon material, the peak intensity of the lithium intercalation peak A with the abscissa between 0.01 < V < 0.1V is IA, and the intensity of the lithium intercalation peak B with the abscissa between 0.1 ≤ V < 0.2V is IB, and IA / IB = 0.8 - 1.2. Thus, the initial efficiency of the lithium secondary battery can be improved to enhance the cycle performance of the lithium secondary battery.

[0011] In some embodiments, at a rate of 0.1C, IA = 4000F - 14000F. Thus, the initial efficiency of the lithium secondary battery can be improved to enhance the cycle performance of the lithium secondary battery.

[0012] In some embodiments, at a rate of 0.1C, IB = 3000F - 18000F. Thus, the initial efficiency of the lithium secondary battery can be improved to enhance the cycle performance of the lithium secondary battery.

[0017]

[0013] In some embodiments, based on the total mass of the silicon-carbon material, the mass proportion of the lithium element is 0.001% - 0.1%. Thus, the initial efficiency of the lithium secondary battery can be improved to enhance the cycle performance of the lithium secondary battery.

[0014] In some embodiments, the mass percentage of lithium element is 0.005%-0.06% based on the total mass of the silicon-carbon material. This can improve the initial efficiency of the lithium secondary battery, thereby enhancing its cycle performance.

[0015] In some embodiments, and / or, based on the total mass of the silicon-carbon material, the mass percentage of silicon is 10%-60%. This can improve the initial efficiency of the lithium-ion secondary battery, thereby enhancing its cycle performance.

[0016] In some embodiments, the specific surface area of ​​the silicon-carbon material is 0.1 m². 2 / g-50m 2 / g. This can improve the initial efficiency of lithium secondary batteries, thereby enhancing their cycle performance.

[0017] In some embodiments, the negative electrode sheet includes a negative electrode active material layer, which comprises the silicon-carbon material, wherein the mass percentage of the silicon-carbon material is 1%-100% based on the total mass of the negative electrode active material layer. This can improve the initial efficiency of the lithium-ion battery, thereby enhancing its cycle performance.

[0018] In some embodiments, the negative electrode sheet includes a negative electrode active material layer, which comprises the silicon-carbon material, wherein the silicon-carbon material accounts for 3%-50% of the total mass of the negative electrode active material layer. This can improve the initial efficiency of the lithium-ion battery, thereby enhancing its cycle performance.

[0019] In some embodiments, the positive electrode active material includes at least one of an olivine-structured lithium phosphate, a lithium transition metal oxide, and their respective modified compounds. This can improve the initial efficiency of the lithium secondary battery, thereby enhancing its cycle performance.

[0020] In some embodiments, the lithium transition metal oxide includes Li x (Ni a Co b Mn c ) 1-d M d O 2-y A y Where x is 0.2-1.2, a is 0.8-1, b is 0-0.15, c is 0-0.15, d is 0-0.02, y is 0-0.1, M includes at least one of Zr, Y, Al, Ti, W, Sr, Ta, Sb, Nb, Na, K, Ca, or Ce, and A includes at least one of N, F, S, or Cl. This can improve the initial efficiency of lithium-ion secondary batteries, thereby enhancing their cycle performance.

[0021] In the second aspect of the present application, a negative electrode active material is proposed. The negative electrode active material includes a silicon-carbon material. The silicon-carbon material includes carbon, silicon material and lithium-containing substance distributed inside the carbon. The carbon material further includes oxygen element, and the oxygen element forms C-O groups and C=O groups with the carbon material. The amount of substance of the C-O groups is n1, and the amount of substance of the C=O groups is n2, and n2 / (n1 + n2)×100% = 55% - 65%. Thus, the negative electrode active material proposed by the present application can improve the initial efficiency of the lithium secondary battery and improve the cycle performance of the lithium secondary battery.

[0022] In some embodiments, in the dQ / dV charging curve of the silicon-carbon material, the peak intensity of the lithium intercalation peak A with the abscissa between 0.01 < V < 0.1V is IA, and the intensity of the lithium intercalation peak B with the abscissa between 0.1 ≤ V < 0.2V is IB, and IA / IB = 0.8 - 1.2. Thus, the initial efficiency of the lithium secondary battery can be improved to improve the cycle performance of the lithium secondary battery.

[0023] In some embodiments, n1 / (n1 + n2)×100% = 35% - 45%. Thus, the initial efficiency of the lithium secondary battery can be improved to improve the cycle performance of the lithium secondary battery. <U+ <U+

[0024] In some embodiments, based on the total mass of the silicon-carbon material, the mass percentage of lithium element is 0.001% - 0.1%; thus, the initial efficiency of the lithium secondary battery can be improved to improve the cycle performance of the lithium secondary battery.

[0025] In some embodiments, based on the total mass of the silicon-carbon material, the mass percentage of silicon element is 10% - 60%. Thus, the initial efficiency of the lithium secondary battery can be improved to improve the cycle performance of the lithium secondary battery.

[0026] In some embodiments, the specific surface area of the silicon-carbon material is 0.1 m 2 / g - 50 m 2 / g.

[0027] In the third aspect of the present application, a preparation method of a negative electrode active material is proposed, including:

[0028] Dissolving lithium单质 and a regulator in an organic solvent to form a prelithiation solution;

[0029] Soaking porous carbon in the prelithiation solution, drying in vacuum, and heat-treating at 500°C - 1100°C in an inert atmosphere to obtain prelithiated porous carbon;

[0030] It should be noted that the "lithium单质" in the original text seems to be an incorrect expression. It should probably be "lithium metal" or other correct terms. You can check and correct it according to the actual situation.Silicon material is deposited on the pre-lithiated porous carbon using a vapor deposition method, and carbon is deposited to cover the silicon material, resulting in a silicon-carbon material, which is the negative electrode active material.

[0031] Therefore, the method for preparing the negative electrode active material proposed in this application begins with pre-lithiation at the porous carbon end, followed by the deposition of silicon and carbon. This allows the active lithium provided by the lithium-containing material to be distributed inside the carbon, while the active lithium can repair defects in the porous carbon portion (such as holes, oxygen-containing functional groups, etc.), thereby improving the first efficiency of the lithium secondary battery and enhancing its cycle performance.

[0032] In some embodiments, the method satisfies one or more of the following conditions: the modifier includes one or more of biphenyl and naphthalene; the organic solvent includes one or more of 2-methyltetrahydrofuran, ethylene glycol dimethyl ether, and tetrahydrofuran. This can improve the initial efficiency of lithium-ion batteries, thereby enhancing their cycle performance.

[0033] In some embodiments, the molar concentration of lithium in the pre-lithiation solution is 0.001 mol / L to 0.5 mol / L. This can improve the initial efficiency of the lithium secondary battery, thereby enhancing its cycle performance.

[0034] In some embodiments, the molar concentration of lithium in the pre-lithiation solution is 0.01 mol / L to 0.1 mol / L. This can improve the initial efficiency of the lithium secondary battery, thereby enhancing its cycle performance.

[0035] In some embodiments, the mass percentage of lithium is 0.001%-4% based on the total mass of the pre-lithiation solution. This can improve the initial efficiency of the lithium secondary battery, thereby enhancing its cycle performance.

[0036] In some embodiments, the soaking time is 1 second to 2 minutes. This can improve the initial efficiency of the lithium secondary battery, thereby enhancing its cycle performance.

[0037] In some embodiments, the time interval between the vacuum drying and the heat treatment is less than or equal to 120 minutes. This can improve the initial efficiency of the lithium-ion battery, thereby enhancing its cycle performance.

[0038] In some embodiments, the method satisfies one or more of the following conditions: the specific surface area of ​​the porous carbon is 700 m². 2 / g-2300m 2 / g, preferably 1200m 2 / g-2000m 2 / g; the heat treatment temperature is 700℃-1000℃; the heat treatment time is 0.2h-2h. This improves the initial efficiency of the lithium secondary battery, thereby enhancing its cycle performance.

[0039] In some embodiments, the deposition temperature of the deposited silicon material is 480°C-550°C. This can improve the initial efficiency of the lithium-ion battery, thereby enhancing its cycle performance.

[0040] In some embodiments, the silicon source flow rate of the deposited silicon material is 0.5 L / min to 10 L / min. This can improve the initial efficiency of the lithium-ion battery, thereby enhancing its cycle performance.

[0041] In some embodiments, the silicon source flow rate of the deposited silicon material is 1 L / min to 5 L / min. This can improve the initial efficiency of the lithium-ion battery, thereby enhancing its cycle performance.

[0042] In some embodiments, the deposition time of the deposited silicon material is 100 min to 900 min; and / or, the mass of the deposited carbon accounts for 2% to 15% of the mass of the silicon-carbon material. This can improve the initial efficiency of the lithium secondary battery, thereby enhancing its cycle performance.

[0043] In some embodiments, the deposition time of the deposited silicon material is 180 min to 600 min; and / or, the mass of the deposited carbon accounts for 4% to 10% of the mass of the silicon-carbon material. This can improve the initial efficiency of the lithium secondary battery, thereby enhancing its cycle performance.

[0044] In a fourth aspect of this application, an electrical device is proposed, comprising the lithium secondary battery described in the first aspect of this application.

[0045] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0046] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0047] Figure 1 This is a schematic diagram of a battery according to one embodiment of this application.

[0048] Figure 2 yes Figure 1An exploded view of a battery according to one embodiment of this application is shown.

[0049] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0050] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0051] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0052] Figure 6 This is a schematic diagram of an electrical device in which a battery is used as a power source according to one embodiment of this application.

[0053] Figure 7 These are the O1s XPS spectra of the silicon-carbon material prepared in Example 1 of this application and the porous carbon in Comparative Example 1.

[0054] Figure 8 This is the O1s XPS spectrum of porous carbon in Comparative Example 1 of this application.

[0055] Figure 9 This is the O1s XPS spectrum of porous carbon in Example 1 of this application.

[0056] Figure 10 This is a dQ / dV charging curve of the silicon-carbon material in Comparative Example 1 of this application.

[0057] Figure 11 This is a dQ / dV charging curve of the silicon-carbon material in Embodiment 1 of this application.

[0058] Explanation of reference numerals in the attached figures:

[0059] 1. Battery cell; 11. Housing; 12. Electrode assembly; 13. Cover plate; 2. Battery module; 3. Battery pack; 31. Upper casing; 32. Lower casing. Detailed Implementation

[0060] The embodiments of the technical solution of this application are described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0061] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0062] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0063] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0064] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0065] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0066] Currently, judging from market trends, the application of rechargeable batteries is becoming increasingly widespread. Rechargeable batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace, among other fields.

[0067] As lithium-ion batteries continue to expand into power and energy storage applications, the demand for high-energy-density batteries is increasing. Silicon-based materials theoretically possess a specific capacity of 3580 mAh / g at room temperature, along with advantages such as low delithiation potential and environmental friendliness, effectively improving battery energy density to meet market demands. However, during charge and discharge, the volume expansion and contraction of silicon-carbon anode active materials cause surface SEI instability, leading to continuous cracking and growth. Furthermore, the presence of micropores, closed pores, defects (carbon atom vacancies, dangling bonds), and impurities within the porous carbon framework results in low initial coulombic efficiency and poor cycle performance for silicon-carbon anode materials.

[0068] The above problems can be solved by using lithium replenishment methods. However, most existing lithium replenishment methods involve carbon coating of silicon-based materials and then pre-lithiation treatment. The internal silicon and carbon framework is not sufficiently pre-lithiated, resulting in poor improvement on the first-cycle coulombic efficiency (first efficiency) and cycle performance of silicon-carbon anode materials.

[0069] The high C=O group content in existing porous carbon is due to the higher thermal stability of C=O groups compared to other oxygen-containing functional groups (such as -COOH, -OH, etc.). During the heat treatment process of porous carbon preparation, some unstable functional groups (such as -COOH) preferentially decompose into gases such as CO2, while C=O groups are more difficult to remove. In addition, during the synthesis of porous carbon, defect sites in the carbon skeleton are prone to react with oxygen to form C=O groups. For example, the C=O group content in existing biomass porous carbon is about 70% in carbon-oxygen functional groups, and the C=O group content in resin porous carbon is about 68% in carbon-oxygen functional groups. Excessively high C=O group content can easily undergo irreversible chemical reactions with lithium ions, thereby consuming active lithium. Therefore, it is necessary to reduce the C=O group content in porous carbon.

[0070] The lithium secondary battery of this application, by placing silicon material and lithium-containing material inside carbon material, achieves two advantages. Firstly, the lithium-containing material is in full contact with both carbon and silicon materials, resulting in thorough pre-lithiation. Addressing the instability of the SEI (Sediment Injection) on the silicon surface, it provides active lithium during charge and discharge. This active lithium participates in SEI film formation, reducing the loss of active lithium from the positive electrode during SEI film formation and quickly achieving lithium replenishment. Secondly, by controlling the content of C=O groups (e.g., -C=O-) to 55%-65%, and considering that C=O groups are mostly irreversible for active lithium, a low content of C=O groups can reduce the loss of active lithium ions and improve the lithium replenishment effect. Therefore, the active lithium provided by the lithium-containing material can repair intrinsic defects within the carbon material (such as carbon atom vacancies, oxygen-containing functional groups, etc.), reducing the consumption of active lithium by these defects. In summary, the lithium secondary battery proposed in this application exhibits excellent initial efficiency and cycle performance.

[0071] The lithium secondary battery disclosed in this application can be used in electrical devices that use batteries as a power source or in various energy storage systems that use batteries as energy storage elements. Electrical devices may include, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys may include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft may include airplanes, rockets, space shuttles, and spacecraft, etc.

[0072] The first aspect of this application discloses a lithium secondary battery, which includes a positive electrode, an electrolyte, and a negative electrode. The negative electrode includes a silicon-carbon material, which comprises carbon material, silicon material, and lithium-containing substances distributed within the carbon material. The carbon material also includes oxygen, which forms CO groups and C=O groups with the carbon material. The amount of substance of the CO groups is n1, the amount of substance of the C=O groups is n2, and n2 / (n1+n2)×100%=55%-65%.

[0073] As an example, n2 / (n1+n2)×100% can be 55%-64%, 57%-62%, 59%-60%, etc.

[0074] The lithium secondary battery of this application, by placing silicon material and lithium-containing material inside carbon material, achieves two advantages. First, the lithium-containing material is in full contact with both carbon and silicon materials, resulting in thorough pre-lithiation. Addressing the instability of the SEI (Sediment Injection) on the silicon surface, it provides active lithium during charge and discharge. This active lithium participates in SEI film formation, reducing the loss of active lithium from the positive electrode during SEI film formation and quickly achieving lithium replenishment. Second, by controlling the content of C=O groups (e.g., -C=O-) in the carbon material to 55%-65%, and considering that C=O groups are mostly irreversible for active lithium, a low content of C=O groups can reduce the loss of active lithium ions and improve the lithium replenishment effect. Therefore, the active lithium provided by the lithium-containing material can repair intrinsic defects within the carbon material (such as carbon atom vacancies, oxygen-containing functional groups, etc.), reducing the consumption of active lithium by these defects. In summary, the lithium secondary battery proposed in this application has excellent initial efficiency and cycle performance.

[0075] It is understandable that the presence of lithium-containing substances within carbon materials can produce the following effects: First, the surface of carbon materials contains some active sites / defects, and the active lithium generated by the lithium-containing substances can form a stable lithium-containing compound layer on these active sites / defects in advance, reducing the side reactions between the electrolyte and the carbon material during the first charge and discharge. Second, the lithium-containing substances can form lithium-carbon compounds or lithium intercalation states in the carbon material, which helps to increase the electronic conduction channels of the carbon material, improve its conductivity, and the lithium-containing substances can react with C=O groups, reducing the content of C=O groups, reducing the oxygen content in the carbon material, and reducing the defects in the carbon material.

[0076] It is understandable that the CO group's reaction with active lithium ions is reversible because the CO bond may undergo breakage and recombination reactions during lithiation. For example, the CO bond may coordinate with lithium ions; when lithium ions are inserted, the electron cloud distribution around the CO bond changes, potentially causing a slight elongation or deformation of the CO bond. However, this change can be reversed during delithiation. In contrast, the C=O bond has strong polarity and readily undergoes irreversible chemical reactions with lithium ions in lithium-containing electrochemical systems, thus consuming active lithium.

[0077] It can be understood that carbon materials are materials made of carbon, such as porous carbon; silicon materials refer to substances containing silicon, such as elemental silicon; and lithium-containing substances refer to substances that can provide lithium elements to participate in electrochemical reactions during the cycling process of lithium secondary batteries, such as elemental lithium.

[0078] In some embodiments, n1 / (n1+n2)×100% = 35%-45%, for example, n1 / (n1+n2)×100% can be 35%-44%, 36%-43%, 37%-42%, 38%-41%, 39%-40%, etc.; controlling the CO group (such as -C-OH) content in the carbon material to 35%-45% is higher than the CO group content in existing carbon materials, which can reduce the content of C=O groups (such as -C=O-). Since the CO group is reversible for active lithium ions, while the C=O group is mostly irreversible for active lithium, the high CO group content can reduce the loss of active lithium ions and improve the lithium replenishment effect. Therefore, the active lithium provided by the lithium-containing material can repair the intrinsic defects (such as carbon atom vacancies, oxygen-containing functional groups, etc.) inside the carbon material, reducing the consumption of active lithium by the above defects. In summary, the lithium secondary battery proposed in this application has excellent first-efficiency and cycle performance.

[0079] It is understandable that "n1 / (n1+n2)×100%" and "n2 / (n1+n2)×100%" can be determined by the following methods:

[0080] The silicon-carbon material is analyzed using an X-ray photoelectron spectrometer Axis Supra / Supra+ with reference to the standard GB / T 33502-2017. The sensitivity is 450W, and it uses an Al Kα / Ag Lα monochromatic X-ray source. The energy resolution is ≤0.45 eV. An O1s XPS spectrum (X-ray photoelectron spectrum) is obtained, and the C-O and C=O spectra are respectively fitted, and the peak areas of each are calculated to obtain n1 / (n1 + n2)×100% and n2 / (n1 + n2)×100%.

[0081] In some embodiments of the present application, based on the total mass of the carbon material, the mass fraction of the oxygen element is 0.2% - 3.5%. For example, based on the total mass of the carbon material, the mass fraction of the oxygen element can be 0.2% - 3.4%, 0.5% - 3%, 1% - 2.5%, 1.5% - 2%, etc. Controlling the content of the oxygen element in the carbon material within the above range can enable the silicon-carbon material to have a high energy density, and is beneficial to keeping the content of C-O groups and C=O groups in the carbon material within the required range, reducing the defects inside the carbon material, reducing the loss of active lithium in the silicon-carbon material during the battery cycle, improving the lithium supplementation effect, and enabling the lithium secondary battery to have excellent initial efficiency and cycle performance. In some other embodiments of the present application, based on the total mass of the carbon material, the mass fraction of the oxygen element is 0.3% - 1.5%.

[0082] It can be understood that "the mass fraction of the oxygen element based on the total mass of the carbon material" can be measured by methods well-known in the art. For example, it can be measured by the following method:

[0083] The carbon material is placed in an organic element analyzer (model FlashSmart CHNSO) with reference to the standard: JY / T 017-1996, and the analysis accuracy is CHNSO ≤ 0.05% abs to analyze the mass fraction of the oxygen element therein.

[0084] In some embodiments of the present application, in the dQ / dV charging curve of the silicon-carbon material, the peak intensity of the lithiation peak A with the abscissa between 0.01 < V < 0.1V is IA, and the intensity of the lithiation peak B with the abscissa between 0.1 ≤ V < 0.2V is IB, and IA / IB = 0.8 - 1.2. For example, IA / IB can be 0.8 - 1.1, 0.9 - 1, 1 - 1.1, etc.

[0085] It can be understood that in the dQ / dV charging curve of the silicon-carbon material, the lithiation peak B represents the process of alloying reaction between elemental Si and elemental Li to form a lower-order lithium-silicon alloy (Li[[ID=十六]] y [[ID=十七]]Si, 0 < y < 3.75), and the lithiation peak A represents two parts of the alloying reaction: ① The lower-order lithium-silicon alloy (Li[[ID=十八]] ySi) continues to undergo an alloying reaction with elemental Li to generate a higher-order lithium-silicon alloy (Li). x ① Si4, 3.75≤x≤4.4); ② Alloying reaction of elemental Si and elemental Li directly generates high-order lithium-silicon alloy (Li x The lithium intercalation peak A indicates deep lithium intercalation. The stronger the intensity of the lithium intercalation peak A, the easier the deep lithium intercalation, indicating good lithium intercalation kinetics and improved cycle life. IA / IB represents the relative amount of low-order and high-order lithium-silicon alloys formed during charging. Controlling the IA / IB value to 0.8-1.2, higher than the existing IA / IB values ​​for silicon-carbon materials (0.45-0.8, not 0.8), allows lithium-containing substances in pre-lithiated porous carbon to rapidly alloy with silicon materials, achieving deep lithium intercalation, accelerating Li-ion transport kinetics, and improving the cycle life of lithium secondary batteries.

[0086] As can be understood, the dQ / dV charging curve represents the capacity released by silicon-carbon materials within a unit voltage range. This is represented by characteristic peaks on the dQ / dV curve, with each peak typically representing an electrochemical reaction. Due to differences in reaction potential and reactivity among different materials, the position and height of these peaks will vary.

[0087] It is understandable that the intensity of lithium intercalation peak A and lithium intercalation peak B can be either the peak value (the vertical axis corresponding to the peak) or the peak area.

[0088] It is understandable that the dQ / dV charging curve of silicon-carbon materials can be obtained through the following methods:

[0089] Silicon carbon material, conductive agent carbon black (Super P), and binder CMC are mixed thoroughly in an appropriate amount of deionized water at a weight ratio of 98:1:1 to form a uniform positive electrode slurry. The positive electrode slurry is coated onto the surface of the positive electrode current collector aluminum foil, and then dried, cold-pressed, slit, and cut to obtain the positive electrode sheet.

[0090] Lithium foil is used as the negative electrode.

[0091] The lithium salt LiPF6 was dissolved in a solvent to obtain the electrolyte. The solvent was a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1, and the lithium salt concentration was 1 mol / L.

[0092] A polyethylene film with a thickness of 13 μm was used as the separator.

[0093] The above-mentioned positive electrode, negative electrode, separator and electrolyte are assembled into a battery.

[0094] Connect the assembled battery to the fixture of the Blue Electric device (Blue Electric CT3002A), set the potential range to 0-2.5V, and the rate of change to 0.1C. The device will perform a cyclic voltammetry scan according to the set parameters, applying a linearly changing voltage and recording the corresponding current response to generate CV curve data. The dQ / dV lithium intercalation curve will then be obtained through further conversion.

[0095] In some embodiments of this application, at a 0.1C rate, IA = 4000F-14000F. For example, in the dQ / dV charging curve of silicon-carbon materials at a 0.1C rate, IA can be 4000F-13000F, 5000F-12000F, 6000F-11000F, 7000F-10000F, 8000F-9000F, etc. By controlling the intensity of the lithium intercalation peak A at a 0.1C rate within the above range, a stronger lithium intercalation peak A accelerates the lithium intercalation reaction, improves the charging window, and further enhances the first-cycle efficiency and cycle performance of the lithium secondary battery.

[0096] It is understood that in the embodiments of this application, IA represents the peak value (the vertical coordinate corresponding to the peak), and its unit is F (farad), 1F = 1C / V (1 farad equals 1 coulomb per volt).

[0097] In some embodiments of this application, at a rate of 0.1C, IB = 3000F-18000F, for example, it can be 3000F-17000F, 4000F-16000F, 5000F-15000F, 8000F-13000F, 10000F-12000F, etc. Controlling the intensity of the lithium intercalation peak B at a rate of 0.1C within the above range is beneficial to controlling the IA / IB value at 0.8-1.2, promoting deep lithium intercalation, improving lithium-ion transport kinetics, and further enhancing the first-efficiency and cycle performance of lithium secondary batteries.

[0098] In some embodiments of this application, the mass percentage of lithium element is 0.001%-0.1% based on the total mass of the silicon-carbon material. For example, it could be 0.001%-0.09%, 0.01%-0.08%, 0.03%-0.06%, 0.04%-0.05%, etc. Controlling the mass percentage of lithium element in the silicon-carbon material within these ranges can reduce the insignificant lithium replenishment effect caused by excessively low lithium content, improving the initial efficiency and cycle performance of lithium secondary batteries containing silicon-carbon materials. It can also reduce the decrease in porous carbon pore volume / specific surface area caused by excessively high lithium content, further reducing the silicon material content, thus giving lithium secondary batteries containing silicon-carbon materials excellent energy density. In other embodiments of this application, the mass percentage of lithium element is 0.005%-0.06% based on the total mass of the silicon-carbon material.

[0099] It is understood that "the mass percentage of lithium based on the total mass of silicon-carbon materials" is a well-known definition in the art and can be determined using methods known in the art, such as the following methods:

[0100] Trace element analysis using ICP: Inductively Coupled Plasma Atomic Emission Spectrometer, iCAP 7400, detection standard: EPA6010D-2018, test procedure as follows:

[0101] 1. Weighing: Accurately weigh approximately 0.1g of the negative electrode material into a 50ml polytetrafluoroethylene digestion tube.

[0102] 2. Add an appropriate amount of inorganic acid (concentrated nitric acid) to each of the weighed sample digestion tubes. Cover the tubes and place them in a stainless steel reaction vessel. Heat the vessel in an oven at 190 degrees Celsius for about 10 hours, then stop heating and let it cool.

[0103] 3. Transfer the cooled solution to a 25ml plastic volumetric flask, and finally dilute to volume with deionized water.

[0104] 4. Prepare standard test solutions. The standard solutions are national standard reference materials, and the concentration points of the curve are 0, 0.5, 1.0, 2.0, and 5.0 mg / L.

[0105] 5. Instrument testing: Refer to standard EPA 6010D-2018. First, use the instrument ICP-OES to prepare a standard solution calibration curve, input the sample mass and volume, and then test the digested solutions in sequence. If the solution exceeds the curve range, dilute it before testing.

[0106] 6. Finally, the final content of Li in each sample is determined by the spectrum, and the test results are obtained.

[0107] In some embodiments of this application, the mass percentage of silicon element in the silicon-carbon material is 10%-60% based on the total mass of the silicon-carbon material. For example, it can be 10%-59%, 20%-50%, 30%-40%, etc. Controlling the silicon content in the silicon-carbon material within these ranges allows the lithium-ion secondary battery containing silicon-carbon material to have excellent energy density, while also reducing the problems of excessive electrode processing and expansion caused by excessive silicon content. This results in the lithium-ion secondary battery having both excellent initial efficiency and cycle performance. In other embodiments of this application, the mass percentage of silicon element in the silicon-carbon material is 25%-55% based on the total mass of the silicon-carbon material.

[0108] It is understood that "the mass percentage of silicon element based on the total mass of silicon-carbon material" is a well-known definition in the art and can be determined using methods known in the art, such as the following methods:

[0109] 1. Weighing: Accurately weigh approximately 0.1g of the negative electrode material into a 50ml polytetrafluoroethylene digestion tube.

[0110] 2. Add appropriate amounts of inorganic acid (concentrated nitric acid + hydrofluoric acid) to the weighed sample digestion tubes. Cover the tubes and place them in a stainless steel reaction vessel. Heat the vessel in an oven at 190 degrees Celsius for about 10 hours, then stop heating and let it cool.

[0111] 3. Transfer the cooled solution to a 25ml plastic volumetric flask, and finally dilute to volume with deionized water.

[0112] 4. Prepare standard test solutions. The standard solutions are national standard reference materials, and the concentration points of the curve are 0, 0.5, 1.0, 2.0, and 5.0 mg / L.

[0113] 5. Instrument testing: Refer to standard EPA 6010D-2018. First, use the instrument ICP-OES to prepare a standard solution calibration curve, input the sample mass and volume, and then test the digested solutions in sequence. If the solution exceeds the curve range, dilute it before testing.

[0114] 6. Finally, the final Si content in each sample is determined by the spectrum, and the test results are obtained.

[0115] In some embodiments of this application, the specific surface area of ​​the silicon-carbon material is 0.1 m². 2 / g-50m 2 / g, for example, the specific surface area of ​​silicon-carbon materials can be 0.1m². 2 / g-49m 2 / g, 1m 2 / g-45m 2 / g, 10m 2 / g-40m 2 / g, 20m 2 / g-30m 2 By controlling the specific surface area of ​​the silicon-carbon material within the above range (e.g., g), silicon and lithium-containing substances can be distributed within the carbon material. This reduces the intrusion of electrolyte into the silicon-carbon material caused by an excessively large specific surface area, thereby reducing side reactions between the silicon and lithium-containing substances and the electrolyte, improving lithium replenishment efficiency, and enhancing the initial efficiency and cycle performance of the lithium-ion secondary battery. In some other embodiments of this application, the specific surface area of ​​the silicon-carbon material is 0.5 m² / g. 2 / g-10m 2 / g.

[0116] It is understood that "specific surface area of ​​silicon-carbon materials" is a well-known definition in the art and can be measured using methods known in the art, such as the following methods:

[0117] In this application, the specific surface area is determined using the specific surface area analyzer-static volumetric method according to standard GB / T 19587-2017. Specifically, according to the embodiments of this application, a flow-type gas adsorption specific surface area measuring device (equipment model: TristarⅡ3020; Micromeritics, USA) can be used for measurement. Before testing, the silicon-carbon material is pretreated by heating at 200°C for 2 hours.

[0118] Typically, a battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active metal ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0119] In some embodiments of this application, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, wherein the positive active material layer includes the aforementioned irreversible positive electrode additive.

[0120] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0121] In some embodiments of this application, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0122] In some embodiments of this application, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries.

[0123] As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this 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 may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.8 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure may include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites. The modified compounds of the above materials may be for doping modification and / or surface coating modification of the materials.

[0124] During the charging and discharging process of a battery, Li undergoes insertion / extraction and consumption, resulting in varying molar Li content at different discharge states. In the examples of positive electrode active materials in this application, the molar Li content refers to the initial state of the material, i.e., the state before material addition. After charge-discharge cycles, the molar Li content changes when the positive electrode active material is applied to the battery system.

[0125] In the examples of positive electrode active materials in this application, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0126] In other embodiments of this application, the lithium transition metal oxide includes Li x (Ni a Co b Mn c ) 1-d M d O 2- y A y Where x is 0.2-1.2, a is 0.8-1, b is 0-0.15, c is 0-0.15, d is 0-0.02, y is 0-0.1, M includes at least one of Zr, Y, Al, Ti, W, Sr, Ta, Sb, Nb, Na, K, Ca or Ce, and A includes at least one of N, F, S or Cl.

[0127] As an example, x can be 0.2-1.1, 0.3-1, 0.4-0.9, 0.5-0.8, 0.6-0.7, etc.; a can be 0.8-0.98, 0.85-0.95, 0.9-0.92, etc.; b can be 0-0.14, 0.05-0.12, 0.08-0.1, etc.; c can be 0-0.14, 0.05-0.12, 0.08-0.1, etc.; d can be 0-0.015, 0.005-0.01, etc.; y can be 0-0.09, 0.02-0.07, 0.05-0.06, etc. The high nickel content in the aforementioned lithium transition metal oxides allows for compatibility with silicon-carbon materials in the negative electrode, improving the energy density of lithium secondary batteries while maintaining excellent initial efficiency and cycle performance.

[0128] In some embodiments of this application, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0129] In some embodiments of this application, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0130] In some embodiments of this application, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder, positive irreversible additive and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0131] In some embodiments of this application, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side of the negative current collector.

[0132] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0133] In some embodiments of this application, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0134] In some embodiments of this application, the negative electrode active material may also be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0135] In some embodiments of this application, the negative electrode active material layer may optionally include a binder. The binder may be selected from at least one of 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).

[0136] In some embodiments of this application, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0137] In some embodiments of this application, the negative electrode active material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0138] In some embodiments of this application, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0139] In some embodiments of this application, the mass percentage of silicon-carbon material in the negative electrode active material layer is 1%-100%, for example, 1%-99%, 10%-90%, 20%-80%, 30%-70%, 50%-60%, etc. Controlling the mass percentage of silicon-carbon material in the negative electrode active material layer within these ranges can improve the energy density of the lithium-ion secondary battery containing it. Simultaneously, the lithium-ion secondary battery exhibits excellent first-efficiency performance and cycle life. In other embodiments of this application, the mass percentage of silicon-carbon material in the negative electrode active material layer is 3%-50%.

[0140] This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or completely solid.

[0141] In some embodiments of this application, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0142] In some embodiments of this application, when the battery is a lithium-ion battery, the electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, or lithium tetrafluorooxalate phosphate.

[0143] In some embodiments of this application, when the battery is a sodium-ion battery, the electrolyte salt may include at least one of sodium hexafluorophosphate, sodium difluorooxalate borate, sodium tetrafluoroborate, sodium dioxalate borate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, or sodium bis(trifluoromethanesulfonyl)imide.

[0144] In some embodiments of this application, the solvent may include at least one selected from ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl 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, ethylene glycol dimethyl ether, methyl ethyl sulfone, or diethyl sulfone.

[0145] In some embodiments of this application, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0146] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0147] In some embodiments of this application, the material of the separator may include at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, or polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0148] The secondary batteries of this application include single-cell battery forms, battery module forms, and battery pack forms. The following description, with appropriate reference to the accompanying drawings, will illustrate the single-cell battery, battery module, and battery pack of this application.

[0149] In some embodiments of this application, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly by a winding process or a stacking process.

[0150] In some embodiments of this application, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0151] In a second aspect of this application, a negative electrode active material is proposed, the negative electrode active material comprising a silicon-carbon material, the silicon-carbon material comprising a carbon material and silicon material and a lithium-containing substance distributed within the carbon material, the carbon material further comprising an oxygen element, the oxygen element forming CO groups and C=O groups with the carbon material, the amount of the CO groups being n1, the amount of the C=O groups being n2, and n2 / (n1+n2)×100%=55%-65%.

[0152] The negative electrode active material of this application, by placing silicon material and lithium-containing material inside carbon material, achieves sufficient contact and pre-lithiation between the lithium-containing material and the carbon and silicon materials. This provides active lithium during charge and discharge, addressing the instability of the SEI on the silicon surface. The active lithium participates in SEI film formation, reducing the loss of active lithium from the positive electrode during SEI film formation and quickly achieving lithium replenishment. Furthermore, by controlling the content of C=O groups (e.g., -C=O-) to 55%-65%, and considering that CO groups are reversible for active lithium ions while C=O groups are mostly irreversible, the loss of active lithium ions can be reduced, improving the lithium replenishment effect. Therefore, the active lithium provided by the lithium-containing material can repair intrinsic defects within the carbon material (such as carbon atom vacancies, oxygen-containing functional groups, etc.), reducing the consumption of active lithium by these defects. In summary, the lithium secondary battery proposed in this application exhibits excellent initial efficiency and cycle performance.

[0153] It is understood that other additional technical features of the negative electrode active material in the embodiments of this application have been described in detail above and will not be repeated here.

[0154] In a third aspect of this application, a method for preparing the negative electrode active material described in the second aspect is proposed, comprising:

[0155] S1. Dissolve elemental lithium and a regulator in an organic solvent to form a pre-lithiation solution.

[0156] This step involves dissolving elemental lithium and a regulator in an organic solvent to form a solution. This facilitates the entry of the lithium-containing material into the pores of the porous carbon. The regulator plays a special role in the pre-lithiation process; it reacts with lithium to form a relatively stable intermediate. This intermediate releases lithium ions in a gentler manner during subsequent pre-lithiation, making the lithium supply more controllable and reducing the potential for violent reactions when lithium directly contacts the porous carbon. Furthermore, elemental lithium may be difficult to dissolve in organic solvents, or the lithium distribution after dissolution may be uneven. The regulator acts as a co-solvent or dispersant, helping lithium dissolve better in the organic solvent and improving the pre-lithiation effect.

[0157] In some embodiments of this application, the modifier includes one or more of biphenyl and naphthalene. This modifier can react with elemental lithium to form an intermediate, converting solid lithium into a liquid form, which facilitates subsequent pre-lithiation of porous carbon. Furthermore, the modifier possesses strong reducing properties, ensuring that the lithium-containing material retains its reducing properties after entering the porous carbon, guaranteeing that the lithium-containing material can provide active lithium. For example, the benzene radicals in biphenyl and naphthalene combine in the form of coordinate bonds, ensuring the reducing properties of lithium.

[0158] In some embodiments of this application, the organic solvent includes one or more of 2-methyltetrahydrofuran, ethylene glycol dimethyl ether, and tetrahydrofuran. These solvents can dissolve elemental lithium and the modifier to form a homogeneous pre-lithiation solution, converting solid lithium into a liquid form, which facilitates subsequent pre-lithiation of porous carbon.

[0159] In some embodiments of this application, the molar concentration of lithium in the pre-lithiation solution is 0.001 mol / L to 0.5 mol / L. For example, it can be 0.001 mol / L to 0.49 mol / L, 0.005 mol / L to 0.45 mol / L, 0.01 mol / L to 0.4 mol / L, 0.05 mol / L to 0.35 mol / L, 0.1 mol / L to 0.3 mol / L, 0.2 mol / L to 0.25 mol / L, etc. Controlling the lithium concentration in the pre-lithiation solution within the above range ensures that the lithium-containing material in the silicon-carbon material provides sufficient active lithium without allowing excessive lithium-containing material to enter the porous carbon, clogging the pores of the porous carbon and reducing its specific surface area, which in turn affects the subsequent deposition of silicon material. This ensures that sufficient silicon material is deposited within the porous carbon pores, improving the capacity, first-time efficiency, and cycle life of the negative electrode active material. In some other embodiments of this application, the molar concentration of lithium in the pre-lithiation solution is 0.01 mol / L to 0.1 mol / L.

[0160] S2. The porous carbon is immersed in the pre-lithiation solution, vacuum dried, and heat-treated at 500℃-1100℃ under an inert atmosphere to obtain pre-lithiated porous carbon.

[0161] In this step, the porous carbon is immersed in the pre-lithiation solution to allow the lithium-containing material to enter the interior of the porous carbon, repair the defects inside the porous carbon, and make full contact with the porous carbon. After that, it is vacuum dried and heat-treated at 500℃-1100℃ in an inert atmosphere to remove the residual organic solvent in the porous carbon pores.

[0162] In some embodiments of this application, the specific surface area of ​​the porous carbon is 700 m². 2 / g-2300m 2 / g, for example, could be 700m 2 / g-2200m 2 / g, 800m 2 / g-2100m 2 / g, 1000m 2 / g-2000m 2 / g, 1500m 2 / g-1800m 2The specific surface area of ​​the porous carbon is controlled within the above range. The porous carbon has abundant pore structures, which facilitates the entry of lithium-containing materials and silicon materials into the porous carbon interior. The lithium-containing materials can fully contact the porous carbon and silicon materials, repairing defects within the porous carbon. Furthermore, it can provide active lithium during charge and discharge to address the instability of the SEI on the silicon surface. This active lithium participates in SEI film formation. In addition, the silicon material is located inside the porous carbon, which can confine the silicon material, reducing its expansion during charge and discharge, further improving the initial efficiency and cycle performance of the lithium secondary battery. In some other embodiments of this application, the specific surface area of ​​the porous carbon is 1200 m². 2 / g-2000m 2 / g.

[0163] It is understood that the method for determining the specific surface area of ​​porous carbon in the embodiments of this application is the same as that for silicon-carbon materials described above, and will not be repeated here.

[0164] In some embodiments of this application, the soaking time is 1s-2min, for example, it can be 1s-1.9min, 30s-1.5min, 1min-1.2min, etc. Controlling the soaking time within the above range is sufficient to allow lithium-containing substances to enter the porous carbon and repair the defects inside the porous carbon.

[0165] In some embodiments of this application, the heat treatment temperature is 500℃-1100℃, for example, 500℃-1000℃, 600℃-900℃, 700℃-800℃, etc. Controlling the heat treatment temperature within this range can decompose the residual organic solvents inside and on the surface of the porous carbon, thus thoroughly removing the residual organic solvents within the porous carbon channels. In other embodiments of this application, the heat treatment temperature is 700℃-1000℃.

[0166] In some embodiments of this application, the heat treatment time is 0.2h-2h, for example, 0.2h-1.9h, 0.5h-1.5h, 0.8h-1h, etc. Controlling the heat treatment time within the above range can effectively remove residual organic solvents in the porous carbon channels. In other embodiments of this application, the heat treatment time is 0.5h-1h.

[0167] In some embodiments of this application, the time interval between the vacuum drying and the heat treatment is less than or equal to 120 minutes. For example, it can be 1 minute to 119 minutes, 10 minutes to 110 minutes, 50 minutes to 100 minutes, etc. Controlling the time interval between vacuum drying and heat treatment, that is, the time between vacuum drying and the start of heat treatment, within the above range can reduce the deterioration caused by prolonged exposure of lithium-containing materials to air, ensure the activity of lithium-containing materials, enable them to provide sufficient active lithium, and improve the first-efficiency and cycle performance of lithium secondary batteries.

[0168] S3. Silicon material is deposited on the pre-lithiated porous carbon using a vapor deposition method, and carbon is deposited to cover the silicon material to obtain silicon-carbon material, which is the negative electrode active material.

[0169] In this step, a vapor deposition method is used to deposit silicon on pre-lithiated porous carbon, and carbon is deposited to cover the silicon (to reduce the contact between silicon and the outside environment and electrolyte, and to confine the silicon to reduce the expansion of silicon-carbon material), thus obtaining silicon-carbon material.

[0170] In some embodiments of this application, the deposition temperature of the silicon material is 480℃-550℃. For example, it can be 480℃-549℃, 490℃-540℃, 500℃-530℃, 510℃-520℃, etc. Controlling the deposition temperature of silicon within the above range is sufficient to allow the silicon source (such as silane) to fully decompose into elemental silicon and deposit it into the porous carbon. It can also reduce the high activity of the silicon source caused by excessively high temperature, which would cause it to deposit on the surface of the porous carbon. Instead, it promotes the deposition of silicon material into the interior of the porous carbon. Silicon material can be deposited on pre-lithiated porous carbon, especially inside it. Since the silicon material mainly exists in the form of elemental silicon, the capacity of silicon-carbon material can be improved, thereby improving the energy density, first efficiency, and cycle performance of lithium secondary batteries.

[0171] In some embodiments of this application, the silicon source flow rate of the deposited silicon material is 0.5 L / min-10 L / min, for example, it can be 0.5 L / min-9.9 L / min, 1 L / min-9 L / min, 2 L / min-8 L / min, 3 L / min-7 L / min, 4 L / min-6 L / min, etc. Controlling the silicon source flow rate within the above range allows for the deposition of sufficient silicon material, especially inside porous carbon, which can improve the capacity of silicon-carbon materials, thereby improving the energy density, first-efficiency, and cycle performance of lithium secondary batteries. In other embodiments of this application, the silicon source flow rate of the deposited silicon material is 1 L / min-5 L / min.

[0172] In some embodiments of this application, the deposition time of the silicon material is 100-900 min, for example, 100-890 min, 200-800 min, 300-700 min, 400-600 min, etc. Controlling the deposition time of silicon within this range allows for the deposition of sufficient silicon material, especially inside porous carbon, which can improve the capacity of silicon-carbon materials, thereby improving the energy density, first-efficiency, and cycle performance of lithium secondary batteries. In other embodiments of this application, the deposition time of the silicon material is 180-600 min.

[0173] In some implementations, the silicon source may be silane.

[0174] In some embodiments of this application, the mass of deposited carbon accounts for 2%-15% of the mass of the silicon-carbon material, for example, 2%-14%, 4%-12%, 5%-10%, etc. Controlling the amount of deposited carbon within the above range can cover the lithium-containing material and silicon material deposited on the porous carbon, reducing their contact with the external environment and electrolyte, and can also reduce the expansion of the silicon-carbon material, further improving the energy density, first-efficiency, and cycle performance of the lithium secondary battery. In other embodiments of this application, the mass of deposited carbon accounts for 4%-10% of the mass of the silicon-carbon material.

[0175] In some implementations, the carbon source for carbon deposition can be acetylene.

[0176] In summary, the method for preparing silicon-carbon materials proposed in this application, which involves pre-lithiation of porous carbon at the ends of the porous carbon, can effectively reduce the Lithium content. + The diffusion time is shortened, allowing for rapid lithium replenishment. Simultaneously, pre-lithiation repairs some intrinsic defects in porous carbon before silicon deposition and carbon coating, ensuring active lithium resides within the silicon-carbon material. This active lithium also repairs defects in the porous carbon (such as holes and oxygen-containing functional groups). During battery charging and discharging, lithium ions are released to participate in the SEI film formation process, reducing the loss of active lithium in the positive electrode during SEI film formation and achieving lithium replenishment. This significantly improves the battery's initial coulombic efficiency, energy density, and cycle performance.

[0177] In some embodiments of this application, the outer packaging of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch-type soft pack. The material of the soft pack can be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0178] It is understood that the lithium secondary battery mentioned above in this application is a single battery cell.

[0179] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 Here is a square-structured battery cell 1 as an example.

[0180] In some embodiments of this application, reference is made to Figure 2 The outer packaging may include a housing 11 and a cover plate 13. The housing 11 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be placed over the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator can be formed into an electrode assembly 12 by a winding process or a stacking process. The electrode assembly 12 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 12. The number of electrode assemblies 12 contained in a single battery cell 1 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0181] In some embodiments of this application, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0182] Figure 3 This is battery module 2 as an example. (See reference...) Figure 3 In battery module 2, multiple battery cells 1 can be arranged sequentially along the length of battery module 2. Of course, they can also be arranged in any other way. Furthermore, these multiple battery cells 1 can be fixed in place using fasteners.

[0183] Optionally, the battery module 2 may also include a housing with a receiving space in which multiple battery cells 1 are received.

[0184] In some embodiments of this application, the battery modules described above can also be assembled into a battery pack. The number of battery modules contained in the battery pack can 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.

[0185] Figure 4 and Figure 5 This is battery pack 3 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 3 may include a battery box and multiple battery modules 2 disposed within the battery box. The battery box includes an upper box 31 and a lower box 32, with the upper box 31 covering the lower box 32 to form a closed space for accommodating the battery modules 2. The multiple battery modules 2 can be arranged in any manner within the battery box.

[0186] In addition, this application also provides an electrical device, which includes the lithium secondary battery provided in the first aspect of this application. The battery cell, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical 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 and satellites, energy storage systems, etc.

[0187] As the electrical equipment, battery cells, battery modules, or battery packs can be selected according to their usage requirements.

[0188] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0189] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0190] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0191] Example 1

[0192] Preparation of silicon-carbon materials:

[0193] (1) Preparation of pre-lithiation solution: 0.5 mol lithium foil and 0.5 mol biphenyl were dissolved in 2-methyl-tetrahydrofuran solution to prepare a pre-lithiation solution with a lithium molar concentration of 0.05 mol / L.

[0194] (2) Porous carbon pre-lithiation: Porous carbon (specific surface area of ​​1703 m²) is used for pre-lithiation. 2 / g (based on the total mass of porous carbon, with oxygen content of 0.83%) was soaked in a pre-lithiation solution for 1 min, then filtered and washed with 2-methyl-tetrahydrofuran. The porous carbon was dried under vacuum for 30 min, and then heat-treated at 800℃ for 1 h under an inert atmosphere to obtain pre-lithiated porous carbon.

[0195] (3) The pre-lithiated porous carbon was kept at 400℃ for 2 hours in a fluidized bed with nitrogen as a protective gas. The temperature was raised to 500℃ and silane gas was introduced. The silane flow rate was 3L / min and the nitrogen flow rate was 20L / min. The deposition was carried out for 300 minutes. Subsequently, carbon coating treatment was carried out: a mixture of acetylene and nitrogen gas was used. The carbon coating mass accounted for 10% of the silicon carbon material.

[0196] n1 / (n1+n2)×100%=39.6%, n2 / (n1+n2)×100%=60.4%.

[0197] 1. Preparation of negative electrode sheet

[0198] The silicon carbon material, graphite, conductive agent, thickener sodium carboxymethyl cellulose (CMC), and binder SBR were mixed in a mass ratio of 0.15:0.8:0.015:0.015:0.02 to obtain a negative electrode slurry. This slurry was coated onto a copper foil current collector. The coated negative electrode sheet was then dried in a vacuum drying oven for 12 hours. The dried negative electrode sheet was then cold-pressed in a rolling mill to obtain the final negative electrode sheet. The compacted density of the negative electrode sheet was 1.6 g / cm³. 3 .

[0199] 2. Preparation of the positive electrode sheet

[0200] NCM ternary material 811 Conductive agent carbon black (Super P) and binder PVDF are mixed thoroughly in an appropriate amount of N-methylpyrrolidone (NMP) at a weight ratio of 98:1:1 to form a uniform positive electrode slurry. The positive electrode slurry is then coated onto the surface of the positive electrode current collector aluminum foil, dried, cold-pressed, slit, and cut to obtain the positive electrode sheet. The compacted density of the positive electrode sheet is 3.5 g / cm³. 3 .

[0201] 3. Preparation of electrolyte

[0202] In an argon-filled glove box with a water content of <1ppm, lithium salt LiPF6 was dissolved in a solvent to obtain an electrolyte. The solvent was a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1, and the lithium salt concentration was 1mol / L.

[0203] 4. Separating membrane

[0204] A polyethylene film with a thickness of 13 μm was used as the separator.

[0205] 5. Preparation of lithium secondary batteries

[0206] The positive and negative electrode plates and the separator are stacked in sequence to form a battery chip. Then, the battery chip is packaged in a suitable container, electrolyte is added and a sealed cap is added to fix the cell assembly, so that it has a certain shape of finished cell. After processes such as formation and settling, the battery is obtained.

[0207] The preparation methods of the lithium-ion batteries in Examples 2-12 and Comparative Example 1 are the same as those in Example 1, except that the process of preparing silicon-carbon materials is different, as shown in Table 1.

[0208] In Comparative Example 1, compared to Example 1, porous carbon (specific surface area of ​​1703 m²) 2 / g, based on the total mass of porous carbon, the mass ratio of oxygen element is 0.83%), without pre-lithiation in steps (1) and (2), directly proceed to step (3).

[0209] Compared with Example 1, in Comparative Example 2, step (3) is performed first, followed by steps (1) and (2), as follows:

[0210] (1) Porous carbon (specific surface area of ​​1703 m²) 2 / g (based on the total mass of porous carbon, with oxygen accounting for 0.83% by mass) was kept at 400℃ for 2h in a fluidized bed, with nitrogen as a protective gas, and the temperature was raised to 500℃. Silane gas was introduced at a flow rate of 3L / min and nitrogen at a flow rate of 20L / min, and deposition was carried out for 300min. Subsequently, carbon coating treatment was performed: a mixture of acetylene and nitrogen was used, and the carbon coating mass accounted for 10% of the silicon-carbon material.

[0211] (2) Preparation of pre-lithiation solution: 0.5 mol lithium foil and 0.5 mol biphenyl were dissolved in 2-methyl-tetrahydrofuran solution to prepare a pre-lithiation solution with a lithium molar concentration of 0.05 mol / L.

[0212] (3) The porous carbon obtained in step (1) is immersed in a pre-lithiation solution for 1 min, then filtered and cleaned with 2-methyl-tetrahydrofuran. The porous carbon is dried in a vacuum environment and heat-treated at 800°C for 1 h in an inert atmosphere to obtain silicon-carbon material.

[0213] Table 1

[0214]

[0215] O1s XPS spectra of the silicon-carbon material prepared in Example 1 and the porous carbon in Comparative Example 1 were obtained. Figure 7 As can be seen, compared to the porous carbon in Comparative Example 1, the state of O changed after pre-lithiation and deposition of silicon materials.

[0216] O1s XPS spectra were generated for the silicon-carbon materials prepared in Example 1 and Comparative Example 1, and for the porous carbon in Comparative Example 1. CO and C=O spectra were then fitted, with their respective area representing the content ratio of CO and C=O. Figure 8 The O1s XPS spectrum of the porous carbon in Comparative Example 1 shows that n1 / (n1+n2)×100% = 31.7% and n2 / (n1+n2)×100% = 68.3%. Figure 9 The O1s XPS spectrum of the silicon-carbon material in Example 1 shows that n1 / (n1+n2)×100%=39.6% and n2 / (n1+n2)×100%=60.4%.

[0217] The dQ / dV charging curves of the silicon-carbon materials prepared in Comparative Example 1 and Example 1 were obtained using the following specific steps:

[0218] Silicon carbon material, conductive agent carbon black (Super P), and binder CMC are mixed thoroughly in an appropriate amount of deionized water at a weight ratio of 98:1:1 to form a uniform positive electrode slurry. The positive electrode slurry is coated onto the surface of the positive electrode current collector aluminum foil, and then dried, cold-pressed, slit, and cut to obtain the positive electrode sheet.

[0219] Lithium foil is used as the negative electrode.

[0220] The lithium salt LiPF6 was dissolved in a solvent to obtain the electrolyte. The solvent was a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1, and the lithium salt concentration was 1 mol / L.

[0221] A polyethylene film with a thickness of 13 μm was used as the separator.

[0222] The above-mentioned positive electrode, negative electrode, separator and electrolyte are assembled into a battery.

[0223] Connect the assembled battery to the fixture of the Blue Electric device (Blue Electric CT3002A), set the potential range to 0-2.5V, and the rate of change to 0.1C. The device will perform a cyclic voltammetry scan according to the set parameters, applying a linearly changing voltage and recording the corresponding current response to generate CV curve data. The dQ / dV lithium intercalation curve will then be obtained through further conversion.

[0224] The dQ / dV charging curves of Comparative Example 1 and Example 1 are as follows: Figure 10 and Figure 11 As shown, it can be seen that Figure 11 Example 1 and Figure 10 Compared to the dQ / dV charging curve of the silicon-carbon material in Comparative Example 1, the lithium intercalation peak A is enhanced, and IA / IB = 1.12 in Example 1.

[0225] The powder resistivity of the silicon-carbon materials obtained in Examples 1-12 and Comparative Examples 1-2 was measured, and the results are shown in Table 2. The measurement process is as follows:

[0226] The resistivity was measured using an ST2722 resistivity meter, and the test was conducted in accordance with the reference standard GB / T 30835-2014.

[0227] As can be seen from Table 2, the powder resistance of the silicon-carbon material in Examples 1-12 of this application is relatively small, indicating that the silicon material is located inside the carbon material. This is because if the silicon material is on the surface of the carbon material, the powder resistance will increase significantly since the silicon material is a semiconductor.

[0228] The delithiation capacity, first-efficiency and cycle performance of the batteries in Examples 1-12 and Comparative Examples 1-2 were characterized, and the characterization results are shown in Table 2.

[0229] 1. Lithium removal capacity test: Connect the battery to the corresponding channel of the Blue Battery tester, with a voltage range of 0.005V-2V and a rate of 0.1C, to obtain the lithium removal capacity.

[0230] 2. Cyclic Performance Test: Each battery cell is charged at 45℃ at a 1C rate to a voltage of 4.25V, and then discharged at a 1C rate to a voltage of 2.5V. The reversible capacity is measured as C0. This charging and discharging process is repeated until the discharge capacity Cn / C0 ≤ 80% in a certain cycle. The total number of cycles is recorded as X-Cycle. Where Cn is the reversible capacity at the nth cycle.

[0231] 3. First-time efficiency test: In the cycle performance test, the first-time efficiency = battery discharge capacity in the first cycle / charge capacity × 100%. The results are shown in Table 2.

[0232] Table 2

[0233] Resistance of silicon carbide powder (Ω·cm) Lithium removal capacity (mAh / g) First effect Number of cycles (laps) Example 1 30 1650 85.2％ 1900 Example 2 40 1624.9 83.5％ 1600 Example 3 33 1634.6 84％ 1800 Example 4 20 1628.6 85％ 1850 Example 5 16 1612.8 84％ 1700 Example 6 10 1608.2 83.6％ 1500 Example 7 36 1611.3 82.8％ 1550 Example 8 24 1654.1 85％ 1870 Example 9 23 1656.0 85.1％ 1850 Example 10 25 1658.0 85.2％ 1890 Example 11 35 1652.9 85.2％ 1880 Example 12 38 1640.5 85％ 1850 Comparative Example 1 50 1596 82％ 1400 Comparative Example 2 40 1605 82.5％ 1450

[0234] As shown in Table 2, in Examples 1-12 of this application, the content of C=O groups is reduced, resulting in fewer defects in the negative electrode active material and improving the initial efficiency and cycle performance of the silicon-carbon material. Furthermore, the inclusion of lithium-containing substances in the silicon material facilitates the extraction of lithium ions to participate in SEI film formation during battery charging and discharging, reducing the loss of active lithium from the positive electrode during SEI film formation and achieving a lithium replenishment effect. This significantly improves the initial coulombic efficiency and cycle performance of the lithium secondary battery. In Comparative Examples 1-2, compared to Examples 1-12, the content of C=O groups is outside the range specified in this application, and the initial coulombic efficiency and cycle performance of the lithium secondary battery are significantly reduced. Therefore, controlling the proportion of C=O groups in this application can significantly improve the initial coulombic efficiency and cycle performance of the lithium secondary battery.

[0235] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A lithium secondary battery, characterized by comprising: The lithium secondary battery includes a positive electrode sheet, an electrolyte, and a negative electrode sheet. The negative electrode sheet includes a silicon-carbon material, the silicon-carbon material includes a carbon material and silicon material and lithium-containing substances distributed inside the carbon material, the carbon material further includes oxygen element, the oxygen element forms C-O groups and C=O groups with the carbon material, the amount of substance of the C-O groups is n1, and the amount of substance of the C=O groups is n2. n2 / (n1 + n2)×100% = 55% - 65%.

2. The lithium secondary battery according to claim 1, characterized by Based on the total mass of the carbon material, the mass proportion of the oxygen element is 0.2% - 3.5%; and / or n1 / (n1 + n2)×100% = 35% - 45%.

3. The lithium secondary battery according to claim 1 or 2, characterized by Based on the total mass of the carbon material, the mass proportion of the oxygen element is 0.3% - 1.5%.

4. The lithium secondary battery according to any one of claims 1 to 3, characterized by, In the dQ / dV charge curve of the silicon-carbon material, the peak intensity of the lithium insertion peak A with the abscissa between 0.01 < V < 0.1V is IA, and the intensity of the lithium insertion peak B with the abscissa between 0.1 ≤ V < 0.2V is IB, and IA / IB = 0.8 - 1.

2.

5. The lithium secondary battery according to claim 4, characterized by At a rate of 0.1C, IA = 4000F - 14000F; and / or At a rate of 0.1C, IB = 3000F - 18000F.

6. The lithium secondary battery according to any one of claims 1 to 5, characterized by, Based on the total mass of the silicon-carbon material, the mass proportion of lithium element is 0.001% - 0.1%.

7. The lithium secondary battery according to any one of claims 1 to 6, characterized by, Based on the total mass of the silicon-carbon material, the mass proportion of lithium element is 0.

8. The lithium secondary battery according to any one of claims 1 to 7, characterized by, ​ 9. The lithium secondary battery according to any one of claims 1 to 8, characterized by, The silicon-carbon material has a specific surface area of 0.1 m 2 / g-50 m 2 / g.

10. The lithium secondary battery according to any one of claims 1 to 9, characterized by, ​ 11. The lithium secondary battery according to any one of claims 1 to 10, characterized by, ​ 12. The lithium secondary battery according to any one of claims 1-11, characterized in that, ​ 13. The lithium secondary battery according to claim 12, characterized by The lithium transition metal oxide includes Li x (Ni a Co b Mn c ) 1-d M d O 2-y A y Where x is 0.2-1.2, a is 0.8-1, b is 0-0.15, c is 0-0.15, d is 0-0.02, y is 0-0.1, M includes at least one of Zr, Y, Al, Ti, W, Sr, Ta, Sb, Nb, Na, K, Ca, Ce, and A includes at least one of N, F, S, or Cl.

14. A negative electrode active material, characterized by, ​ ​ 15. The negative electrode active material according to claim 14, characterized by ​ ​ 16. The negative electrode active material according to claim 14 or 15, characterized by ​ ​ Based on the total mass of the silicon-carbon material, the mass percentage of silicon is 10%-60%; The silicon-carbon material has a specific surface area of 0.1 m 2 / g-50 m 2 / g.

17. A method for producing a negative electrode active material, characterized by, include: Elemental lithium and a modifier are dissolved in an organic solvent to form a pre-lithiation solution; The porous carbon was immersed in the pre-lithiation solution, vacuum dried, and heat-treated at 500℃-1100℃ under an inert atmosphere to obtain pre-lithiated porous carbon. Silicon material is deposited on the pre-lithiated porous carbon using a vapor deposition method, and carbon is deposited to cover the silicon material, resulting in a silicon-carbon material, which is the negative electrode active material.

18. The method of claim 17, wherein, The method satisfies one or more of the following conditions: The molar concentration of lithium in the pre-lithiation solution is 0.001 mol / L-0.5 mol / L, and can be selected as 0.01 mol / L-0.1 mol / L; The soaking time is 1 second to 2 minutes; The silicon source flow rate of the deposited silicon material is 0.5L / min-10L / min, and can be selected as 1L / min-5L / min.

19. The method of claim 17 or 18, wherein, The method satisfies one or more of the following conditions: The regulator includes one or more of biphenyl and naphthalene; The organic solvent includes one or more of 2-methyltetrahydrofuran, ethylene glycol dimethyl ether, and tetrahydrofuran; The time interval between the vacuum drying and the heat treatment is less than or equal to 120 minutes; The specific surface area of the porous carbon is 700 m 2 / g-2300 m 2 / g, preferably 1200 m 2 / g-2000 m 2 / g; The heat treatment temperature is 700℃-1000℃; The heat treatment time is 0.2h-2h; The deposition temperature of the silicon material is 480℃-550℃; The deposition time of the silicon material is 100 min-900 min, and can be selected as 180 min-600 min; The deposited carbon accounts for 2%-15% of the mass of the silicon-carbon material, optionally 4%-10%.

20. An electrical appliance, characterized in that, The lithium secondary battery includes any one of claims 1-13.

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