Modified silicon-based active materials, their preparation and use

Abstract

The application belongs to the field of silicon-based electrode materials, and particularly relates to a preparation method of modified silicon-based active material, wherein a silicon raw material is pretreated in an oxidizing acid solution to obtain pretreated material; the pretreated material is subjected to carbon coating treatment to obtain carbon-coated material; the carbon-coated material and a lithium source are subjected to lithiumization roasting to obtain lithiumized material; the lithiumized material is placed in a modification liquid to be subjected to modification treatment, so that the modified silicon-based active material is prepared; the modification liquid contains (NH4)2S2O3. The application also includes the material prepared by the preparation method and application thereof. The method can improve the initial efficiency and high-rate long-term cycle stability of the modified silicon-based material.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery anode materials, and particularly relates to the field of silicon-based anode active materials. Background Technology

[0002] Lithium-ion batteries have developed rapidly since their inception and are now widely used in portable electronic devices, transportation, energy storage power stations, and aerospace. Graphite is currently the mainstream anode material. However, with the development and widespread application of 8-series and 9-series high-nickel ternary cathode materials, the specific capacity of traditional graphite anodes has approached their theoretical capacity, making it difficult to meet the current demand for high-energy-density lithium-ion batteries in the power and energy storage markets. Silicon-based anodes (elemental silicon and silicon-oxygen anode materials SiOx, x<2) are considered the most effective and feasible materials for improving the electrochemical performance of lithium-ion batteries due to their much higher theoretical capacity than graphite. However, silicon and silicon-oxygen anodes generally suffer from low initial coulombic efficiency in lithium-ion battery systems, leading to irreversible lithium consumption in practical applications and hindering their commercial application.

[0003] To address the issue of initial efficiency, existing technologies have provided several modification solutions. For example, US Patent Publication No. US11848437A2 discloses a concept for a pre-lithiated silicon-based material. Chinese Patent Publication No. CN116706073A discloses a pre-lithiated anode, its preparation method, and its applications.

[0004] While pre-lithiation of silicon-based materials can improve their first-efficiency performance to some extent, inappropriate pre-lithiation processes can easily lead to further agglomeration between silicon grains. This, combined with the large volume expansion characteristics of silicon-based materials, can significantly affect the material's performance under high current, as well as its fast charging and low-temperature stability. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the primary objective of this invention is to provide a method for preparing modified silicon-based active materials, aiming to improve their initial efficiency, fast charging, and low-temperature performance.

[0006] The second objective of this invention is to provide the modified silicon-based active material prepared by the aforementioned method and its application in lithium secondary batteries.

[0007] A third objective of this invention is to provide a lithium secondary battery comprising the modified silicon-based active material, as well as its negative electrode and negative electrode material.

[0008] Silicon-based materials exhibit significant volume expansion, making them susceptible to the substantial volume expansion caused by high-current cycling, thus hindering the achievement of excellent fast-charging performance. Furthermore, their initial efficiency is relatively low. While pre-lithiation can improve initial efficiency to some extent, inappropriate pre-lithiation processes can further increase the risk of grain agglomeration, further reducing the material's structural stability against high-current cycling, making it difficult to simultaneously achieve high initial efficiency, fast charging, and low-temperature performance. To address this issue, this invention provides the following improvement:

[0009] A method for preparing modified silicon-based active materials involves pretreating silicon raw materials in an oxidizing acid solution to obtain pretreated materials.

[0010] The pretreated material is carbon-coated to obtain carbon-coated material;

[0011] The carbon-coated material and the lithium source are calcined to obtain the lithiated material;

[0012] The lithium-based material was placed in a modification liquid and modified to obtain the modified silicon-based active material.

[0013] The modified liquid contains (NH4)2S2O3.

[0014] This invention pre-treats and carbon-coates silicon raw materials, followed by lithiation calcination and subsequent modification in a modification solution containing (NH4)2S2O3. This enables pre-lithiation of silicon materials, significantly reduces grain agglomeration during processing, and improves grain stability. Research in this invention shows that the described process can significantly improve the first-cycle efficiency, fast charging performance, and low-temperature stability of silicon-based materials.

[0015] In this invention, the silicon raw material can be any silicon-based active material with modification requirements that is known in the industry, such as conventional silicon element and / or silicon oxide.

[0016] In this invention, the silicon raw material is nano-sized and / or micro-sized particles;

[0017] In this invention, the silicon raw material is nano-silicon powder, and its particle size is preferably 10-200 nm, more preferably 30-80 nm;

[0018] Alternatively, the silicon raw material is micron-sized silicon oxide SiOx, x<2 (further, it can be 0.5 to 1.2), with a particle size of 2 to 10 μm, preferably 4 to 8 μm.

[0019] The pretreatment and carbon coating before lithiation roasting, as described in this invention, and the direct modification treatment with the modified liquid after lithiation roasting are key to synergistically improving the material's first-time performance, fast charging, and low-temperature stability.

[0020] In this invention, the oxidizing acid solution is an aqueous solution containing an oxidizing acid substance, or a mixed aqueous solution containing an oxidant and an acid;

[0021] In this invention, the oxidizing acidic substance is nitric acid; the oxidizing agent is nitric acid and / or hydrogen peroxide; and the acid is at least one of sulfuric acid, nitric acid, and hydrochloric acid.

[0022] In this invention, the concentration of the solute in the oxidizing acidic substance is 2-18 M, and more specifically 3-10 M.

[0023] In this invention, the liquid-to-solid ratio (ml / g) in the pretreatment stage can be adjusted as needed, for example, it can be 1 to 10 ml / g, and further, it can be 3 to 5 ml / g.

[0024] In this invention, the temperature of the pretreatment stage is 20–100°C, and can be further 35–55°C;

[0025] In this invention, the pretreatment stage takes more than 0.5 hours, preferably 0.5 to 2 hours;

[0026] In this invention, after pretreatment, the material can be obtained by solid-liquid separation, water washing, and drying.

[0027] In this invention, the pretreated material can be carbon coated using conventional methods.

[0028] The pretreated material and carbon source are mixed and heated to perform carbon coating treatment;

[0029] In this invention, the carbon source can be in solid, liquid, or gaseous form. The solid carbon source may be, for example, a polymer or asphalt; the liquid carbon source may be, for example, a molten carbon source or a solution containing dissolved carbon; and the gaseous carbon source may be, for example, a carbon-containing gas, such as a gaseous alkane.

[0030] In this invention, the heating temperature during the carbon coating stage is 550–1000°C, and can be further 800–950°C;

[0031] In this invention, when a solid or liquid carbon source is used, its amount can be 10-25% of the pretreated material. When a gaseous carbon source is used, the carbon coating amount can be controlled by controlling the gas-phase carbon deposition time, for example, 1-3 hours. During the gas-phase deposition process, the volume content of the gaseous carbon source in the atmosphere can be 10-99 vol% (more preferably 50-90%), and the remainder can be at least one of hydrogen, nitrogen, inert gas, etc. The temperature during the gas-phase deposition stage can be 800-900°C. In this invention, there are no special requirements for the carbon coating amount; for example, it can be 2-10%.

[0032] In this invention, carbonized material and lithium source are mixed and heated to undergo lithiation roasting treatment.

[0033] In this invention, the lithium source can be any component containing lithium, such as at least one of lithium oxide, lithium nitride, lithium phosphide, lithium boride, and lithium hydride.

[0034] In this invention, the weight ratio of carbon material to lithium source is 100:0.5 to 8, and can be further 100:0.7 to 2.5;

[0035] In this invention, the lithiation calcination temperature is 600–900°C, and can be further 650–800°C;

[0036] In this invention, the holding time at the lithiation calcination temperature is 6 to 12 hours, and can be further 7 to 10 hours;

[0037] In this invention, the atmosphere during the lithiation roasting stage includes at least one of nitrogen, argon, nitrogen + hydrogen, and argon + hydrogen.

[0038] In this invention, the solvent in the modified liquid includes water;

[0039] In this invention, the concentration of (NH4)2S2O3 in the modified solution is 0.5-2M, more preferably 0.7-1.2M, and more preferably 0.8-1M;

[0040] In this invention, the modified liquid further contains one or more auxiliary components selected from hydrofluoric acid, ammonium fluoride, ammonium chloride, ammonium nitrate, and ammonium nitrite.

[0041] In this invention, the concentration of the auxiliary component in the modified liquid is less than or equal to 1M, and can be further 0.1 to 1M, or further 0.1 to 0.3M;

[0042] Preferably, the liquid-to-solid ratio during the modification treatment stage is 1–10 ml / g, and more preferably 3–6 ml / g;

[0043] Preferably, the temperature during the modification treatment stage is 20–80°C, and more preferably 30–65°C;

[0044] Preferably, the modification time is 0.5 hours or more, and more preferably 0.5 to 2 hours;

[0045] Preferably, the modification process is carried out under positive pressure, wherein the positive pressure is 2 to 5 atm (atm is standard atmospheric pressure), and more preferably 3 to 4 atm. The positive pressure can be controlled by introducing at least one gas selected from nitrogen and inert gases.

[0046] The present invention also provides a modified silicon-based active material prepared by the preparation method described above.

[0047] In this invention, the preparation method can endow the prepared material with special physicochemical structural characteristics, and the material with these characteristics can unexpectedly exhibit excellent first-time efficiency and fast-charging stability.

[0048] The present invention also provides an application of the modified silicon-based active material prepared by the above preparation method, which is used as a negative electrode active material for the preparation of lithium secondary batteries.

[0049] In this invention, the modified silicon-based active material described herein can be used as a negative electrode active material based on conventional methods, principles, and equipment to prepare the desired lithium secondary battery and its negative electrode, negative electrode material, and other components.

[0050] The present invention also provides a negative electrode material for a lithium secondary battery, including a negative electrode active material, wherein the negative electrode active material includes the modified silicon-based active material prepared by the preparation method described above.

[0051] In this invention, the modified silicon-based active material in the negative electrode active material contains 10 wt.% or more, preferably 50 wt.% or more, and further 90 wt.% or more. A certain amount of conventional negative electrode active material is permitted in the negative electrode active material.

[0052] In this invention, the negative electrode material further includes a binder and a conductive agent;

[0053] In this invention, the weight ratio of the negative electrode active material, binder, and conductive agent in the negative electrode material can be adjusted as needed, for example, it can be 50-90:1-20:1-20, further it can be 70-90:5-15:5-15, and even more preferably 85-90:5-6:5-6.

[0054] The present invention also provides a negative electrode for a lithium secondary battery, comprising a current collector and a negative electrode active material composite thereon, wherein the negative electrode active material is the negative electrode material comprising the modified silicon-based material described in the present invention.

[0055] The present invention also provides a lithium secondary battery comprising a negative electrode containing the modified silicon-based material described in the present invention.

[0056] The lithium secondary battery, its negative electrode, and the negative electrode material described in this invention, except for the modified silicon-based material described in this invention, can have conventional components and structural relationships between components.

[0057] Beneficial effects

[0058] This invention pre-treats and carbon-coates silicon raw materials, followed by lithiation calcination and subsequent modification in a modification solution containing (NH4)2S2O3. This enables pre-lithiation of silicon materials, significantly reduces grain agglomeration during processing, and improves grain stability. Research in this invention shows that the described process can significantly improve the first-cycle efficiency and fast-charging stability of silicon-based materials.

[0059] This invention also shows that using a preferred combination of modifying liquids, and / or a pressurized modification approach, helps to further improve the initial efficiency and high-rate long-range cycling stability of the obtained modified silicon-based materials. Attached Figure Description

[0060] Figure 1 SEM image of the carbon-coated sample prepared in Example 1;

[0061] Figure 2 SEM image of the lithium-ion sample prepared in Example 1;

[0062] Figure 3 This is a SEM image of the modified silicon-based active material prepared in Example 1. Detailed Implementation

[0063] One exemplified embodiment of the present invention includes the following steps:

[0064] Step (1): The silicon powder (nano silicon or micron silicon oxide powder raw material) is first pretreated in an oxidizing acidic medium to obtain pretreated silicon;

[0065] Step (2): Perform surface carbon coating treatment on the pretreated silicon;

[0066] Step (3): Mix the pre-carbon-coated silicon powder and lithium source and perform lithiation roasting to obtain lithiation material;

[0067] Step (4): After stirring the obtained lithium material in the modified liquid, the solid and liquid are separated, washed and dried.

[0068] In this invention, the silicon powder is elemental silicon with a particle size of 10-200 nm, preferably 30-80 nm, or silicon oxide SiOx (x<2) with a particle size of 2-10 μm, preferably 4-8 μm.

[0069] The oxidizing acidic medium mentioned in step (1) refers to one of the following systems: sulfuric acid, sulfuric acid + hydrogen peroxide, nitric acid, nitric acid + hydrogen peroxide, or hydrochloric acid + nitric acid. The molar concentration of the acidic medium is 2–18 M, the liquid-to-solid ratio (ml / g) is 3–5:1, the reaction temperature is 30–100 °C, the reaction conditions can be atmospheric pressure or a closed environment, and the reaction time is 0.5–2 h. After the reaction is completed, the solid and liquid are separated, washed, dried, and dispersed for later use.

[0070] The surface carbon coating in step (2) is carried out by using solid phase, liquid phase or gas phase methods, wherein the carbon coating amount is 2 to 10%.

[0071] The pre-lithiation treatment mentioned in step (3) refers to pre-lithiation through lithium alloy additives or chemical pre-lithiation. Preferably, the sample obtained in step (2) is mixed with lithium alloys such as lithium oxide, lithium nitride, lithium phosphide, lithium boride, and lithium hydride, and then heat-treated in an inert atmosphere. The amount of lithium alloy added is 0.5-5%, the heat treatment temperature is 600-900℃, the heat treatment atmosphere is one of nitrogen, argon, nitrogen + hydrogen, or argon + hydrogen, and the heat treatment time is 6-12 hours.

[0072] The modified liquid in step (4) contains (NH4)2S2O3 and selectively contains one or more auxiliary components such as ammonium fluoride, ammonium chloride, ammonium nitrate, and ammonium nitrite. The concentration of (NH4)2S2O3 is 0.5–2 M, the concentration of auxiliary components is 0.1–1 M, the liquid-to-solid ratio (ml / g) is 3–10:1, the treatment temperature is 20–80 °C, preferably 30–65 °C, the reaction conditions can be atmospheric pressure or a closed environment, and the reaction time is 0.5–2 h. After the reaction is completed, the solid and liquid are separated, the filter cake is washed, dried, and dispersed for later use.

[0073] As a typical application approach, the present invention also provides a negative electrode for a lithium-ion battery, including a current collector and a negative electrode material composited on its surface, wherein the negative electrode material includes an active material, and the active material comprises a silicon-based negative electrode material prepared by the method of the present invention.

[0074] Preferably, the negative electrode material further includes a binder and a conductive agent.

[0075] As a solution to the same application concept, the present invention also provides a lithium-ion battery comprising a negative electrode containing the silicon-based negative electrode material described in the present invention.

[0076] In this invention, the silicon-based anode material can be used as the anode active material, and based on known processes and principles, the desired lithium-ion battery and its anode components can be prepared. That is, the lithium-ion battery and its anode described in this invention, apart from containing the silicon-based anode material described in this invention, all other components and structural parts can be known.

[0077] I. Silicon-based solution:

[0078] Example 1

[0079] Step (1): Weigh a certain amount of nano-silicon powder (d50=30nm, silicon raw material) according to a liquid-solid ratio of 5:1 (ml / g) and soak it in a 5M sulfuric acid + 30% hydrogen peroxide (volume ratio 9:1) solution. Stir and react at 50℃ under normal pressure for 1 hour. Then, perform solid-liquid separation, wash with water until the filtrate is neutral, dry it, and break it up to obtain the pretreated material.

[0080] Step (2): After uniformly mixing the pretreated powder obtained in step (1) with 15% of its weight of asphalt, place it in an atmosphere furnace, and under argon protection, heat it to 900℃ and hold it for 2 hours. After naturally cooling to room temperature, break it up to obtain the carbon-coated material (see SEM). Figure 1 );

[0081] Step (3): After uniformly mixing the carbon-coated powder obtained in step (2) with 0.8% of its weight of lithium hydride (lithium source), the mixture is placed under argon protection and heated to 650°C and held for 10 hours. After naturally cooling to room temperature, the mixture is broken up to obtain the lithium material (see SEM). Figure 2 );

[0082] Step (4): Immerse the lithium powder obtained in step (3) in a 1M (NH4)2S2O3 solution (modification solution) at a liquid-to-solid ratio of 4 ml / g. Stir and react at 40°C under normal pressure for 1 hour. Then perform solid-liquid separation, washing with water, and drying to obtain the modified silicon-based active material (SEM image shown). Figure 3 ).

[0083] Silicon-based electrode fabrication:

[0084] The prepared modified silicon-based active material, conductive agent (conductive carbon black), and binder (sodium alginate) were mixed in a weight ratio of 9:0.5:0.5, slurried and coated on Cu foil, and dried to obtain a silicon-based anode.

[0085] CR2025 coin cells were assembled in an argon-filled dry glove box using the silicon-based negative electrode as the working electrode, lithium metal as the negative electrode, 1 mol / L LiPF6 EC / EMC (volume ratio 1:1, with 10% FEC added) as the electrolyte, and a PE-PP composite membrane as the separator. Electrochemical performance was tested at temperatures of 25℃ and -10℃, and within a voltage range of 0.001-2.0V.

[0086] At 25℃: the first reversible capacity at 0.2C is 2469mAh / g, with a coulombic efficiency of 91.8%; the first reversible specific capacity at 5C charge / discharge rate is 1203mAh / g, and the capacity retention rate after 1000 cycles is 91.2%.

[0087] At -10℃ and 0.2C, the initial reversible capacity is 2011 mAh / h, and the capacity retention rate after 500 cycles is 81.1%.

[0088] Example 2

[0089] Compared with Example 1, the only difference is that step (2) is changed as follows: the powder obtained in step (1) is placed in a tube furnace, heated to 850°C under argon protection, and then acetylene gas at a flow rate of 400 ml / min and hydrogen gas at a flow rate of 50 ml / min are introduced and kept at this temperature for 2 hours. The introduction of acetylene and hydrogen gas is then stopped, and the mixture is allowed to cool naturally to room temperature and then broken up for later use. Other conditions remain unchanged.

[0090] The test was conducted according to the method in Example 1, and the results are as follows:

[0091] At 25℃ and 0.2C, the first reversible capacity is 2476mAh / g and the coulombic efficiency is 92.2%; the first reversible specific capacity at 5C charge / discharge rate is 1210mAh / g and the capacity retention rate after 1000 cycles is 90.8%.

[0092] At -10℃ and 0.2C, the initial reversible capacity is 2009 mAh / h, and the capacity retention rate after 500 cycles is 81.3%.

[0093] Example 3

[0094] Compared with Example 1, the only difference is that step (3) uses an equal weight of lithium oxide as the lithium source, while the other operations are the same.

[0095] The test was conducted according to the method in Example 1, and the results are as follows:

[0096] At 25℃ and 0.2C, the first reversible capacity is 2467mAh / g and the coulombic efficiency is 91.5%; the first reversible specific capacity at 5C charge / discharge rate is 1316mAh / g and the capacity retention rate after 1000 cycles is 91.2%.

[0097] At -10℃ and 0.2C, the initial reversible capacity is 2112 mAh / h, and the capacity retention rate after 500 cycles is 81.5%.

[0098] Example 4

[0099] Compared with Example 1, the only difference is that the composition of the solute in the modified solution in step (4) is changed, and the specific groups are as follows:

[0100] Group A: 0.8M (NH4)2S2O3 + 0.2M hydrofluoric acid

[0101] The test results are as follows:

[0102] At 25℃, the first reversible capacity at 0.2C is 2584mAh / g with a coulombic efficiency of 92.6%; the first reversible specific capacity at 5C charge / discharge rate is 1347mAh / g, and the capacity retention rate after 1000 cycles is 91.8%.

[0103] At -10℃, the initial reversible capacity at 0.2C is 2141 mAh / h, and the capacity retention rate after 500 cycles is 82.2%.

[0104] Group B: 0.8M (NH4)2S2O3 + 0.2M ammonium fluoride

[0105] The test results are as follows:

[0106] At 25℃, the first reversible capacity at 0.2C is 2591mAh / g with a coulombic efficiency of 92.7%; the first reversible specific capacity at 5C charge / discharge rate is 1353mAh / g, and the capacity retention rate after 1000 cycles is 91.7%.

[0107] At -10℃, the initial reversible capacity at 0.2C is 2139mAh / h, and the capacity retention rate after 500 cycles is 82.3%.

[0108] Group C: 0.8M (NH4)2S2O3 + 0.2M ammonium nitrate

[0109] The test results are as follows:

[0110] At 25℃, the first reversible capacity at 0.2C is 2590mAh / g with a coulombic efficiency of 92.5%; the first reversible specific capacity at 5C charge / discharge rate is 1346mAh / g, and the capacity retention rate after 1000 cycles is 91.6%.

[0111] At -10℃, the initial reversible capacity at 0.2C is 2127 mAh / h, and the capacity retention rate after 500 cycles is 82.1%.

[0112] In summary, by using a preferred combination of modifiers, synergistic effects can be unexpectedly achieved, resulting in better coulombic efficiency, higher rate capability, and longer-term cycling stability.

[0113] Example 5

[0114] Compared with Example 1, the only difference is that in step (4), the modification process is carried out under pressure of 3 to 4 atm; the temperature of the modification process is 30°C for 1 hour, and other operations and parameters are the same as in Example 1.

[0115] The test was performed according to the method in Example 1:

[0116] At 25℃, the first reversible capacity at 0.2C is 2588mAh / g with a coulombic efficiency of 92.4%; the first reversible specific capacity at 5C charge / discharge rate is 1358mAh / g, and the capacity retention rate after 1000 cycles is 92.8%.

[0117] At -10℃, the initial reversible capacity at 0.2C is 2120mAh / h, and the capacity retention rate after 500 cycles is 82.1%.

[0118] In summary, by adopting the preferred positive pressure modification method, it is possible to unexpectedly obtain better coulombic efficiency, high rate capability, and long-range cycling stability under milder conditions.

[0119] Comparative Example 1

[0120] Compared with Example 1, step (1) is omitted. Instead, silicon raw material is directly used to replace the pretreatment material in step 2 for step 2 and subsequent processing. Other operations and parameters are the same as in Example 1.

[0121] The test was conducted according to the method in Example 1, and the results are as follows:

[0122] The initial reversible capacity at 25℃ and 0.2C is 1811mAh / g, and the coulombic efficiency is 76.2%.

[0123] At -10℃, the initial reversible capacity at 0.2C is 1101 mAh / h, and the capacity retention rate after 500 cycles is 48.1%.

[0124] Comparative Example 2

[0125] Compared with Example 1, step (2) is omitted. Instead, the pre-treated material of step (1) is used to replace the carbon-coated material of step (3) for step 3 and subsequent processing. Other operations and parameters are the same as in Example 1.

[0126] The test was conducted according to the method in Example 1, and the results are as follows:

[0127] At 25℃, the first reversible capacity at 0.2C is 1749mAh / g and the coulombic efficiency is 72.4%.

[0128] At -10℃, the initial reversible capacity at 0.2C is 1003 mAh / h, and the capacity retention rate after 500 cycles is 44.2%.

[0129] Comparative Example 3

[0130] Compared with Example 1, step (3) is omitted. Instead, the carbon-coated material from step (2) replaces the lithium-ion material from step 4 and directly participates in the processing of step 4. Other operations and parameters are the same as in Example 1.

[0131] The test was conducted according to the method in Example 1, and the results are as follows:

[0132] At 25℃, the first reversible capacity at 0.2C is 1732mAh / g and the coulombic efficiency is 68.3%.

[0133] At -10℃, the initial reversible capacity at 0.2C is 913 mAh / h, and the capacity retention rate after 500 cycles is 46.2%.

[0134] Comparative Example 4

[0135] Compared with Example 1, step (4) is omitted, while other operations remain the same.

[0136] The test was conducted according to the method in Example 1, and the results are as follows:

[0137] At 25℃, the first reversible capacity at 0.2C is 1712 mAh / g, and the coulombic efficiency is 62.4%.

[0138] At -10℃, the initial reversible capacity at 0.2C is 901mAh / h, and the capacity retention rate after 500 cycles is 47.5%.

[0139] Comparative Example 5

[0140] Compared with Example 1, step (4) uses hydrochloric acid of equimolar concentration instead of (NH4)2S2O3, while the other operations are the same.

[0141] The test was conducted according to the method in Example 1, and the results are as follows:

[0142] At 25℃, the first reversible capacity at 0.2C is 1733mAh / g and the coulombic efficiency is 62.6%.

[0143] At -10℃, the initial reversible capacity at 0.2C is 889mAh / h, and the capacity retention rate after 500 cycles is 52.1%.

[0144] Comparative Example 6

[0145] Compared with Example 1, the only difference is that the type of solute in the modified solution is changed; all other operations and parameters are the same as in Example 1, specifically:

[0146] Group A: The solute is replaced with an equimolar amount of Na2S2O3;

[0147] The test was conducted according to the method in Example 1, and the results are as follows:

[0148] At 25℃, the first reversible capacity at 0.2C is 1631mAh / g, and the coulombic efficiency is 70.2%.

[0149] At -10℃, the initial reversible capacity at 0.2C is 902 mAh / h, and the capacity retention rate after 500 cycles is 42.6%.

[0150] Group B: The solute is replaced with an equimolar amount of ammonium fluoride;

[0151] The test was conducted according to the method in Example 1, and the results are as follows:

[0152] At 25℃, the first reversible capacity at 0.2C is 1722mAh / g, and the coulombic efficiency is 73.1%.

[0153] At -10℃, the initial reversible capacity at 0.2C is 881mAh / h, and the capacity retention rate after 500 cycles is 44.3%.

[0154] Comparative Example 7

[0155] Compared with Example 1, the only difference is that after step (3), a second carbon coating treatment is performed (the steps and parameters are the same as in step 2), followed by step (4). Other operations and parameters are the same as in Example 1.

[0156] The results are as follows: The test was conducted according to the method in Example 1, and the results are as follows:

[0157] At 25℃, the first reversible capacity at 0.2C is 1921mAh / g and the coulombic efficiency is 71.2%.

[0158] At -10℃, the initial reversible capacity at 0.2C is 779mAh / h, and the capacity retention rate after 500 cycles is 54.8%.

[0159] Comparative Example 8

[0160] Compared with Example 1, the only difference is that after step 1, step 3 is performed directly, followed by step 2, and finally step 4. All other operations and parameters are the same as in Example 1.

[0161] The results are as follows: The test was conducted according to the method in Example 1, and the results are as follows:

[0162] At 25℃, the first reversible capacity at 0.2C is 1455mAh / g and the coulombic efficiency is 65.2%.

[0163] At -10℃, the initial reversible capacity at 0.2C is 681mAh / h, and the capacity retention rate after 500 cycles is 53.3%.

[0164] II. SiOx Scheme:

[0165] Example 6

[0166] Step (1): Weigh a certain amount of micron-sized silica powder (SiO, d50 = 5μm) according to a liquid-to-solid ratio of 3:1 (ml / g) and soak it in a 3M nitric acid solution. Place it in a sealed polytetrafluoroethylene container at 50℃ for 0.5h, then perform solid-liquid separation, wash with water and dry, and break it up for later use.

[0167] Step (2): Place the powder obtained in step (1) in a tube furnace, and under argon protection, heat it to 850°C. Then, introduce 400 ml / min of acetylene gas and 50 ml / min of hydrogen gas, and keep it at the temperature for 2 hours. Then, stop the introduction of acetylene gas and hydrogen gas, let it cool naturally to room temperature, and break it up for later use.

[0168] Step (3): After mixing the powder obtained in step (2) with 2% of its weight of lithium boride, the mixture is placed under argon protection and heated to 700°C and kept at that temperature for 7 hours. After cooling naturally to room temperature, it is broken up and set aside.

[0169] Step (4): Immerse the powder obtained in step (3) in a 0.5M (NH4)2S2O3 solution at a liquid-to-solid ratio of 5ml / g, stir and react at 60℃ under normal pressure for 1h, then perform solid-liquid separation, wash with water and dry to obtain the material.

[0170] The test was conducted according to the method in Example 1, and the results are as follows:

[0171] At 25℃, the first reversible capacity at 0.2C is 1238mAh / g with a coulombic efficiency of 91.4%; the first reversible specific capacity at 5C charge / discharge rate is 713mAh / g, and the capacity retention rate after 1000 cycles is 91.4%.

[0172] At -10℃, the initial reversible capacity at 0.2C is 1038mAh / h, and the capacity retention rate after 500 cycles is 84.1%.

[0173] Example 7

[0174] Compared with Example 6, the only difference is that steps (3) and (4) are changed, specifically:

[0175] Step (3): After mixing the powder obtained in step (2) with 1% of its weight of lithium nitride, place it under argon protection and heat it to 800°C and keep it at that temperature for 8 hours. Then, let it cool naturally to room temperature and break it up for later use.

[0176] Step (4): Immerse the powder obtained in step (3) in a 2M (NH4)2S2O3 solution at a liquid-to-solid ratio of 8 ml / g, react in a sealed environment at 60°C for 0.5 h, and then perform solid-liquid separation, washing with water and drying to obtain the material.

[0177] The test was conducted according to the method in Example 1, and the results are as follows:

[0178] At 25℃, the first reversible capacity at 0.2C is 1244mAh / g with a coulombic efficiency of 91.5%; the first reversible specific capacity at 5C charge-discharge rate is 658mAh / g, and the capacity retention rate after 1000 cycles is 91.1%.

[0179] At -10℃, the initial reversible capacity at 0.2C is 1024 mAh / h, and the capacity retention rate after 500 cycles is 83.2%.

[0180] Example 8

[0181] Compared with Example 1, the only difference is that in step (1), the silicon raw material used is micron-sized silicon oxide powder (SiO2). 1.1 (d50=4μm), other conditions are the same.

[0182] The test was conducted according to the method in Example 1, and the results are as follows:

[0183] At 25℃, the first reversible capacity at 0.2C is 1253mAh / g with a coulombic efficiency of 91.2%; the first reversible specific capacity at 5C charge-discharge rate is 688mAh / g, and the capacity retention rate after 1000 cycles is 91.3%.

[0184] At -10℃, the initial reversible capacity at 0.2C is 1019 mAh / h, and the capacity retention rate after 500 cycles is 83.1%.

[0185] Example 9

[0186] Compared with Example 1, the only difference is that in step (1), the silicon raw material used is micron-sized silicon oxide powder (SiO2). 0.8 (d50=5μm), other conditions are the same.

[0187] The test was conducted according to the method in Example 1, and the results were as follows: at 25°C, the first reversible capacity at 0.2C was 1248 mAh / g, and the coulombic efficiency was 92.1%; the first reversible specific capacity at 5C charge-discharge rate was 704 mAh / g, and the capacity retention rate after 1000 cycles was 91.6%.

[0188] At -10℃, the initial reversible capacity at 0.2C is 1013 mAh / h, and the capacity retention rate after 500 cycles is 83.4%.

Claims

1. A method for preparing modified silicon-based active materials, characterized in that, The silicon raw material is pretreated in an oxidizing acid solution to obtain a pretreated material; the silicon raw material is elemental silicon and / or silicon oxide; the oxidizing acid solution is an aqueous solution containing an oxidizing acid substance, or a mixed aqueous solution containing an oxidant and an acid. The pretreated material is carbon-coated to obtain carbon-coated material; The carbon-coated material and the lithium source are calcined to obtain the lithiated material; The lithium-based material was placed in a modification liquid and modified to obtain the modified silicon-based active material. The modified liquid contains (NH4)2S2O3.

2. The method for preparing the modified silicon-based active material as described in claim 1, characterized in that, The silicon raw material is in the form of nano- and / or micro-sized particles.

3. The method for preparing the modified silicon-based active material as described in claim 1, characterized in that, The silicon raw material is nano-silicon powder with a particle size of 10~200nm; Alternatively, the silicon raw material is micron-sized silicon oxide SiOx, where x < 2, and its particle size is 2~10 μm.

4. The method for preparing the modified silicon-based active material as described in claim 3, characterized in that, The particle size of the nano-silicon powder is 30~80nm; Alternatively, the particle size of the micron-sized silicon oxide SiOx is 4~8μm.

5. The method for preparing the modified silicon-based active material as described in claim 1, characterized in that, The oxidizing acid is nitric acid; the oxidizing agent is nitric acid and / or hydrogen peroxide; the acid is at least one of sulfuric acid, nitric acid, and hydrochloric acid.

6. The method for preparing the modified silicon-based active material as described in claim 1, characterized in that, In the aforementioned oxidizing acidic substance, the concentration of the solute is 2~18M; The liquid-to-solid ratio during the pretreatment stage is 1~10 ml / g; The temperature during the pretreatment stage is 20~100℃; The pretreatment stage takes 0.5 to 2 hours.

7. The method for preparing the modified silicon-based active material as described in claim 1, characterized in that, The pretreated material and carbon source are mixed and heated to perform carbon coating treatment; The carbon source can be in solid, liquid, or gaseous form. The heating temperature during the carbon coating stage is 550~1000℃; The carbon coating content is 2-10%.

8. The method for preparing the modified silicon-based active material as described in claim 1, characterized in that, The lithium source includes at least one of lithium oxide, lithium nitride, lithium phosphide, and lithium boride; The weight ratio of carbon material to lithium source is 100:0.5~8; The calcination temperature for lithiation is 600~900℃.

9. The method for preparing the modified silicon-based active material as described in claim 1, characterized in that, The holding time at the lithiation calcination temperature is 6~12h; The atmosphere during the lithiation roasting stage includes at least one of nitrogen, argon, nitrogen + hydrogen, and argon + hydrogen.

10. The method for preparing the modified silicon-based active material as described in claim 1, characterized in that, The solvent in the modified liquid includes water; In the modified solution, the concentration of (NH4)2S2O3 is 0.5~2M.

11. The method for preparing the modified silicon-based active material as described in claim 1, characterized in that, The modified liquid also contains one or more auxiliary components selected from hydrofluoric acid, ammonium fluoride, ammonium chloride, ammonium nitrate, and ammonium nitrite. In the modified solution, the concentration of auxiliary components is 0.1~1M.

12. The method for preparing the modified silicon-based active material as described in claim 1, characterized in that, The liquid-to-solid ratio during the modification treatment stage is 1~10 ml / g; The temperature during the modification treatment stage is 20~80℃; The modification time is more than 0.5 hours.

13. The method for preparing the modified silicon-based active material as described in claim 12, characterized in that, The temperature during the modification treatment stage is 30~65℃; The modification time is 0.5~2 hours.

14. The method for preparing the modified silicon-based active material as described in claim 1, characterized in that, The modification process is carried out under positive pressure, which is 2 to 5 atm.

15. A modified silicon-based active material prepared by the preparation method according to any one of claims 1 to 14.

16. The application of a modified silicon-based active material prepared by the preparation method according to any one of claims 1 to 14, characterized in that, It is used as a negative electrode active material in the preparation of lithium secondary batteries.

17. A negative electrode material for a lithium secondary battery, comprising a negative electrode active material, characterized in that, The negative electrode active material includes the modified silicon-based active material prepared by the preparation method according to any one of claims 1 to 14.

18. The negative electrode material of the lithium secondary battery as described in claim 17, characterized in that, In the negative electrode active material, the content of the modified silicon-based active material is above 10 wt.%.

19. The negative electrode material of the lithium secondary battery as described in claim 18, characterized in that, In the negative electrode active material, the content of the modified silicon-based active material is above 50 wt.%.

20. The negative electrode material of the lithium secondary battery as described in claim 18, characterized in that, In the negative electrode active material, the content of the modified silicon-based active material is above 90 wt.%.

21. The negative electrode material of the lithium secondary battery according to any one of claims 17 to 20, characterized in that, The negative electrode material also includes a binder and a conductive agent.

22. The negative electrode material of the lithium secondary battery as described in claim 21, characterized in that, In the aforementioned negative electrode material, the weight ratio of negative electrode active material, binder, and conductive agent is 50~90:1~20:1~20.

23. A negative electrode for a lithium secondary battery, comprising a current collector and a negative electrode active material composited thereon, characterized in that, The negative electrode active material is the negative electrode material according to any one of claims 17 to 22.

24. A lithium secondary battery, characterized in that, Includes the negative electrode as described in claim 23.

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