Modified silicon oxide and its preparation and application in lithium-ion batteries

Abstract

This invention belongs to the field of lithium battery negative electrode materials and specifically relates to a method for modifying silicon oxide. Silicon oxide and a lithium salt are pre-calcined in a first stage, followed by a second stage heat treatment. The first stage calcination temperature is 400-600°C, and the second stage calcination temperature is 800-1000°C. The product of the lithium calcination is placed in a heat-conducting container, sealed, and heat-treated under a protective atmosphere. The container is then quenched in a cooling medium to produce modified silicon oxide. The heat treatment temperature is 800-1200°C. The invention also includes silicon oxide materials produced by the preparation method and their use in lithium secondary batteries. The silicon oxide modified by the present method exhibits excellent electrochemical properties.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion battery electrode materials, and in particular relates to a method for producing silicon monoxide negative electrode materials. Background Art

[0002] Lithium-ion batteries are one of the most widely used and fastest-growing energy storage technologies due to their high energy density, high cell voltage, and lack of memory effect. Lithium-ion batteries are primarily composed of a positive electrode, a negative electrode, a separator, and an electrolyte. The most critical of these are the positive and negative electrode materials, whose performance determines the performance of the lithium-ion battery. Currently, commercially available positive electrode materials are primarily lithium cobalt oxide, lithium iron phosphate, and ternary materials, while negative electrode materials are primarily carbon materials such as graphite. This commercial lithium-ion battery system has gradually failed to meet consumer demand, and the development of electrode materials with even higher performance has become a current research and development hotspot and priority.

[0003] Silicon currently has the highest theoretical capacity among lithium-ion battery anode materials, reaching 4200mAh / g, which is 10 times the theoretical capacity of graphite (372mAh / g). Its successful development and application will bring about a huge leap in the energy density of lithium-ion battery systems. However, some shortcomings of silicon have become key obstacles to its application. First, as a semiconductor material, silicon has low electrical conductivity, resulting in low electrochemical reaction activity and poor rate performance. Second, during the charge and discharge process, silicon undergoes a huge volume change (about 300%) as lithium ions are inserted and removed. As the cycle progresses, this repeated huge volume change will cause the anode to break and pulverize, losing electrical contact with the current collector and failing. In addition, the volume effect of silicon will cause the SEI film formed on its surface to repeatedly break up, preventing it from forming a stable SEI film. The constantly exposed fresh silicon surface will consume a large amount of the limited electrolyte in the lithium-ion battery, causing its performance to degrade rapidly.

[0004] As research deepened, people discovered that some methods could be used to alleviate or even overcome the negative impact of silicon's volume effect and improve its electrochemical performance, such as nano-sizing, pre-pore structure design, material composite design, element doping, etc. However, these methods are either cumbersome and difficult to popularize, or they are expensive and difficult to expand. As a compromise for silicon materials, silicon oxide attracted people's attention as soon as it was discovered. The first coulombic efficiency and gram capacity of this material are lower than those of silicon, but because it contains some oxygen, an inert silicate phase is formed during the electrochemical reaction, providing mechanical support for the material and making its cycle performance very excellent. At the same time, because this part of oxygen consumes a large amount of lithium ions and is converted into an irreversible inert phase, its first coulombic efficiency is low. Maintaining the cycle stability of silicon oxide negative electrodes while improving their first coulombic efficiency is a key and difficult issue in the research and development of silicon oxide. Summary of the Invention

[0005] In order to solve the problem of unsatisfactory electrochemical performance of existing silicon oxide materials, the first object of the present invention is to provide a method for modifying silicon oxide, aiming to improve the electrochemical performance of the modified silicon oxide.

[0006] The second object of the present invention is to provide the prepared modified silicon monoxide and its application in lithium ion batteries.

[0007] The third object of the present invention is to provide a lithium ion battery and a negative electrode thereof comprising the modified silicon monoxide.

[0008] Silicon oxide is rich in oxygen. During heat treatment, the energy applied by the outside world makes the oxygen active. As the heat treatment proceeds, oxygen will be enriched in the silicon oxide system to varying degrees, affecting the performance of the silicon oxide. How to control the oxygen content of silicon oxide during heat treatment is a technical challenge. To address the problems of silicon oxide's oxygen being difficult to control, poor structural stability, and unsatisfactory electrochemical performance, the present invention provides the following solutions:

[0009] A method for modifying silicon dioxide comprises the following steps:

[0010] Step (1): Calcination with lithium

[0011] Silicon dioxide and lithium salt are pre-calcined in the first stage, and then subjected to the second stage heat treatment;

[0012] The temperature of the first stage calcination treatment is 400-600°C, and the temperature of the second stage calcination treatment is 800-1000°C.

[0013] Step (2): Secondary conduction heat treatment-quenching

[0014] The product after lithium calcination is filled and sealed in a heat-conducting container under a protective atmosphere, and the heat-conducting container is heat-treated under the protective atmosphere. Subsequently, the heat-treated heat-conducting container is directly placed in a cooling medium for quenching while still hot to obtain modified silicon dioxide.

[0015] The temperature of heat treatment is 800-1200℃;

[0016] The melting point of the wall material of the heat-conducting container is greater than or equal to 1200° C., and the thermal conductivity is greater than or equal to 100 W / m·K.

[0017] This invention utilizes pre-lithiation technology to initially provide a protective layer for silicon oxide, simultaneously locking in oxygen. The subsequent heat-cold coupled secondary heat transfer process then directs and regulates oxygen in the silicon oxide, enriching it on the surface while simultaneously creating a rich internal defect structure, thereby improving its performance. This invention innovatively pre-lithiates the silicon oxide with a two-stage lithium calcination, coupled with a subsequent secondary heat treatment-quenching process (also referred to as indirect heat treatment-quenching in this invention) and a parameterized process, achieving synergy and unexpectedly improving the electrochemical properties of the resulting material.

[0018] In the present invention, the two-stage gradient pre-lithium calcination-secondary conduction heat treatment-rapid cooling treatment is the key to regulating the oxygen properties of silicon oxide and improving its structure and electrochemical properties. Studies have also found that further controlling the conditions of lithium calcination, the methods and conditions of secondary conduction heat treatment and cold treatment can help further improve the oxygen properties, structure and electrochemical properties of silicon oxide.

[0019] In the present invention, the particle size of silicon monoxide is 100 nm to 20 μm;

[0020] In the present invention, lithium-addition calcination refers to the process of mixing silicon oxide with a lithium salt and then calcining it. Research has found that a two-stage gradient lithium-addition calcination of silicon oxide, combined with the combined control of the lithium salt and sintering mechanism, facilitates synergy with the subsequent secondary conduction heat treatment-quenching process, further improving the electrochemical performance of silicon oxide.

[0021] Preferably, the lithium salt is organic lithium and / or inorganic lithium;

[0022] Preferably, the inorganic lithium is at least one of lithium carbonate, lithium bicarbonate, lithium hydroxide, lithium oxide, lithium sulfate, and lithium phosphate;

[0023] Preferably, the organic lithium is at least one of a C1-C6 lithium alkoxide and a C1-C10 lithium carboxylate;

[0024] Preferably, the lithium salt is two or more inorganic salts; more preferably, it is a composite salt of lithium hydroxide and lithium carbonate, and even more preferably, the mass ratio of lithium hydroxide to lithium carbonate is 1 to 10:1. In the present invention, the use of the preferred lithium salt, combined with the two-stage lithium calcination and subsequent secondary conduction heat-cooling treatment, can effectively synergistically improve the electrochemical properties of silicon oxide.

[0025] Preferably, the weight ratio of silicon oxide to lithium salt is 5 to 50:1, more preferably 5 to 10:1;

[0026] Preferably, the atmosphere in the lithium calcination stage is one or more of hydrogen, argon, helium, carbon dioxide and nitrogen.

[0027] Preferably, in the lithium calcination stage, the temperature (T1) of the first calcination treatment is 500-600°C, and the temperature (T2) of the second calcination treatment is 900-1000°C.

[0028] Preferably, in the lithium calcination stage, the heating rate of the first calcination treatment (the heating rate from the starting temperature to the T1 stage) is 5-20°C / min, more preferably 10-20°C / min, and the heating rate of the second calcination treatment (the heating rate from T1 to T2 stage) is 1-10°C / min, preferably 2-5°C / min.

[0029] Preferably, in the lithium calcination, the first calcination time (holding time at T1) is 1 to 5 hours, more preferably 2 to 3 hours, and the second calcination time is 2 to 8 hours, more preferably 2 to 5 hours.

[0030] In the present invention, the product after lithium calcination is pre-filled and sealed in a heat-conducting container, and heat treatment and quenching treatment are carried out by means of conduction through the wall of the heat-conducting container. In this way, the distribution, phase and morphology of silicon dioxide can be unexpectedly regulated, and the electrochemical properties of the material can be unexpectedly improved.

[0031] In the present invention, the secondary heat transfer heat treatment refers to the heat treatment mediated by the wall of the heat-conducting container.

[0032] In the present invention, the heat-conducting container is a heat-conducting container resistant to high and low temperatures.

[0033] In the present invention, the wall material of the heat-conducting container is an alloy material, more preferably one of stainless steel, aluminum alloy, copper alloy, molybdenum alloy, tungsten alloy, niobium alloy, and nickel alloy.

[0034] Preferably, the wall material of the heat-conducting container does not undergo brittle fracture at -200°C;

[0035] In the present invention, the wall material of the heat-conducting container is preferably at least one of 310S, 304, US366, and GH188.

[0036] The silicon 2 oxide is loaded into the heat-conducting container chamber under a protective atmosphere and then sealed;

[0037] Preferably, the protective gas is at least one of nitrogen, inert gas, carbon dioxide and hydrogen;

[0038] Preferably, the filling capacity of the product after lithium calcination is greater than or equal to 50%, more preferably 50 to 95%.

[0039] In the present invention, a heat-conducting container enclosing a product calcined with lithium is placed in a heating furnace chamber, and silicon oxide in the heat-conducting container chamber is modified and reformed through secondary heat conduction through the heat conductor wall.

[0040] In the present invention, the heat-conducting container can be placed in a nitrogen or inert gas atmosphere (such as neon or argon) for heat treatment. For example, the sealed heat-conducting container filled with the lithium-containing calcined product can be placed in the furnace chamber of a tube furnace or a box furnace, and then a protective atmosphere is introduced into the furnace chamber. The temperature is then increased for heat treatment, thereby performing the two-stage conduction heat treatment.

[0041] Preferably, the temperature of the heat treatment is 1000-1100°C.

[0042] Preferably, the heating rate in the heat treatment stage is 2 to 30°C / min, more preferably 2 to 5°C / min;

[0043] Preferably, the heat treatment time is 5 to 8 hours.

[0044] In step (2), the heat-treated, sealed thermal container is placed in a cooling medium while still hot for rapid cooling. In the present invention, "while still hot" means that after heat treatment, the thermal container is cooled by less than or equal to 100°C, and more preferably, by less than or equal to 50°C, and then directly placed in a cooling medium for rapid cooling.

[0045] Preferably, the cooling medium is a liquid cooling medium or a gas cooling medium;

[0046] Preferably, the cooling medium is one or more of anhydrous ethanol, polyethylene glycol, deionized water, liquid nitrogen, dry ice, air, argon, and nitrogen;

[0047] Preferably, the temperature difference between the heat transfer container and the initial cooling medium is greater than or equal to 750°C.

[0048] Preferably, the cooling rate of the rapid cooling is 10-10000°C / min.

[0049] A preferred method of the present invention comprises the following steps:

[0050] Step 1: Mix silicon dioxide raw materials and lithium salt evenly:

[0051] Mix silicon oxide powder and lithium salt in a mixer according to a certain mass ratio for 5 to 10 hours to mix them evenly, and then take out to obtain a mixed material;

[0052] Step 2: The mixed material obtained in step 1 is subjected to a high-temperature two-stage stepped heat treatment under a protective atmosphere to achieve pre-lithiation of silicon oxide. The temperature of the first stage of pre-lithiation is 500-600°C, the time is 1-5 hours, and the heating rate is 5-10°C / min. The temperature of the second stage is 800-1000°C, the time is 2-8 hours, and the heating rate is 1-10°C / min. After the heat treatment is completed, the pre-lithiation silicon oxide powder is taken out by cooling the furnace;

[0053] Step 3: The pre-lithiated silicon oxide powder obtained in step 2 is subjected to a special high-temperature heat treatment in a tube furnace under a non-oxidizing atmosphere. The temperature of the process is 1000-1100°C, the heating rate is 2-20°C / min, and the time is 5-8h;

[0054] Step 4: The heat-treated material obtained in step 3 is quickly transferred to a cooling medium under sealed high-temperature conditions so that it is fully wrapped by the cooling medium, and is continuously stirred to accelerate cooling. After cooling for 2 to 6 hours, it is placed in an oven at 80 to 120° C. for drying, and a high-performance pre-lithiated silicon oxide negative electrode material for lithium-ion batteries is obtained.

[0055] The present invention also provides modified silicon iodide prepared by the modification method.

[0056] The preparation method of the present invention can impart special physical and chemical properties to the prepared silicon monoxide, thereby further improving the electrochemical properties of the prepared material.

[0057] In the present invention, the oxygen of the modified silicon oxide prepared tends to be enriched on the surface and contains abundant defects inside.

[0058] The material is a double-layer micro / nano material, and its particle size is less than or equal to 30 μm; more preferably less than or equal to 10 μm.

[0059] The present invention also provides an application of the prepared modified silicon oxide, which is used to prepare a lithium ion battery; preferably, it is used to prepare the negative electrode of the lithium ion battery.

[0060] In the present invention, the prepared modified silicon monoxide can be used to prepare lithium ion batteries and components thereof by existing means.

[0061] The present invention also provides a lithium ion battery negative electrode, comprising a current collector and a negative electrode material composited on the surface of the current collector, wherein the negative electrode material contains the modified silicon oxide;

[0062] Preferably, the negative electrode material further contains at least one of a binder and a conductive agent.

[0063] The present invention also provides a lithium ion battery negative electrode, comprising the negative electrode.

[0064] Silicon oxide materials suffer from low Coulombic efficiency, unstable properties, and difficulty in modification and expansion. To address these issues that hinder the practical application of silicon oxide materials and further improve their performance, the present invention innovatively utilizes the aforementioned lithium-addition roasting, specifically a two-stage lithium-addition roasting and a secondary conduction heat treatment-quenching treatment. This synergistic approach allows for the production of a pre-lithiated silicon oxide negative electrode material with uniform morphology, excellent conductivity and mechanical properties, and a unique internal microstructure, resulting in superior electrochemical performance.

[0065] Compared with the existing technology, the present invention has the following advantages:

[0066] Pre-calcining silicon oxide with lithium, followed by a secondary conduction heat treatment and quenching, combined with the coordinated control of process parameters, unexpectedly achieves synergy, significantly improving the physical phase, morphology, and electrochemical properties of the modified silicon oxide. Furthermore, a two-stage gradient calcination using a coordinated lithium salt, combined with the aforementioned secondary conduction heat treatment and quenching, unexpectedly yields a material with even better electrochemical properties.

[0067] The oxygen in the silicon oxide prepared by the present invention tends to be enriched on the surface, which is conducive to forming a protective layer on the surface of the silicon oxide. It can also contain abundant defects inside, which improves the efficiency of ion shuttling. At the same time, the addition of lithium salt enables the modified silicon oxide to form a double-layer structure, further improving the performance of the material. These are advantages that the existing technology does not have. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Attachment Figure 1 This is an SEM image of the high-performance lithium-ion battery pre-lithiated silicon dioxide negative electrode material prepared in Example 1.

[0069] Attachment Figure 2 This is the XRD pattern of the high-performance lithium-ion battery pre-lithiated silicon dioxide negative electrode material prepared in Example 1.

[0070] By the attached Figure 1 It can be seen that the high performance lithium ion battery pre-lithiated silicon oxide negative electrode material prepared in Example 1 of the present invention has an irregular polygonal shape with a size of 0.2 to 2 μm. Figure 2 It can be seen that the main phase of the pre-lithiated silicon dioxide negative electrode material obtained after treatment in Example 1 of the present invention is SiO x and some lithium silicate salts. DETAILED DESCRIPTION

[0071] The present invention will be further described in detail below with reference to specific examples, but the present invention is not limited to the following examples.

[0072] In the present invention, the heat-conducting containers are all made of metal, especially alloys that are resistant to pressure and temperature, for example, with a thermal conductivity greater than 100 W / m·K. For example, in the following cases, unless otherwise stated, the heat-conducting containers are high / low temperature resistant chromium-nickel stainless steel containers, the material type of which is 304. The high / low temperature resistant nickel-based stainless steel containers, the material type of which is 310S.

[0073] Example 1:

[0074] ① Take 10g of silicon oxide powder with a size of 0.1-2μm and 1g of lithium hydroxide and mix them in a mixer for 6h to mix them evenly, then take out to obtain a mixed material;

[0075] ② The mixture of step ① was subjected to a high-temperature two-stage step-by-step heat treatment under an argon atmosphere to achieve pre-lithiation of silicon oxide powder. The two-stage step-by-step heat treatment procedure was first to heat from room temperature to 500°C (T1) at a heating rate of 10°C / min, and then to 1000°C (T2) at a heating rate of 5°C / min, and then to heat for 5 hours. After the heat treatment, the mixture was cooled in the furnace and taken out to obtain pre-lithiation silicon oxide powder;

[0076] ③ The pre-lithiated silicon oxide powder obtained in step ② is sealed in a 304φ30*80mm high / low temperature resistant chromium-nickel stainless steel container (304) in an argon-filled glove box with a filling capacity of 80%, and then taken out and placed in the heating chamber of a tube furnace, an argon atmosphere is introduced into the heating chamber and a secondary conduction (Ar-wall secondary conduction) high-temperature heat treatment is performed. The heat treatment program is: heating from room temperature to 1000°C at a heating rate of 5°C / min and keeping warm for 5h;

[0077] ④ Open the tube furnace in step ③, and quickly transfer the entire high / low temperature resistant chromium-nickel stainless steel container (maintaining a sealed state) to 5L-196°C liquid nitrogen, so that it is fully wrapped with liquid nitrogen, and stir continuously to accelerate cooling, achieve instantaneous rapid cooling, place it in a 100°C oven for drying after the temperature stabilizes for 3h, and after drying, disassemble the high / low temperature resistant chromium-nickel stainless steel container to obtain a high-performance pre-lithiated silicon oxide negative electrode material for lithium ion batteries; SEM and XRD show Figure 1 and 2 .

[0078] The obtained high-performance pre-lithiated silicon dioxide anode material has a particle size of 0.2 to 2 μm, is free of other impurity phases, and has a uniform morphology.

[0079] The electrochemical performance of the material was tested using a 2025 lithium half-cell:

[0080] Super P is used as a conductive agent, sodium alginate as a binder, and deionized water as a solvent. A slurry is made in a mass ratio of active material: conductive agent: binder = 8:1:1 and evenly coated on copper foil. After drying, it is punched into pole pieces and assembled into 2025 button batteries with lithium sheets as counter electrodes. The electrolyte uses a silicon-based negative electrode material electrolyte (1 mol / LLiPF6, EC:DEC = 1:1, 10% FEC), and the separator is made of PP / PE / PP material.

[0081] The half-cell charge and discharge tests were performed using a CT2001A battery test system produced by Wuhan Blue Electric Electronics Co., Ltd. The test range was 0.01V to 1.2V and the test temperature was 25°C.

[0082] After being assembled into a half-cell, the first coulombic efficiency of 0.2C charge and discharge was 88.45%, and the reversible capacity after 500 cycles was 1015.6 mAh / g.

[0083] Example 2:

[0084] ① Take 10g of silicon oxide powder (same as in Example 1) and 1g of lithium oxalate and mix them in a mixer for 5h to mix them evenly, then take out to obtain a mixed material;

[0085] ② The mixture of step ① was subjected to a high-temperature two-stage stepped heat treatment under an argon atmosphere to achieve pre-lithiation of silicon oxide powder. The two-stage stepped heat treatment procedure was first to heat from room temperature to 600°C at a heating rate of 10°C / min, hold for 3 hours, then to 900°C at a heating rate of 2°C / min, hold for 4 hours, and after the heat treatment was completed, the pre-lithiation silicon oxide powder was obtained by cooling the furnace and taking it out;

[0086] ③ The pre-lithiated silicon oxide powder obtained in step ② was sealed in a 304φ30*80mm high / low temperature resistant chromium-nickel stainless steel container in an argon-filled glove box with a filling capacity of 80%. The powder was then taken out and placed in the heating chamber of a tube furnace. Argon atmosphere was introduced into the heating chamber and a secondary conduction high-temperature heat treatment was performed. The heat treatment program was: heating from room temperature to 1100°C at a heating rate of 2°C / min and holding for 6 hours.

[0087] ④ Carry out subsequent operations according to Example 1 to obtain a high-performance pre-lithiated silicon dioxide negative electrode material for lithium-ion batteries.

[0088] The obtained high-performance pre-lithiated silicon 2 Oxide negative electrode material has a particle size of 0.6 to 1.2 μm, is free of other impurity phases, and has a uniform morphology. After being assembled into a half-cell according to the method of Example 1, the first coulombic efficiency of 0.2C charge and discharge is 89.68%, and the reversible capacity after 500 cycles is 1105.3 mAh / g.

[0089] Example 3:

[0090] ① Take 20g of silicon oxide powder with a size of 1-5μm, 1g of lithium oxalate and 1g of lithium acetate and mix them in a mixer for 8h to mix them evenly, then take out to obtain a mixed material;

[0091] ② The mixture of step ① was subjected to a high-temperature two-stage stepped heat treatment under an argon atmosphere to achieve pre-lithiation of silicon oxide powder. The two-stage stepped heat treatment procedure was firstly to increase the temperature from room temperature to 600°C at a heating rate of 20°C / min, and to keep the temperature for 2 hours, and then to 800°C at a heating rate of 5°C / min, and to keep the temperature for 3 hours. After the heat treatment, the mixture was cooled in the furnace and taken out to obtain pre-lithiation silicon oxide powder;

[0092] ③ The pre-lithiated silicon oxide powder obtained in step ② was sealed in a 310Sφ50*100mm high / low temperature resistant nickel-based stainless steel container in an argon-filled glove box with a filling capacity of 90%, and then taken out and placed in the heating chamber of a tube furnace. Argon atmosphere was introduced into the heating chamber and a secondary conduction high-temperature heat treatment was performed. The heat treatment program was: heating from room temperature to 1100°C at a heating rate of 10°C / min and holding for 4 hours;

[0093] ④ At the moment of completing the step high temperature heat treatment, the tubular furnace in step ③ is opened, and the entire high / low temperature resistant nickel-based stainless steel container (maintaining a sealed state) is quickly transferred to 10L 10°C cooling water so that it is fully wrapped by the cooling water, and continuously stirred to accelerate cooling, achieving instantaneous rapid cooling. After standing for 3 hours until the temperature stabilizes, it is placed in a 100°C oven for drying. After drying is completed, the high / low temperature resistant nickel-based stainless steel container is disassembled to obtain a high-performance pre-lithiated silicon oxide negative electrode material for lithium-ion batteries;

[0094] The obtained high-performance pre-lithiated silicon 2 oxide negative electrode material has a particle size of 1 to 5 μm, is free of other impurity phases, and has a uniform morphology. After being assembled into a half-cell according to the method of Example 1, the first coulombic efficiency of 0.2C charge and discharge is 90.23%, and the reversible capacity after 500 cycles is 1002.5 mAh / g.

[0095] Example 4:

[0096] ① Take 20g of 500nm silicon oxide powder, 1g of lithium oxide and 1g of lithium hydroxide and mix them in a mixer for 6h to mix them evenly, then take out the mixture;

[0097] ② The mixture of step ① was subjected to a high-temperature two-stage stepped heat treatment under a nitrogen atmosphere to achieve pre-lithiation of silicon oxide powder. The two-stage stepped heat treatment procedure was first to heat from room temperature to 600°C at a heating rate of 20°C / min, hold for 2 hours, then to 900°C at a heating rate of 10°C / min, hold for 5 hours, and after the heat treatment was completed, the pre-lithiation silicon oxide powder was obtained by cooling the furnace and taking it out;

[0098] ③ The pre-lithiated silicon oxide powder obtained in step ② was sealed in a 310Sφ50*100mm high / low temperature resistant nickel-based stainless steel container in an argon-filled glove box with a filling capacity of 90%, and then taken out and placed in the heating chamber of a tube furnace. Argon atmosphere was introduced into the heating chamber and a secondary conduction high-temperature heat treatment was performed. The heat treatment program was: heating from room temperature to 1050°C at a heating rate of 6°C / min and holding for 3 hours;

[0099] ④ At the moment of completing the step high temperature heat treatment, the tubular furnace in step ③ is opened, and the entire high / low temperature resistant nickel-based stainless steel container (maintaining a sealed state) is quickly transferred to 10L 10°C polyethylene glycol so that it is fully wrapped with polyethylene glycol, and stirring is continued to accelerate cooling to achieve instantaneous rapid cooling. After standing for 3 hours and the temperature is stabilized, it is placed in an 80°C oven for drying. After drying is completed, the high / low temperature resistant nickel-based stainless steel container is disassembled to obtain a high-performance pre-lithiated silicon oxide negative electrode material for lithium ion batteries; the obtained high-performance pre-lithiated silicon oxide negative electrode material has a particle size of 600nm, no other impurity phases, and a uniform morphology. After being assembled into a half-cell according to the method of Example 1, the first coulombic efficiency of 0.2C charge and discharge is 87.19%, and the reversible capacity after 500 cycles is 1119.5mAh / g.

[0100] Example 5

[0101] Compared with Example 1, the only difference is that a mixture of lithium hydroxide and lithium carbonate with a mass ratio of 2:1 is used to replace the lithium hydroxide, and the weight ratio of the mixture to silicon dioxide and other operating processes are the same as in Example 1. Other operations and parameters are the same as in Example 1.

[0102] Electrochemical performance was measured according to the method of Example 1. The results showed that the initial coulombic efficiency of 0.2C charge and discharge was 92.50%, and the reversible capacity after 500 cycles was 1213.6 mAh / g.

[0103] Comparative Example 1:

[0104] Compared with Example 1, the only difference is that the silicon iodide raw material is not subjected to the pre-lithiation treatment of steps ① and ②, but is directly subjected to the treatment of steps ③ and ④.

[0105] After the half-cell was assembled according to the method of Example 1, the initial coulombic efficiency of 0.2C charge and discharge was 61.57%, and the reversible capacity after 500 cycles was 756.8 mAh / g.

[0106] Comparative Example 2:

[0107] Compared with Example 1, the only difference is that the mixed material is directly processed through steps ③ and ④ without going through step ②.

[0108] The obtained material had uneven morphology and non-uniform particle size. After being assembled into a half-cell according to the method of Example 1, the first coulombic efficiency of 0.2C charge and discharge was 70.25%, and the reversible capacity after 500 cycles was 864.3 mAh / g.

[0109] Comparative Example 3:

[0110] Compared with Example 1, the only difference is that in step ②, no two-stage heat treatment is performed. For example, the holding process T1 is omitted, and the temperature is directly raised to 1000°C and then held, and a single-stage heat treatment is performed. The specific operations are as follows:

[0111] ① According to the operation of Example 1, a mixed material is obtained;

[0112] ② The mixture of step ① is subjected to a single-stage heat treatment under an argon atmosphere. The single-stage heat treatment procedure is to heat the mixture from room temperature to 1000°C at a heating rate of 10°C / min and hold the temperature for 5 hours. After the heat treatment is completed, the mixture is cooled in the furnace and taken out to obtain pre-lithiated silicon oxide powder;

[0113] ③ Carry out subsequent operations according to Example 1 to obtain the negative electrode material.

[0114] The obtained material had uneven morphology and non-uniform particle size. After being assembled into a half-cell according to the method of Example 1, the first coulombic efficiency of 0.2C charge and discharge was 51.20%, and the reversible capacity after 500 cycles was 452.6 mAh / g.

[0115] Comparative Example 4:

[0116] Compared with Example 1, the only difference is that step ③ is not performed, but the product of pre-lithiated silicon oxide powder in step ② is subjected to cold treatment in step ④, and the steps are, for example:

[0117] Pre-lithiated silicon oxide powder was obtained according to the method of Example 1;

[0118] The obtained pre-lithiated silicon oxide powder was sealed in a 304φ30*80mm high / low temperature resistant chromium-nickel stainless steel container in an argon-filled glove box and directly transferred to 5L-196°C liquid nitrogen. The subsequent operations were the same as in Example 1 to obtain the negative electrode material.

[0119] After the half-cell was assembled according to the method of Example 1, the initial coulombic efficiency of 0.2C charge and discharge was 74.86%, and the reversible capacity after 500 cycles was 852.6 mAh / g.

[0120] Comparative Example 5:

[0121] Compared with Example 1, the only difference is that a foamed ceramic container (with a thermal conductivity of less than 50 W / m·K) is used to replace the high / low temperature resistant chromium-nickel stainless steel container. Other parameters and operations are the same as those in Example 1.

[0122] The obtained material was assembled into a half-cell according to the method of Example 1. The initial coulombic efficiency of 0.2C charge and discharge was 28.56%, and the reversible capacity after 500 cycles was 156.2 mAh / g.

[0123] Comparative Example 6:

[0124] Compared with Example 1, the only difference is that the temperature of ③ is not controlled within the range required by the present invention. The difference is that step ③ is: the pre-lithiated silicon oxide powder is sealed in a 304φ30*80mm high / low temperature resistant chromium-nickel stainless steel container in an argon-filled glove box with a filling capacity of 80%, and then taken out and placed in the heating chamber of a tube furnace, an argon atmosphere is introduced into the heating chamber and a secondary conduction high-temperature heat treatment is performed. The heat treatment procedure is: from room temperature to 600°C at a heating rate of 5°C / min, and kept warm for 5h; the other operations and steps are the same as in Example 1.

[0125] After the half-cell was assembled according to the method of Example 1, the initial coulombic efficiency of 0.2C charge and discharge was 38.64%, and the reversible capacity after 500 cycles was 126.5 mAh / g.

[0126] Comparative Example 7:

[0127] Compared with Example 1, the only difference is that the indirect rapid cooling treatment required in step ④ is not performed, but furnace cooling is performed.

[0128] After the half-cell was assembled according to the method of Example 1, the initial coulombic efficiency of 0.2C charge and discharge was 69.52%, and the reversible capacity after 500 cycles was 742.6 mAh / g.

[0129] Comparative Example 8

[0130] Compared with Example 1, the only difference is that steps ③ and ④ do not use the heat treatment and rapid cooling treatment mediated by the heat-conducting container for secondary treatment. The different steps are:

[0131] The pre-lithiated silicon oxide powder is not sealed in a high / low temperature resistant chromium-nickel stainless steel container, and step ③ is directly performed, and then the obtained material is directly placed in liquid nitrogen for rapid cooling.

[0132] After the half-cell was assembled according to the method of Example 1, the initial coulombic efficiency of 0.2C charge and discharge was 23.51%, and the reversible capacity after 500 cycles was 65.44 mAh / g.

[0133] Through the examples and comparative examples, it is concluded that pre-lithiation technology not only helps improve the material's Coulombic efficiency but also generates an inert phase within the silicon oxide material to buffer stress, thereby enhancing the material's cycling performance. Special high-temperature heat treatment can achieve microscopic and structural transformations in the pre-lithiated silicon oxide material, fundamentally improving the material's electrochemical performance. A unique cooling process helps stabilize the material's performance, allowing its unique characteristics to be fully utilized. The uniformity of the mixing also directly affects the material's performance. Ultimately, the synergistic effect of these various process steps and preparation parameters is crucial to fully realize the advantages of the present invention and produce a pre-lithiated silicon oxide negative electrode material with excellent performance for lithium-ion batteries.

Claims

1. A method for modifying silicon dioxide, characterized in that the steps include: Step (1): Calcination with lithium Silicon dioxide and lithium salt are pre-calcined in the first stage, and then subjected to the second stage heat treatment; The temperature of the first stage calcination treatment is 400~600℃, and the temperature of the second stage calcination treatment is 800~1000℃; Step (2): Heat treatment-quenching The product after lithium calcination is filled and sealed in a heat-conducting container under a protective atmosphere, and the heat-conducting container is heat-treated under the protective atmosphere. Subsequently, the heat-treated heat-conducting container is placed in a cooling medium for quenching treatment while still hot to obtain modified silicon dioxide; The temperature of heat treatment is 800~1200℃; The melting point of the wall material of the heat-conducting container is greater than or equal to 1200° C., and the thermal conductivity is greater than or equal to 100 W / m·K.

2. The method for modifying silicon dioxide according to claim 1, wherein: The particle size of the silicon monoxide is 100 nm to 20 μm.

3. The method for modifying silicon dioxide according to claim 1, wherein: The lithium salt added in the lithium calcination stage is organic lithium and / or inorganic lithium.

4. The method for modifying silicon 2 oxide according to claim 3, wherein: The inorganic lithium is at least one of lithium carbonate, lithium bicarbonate, lithium hydroxide, lithium oxide, lithium sulfate, and lithium phosphate; The organic lithium is at least one of C1-C6 lithium alcoholate and C1-C10 lithium carboxylate.

5. The method for modifying silicon 2 oxide according to claim 4, wherein: The lithium salts are two or more inorganic salts.

6. The method for modifying silicon 2 oxide according to claim 5, wherein: The lithium salt is a composite salt of lithium hydroxide and lithium carbonate.

7. The method for modifying silicon 2 oxide according to claim 6, wherein: The mass ratio of lithium hydroxide to lithium carbonate is 1~10:

1.

8. The method for modifying silicon 2 oxide according to claim 1, wherein: The weight ratio of silicon oxide to lithium salt is 5~50:

1.

9. The method for modifying silicon dioxide according to claim 1, wherein: The atmosphere in the lithium calcination stage is one or more of hydrogen, argon, helium, carbon dioxide and nitrogen.

10. The method for modifying silicon 2 oxide according to claim 1, wherein: In the lithium calcination stage, the heating rate of the first calcination process is 5-20°C / min; the heating rate of the second calcination process is 1-10°C / min.

11. The method for modifying silicon 2 oxide according to claim 1, wherein: In the lithium roasting, the first roasting time is 1~5h, and the second roasting time is 2~8h.

12. The method for modifying silicon 2 oxide according to claim 1, wherein: The wall material of the heat-conducting container does not suffer from brittle fracture at -200°C.

13. The method for modifying silicon 2 oxide according to claim 1, wherein: The wall material of the heat-conducting container is an alloy material.

14. The method for modifying silicon 2 oxide according to claim 13, wherein: The wall material of the heat-conducting container is one of stainless steel, aluminum alloy, copper alloy, molybdenum alloy, tungsten alloy, niobium alloy and nickel alloy.

15. The method for modifying silicon 2 oxide according to claim 14, wherein: The wall material of the heat-conducting container is at least one of 310S, 304, US366, and GH188.

16. The modification method according to claim 1, wherein The product after lithium calcination is filled into a heat-conducting container chamber under a protective atmosphere and then sealed.

17. The modification method according to claim 16, wherein: The protective atmosphere is at least one of nitrogen, inert gas, carbon dioxide and hydrogen.

18. The modification method according to claim 16, wherein: The filling capacity of the product calcined with lithium is greater than or equal to 50%.

19. The modification method according to claim 1, wherein In step (2), the heat treatment temperature is 1000~1100℃.

20. The modification method according to claim 1, wherein In step (2), the heating rate of the heat treatment stage is 2~30℃ / min.

21. The modification method according to claim 1, wherein The heat treatment time is 5~8h.

22. The modification method according to claim 1, wherein In step (2), the heat-treated and sealed heat-conducting container is directly placed in a cooling medium for quenching.

23. The modification method according to claim 22, wherein: The cooling medium is a liquid cooling medium or a gas cooling medium.

24. The modification method according to claim 23, wherein: The cooling medium is one or more of anhydrous ethanol, polyethylene glycol, deionized water, liquid nitrogen, dry ice, air, argon, and nitrogen.

25. The modification method according to claim 1, wherein The temperature difference between the heat-conducting container and the initial cooling medium is greater than or equal to 800°C.

26. A modified silicon oxide obtained by the modification method according to any one of claims 1 to 25.

27. A use of the modified silicon oxide according to claim 26, characterized in that: It is used to prepare lithium-ion batteries.

28. The use of modified silicon oxide according to claim 27, characterized in that: It is used to prepare the negative electrode of lithium-ion battery.

29. A negative electrode for a lithium-ion battery, comprising a current collector and a negative electrode material composited on the surface of the current collector, characterized in that: The negative electrode material contains modified silicon oxide obtained by the modification method according to any one of claims 1 to 25.

30. The lithium ion battery negative electrode according to claim 29, wherein: The negative electrode material further contains at least one of a binder and a conductive agent.

31. A lithium ion battery negative electrode, characterized in that: Comprising the negative electrode according to claim 29 or 30.

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