Negative electrode material and preparation method thereof, negative electrode sheet, secondary battery and electronic device

Abstract

This application provides a negative electrode material, a preparation method thereof, a negative electrode plate, a secondary battery, and an electronic device. The negative electrode material comprises: a pre-lithiated amorphous silicon-carbon composite; and a lithium titanate nitride coating layer covering at least a portion of the surface of the pre-lithiated amorphous silicon-carbon composite; wherein the pre-lithiated amorphous silicon-carbon composite comprises at least one of carbon nitride, titanium nitride, and lithium nitride. The negative electrode material provided herein can improve the initial coulombic efficiency, rate capability, and cycle performance of a secondary battery.

Description

Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to a negative electrode material and a preparation method thereof, a negative electrode plate, a secondary battery and an electronic device. Background Art

[0002] Secondary batteries, represented by lithium-ion batteries, have advantages such as high operating voltage, high energy density, good safety, and no memory effect. They have achieved great success in portable electronic devices, electric vehicles, and hybrid vehicles. In recent years, with the increasing penetration of new energy vehicles, secondary battery technology has also been continuously improved. Improving the energy density and fast charging capabilities of secondary batteries is an important method to improve the efficiency of new energy vehicles. As the charging power of electric vehicles increases from 250kW to 350kW and the charging voltage increases from 400V to 800V, higher requirements are placed on the rate capability, initial coulombic efficiency, and cycle performance of secondary batteries. Summary of the Invention

[0003] Based on this, the present application provides a negative electrode material and a preparation method thereof, a negative electrode plate, a secondary battery and an electronic device, aiming to improve the first coulombic efficiency, rate or cycle performance of the secondary battery.

[0004] The first aspect of the present application provides a negative electrode material, comprising:

[0005] Pre-lithiated amorphous silicon-carbon composites; and

[0006] a lithium titanate nitride coating layer coating at least a portion of the surface of the pre-lithiated amorphous silicon-carbon composite;

[0007] Wherein, the pre-lithiated amorphous silicon-carbon composite contains at least one of silicon nitride, carbon nitride, titanium nitride and lithium nitride.

[0008] According to any embodiment of the first aspect of the present application, the negative electrode material satisfies at least one of the following conditions:

[0009] (1) The thickness of the lithium titanate nitride coating layer is 2 nm to 2000 nm;

[0010] (2) The mass percentage of carbon element in the pre-lithiated amorphous silicon-carbon composite is 10% to 98%;

[0011] (3) The mass percentage of titanium element in the pre-lithiated amorphous silicon-carbon composite is 0.1% to 5%;

[0012] (4) The mass percentage of lithium element in the pre-lithiated amorphous silicon-carbon composite is 0.01% to 20%;

[0013] (5) The mass percentage of silicon element in the pre-lithiated amorphous silicon-carbon composite is 0.01% to 40%.

[0014] A second aspect of the present application provides a method for preparing a negative electrode material, comprising:

[0015] Composite treatment of graphite and lithium metal to obtain graphite lithium compound;

[0016] alloying the graphite lithium compound with a first titanium source, a silicon source, and other metals to obtain a pre-lithiated amorphous silicon-carbon composite;

[0017] Mixing and calcining the pre-lithiated amorphous silicon-carbon composite with a second titanium source and a lithium source to form a lithium titanate coating layer on the surface of the pre-lithiated amorphous silicon-carbon composite to obtain a pre-lithiated lithium titanate-coated amorphous silicon-carbon composite; and

[0018] The pre-lithiated lithium titanate-coated amorphous silicon-carbon composite is nitrided to form a pre-lithiated lithium nitride titanate-coated amorphous silicon-carbon composite to obtain a negative electrode material, wherein the pre-lithiated lithium nitride titanate-coated amorphous silicon-carbon composite contains at least one of silicon nitride, carbon nitride, titanium nitride and lithium nitride.

[0019] According to any implementation of the second aspect of the present application, the method satisfies at least one of the following conditions:

[0020] (1) The temperature of the composite treatment is 200°C to 700°C, preferably 300°C to 500°C;

[0021] (2) The composite treatment time is 1 hour to 30 hours, preferably 5 hours to 15 hours;

[0022] (3) The environment of the composite treatment is a vacuum or inert atmosphere;

[0023] (4) The molecular formula of the graphite lithium compound is LiC x , where X>6.

[0024] According to any embodiment of the second aspect of the present application, the alloying treatment of the graphite lithium compound with the first titanium source, the silicon source and the other metals includes:

[0025] Melting and mixing the graphite lithium compound, the first titanium source, the silicon source, and the other metals to form an alloy composite material;

[0026] The alloy composite material is subjected to amorphization and granulation treatment by a ball milling method.

[0027] According to any embodiment of the second aspect of the present application, before the alloy composite material is subjected to amorphization and granulation treatment by ball milling, the method further comprises:

[0028] The alloy composite material is subjected to an amorphization treatment by a quenching method or an atomization method.

[0029] According to any embodiment of the second aspect of the present application, the temperature of the melt mixing is 1000°C to 2000°C, preferably 1100°C to 1500°C.

[0030] According to any implementation of the second aspect of the present application, the method satisfies at least one of the following conditions:

[0031] (1) The molar ratio of the graphite lithium compound, the mixture of the first titanium source and the silicon source, and the other metal is (99-60):(0.1-30):(0.01-20), preferably (90-75):(10-25):(1-10);

[0032] (2) The first titanium source includes titanium element;

[0033] (3) The silicon source includes silicon element;

[0034] (4) The other metals include one or more of cobalt, manganese, nickel, indium, titanium, aluminum, iron, magnesium, copper, zirconium, niobium, antimony, bismuth, vanadium, zinc, germanium, palladium, molybdenum, and tungsten.

[0035] According to any implementation of the second aspect of the present application, the method satisfies at least one of the following conditions:

[0036] (1) The second titanium source includes one or more of titanium dioxide, titanium tetroxide, titanium fluoride and titanium hydroxide;

[0037] (2) The lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium acetate, lithium oxide and lithium nitride;

[0038] (3) the molar ratio of the second titanium source to the pre-lithiated amorphous silicon-carbon composite is 0.01 to 10;

[0039] (4) The molar ratio of the second titanium source to the lithium source is 1.25:(1-1.10);

[0040] (5) The calcination temperature is 500°C to 1000°C, preferably 700°C to 900°C;

[0041] (6) The calcination treatment time is 5 hours to 30 hours, preferably 10 hours to 20 hours.

[0042] According to any embodiment of the second aspect of the present application, the nitriding treatment of the pre-lithiated lithium titanate-coated amorphous silicon-carbon composite comprises:

[0043] The pre-lithiated lithium titanate-coated amorphous silicon-carbon composite is reacted with a nitrogen source to form the pre-lithiated lithium nitride titanate-coated amorphous silicon-carbon composite through a nitridation reaction.

[0044] According to any implementation of the second aspect of the present application, the method satisfies at least one of the following conditions:

[0045] (1) The nitrogen source includes at least one of ammonia, urea, ethylenediamine and nitrogen-containing ionic liquid;

[0046] (2) The temperature of the nitriding treatment is 300°C to 1000°C, preferably 500°C to 700°C;

[0047] (3) The nitriding treatment time is 5h to 30h, preferably 5h to 10h;

[0048] (4) The nitriding treatment is carried out in a vacuum or inert atmosphere.

[0049] The third aspect of the present application provides a negative electrode plate, comprising the negative electrode material provided in the first aspect of the present application or the negative electrode material prepared by the method described in the second aspect of the present application.

[0050] The fourth aspect of the present application provides a secondary battery, comprising the negative electrode plate provided in the third aspect of the present application.

[0051] A fifth aspect of the present application provides an electronic device, comprising the secondary battery provided in the fourth aspect of the present application.

[0052] The electronic device of the present application includes the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery.

[0053] The negative electrode material provided by the present application includes a pre-lithiated amorphous silicon-carbon composite and a lithium titanate nitride coating layer coated on at least a portion of the surface of the pre-lithiated amorphous silicon-carbon composite, wherein the graphite lithium compound can effectively improve the coulombic efficiency, charge and discharge specific capacity conductivity and cycle performance of the negative electrode material; the lithium titanate nitride coating layer can effectively inhibit the volume expansion of the amorphous silicon-carbon composite during charge and discharge, enhance the structural stability of the negative electrode material, and at the same time, the lithium titanate nitride itself also has excellent high-rate charge and discharge and low-temperature charge and discharge performance, thereby improving the cycle performance, rate performance and low-temperature charge and discharge performance of the negative electrode material and the secondary battery as a whole. In addition, the carbon nitride, titanium nitride and lithium nitride distributed in the amorphous silicon-carbon composite can play a good conductive role, which is conducive to accelerating the transmission of active ions in the negative electrode during the cycle of the secondary battery, reducing the polarization of the negative electrode, thereby improving the conductivity and rate performance of the negative electrode material and the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 This is an SEM image of the pre-lithiated amorphous silicon-carbon composite prepared in step (2) of Example 1.

[0055] Figure 2 This is an SEM image of the pre-lithiated lithium titanate nitride-coated amorphous silicon-carbon composite prepared in step (4) of Example 1.

[0056] Figure 3 This is the EDS image of the pre-lithiated amorphous silicon-carbon composite prepared in step (2) of Example 3.

[0057] Figure 4 This is an SEM image of the pre-lithiated lithium titanate nitride-coated amorphous silicon-carbon composite prepared in Example 7.

[0058] Figure 5 This is a bar chart comparing the -40°C, 0.5C discharge capacities of the 10mAh lithium-ion batteries in Examples 1-9 and Comparative Examples 1-2.

[0059] Figure 6 This is a bar chart comparing the 25°C, 5C discharge capacities of the 10mAh lithium-ion batteries in Examples 1-9 and Comparative Examples 1-2. DETAILED DESCRIPTION

[0060] To facilitate understanding of the present application, a more comprehensive description of the present application will be provided below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present application. However, the present application may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure of the present application.

[0061] For simplicity, this application only explicitly discloses certain numerical ranges. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, although not explicitly stated, each point or individual value between the endpoints of a range is included in the range. Thus, each point or individual value may serve as its own lower limit or upper limit and be combined with any other point or individual value, or with other lower limits or upper limits, to form an unspecified range.

[0062] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. It should be noted that, unless otherwise stated, the term "and / or" used herein includes any and all combinations of one or more related listed items, and "above" and "below" are inclusive of the number, and the meaning of "a variety" in "one or more" is more than two.

[0063] The above disclosure of the present application is not intended to describe every disclosed embodiment or every implementation in the present application. The following description more specifically illustrates exemplary embodiments. In many places throughout the application, guidance is provided through a series of examples, which can be used in various combinations. In each example, the enumeration is intended only as a representative group and should not be construed as exhaustive.

[0064] During their research, the inventors discovered that conventional graphite and silicon-carbon anode materials in traditional secondary batteries, such as lithium-ion batteries, form a solid electrolyte interphase (SEI) during the initial charge and discharge process, resulting in low initial coulombic efficiency. To improve the initial efficiency, specific capacity, electrochemical performance, and processing performance of conventional graphite and silicon-carbon anode materials, as well as their processing performance during battery production, the inventors proposed the following technical solution.

[0065] A first aspect of an embodiment of the present application provides a negative electrode material, comprising: a pre-lithiated amorphous silicon-carbon composite; and a lithium titanate nitride coating layer coated on at least a portion of the surface of the pre-lithiated amorphous silicon-carbon composite; wherein the pre-lithiated amorphous silicon-carbon composite contains at least one of silicon nitride, carbon nitride, titanium nitride and lithium nitride.

[0066] The negative electrode material provided by the present application includes a pre-lithiated amorphous silicon-carbon composite and a lithium titanate nitride coating layer coated on at least part of the surface of the pre-lithiated amorphous silicon-carbon composite, wherein the lithium titanate nitride coating layer can effectively inhibit the volume expansion of the amorphous silicon-carbon composite during charge and discharge, and enhance the structural stability of the negative electrode material; at the same time, the lithium titanate nitride itself also has excellent high-rate charge and discharge and low-temperature charge and discharge performance, and does not form an SEI film during the charge and discharge process, thereby improving the cycle performance, rate performance, low-temperature charge and discharge performance and first coulomb efficiency of the negative electrode material and the secondary battery as a whole. In addition, the carbon nitride, titanium nitride and lithium nitride distributed in the pre-lithiated amorphous silicon-carbon composite can play a good conductive role, which is conducive to accelerating the transmission of active ions in the negative electrode during the cycle of the secondary battery, reducing the polarization of the negative electrode, thereby improving the conductivity and rate performance of the negative electrode material and the secondary battery.

[0067] In some embodiments, the thickness of the lithium titanate nitride coating layer is between 2 nm and 2000 nm. For example, the thickness of the lithium titanate nitride coating layer can be 5 nm, 10 nm, 50 nm, 100 nm, 500 nm, 1000 nm, 1500 nm, or any range thereof. When the thickness of the lithium titanate nitride coating layer is within a suitable range, the volume expansion of the amorphous silicon-carbon composite can be further enhanced during charge and discharge, thereby further improving the structural stability of the negative electrode material and the cycle performance of the negative electrode material and the secondary battery.

[0068] In some embodiments, the mass percentage of carbon element in the pre-lithiated amorphous silicon-carbon composite is 10% to 98%.

[0069] In some embodiments, the mass percentage of titanium element in the pre-lithiated amorphous silicon-carbon composite is 0.1% to 5%.

[0070] In some embodiments, the mass percentage of lithium element in the pre-lithiated amorphous silicon-carbon composite is 0.01% to 20%.

[0071] In some embodiments, the mass percentage of silicon in the pre-lithiated amorphous silicon-carbon composite is 0.01% to 40%.

[0072] The content of each element in the pre-lithiated amorphous silicon-carbon composite is within the above range, which is beneficial to improving the electrochemical performance of the negative electrode material and further improving the performance of the battery using the negative electrode material.

[0073] A second aspect of the present application provides a method for preparing a negative electrode material, comprising the following steps:

[0074] S10, performing composite treatment on graphite and lithium metal to obtain a graphite lithium compound;

[0075] S20, alloying the graphite lithium compound with a first titanium source, a silicon source, and other metals to obtain a pre-lithiated amorphous silicon-carbon composite;

[0076] S30, mixing and calcining the pre-lithiated amorphous silicon-carbon composite with a second titanium source and a lithium source to form a lithium titanate coating layer on the surface of the pre-lithiated amorphous silicon-carbon composite to obtain a pre-lithiated lithium titanate-coated amorphous silicon-carbon composite;

[0077] S40. Nitriding the pre-lithiated lithium titanate-coated amorphous silicon-carbon composite to form a pre-lithiated lithium nitride titanate-coated amorphous silicon-carbon composite to obtain a negative electrode material, wherein the pre-lithiated lithium nitride titanate-coated amorphous silicon-carbon composite contains at least one of silicon nitride, carbon nitride, titanium nitride and lithium nitride.

[0078] The method for preparing a negative electrode material provided by the present application is first to heat-treat graphite and lithium metal so that graphite reacts with lithium metal at high temperature to generate a graphite lithium compound in which lithium is evenly distributed in a graphite layered structure. The graphite lithium compound is then alloyed with a first titanium source, a silicon source, and other metals to fuse the graphite lithium compound with a silicon alloy formed by the first titanium source, the silicon source, and other metals, thereby dispersing lithium metal and graphite in the silicon alloy. This can significantly improve the coulombic efficiency of the material, improve the material's gram capacity and conductivity, improve the volume expansion of the silicon alloy during the charge and discharge process, improve the structural stability of the silicon alloy, and improve the cycle efficiency of the negative electrode material. The graphite lithium compound with high reactivity is evenly dispersed in the silicon alloy, and the prepared pre-lithiated amorphous silicon-carbon composite can be stably present in the air, which is beneficial to improving the applicability of the negative electrode material.

[0079] The pre-lithiated amorphous silicon-carbon composite is then calcined with a second titanium source and a lithium source to form a lithium titanate coating on the surface of the pre-lithiated amorphous silicon-carbon composite. This can utilize the characteristics of lithium titanate, such as small volume change, high rate performance, and good low-temperature performance during charge and discharge, to effectively alleviate the volume expansion of the pre-lithiated amorphous silicon-carbon composite during charge and discharge, thereby improving the structural stability of the material and thus improving the cycle performance, rate performance, and low-temperature charge and discharge performance of the negative electrode material. Finally, the pre-lithiated lithium titanate-coated amorphous silicon-carbon composite is nitrided to nitride the silicon, carbon, titanium, and lithium elements in the material to generate silicon nitride, carbon nitride, titanium nitride, and lithium nitride. Among them, carbon nitride, titanium nitride, and lithium nitride can play a good conductive role, which is beneficial to accelerate the transmission of active ions in the negative electrode during the cycle of the secondary battery, reduce the polarization of the negative electrode, and thus improve the conductivity and rate performance of the negative electrode material and the secondary battery. Accordingly, the products generated in the above steps, through mutual synergy, are beneficial to improving the overall electrochemical performance of the negative electrode material and the secondary battery.

[0080] In some implementations, step S10 may specifically include the following steps:

[0081] S100, stirring and mixing graphite and lithium metal under high temperature vacuum or inert atmosphere to obtain a graphite lithium compound.

[0082] In some embodiments, the temperature of the heat treatment in step S10 is 200°C to 700°C, preferably 300°C to 500°C.

[0083] In some embodiments, the heat treatment time in step S10 is 1 hour to 30 hours, preferably 5 hours to 15 hours.

[0084] In some embodiments, the heat treatment environment in step S10 is a vacuum atmosphere or an inert atmosphere. For example, the inert atmosphere can be helium, argon, etc.

[0085] In some embodiments, the molecular formula of the graphite lithium compound is LiC x , where X>6.

[0086] By performing composite treatment on graphite and lithium metal in step S10, graphite can react with lithium metal at high temperature to generate graphite lithium compound LiC in which lithium is evenly distributed in the graphite layer structure. x The above reaction temperature and time can effectively promote the distribution of lithium into the graphite layer structure, and obtain the graphite lithium compound LiC in which lithium is evenly distributed in the graphite layer structure. x .

[0087] In some embodiments, step S20 may further include the following steps:

[0088] S200, melting and mixing the graphite lithium compound, the first titanium source, the silicon source, and the other metals to form an alloy composite material;

[0089] S220, performing amorphization and granulation treatment on the alloy composite material by ball milling.

[0090] In some embodiments, before the alloy composite material is crushed by ball milling in step S220, the following steps are further included:

[0091] S210, performing amorphization treatment on the alloy composite material by a quenching method or an atomization method.

[0092] In the embodiments of the present application, ball milling, atomization and quenching are well known in the art. As an example, ball milling can be a method of grinding micron or submicron particles for a long time and then dispersing them into a medium; atomization can be a method of directly crushing liquid metal or alloy into powder particles; and quenching can be a method of heating a small amount of sample to a predetermined temperature, keeping the temperature to reach phase equilibrium, and then rapidly quenching the sample to form an amorphous crystal structure.

[0093] In some embodiments, the temperature of the melt mixing in step S200 is 1000°C to 2000°C, preferably 1100°C to 1500°C.

[0094] In some embodiments, in step S200, the molar ratio of the graphite lithium compound, the mixture of the first titanium source and the silicon source, and the other metals is (99-60):(0.1-30):(0.01-20), preferably (90-75):(10-25):(1-10).

[0095] In some embodiments, the first titanium source is titanium alone, and the silicon source is silicon alone.

[0096] In some embodiments, the types of other metals are not particularly limited and may include cobalt, manganese, nickel, indium, titanium, aluminum, iron, magnesium, copper, zirconium, niobium, antimony, bismuth, vanadium, zinc, germanium, palladium, molybdenum, tungsten, and the like.

[0097] By alloying the graphite lithium compound with the first titanium source, silicon source and other metals in step S20, the graphite lithium compound can be evenly fused with the silicon alloy formed by the first titanium source, silicon source and other metals, so that lithium metal and graphite are dispersed in the silicon alloy, which can significantly improve the coulomb efficiency and conductivity of the silicon alloy, improve the volume expansion of the silicon alloy during the charge and discharge process, improve the structural stability of the silicon alloy, and improve the cycle efficiency of the negative electrode material. The highly reactive graphite lithium compound is evenly dispersed in the silicon alloy, and the prepared pre-lithiated amorphous silicon-carbon composite can exist stably in the air, which is beneficial to improving the applicability of the negative electrode material. The selection of temperature, time, material type and material ratio in step S30 is also more conducive to the dispersion of lithium metal and graphite in the silicon alloy, thereby effectively improving the electrochemical performance of the negative electrode material.

[0098] In some implementations, step S30 may specifically include the following steps:

[0099] S300 , mixing the pre-lithiated amorphous silicon-carbon composite with a second titanium source and a lithium source, and calcining the mixture under vacuum or inert atmosphere to prepare a pre-lithiated lithium titanate-coated amorphous silicon-carbon composite.

[0100] In some embodiments, the temperature of the calcination treatment in step S30 is 500°C to 1000°C, preferably 700°C to 900°C.

[0101] In some embodiments, the calcination treatment time in step S30 is 5 hours to 30 hours, preferably 10 hours to 20 hours.

[0102] In some embodiments, the inert atmosphere in step S300 may be helium, argon, neon, or the like.

[0103] In some embodiments, the second titanium source in step S30 may be selected from titanium compounds, for example, may include one or more of titanium dioxide, titanium tetroxide, titanium fluoride, and titanium hydroxide.

[0104] In some embodiments, the type of lithium source in step S30 is not particularly limited and can be selected according to actual needs. For example, it can be one or more of lithium carbonate, lithium hydroxide, lithium acetate, lithium oxide and lithium nitride.

[0105] In some embodiments, the molar ratio of the second titanium source to the pre-lithiated amorphous silicon-carbon composite in step S30 is 0.01-10.

[0106] In some embodiments, the molar ratio of the second titanium source to the lithium source in step S30 is 1.25:(1-1.10).

[0107] By calcining the pre-lithiated amorphous silicon-carbon composite with the second titanium source and the lithium source in step S30, a lithium titanate coating is formed on the surface of the pre-lithiated amorphous silicon-carbon composite. This can fully utilize the characteristics of lithium titanate during charge and discharge, such as small volume change, high rate capability, and good low-temperature performance. This effectively alleviates the volume expansion of the amorphous silicon-carbon composite during charge and discharge, improves the structural stability of the material, and thus improves the cycle performance, rate capability, and low-temperature charge and discharge performance of the negative electrode material. The selection of temperature, time, material type, and material ratio in step S30 is also conducive to forming a coating with better morphology and bonding, further improving the electrochemical performance of the negative electrode material.

[0108] In some implementations, step S40 may further include the following steps:

[0109] S400 , contacting the pre-lithiated lithium titanate-coated amorphous silicon-carbon composite with a nitrogen source to form a pre-lithiated nitrided lithium titanate-coated amorphous silicon-carbon composite through a nitridation reaction.

[0110] In some embodiments, the nitrogen source includes at least one of ammonia, urea, ethylenediamine and nitrogen-containing ionic liquids. As a specific example, the nitrogen-containing ionic liquid can be 1-butylpyridine dinitrile amine salt (C 11 H 14 N4) or 1-butyl-3-methylimidazolium dicyanamide (C 10 H 15N5) etc.

[0111] In some embodiments, the temperature of the nitriding treatment in step S40 is 300°C to 1000°C, preferably 500°C to 700°C.

[0112] In some embodiments, the nitriding treatment time in step S40 is 5 hours to 30 hours, preferably 5 hours to 10 hours.

[0113] In some embodiments, the nitridation treatment environment in step S40 is a vacuum atmosphere or an inert atmosphere. For example, the inert atmosphere may be helium, argon, or the like.

[0114] By nitriding the pre-lithiated lithium titanate-coated amorphous silicon-carbon composite in step S40, the silicon, carbon, titanium, and lithium elements in the material can be nitrided to generate silicon nitride, carbon nitride, titanium nitride, and lithium nitride, among others. Carbon nitride, titanium nitride, and lithium nitride are excellent conductors, which are beneficial for accelerating the transport of active ions in the negative electrode during the secondary battery cycle, reducing negative electrode polarization, and thereby improving the conductivity and rate performance of the negative electrode material and the secondary battery. The temperature in step S40 allows the nitrogen element to enter the pre-lithiated lithium titanate-coated amorphous silicon-carbon composite at an appropriate temperature and nitride with the silicon, carbon, titanium, and lithium elements therein. The reaction time is sufficient to ensure a complete reaction without wasting time.

[0115] A third aspect of the embodiments of the present application provides a negative electrode plate, comprising the negative electrode material provided in the first aspect of the present application or the negative electrode material prepared by the method described in the second aspect of the present application.

[0116] It should be noted that the negative electrode material provided herein can be used alone in a negative electrode sheet or mixed with graphite in any proportion. When mixed with graphite in any proportion and used in a negative electrode sheet, the gram capacity of the negative electrode material provided herein can be controlled to be 400 mAh / g to 2000 mAh / g.

[0117] In some embodiments, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, and the negative electrode film layer includes the negative electrode material of the second aspect of the present application.

[0118] A fourth aspect of the embodiments of the present application provides a secondary battery, comprising the negative electrode sheet provided in the third aspect of the present application.

[0119] In some embodiments, the type of secondary battery is not particularly limited and may include any battery in which an electrochemical reaction occurs to convert chemical energy into electrical energy, for example, a lithium ion battery or a sodium ion battery.

[0120] In some embodiments, a secondary battery further comprises a positive electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are intercalated and released between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0121] A fifth aspect of the embodiments of the present application provides an electronic device, comprising the secondary battery provided in the fourth aspect of the present application, wherein the secondary battery can be used as a power source in the electronic device.

[0122] In some embodiments, the type of electronic device is not particularly limited and can be any electronic device known in the art. For example, the electronic device can include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0123] Example

[0124] The following are specific examples, which describe the present disclosure in more detail. These examples are intended for illustrative purposes only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing. The instruments used in the examples are also commercially available.

[0125] Example 1

[0126] (1) 500 g of artificial graphite (purity > 98.0%) and 20 g of metallic lithium flakes (purity > 99.0%) were mixed in a reactor, heated and vacuumed for 2 hours, the temperature was kept constant at 500°C, and rapidly stirred for 10 hours. During the stirring process, vacuum was maintained to generate a dark blue graphite lithium compound LiC 14.45 .

[0127] (2) Silicon powder (purity>99.0%), titanium powder (purity>99.0%), cobalt powder (purity>99.0%) and zinc powder (purity>99.0%) were stirred and mixed uniformly in a stoichiometric molar ratio of 9:0.8:0.1:0.1, and then the graphite lithium compound LiC prepared in step (1) was added in a mass ratio of 70:30. 14.45 , placed in a vacuum melting furnace, the temperature is set to 1150℃, the melting time is 30 minutes, and the quenching method is used to rapidly pour the molten alloy mixture into a cooling copper mold for cooling. The cooled product is crushed, and then the stirred ball milling method is used. Under vacuum conditions, the temperature is kept at 25℃, and 2 mm stainless steel balls are used for high-speed stirring and ball milling for 30 hours to prepare a pre-lithiated amorphous silicon-carbon composite.

[0128] (3) The product of step (2) is coated with lithium titanate at a mass percentage of 5% (relative to the amorphous silicon-carbon composite), and the prepared pre-lithiated amorphous silicon-carbon composite is uniformly mixed with titanium dioxide and lithium carbonate. In a high-purity argon (purity>99.0%) atmosphere, the temperature is raised from room temperature to 800°C at a rate of 5°C / min, maintained at this temperature for 2 hours, and naturally cooled to obtain a pre-lithiated lithium titanate-coated amorphous silicon-carbon composite.

[0129] (4) Urea and the pre-lithiated lithium titanate-coated amorphous silicon-carbon composite prepared in step (3) are mixed uniformly at a molar ratio of nitrogen to titanium of 0.5:1, and the temperature is raised to 700°C at a rate of 5°C / min under vacuum conditions, maintained at this temperature for 2 hours, and naturally cooled to obtain a pre-lithiated lithium nitride titanate-coated amorphous silicon-carbon composite.

[0130] (5) The pre-lithiated lithium titanate nitride-coated amorphous silicon-carbon composite prepared in step (4) is uniformly mixed with artificial graphite at a gram capacity of 500 mAh / g to prepare a negative electrode material.

[0131] Example 2

[0132] The preparation method of Example 2 is similar to that of Example 1, except that:

[0133] In step (1), 500 g of artificial graphite (purity > 98.0%) and 48 g of metallic lithium flakes (purity > 99.0%) are mixed in a reactor, heated and vacuumed for 2 hours, the temperature is kept constant at 500°C, and rapidly stirred for 10 hours. The vacuum is maintained during the stirring process to generate a golden graphite lithium compound LiC6.

[0134] In step (5), the gram capacity of the negative electrode material is 820 mAh / g.

[0135] Example 3

[0136] The preparation method of Example 3 is similar to that of Example 1, except that:

[0137] In step (2), silicon powder (purity>99.0%), titanium powder (purity>99.0%) and cobalt powder (purity>99.0%) were stirred and mixed uniformly according to the stoichiometric molar ratio of 9:0.2:0.8, and then the graphite lithium compound LiC prepared in step (1) was added according to the mass ratio of 80:20. 14.45 , placed in a vacuum melting furnace, the temperature is set to 1200℃, the melting time is 1 hour, the molten alloy mixture is cooled by a rapid nitrogen flow using an atomization method, the cooled product is crushed, and then the stirred ball milling method is used. Under vacuum conditions, the temperature is kept at 25℃, and a 2 mm stainless steel ball is used for high-speed stirring and ball milling for 24 hours to prepare a pre-lithiated amorphous silicon-carbon composite.

[0138] In step (5), the gram capacity of the negative electrode material is 510 mAh / g.

[0139] Example 4

[0140] The preparation method of Example 4 is similar to that of Example 1, except that:

[0141] In step (4), ethylenediamine and the pre-lithiated lithium titanate-coated amorphous silicon-carbon composite prepared in step (3) are mixed uniformly in a ratio of nitrogen to titanium of 0.3:1, and the temperature is raised to 850°C at a rate of 5°C / min under vacuum conditions, maintained at this temperature for 1 hour, and naturally cooled to obtain a pre-lithiated lithium nitride titanate-coated amorphous silicon-carbon composite.

[0142] In step (5), the gram capacity of the negative electrode material is 490 mAh / g.

[0143] Example 5

[0144] The preparation method of Example 5 is similar to that of Example 1, except that:

[0145] In step (1), 500 g of artificial graphite (purity>98.0%) and 48 g of metallic lithium flakes (purity>99.0%) were mixed in a reactor, heated and vacuumed for 0.5 hours, kept constant at 450°C, and rapidly stirred for 5 hours, maintaining vacuum during the stirring process, to generate a dark blue-black graphite lithium compound LiC 29 .

[0146] In step (5), the gram capacity of the negative electrode material is 485 mAh / g.

[0147] Example 6

[0148] The preparation method of Example 6 is similar to that of Example 1, except that:

[0149] In step (2), silicon powder (purity>99.0%), titanium powder (purity>99.0%), cobalt powder (purity>99.0%) and nickel powder (purity>99.0%) are stirred and mixed uniformly in a stoichiometric molar ratio of 8:1:0.5:0.5, and then the graphite lithium compound LiC prepared in step (1) is added in a mass ratio of 90:10. 14.45 , placed in a vacuum melting furnace, the temperature is set to 1200℃, the melting time is 1 hour, and the quenching method is used to rapidly pour the molten alloy mixture into a cooling copper mold for cooling. The cooled product is crushed, and then the stirred ball milling method is used. Under vacuum conditions, the temperature is constant at 25℃, and 2 mm stainless steel balls are used for high-speed stirring ball milling for 40 hours to prepare a lithiated amorphous silicon-carbon composite.

[0150] In step (5), the gram capacity of the negative electrode material is 540 mAh / g.

[0151] Example 7

[0152] The preparation method of Example 7 is similar to that of Example 1, except that:

[0153] In step (5), the pre-lithiated lithium titanate nitride-coated amorphous silicon-carbon composite prepared in step (4) is uniformly mixed with artificial graphite at a gram capacity of 450 mAh / g.

[0154] Example 8

[0155] The preparation method of Example 8 is similar to that of Example 1, except that:

[0156] In step (4), urea and ethylenediamine (molar ratio of 1:1) and the pre-lithiated lithium titanate-coated amorphous silicon-carbon composite prepared in step (3) are mixed uniformly in a ratio of nitrogen element to titanium element of 1:1, and the temperature is raised to 700°C at a rate of 5°C / min under vacuum conditions, maintained at this temperature for 2 hours, and naturally cooled to obtain a pre-lithiated lithium nitride titanate-coated amorphous silicon-carbon composite.

[0157] In step (5), the pre-lithiated lithium titanate nitride-coated amorphous silicon-carbon composite prepared in step (4) is uniformly mixed with artificial graphite at a gram capacity of 500 mAh / g.

[0158] Example 9

[0159] The preparation method of Example 9 is similar to that of Example 1, except that:

[0160] In step (1), 500 g of artificial graphite (purity> 98.0%) and 35 g of metallic lithium flakes (purity> 99.0%) were mixed in a reactor, heated and vacuumed for 0.5 hours, the temperature was kept constant at 350°C, and rapidly stirred for 3 hours, while maintaining vacuum during the stirring process, to generate brown graphite lithium compound LiC 8.3 .

[0161] In step (5), the pre-lithiated lithium titanate nitride-coated amorphous silicon-carbon composite prepared in step (4) is uniformly mixed with artificial graphite at a gram capacity of 600 mAh / g.

[0162] Comparative Example 1

[0163] Commercial silicon-carbon composite materials are evenly mixed with artificial graphite as negative electrode materials, and the gram capacity of the negative electrode material is 500mAh / g.

[0164] Comparative Example 2

[0165] Commercial silicon-carbon composite materials are evenly mixed with artificial graphite as negative electrode materials, and the gram capacity of the negative electrode material is 820mAh / g.

[0166] The negative electrode materials prepared in Examples 1-10 and Comparative Examples 1-2 or the lithium-ion batteries further prepared therefrom were subjected to relevant performance tests, and the test results are shown in Table 1 below.

[0167] Among them, the test conditions or test standards for each performance test item are as follows:

[0168] (1) SEM test of negative electrode materials

[0169] The surface morphology of the materials was measured on a JSM-6510 scanning electron microscope from JEOL, Japan, and an EV018 scanning electron microscope (SEM) from Zeiss, Germany. The X-ray energy scattering (EDS) spectrum and element surface distribution map were obtained on an Oxford X-MAX 20 energy spectrometer.

[0170] (2) Test of element mass percentage of negative electrode material

[0171] The mass percentage of element nickel was determined by gravimetric method; the mass percentage of element cobalt was determined by potentiometric titration; the mass percentage of element manganese was determined by titration; and the contents of other metal elements were determined by ICP method.

[0172] (3) XRD test of negative electrode materials

[0173] The crystal structure test was carried out on a D / max 2500VL / PC XRD diffractometer from Rigaku Corporation, Japan, using a copper target, with a test accuracy of ±0.02° and a scanning range of 5° to 90°.

[0174] (4) Electrochemical performance test of lithium-ion batteries

[0175] A 10mAh lithium-ion battery pair consisted of a pre-lithiated lithium nitride titanate coated with an amorphous silicon-carbon composite as the negative electrode and a 523-type lithium nickel cobalt manganese oxide as the positive electrode. The pair was charged at -40°C, 25°C, and 45°C at a constant current of 0.5C to 4.25V, then charged at a constant voltage to a current of 0.05C, allowed to rest for 5 minutes, and then discharged at a constant current of 0.5C to 3.0V. This constituted one charge-discharge cycle, and the discharge capacity at this point was recorded. The lithium-ion battery was cycled 200 times using this charge-discharge process, and the discharge capacity at the 200th cycle was recorded. The test data is summarized in Table 1 below.

[0176] Table 1

[0177]

[0178] from Figure 1-2 and Figure 4 It can be seen that the particle size distribution of the negative electrode material prepared in this application is relatively uniform; from Table 1 and Figure 5 、 Figure 6 It can be seen that compared with Comparative Examples 1-2, the negative electrode material prepared by the method of the present application greatly improves the initial charge and discharge coulombic efficiency (>90%), cycle capacity retention rate, low temperature and rate performance of the secondary battery.

[0179] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0180] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A method for preparing a negative electrode material, characterized in that: include: Composite treatment of graphite and lithium metal to obtain graphite lithium compound; alloying the graphite lithium compound with a first titanium source, a silicon source, and other metals to obtain a pre-lithiated amorphous silicon-carbon composite; Mixing and calcining the pre-lithiated amorphous silicon-carbon composite with a second titanium source and a lithium source to form a lithium titanate coating layer on at least a portion of the surface of the pre-lithiated amorphous silicon-carbon composite to obtain a pre-lithiated lithium titanate-coated amorphous silicon-carbon composite; and The pre-lithiated lithium titanate-coated amorphous silicon-carbon composite is nitrided to form a pre-lithiated lithium nitride titanate-coated amorphous silicon-carbon composite to obtain a negative electrode material, wherein the pre-lithiated lithium nitride titanate-coated amorphous silicon-carbon composite contains at least one of silicon nitride, carbon nitride, titanium nitride and lithium nitride.

2. The method according to claim 1, characterized in that The method satisfies at least one of the following conditions: (1) The temperature of the composite treatment is 200°C to 700°C; (2) The composite treatment time is 1 hour to 30 hours; (3) The environment of the composite treatment is a vacuum or inert atmosphere; (4) The molecular formula of the graphite lithium compound is LiC x , where X>6.

3. The method according to claim 2, characterized in that One or more of the following conditions are met: (1) The temperature of the composite treatment is 300° C. to 500° C.; (2) The time of the composite treatment is 5 hours to 15 hours.

4. The method according to claim 1, wherein Alloying the graphite lithium compound with the first titanium source, the silicon source and other metals, including: Melting and mixing the graphite lithium compound, the first titanium source, the silicon source, and the other metals to form an alloy composite material; The alloy composite material is subjected to amorphization and granulation treatment by a ball milling method.

5. The method according to claim 4, characterized in that Before the alloy composite material is subjected to amorphization and granulation treatment by ball milling, the method further comprises: The alloy composite material is subjected to an amorphization treatment by a quenching method or an atomization method.

6. The method according to claim 4 or 5, characterized in that The temperature of the melt mixing is 1000°C to 2000°C.

7. The method according to claim 6, characterized in that The temperature of the melt mixing is 1100°C to 1500°C.

8. The method according to any one of claims 1, 4 or 5, characterized in that The method satisfies at least one of the following conditions: (1) The molar ratio of the graphite lithium compound, the mixture of the first titanium source and the silicon source, and the other metal is (99-60):(0.1-30):(0.01-20); (2) The first titanium source is titanium element; (3) The silicon source is silicon element; (4) The other metals include one or more of cobalt, manganese, nickel, indium, aluminum, iron, magnesium, copper, zirconium, niobium, antimony, bismuth, vanadium, zinc, germanium, palladium, molybdenum, and tungsten.

9. The method according to claim 8, characterized in that The molar ratio of the graphite lithium compound, the mixture of the first titanium source and the silicon source, and the other metals is (90-75):(10-25):(1-10).

10. The method according to claim 1, characterized in that The method satisfies at least one of the following conditions: (1) The second titanium source is one or more of titanium dioxide, methyl titanate, ethyl titanate, n-propyl titanate, tetrabutyl titanate, and tetraisopropyl titanate; (2) The lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium acetate, lithium oxide and lithium nitride; (3) the molar ratio of the second titanium source to the pre-lithiated amorphous silicon-carbon composite is 0.01 to 10; (4) The molar ratio of the second titanium source to the lithium source is 1.25:(1-1.10); (5) The calcination temperature is 500° C. to 1000° C. (6) The calcination time is 5 hours to 30 hours.

11. The method according to claim 10, characterized in that One or more of the following conditions are met: (1) The calcination temperature is 700° C. to 900° C. (2) The calcination treatment time is 10 hours to 20 hours.

12. The method according to claim 1, characterized in that The pre-lithiated lithium titanate-coated amorphous silicon-carbon composite is subjected to nitriding treatment, comprising: The pre-lithiated lithium titanate-coated amorphous silicon-carbon composite is reacted with a nitrogen source to form the pre-lithiated lithium nitride titanate-coated amorphous silicon-carbon composite through a nitridation reaction.

13. The method according to claim 12, characterized in that The method satisfies at least one of the following conditions: (1) The nitrogen source includes at least one of ammonia, urea, ethylenediamine and nitrogen-containing ionic liquid; (2) The temperature of the nitriding treatment is 300° C. to 1000° C.; (3) The nitriding treatment time is 5h to 30h; (4) The nitriding treatment is carried out in a vacuum or inert atmosphere.

14. The method according to claim 13, characterized in that One or more of the following conditions are met: (1) The temperature of the nitriding treatment is 500° C. to 700° C.; (2) The nitriding treatment time is 5 hours to 10 hours.

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