Negative electrode material with morphology-controllable surface carbon coating layer, preparation method of negative electrode material and lithium ion battery

Abstract

The invention provides a negative electrode material with a morphology-controllable surface carbon coating layer, a preparation method of the negative electrode material and a lithium ion battery, and relates to the technical field of lithium ion batteries. The preparation method of the negative electrode material comprises the following steps: putting a negative electrode material precursor into a gas-phase reaction furnace, introducing an organic carbon source gas and a carrier gas, and carrying out heating reaction to carry out gas-phase carbon coating treatment; in the reaction process, the volume ratio of C6H6 gas to C2H2 gas in the tail gas of the gas-phase reaction furnace is controlled, the negative electrode material with the surface carbon coating layer controllable in morphology is obtained, and if the volume ratio of C6H6 to C2H2 is larger than 2 and smaller than or equal to 8, the carbon coating layer is in an onion shape; and if the volume ratio of C6H6 to C2H2 is between 0.5 and 2, the carbon coating layer is in a burr shape. According to the preparation method of the negative electrode material, accurate control of the morphology structure of the surface carbon coating layer can be realized, so that the stability of the carbon-coated modified negative electrode material in a battery system is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly to a negative electrode material with a controllable morphology of a surface carbon coating layer, a preparation method thereof, and a lithium-ion battery including the negative electrode material with a controllable morphology of the surface carbon coating layer. Background Art

[0002] With the development of the electric vehicle industry, the performance requirements for power batteries are also getting higher and higher. Especially nowadays, the battery system puts forward higher requirements for the fast charging performance of lithium battery negative electrode materials, requiring the negative electrode materials to have a fast lithium ion insertion / extraction rate and electron conductivity to meet the fast charging requirements of the battery. The most common modification method is carbon coating on the surface of the negative electrode material, and the carbon coating methods can be divided into solid-phase carbon coating, liquid-phase carbon coating, and gas-phase carbon coating. Due to the advantages of uniform coating effect and controllable coating thickness, the gas-phase carbon coating process has gradually become the mainstream solution for carbon coating modification means.

[0003] For the continuous gas-phase carbon coating process, the coating reaction time is long, and the composition of the system is complex. The morphological structure of the surface carbon coating layer of the materials produced and prepared under different conditions may often have certain fluctuations, which in turn affects the stable performance of the materials in the battery system. For example, Patent CN115188938A discloses a silicon negative electrode material, a preparation method of a silicon-containing negative electrode, and a battery thereof. A stable and continuous core-shell coating structure is constructed by a double-layer coating carbon layer. The reversible capacity of the material reaches 1424 mAh / g, the initial efficiency is 87.8%, and the pole piece swelling rate after 50 cycles is 102%. Although this method adopts a double-layer coating structure to enhance the stability of the carbon coating layer, the carbon coating layer is too thick, which will further slow down the rapid insertion and extraction of lithium ions and affect the capacity performance of the material; Patent CN113991090B designs from the perspectives of particle size, reactor structure, etc. to construct a stable core-shell coating layer on the surface of the material to improve the conductivity of the material, the rate performance, and the cycle performance of the battery. Although the granulation method is used to adjust the particle size to facilitate the formation of a dense coating layer on the particle surface, there are still uncoated surfaces inside the composite particles, which are prone to particle disintegration during the cycling process, and the uncoated surfaces are exposed to the electrolyte to continuously cause the consumption of active lithium.

[0004] Therefore, how to ensure the stability and controllability of the prepared negative electrode materials during the gas-phase carbon coating process has become an urgent problem to be solved. Summary of the Invention

[0005] Aiming at the above problems existing in the prior art, the purpose of the present invention is to provide a negative electrode material with a controllable morphology of a surface carbon coating layer and a preparation method thereof. The method is to control C in the tail gas during the process of gas-phase carbon coating on the surface of the negative electrode material 2 H2 (acetylene) gas and C 6 H 6 (benzene) gas volume ratio, so as to achieve controllable morphology and structure of the carbon coating layer on the surface of the negative electrode material.

[0006] Another object of the present invention is to provide the application of the above negative electrode material in a lithium-ion battery. The negative electrode material with a controllable morphology of the surface carbon coating layer prepared by the method of the present invention improves the stability of the lithium-ion battery system.

[0007] In the experiment of gas-phase carbon coating on the surface of the negative electrode material of the present invention, it was unexpectedly found that the operating temperature under this reaction condition is relatively high, generally in the range of 600 - 1000 °C. During the reaction process of chemical vapor deposition high-temperature carbon coating treatment, C 2 H 2 (acetylene) and C 6 H 6 (benzene) gas are generated, which is related to the morphology of the generated carbon coating layer. It was found that by controlling the ratio of C 2 H 2 and C 6 H 6 in the tail gas discharged from the gas-phase reaction furnace, the morphology of the carbon coating layer on the surface of the negative electrode material can be controlled. And, since the temperature of the tail gas discharged from the reaction furnace is still relatively high (usually > 100 °C), the benzene in it still exists in a gaseous form. After a long time of cooling, the macromolecular aromatic hydrocarbon components in the tail gas will condense into a viscous liquid phase. Therefore, the present invention specifically controls the volume ratio of C 2 H 2 (acetylene) and C 6 H 6 (benzene) gas in the tail gas discharged from the gas-phase reaction furnace.

[0008] To achieve the above object, the technical solution of the present application is as follows:

[0009] The first aspect of the present invention provides a preparation method of a negative electrode material with a controllable morphology of the surface carbon coating layer, and the steps include:

[0010] Put the negative electrode material precursor into a gas-phase reaction furnace, introduce an organic carbon source gas and a carrier gas, and raise the temperature for reaction to carry out gas-phase carbon coating treatment;

[0011] During the reaction process, control the volume ratio of C 6 H 6 (benzene) gas and C 2 H 2 (acetylene) gas in the tail gas of the gas-phase reaction furnace to obtain a negative electrode material with a controllable morphology of the surface carbon coating layer, where

[0012] If C 6 H 6 : C2 H 2 The volume ratio of is >2 and ≤8, preferably ≥3 and ≤5, and the morphology of the carbon coating layer is "onion-like";

[0013] If C 6 H 6 : C 2 H 2 The volume ratio of is between 0.5 and 2, preferably between 1 and 2, and the morphology of the carbon coating layer is "burr-like".

[0014] In some specific examples of the present invention, the anode material precursor is selected from at least one of graphite anode materials, silicon-oxygen anode materials, and silicon-carbon anode materials, preferably silicon monoxide anode materials.

[0015] In some specific examples of the present invention, the organic carbon source gas is selected from at least one of C1-C4 alkanes, C1-C4 alkenes, and C1-C4 alkynes.

[0016] In some specific examples of the present invention, the carrier gas is selected from at least one of nitrogen and inert gases, preferably at least one of nitrogen, argon, and helium.

[0017] In some specific examples of the present invention, the gas-phase reaction furnace is selected from a continuous rotary kiln and a fluidized bed gas-phase reaction furnace;

[0018] Preferably, a tail gas monitoring device is provided at the exhaust end of the gas-phase reaction furnace for detecting the content of C 6 H 6 gas and C 2 H 2 gas in the tail gas of the gas-phase reaction furnace during the treatment process;

[0019] Preferably, the setting of the tail gas monitoring device includes: reserving a gas detection interface at the exhaust end of the gas-phase reaction furnace, leading the discharged gas to a gas chromatograph analyzer through a pipeline, and analyzing in real time to obtain the content of C 6 H 6 and C 2 H 2 gas in the tail gas.

[0020] In some specific examples of the present invention, the flow rate of the organic carbon source gas introduced into the gas-phase reaction furnace is 50-150 L / h, preferably 60-90 L / h.

[0021] In some specific examples of the present invention, the flow rate ratio of the carrier gas to the organic carbon source gas introduced into the gas-phase reaction furnace is 0.1-10:1, preferably 0.2-3:1.

[0022] In some specific examples of the present invention, during the gas-phase carbon coating treatment process, the reaction temperature is 600 - 1000 °C, preferably 800 - 900 °C; the reaction time is 1 - 5 h, preferably 2 - 3 h; the reaction pressure is 10 - 1000 PaG, preferably 20 - 200 PaG.

[0023] The second aspect of the present invention provides a negative electrode material with a controllable surface carbon coating layer morphology, which is prepared by using the preparation method of the above negative electrode material.

[0024] The third aspect of the present invention provides a lithium-ion battery, including the above negative electrode material with a controllable surface carbon coating layer morphology.

[0025] In some preferred examples of the present invention, in the lithium-ion battery, using a negative electrode material with a burr-shaped carbon coating layer can shorten the transmission path of lithium ions, making the battery more advantageous in rate performance; using a negative electrode material with an onion-shaped carbon coating layer, due to the smaller specific surface area, the fabricated battery has more advantages in cycle performance.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] In the gas-phase carbon coating process of the present invention, by controlling the volume ratio of C 6 H 6 : C 2 H 2 in the tail gas to fluctuate within a certain range, the morphology structure of the carbon layer on the surface of the negative electrode material can be controlled, thereby improving the stability of the negative electrode material.

[0028] The negative electrode material prepared by the method of the present invention can achieve precise control of the morphology structure of the carbon coating layer on the surface of the negative electrode material, thereby solving the technical problem of unstable surface morphology of the negative electrode material prepared in the continuous gas-phase coating process, and improving the stability of the carbon-coated modified negative electrode material in the battery system. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application and should not be regarded as limiting the scope of the present application.

[0030] Figure 1 TEM pictures (20 nm, 5 nm) of the "burr-shaped" carbon layer morphology of carbon-coated silicon suboxide prepared in Example 1;

[0031] Figure 2 TEM pictures (20 nm, 5 nm) of the "onion-shaped" carbon layer morphology of carbon-coated silicon suboxide prepared in Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0032] As used herein, the terms:

[0033] The terms "comprising", "including", "having", "containing", or any other variation thereof as used herein are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that comprises the recited elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0034] When a volume ratio, flow rate, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values and lower preferred values, this should be understood to specifically disclose all ranges formed by any pairing of any upper range limit or preferred value with any lower range limit or preferred value, whether or not the ranges are separately disclosed. For example, when the range "1 to 5" is disclosed, the described range should be interpreted to include the ranges "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values and all integers and fractions within the range.

[0035] "And / or" is used to indicate that either or both of the stated circumstances may occur, e.g., A and / or B includes (A and B) and (A or B).

[0036] This application provides a method for preparing a negative electrode material with a controllable surface carbon coating morphology, and the steps include:

[0037] Put the negative electrode material precursor into a gas-phase reaction furnace, introduce an organic carbon source gas and a carrier gas, and raise the temperature for reaction to perform gas-phase carbon coating treatment;

[0038] During the reaction, control the volume ratio of C 6 H 6 gas and C 2 H 2 gas in the tail gas of the gas-phase reaction furnace to obtain a negative electrode material with a controllable surface carbon coating morphology, wherein,

[0039] If the volume ratio of C 6 H 6 : C 2 H 2 > 2 and ≤ 8, such as 2.1, 2.5, 3, 4, 5, 6, 7, 8, preferably ≥ 3 and ≤ 5, the carbon coating morphology is "onion-like";

[0040] If the volume ratio of C 6 H 6 : C 2 H 2The volume ratio is between 0.5 and 2, such as 0.5, 1, 1.5, 2, preferably between 1 and 2, and the morphology of the carbon coating layer is "burr-like".

[0041] Among them, a tail gas monitoring device is arranged at the exhaust end of the gas-phase reaction furnace to detect C in the tail gas 6 H 6 and C 2 H 2 gas concentrations, and then the volume ratio of C 6 H 6 : C 2 H 2 gas can be analyzed and calculated. By regulating the reaction conditions during the gas-phase carbon coating treatment in the gas-phase reaction furnace, it can be ensured that the volume ratio of C 6 H 6 and C 2 H 2 gas in the tail gas discharged from the gas-phase reaction furnace fluctuates within a certain range, and finally the morphology of the carbon layer on the surface of the prepared negative electrode material is controllable.

[0042] Specifically, when the volume ratio of C 6 H 6 : C 2 H 2 gas > 2 and ≤ 8, the morphology of the carbon layer on the surface of the negative electrode material prepared by gas-phase carbon coating is "onion-like"; when the volume ratio of C 6 H 6 : C 2 H 2 gas is between 0.5 and 2, for example, it can be 0.5, 1, 1.5, 2 or any value between 0.5 and 2, the morphology of the carbon layer on the surface of the negative electrode material prepared by gas-phase carbon coating is "burr-like".

[0043] In a preferred embodiment, the negative electrode material precursor is selected from at least one of a graphite negative electrode material, a silicon-oxygen negative electrode material, and a silicon-carbon negative electrode material. Among them, the negative electrode material precursor refers to a negative electrode material whose surface has not been modified by carbon layer coating.

[0044] Considering factors such as the material performance and cost after carbon coating on the surfaces of different types of negative electrode material precursors using gas-phase carbon coating, the initial negative electrode material used in the present invention is preferably a silicon monoxide negative electrode material when using gas-phase carbon coating.

[0045] In a preferred embodiment, the organic carbon source gas is selected from at least one of C1-C4 alkanes, C1-C4 alkenes, and C1-C4 alkynes. For example, at least one gas such as methane, ethane, ethylene, acetylene, propane, propylene, and propyne can be selected as the organic carbon source gas in the gas-phase carbon coating.

[0046] In a preferred embodiment, the carrier gas is selected from at least one of nitrogen and inert gases. Preferably, the carrier gas is selected from at least one of nitrogen, argon, and helium.

[0047] In the present invention, the C 6 H 6 gas and the C 2 H 2 gas in the tail gas of the gas-phase reaction furnace are generated during the gas-phase carbon coating process, wherein the gaseous C 6 H 6 (benzene) is generated by high-temperature addition cyclization of small molecule raw material gases. C 2 H 2 is not only the gas raw material introduced into the reaction, but also generated by high-temperature dehydrogenation of larger small molecule gases (such as C3 and C4) during the reaction process or is a by-product during the cyclization process. The volume ratio of the two is affected by reaction conditions, including the gas-phase reaction temperature, the flow rate of the organic carbon source gas, the ratio of the flow rate of the carrier gas to the flow rate of the organic carbon source gas, etc. The present invention finds that by controlling these reaction conditions within a certain range, the volume ratio of these two gases in the tail gas can be ensured to fluctuate within the corresponding range, thereby realizing the controllable morphology and structure of the carbon coating layer on the surface of the negative electrode material. Specifically, the regulation process of the reaction conditions is a conventional operation in the chemical field, and the present invention does not make special explanations; for example, if the volume ratio of C 6 H 6 : C 2 H 2 is between 0.5 and 2, the volume ratio of C 6 H 6 : C 2 H 2 in the tail gas can be made >2 and ≤8 by at least one of the methods of increasing the reaction temperature of the gas-phase reaction furnace, decreasing the ratio of the flow rate of the carrier gas to the flow rate of the organic carbon source gas, and increasing the flow rate of the organic carbon source gas.

[0048] In a preferred embodiment, the reaction conditions for adjusting the gas-phase carbon coating treatment in the present invention include: gas-phase reaction temperature, flow rate of the organic carbon source gas, and ratio of the flow rate of the carrier gas to the flow rate of the organic carbon source gas;

[0049] It should be noted that by regulating these reaction conditions, the reaction rate of converting the organic carbon source into the carbon coating layer can be adjusted. If the reaction temperature is too high and the gas flow rate of the organic carbon source gas is too large, the formation rate of the carbon coating layer can be accelerated.

[0050] In a preferred embodiment, the flow rate of the organic carbon source gas introduced into the gas-phase reaction furnace is 50 - 150 L / h, such as 50 L / h, 70 L / h, 90 L / h, 110 L / h, 130 L / h, 150 L / h, preferably 60 - 90 L / h.

[0051] In a preferred embodiment, the flow rate ratio of the carrier gas to the organic carbon source gas introduced into the gas-phase reaction furnace is 0.1 - 10:1, such as 0.1:1, 0.5:1, 1:1, 3:1, 5:1, 7:1, 10:1, preferably 0.2 - 3:1.

[0052] In a preferred embodiment, during the gas-phase carbon coating treatment process, the reaction temperature is 600 - 1000 °C, such as 600 °C, 700 °C, 800 °C, 900 °C, 1000 °C, preferably 800 - 900 °C; the reaction time is 1 - 5 h, such as 1 h, 2 h, 3 h, 4 h, 5 h, preferably 2 - 3 h; the reaction pressure is 10 - 1000 PaG, such as 10 PaG, 50 PaG, 100 PaG, 300 PaG, 500 PaG, 700 PaG, 900 PaG, 1000 PaG, preferably 20 - 200 PaG.

[0053] In a preferred embodiment, the gas-phase reaction furnace is a continuous rotary kiln, and a tail gas monitoring device is provided at its exhaust end; the setting of the tail gas monitoring device includes: reserving a gas detection interface at the exhaust end of the kiln tail of the continuous rotary kiln, leading the discharged gas through a pipeline to a gas chromatograph analyzer, and obtaining the C 6 H 6 and C 2 H 2 gas content in the tail gas by real-time analysis.

[0054] It should be noted that using a continuous rotary furnace can continuously and mass-produce anode materials with a surface modified by a carbon coating layer. However, in the existing process, during continuous production, if the reaction parameters in the rotary furnace change, it will affect the morphology of the carbon coating layer on the surface of the finally prepared anode material, and further cause changes in the performance of the anode material. Therefore, by using the technical solution of the present invention, at the exhaust end of the kiln tail of the continuous rotary kiln, by setting a tail gas detection device that can detect the C 6 H 6 and C 2 H 2 gas concentration, comparing the two gas contents, if it is found that C 6 H 6 : C 2 H 2If the gas volume ratio of [C][H] has been between 0.5 and 2, or has been at a value greater than 2 and less than or equal to 8, then by maintaining the conditions of the relevant gas-phase reaction to ensure stable gas-phase deposition, a negative electrode material with a consistent surface carbon layer morphology can be obtained.

[0055] Further, if it is found that the gas volume ratio value of [C][H] at the exhaust end of the continuous rotary kiln has a tendency to gradually increase from low and approach 2, then it is necessary to appropriately lower the reaction temperature and / or reduce the flow rate of the organic carbon source gas, or increase the flow rate ratio of the carrier gas to the organic carbon source gas, etc., to ensure that the gas volume ratio of [C][H] can be maintained between 0.5 and 2 all the time. In this way, during the entire gas-phase coating process, a negative electrode material with a burr-like surface carbon layer morphology can be prepared; if the gas volume ratio of [C][H] at the exhaust end is greater than 2 and less than or equal to 8, but after a certain reaction time, this volume ratio value gradually decreases and approaches 2, then it is necessary to increase the gas-phase reaction rate, by appropriately increasing the reaction temperature and / or increasing the gas flow rate of the organic carbon source gas, or reducing the gas flow rate ratio of the carrier gas to the organic carbon source gas, etc., so that the negative electrode materials prepared during the entire gas-phase coating process all have an onion-like surface carbon coating layer morphology. 6 H 6 :[C] 2 H 2 If the gas volume ratio value of [C][H] has a tendency to gradually increase from low and approach 2, then it is necessary to appropriately lower the reaction temperature and / or reduce the flow rate of the organic carbon source gas, or increase the flow rate ratio of the carrier gas to the organic carbon source gas, etc., to ensure that the gas volume ratio of [C][H] can be maintained between 0.5 and 2 all the time. In this way, during the entire gas-phase coating process, a negative electrode material with a burr-like surface carbon layer morphology can be prepared; if the gas volume ratio of [C][H] at the exhaust end is greater than 2 and less than or equal to 8, but after a certain reaction time, this volume ratio value gradually decreases and approaches 2, then it is necessary to increase the gas-phase reaction rate, by appropriately increasing the reaction temperature and / or increasing the gas flow rate of the organic carbon source gas, or reducing the gas flow rate ratio of the carrier gas to the organic carbon source gas, etc., so that the negative electrode materials prepared during the entire gas-phase coating process all have an onion-like surface carbon coating layer morphology. 6 H 6 :[C] 2 H 2 If the gas volume ratio value of [C][H] has a tendency to gradually increase from low and approach 2, then it is necessary to appropriately lower the reaction temperature and / or reduce the flow rate of the organic carbon source gas, or increase the flow rate ratio of the carrier gas to the organic carbon source gas, etc., to ensure that the gas volume ratio of [C][H] can be maintained between 0.5 and 2 all the time. In this way, during the entire gas-phase coating process, a negative electrode material with a burr-like surface carbon layer morphology can be prepared; if the gas volume ratio of [C][H] at the exhaust end is greater than 2 and less than or equal to 8, but after a certain reaction time, this volume ratio value gradually decreases and approaches 2, then it is necessary to increase the gas-phase reaction rate, by appropriately increasing the reaction temperature and / or increasing the gas flow rate of the organic carbon source gas, or reducing the gas flow rate ratio of the carrier gas to the organic carbon source gas, etc., so that the negative electrode materials prepared during the entire gas-phase coating process all have an onion-like surface carbon coating layer morphology. 6 H 6 :[C] 2 H 2 If the gas volume ratio of [C][H] is greater than 2 and less than or equal to 8, but after a certain reaction time, this volume ratio value gradually decreases and approaches 2, then it is necessary to increase the gas-phase reaction rate, by appropriately increasing the reaction temperature and / or increasing the gas flow rate of the organic carbon source gas, or reducing the gas flow rate ratio of the carrier gas to the organic carbon source gas, etc., so that the negative electrode materials prepared during the entire gas-phase coating process all have an onion-like surface carbon coating layer morphology.

[0056] In another preferred embodiment of the present invention, the gas-phase reaction furnace can also be other devices capable of chemical vapor deposition, such as a fluidized bed. Similarly, the gas concentrations of [C][H] and [C][H] in the tail gas at the exhaust end of the fluidized bed can be detected, and then the gas volume ratio of the two can be analyzed and calculated, so as to further regulate the production conditions in the fluidized bed to make the morphology structure of the surface carbon layer of the prepared negative electrode material controllable. 6 H 6 and [C] 2 H 2 In another preferred embodiment of the present invention, the gas-phase reaction furnace can also be other devices capable of chemical vapor deposition, such as a fluidized bed. Similarly, the gas concentrations of [C][H] and [C][H] in the tail gas at the exhaust end of the fluidized bed can be detected, and then the gas volume ratio of the two can be analyzed and calculated, so as to further regulate the production conditions in the fluidized bed to make the morphology structure of the surface carbon layer of the prepared negative electrode material controllable.

[0057] The present invention also provides a negative electrode material with a controllable surface carbon coating layer morphology, which is prepared by using the above-mentioned method for preparing a negative electrode material.

[0058] The present invention also provides a lithium-ion battery, including the above-mentioned negative electrode material with a controllable surface carbon coating layer morphology.

[0059] By making the negative electrode material into a negative electrode plate and then assembling it with other structures in the battery, a lithium-ion battery is prepared.

[0060] The method of making the negative electrode material into a negative electrode plate and the method of assembling the negative electrode plate with other structures in the battery into a battery in the present invention are all prior arts and are not particularly limited. Those skilled in the art can screen and combine according to needs through existing disclosed methods to prepare, for example, they can refer to the methods disclosed in patents CN115132982A, CN117038928A, etc. to prepare.

[0061] The following will describe the implementation schemes of the present application in detail with specific examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. For those not specified in the examples, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0062] Example 1

[0063] Prepare a silicon suboxide negative electrode material with a carbon coating layer on the surface, and the morphology of the carbon coating layer is "burr-like". The steps are as follows:

[0064] Put the silicon suboxide negative electrode material without carbon coating layer modification on the surface into a rotary kiln equipment, evacuate to a negative pressure of -15 kPaG after sealing, then introduce carrier gas nitrogen for protection, and at the same time heat the rotary kiln. When the temperature reaches 800 °C, then introduce a mixed organic carbon source gas of methane and acetylene (the mixed volume ratio of methane and acetylene is 8:2) into the rotary kiln. The gas flow rate of the mixed organic carbon source gas is 90 L / h, and the gas flow rate of the carrier gas is 1.5 times that of the mixed organic carbon source gas flow rate;

[0065] Leave a gas detection interface at the exhaust end of the kiln furnace of the rotary kiln, and introduce the exhaust gas in the kiln furnace into a gas chromatograph online analyzer for analysis to obtain the gas concentrations of C 2 H 2 and C 6 H 6 in real time, and at the same time analyze to obtain the gas volume ratio of C 6 H 6 : C 2 H 2 ;

[0066] Under the above reaction conditions, the gas volume ratio of C 6 H 6 : C 2 H 2The volume ratio is 1 - 1.5. Meanwhile, when the flow rate of the organic carbon source gas is 75 - 105 L / h and the flow rate ratio of the carrier gas to the organic carbon source gas is 1.3 - 1.7:1, the reaction pressure is 10 - 50 PaG, and the reaction temperature is within the range of 750 - 850 °C, the reaction conditions are regulated, and the reaction lasts for 2 h. During this period, it is ensured that the volume ratio of C 6 H 6 :C 2 H 2 in the gas discharged from the tail end of the kiln furnace is always between 0.5 - 2, thereby obtaining a silicon monoxide negative electrode material with a burr-like surface carbon-coated morphology, and the morphology is as shown in Figure 1 shown.

[0067] As shown in Figure 1 shown, when the carbon-coated layer has a burr-like morphological feature, the carbon layer structure is perpendicular to the surface of the matrix. When the lithiation reaction occurs, lithium ions quickly embed into the interior of the matrix from between the layers, and the transmission path is more direct, improving the lithium ion transmission rate, enabling ions and electrons to quickly reach the surface of the matrix, and thus having advantages in high capacity and rate performance.

[0068] Example 2

[0069] Prepare a silicon monoxide negative electrode material with a carbon-coated layer on the surface, and the morphology of the carbon-coated layer is "onion-like". The steps are as follows:

[0070] Put the silicon monoxide negative electrode material without carbon-coated layer modification on the surface into a rotary kiln device, evacuate to a negative pressure of -15 kPaG after sealing, and then introduce the carrier gas nitrogen for protection. At the same time, heat up the rotary kiln. When the temperature reaches 900 °C, then introduce the organic carbon source gas of ethane and propyne (the mixed volume ratio of ethane and propyne is 2:8) into the rotary kiln, and the gas flow rate of the mixed organic carbon source gas is 60 L / h. The gas flow rate of the carrier gas is 8 times that of the mixed organic carbon source gas flow rate;

[0071] Leave a gas detection interface at the exhaust of the kiln furnace at the tail end of the rotary kiln, introduce the waste gas discharged from the kiln furnace into a gas chromatograph online analyzer through a pipeline for analysis, and obtain the gas concentration of C 2 H 2 and C 6 H 6 in the tail gas in real time. At the same time, analyze and obtain the gas volume ratio of C 6 H 6 :C 2 H 2 ;

[0072] Under the above reaction conditions, it is tested that the volume ratio of C 6 H 6 :C 2 H 2The volume ratio is 3 - 5. Meanwhile, when the flow rate of the organic carbon source gas is 50 - 70 L / h, the flow rate ratio of the carrier gas to the organic carbon source gas is 7 - 9.5:1, the reaction pressure is 800 - 1000 PaG, and the reaction temperature is in the range of 850 - 950 °C, adjust the reaction conditions and react for 3 h. During this period, ensure that the volume ratio of C 6 H 6 : C 2 H 2 in the gas discharged from the tail end of the kiln is > 2 and ≤ 8, so as to obtain a silicon monoxide negative electrode material with an onion-like surface carbon-coated morphology, and the morphology is as shown in Figure 2 shown.

[0073] As shown in Figure 2 shown, when the carbon-coated layer has an onion-like morphological feature, the carbon layer structure is parallel to the substrate surface, which can cover the holes, defects, etc. on the original substrate surface, slow down the irreversible lithium consumption generated during the first lithium intercalation, and thus has the advantages of high capacity, high initial efficiency and storage performance.

[0074] Example 3

[0075] Prepare a graphite negative electrode material with a carbon-coated layer on the surface. The morphology of the carbon-coated layer is "burr-like". The steps are as follows:

[0076] Put the graphite material without carbon-coated layer modification on the surface into a box furnace equipment, evacuate to a negative pressure of -5 kPaG after sealing, and then introduce the carrier gas nitrogen for protection. At the same time, heat up the box furnace. When the temperature reaches 600 °C, then introduce the organic carbon source gas of methane and ethylene (the mixed volume ratio of methane and ethylene is 4:6) into the box furnace. The gas flow rate of the mixed organic carbon source gas is 50 L / h, and the gas flow rate of the carrier gas is 0.3 times that of the mixed organic carbon source gas;

[0077] Leave a gas detection interface at the exhaust end of the tail of the box furnace, introduce the waste gas discharged from the kiln into a gas chromatograph online analyzer through a pipeline for analysis, and obtain the gas concentrations of C 2 H 2 and C 6 H 6 in the tail gas in real time. At the same time, analyze and obtain the gas volume ratio of C 6 H 6 : C 2 H 2 ;

[0078] Under the above reaction conditions, it is tested that the volume ratio of C 6 H 6 : C 2 H 2The volume ratio is 0.6 - 0.9. Meanwhile, when the flow rate of the organic carbon source gas is 50 - 80 L / h, the flow rate ratio of the carrier gas to the organic carbon source gas is 0.2 - 0.5:1, the reaction pressure is 50 - 200 PaG, and the reaction temperature is within the range of 600 - 700 °C, the reaction conditions are regulated, and the reaction lasts for 5 h. During this period, it is ensured that in the gas discharged from the tail end of the furnace, the C 6 H 6 :C 2 H 2 volume ratio has been between 0.5 - 2, thereby obtaining a silicon monoxide negative electrode material with a burr-like surface carbon-coated morphology.

[0079] Example 4

[0080] To prepare a graphite negative electrode material with a carbon-coated layer on the surface, and the morphology of the carbon-coated layer is "onion-like". The steps are as follows:

[0081] Put the graphite material without carbon-coated layer modification on the surface into a box furnace equipment, evacuate to a negative pressure of -5 kPaG after sealing, and then introduce the carrier gas nitrogen for protection. At the same time, heat up the box furnace. When the temperature reaches 1000 °C, then introduce an organic carbon source gas of propane and propylene (the mixed volume ratio of propane and propylene is 5:5) into the box furnace. The gas flow rate of the mixed organic carbon source gas is 150 L / h, and the gas flow rate of the carrier gas is 4 times that of the mixed organic carbon source gas flow rate;

[0082] Leave a gas detection interface at the exhaust of the tail end of the box furnace, introduce the waste gas discharged from the kiln furnace into a gas chromatograph online analyzer through a pipeline for analysis, and obtain the C 2 H 2 and C 6 H 6 gas concentrations in the tail gas in real time, and at the same time analyze and obtain the C 6 H 6 :C 2 H 2 gas volume ratio;

[0083] Under the above reaction conditions, it is tested that the C 6 H 6 :C 2 H 2 volume ratio is 5 - 8. Meanwhile, when the flow rate of the organic carbon source gas is 120 - 150 L / h, the flow rate ratio of the carrier gas to the organic carbon source gas is 3 - 5:1, the reaction pressure is 600 - 800 PaG, and the reaction temperature is within the range of 900 - 1000 °C, the reaction conditions are regulated, and the reaction lasts for 1 h. During this period, it is ensured that in the gas discharged from the tail end of the furnace, the C 6 H 6 :C 2 H 2The volume ratio has been between >2 and ≤8, thereby obtaining a silicon monoxide negative electrode material with a burr-like surface carbon-coated morphology.

[0084] Comparative Example 1

[0085] Referring to the method of Example 1, the only difference is that: within the range where the flow rate of the organic carbon source gas is 75 - 105 L / h, the flow rate ratio of the carrier gas to the organic carbon source gas is 1.3 - 1.7:1, and the reaction temperature is 750 - 850 °C, the reaction conditions are regulated, and the reaction is carried out for 2 h. During this period, C in the gas discharged from the tail end of the kiln 6 H 6 :C 2 H 2 The volume ratio has been <0.5, obtaining a surface carbon-coated silicon monoxide negative electrode material with a morphology similar to "onion-like".

[0086] Comparative Example 2

[0087] Referring to the method of Example 1, the only difference is that: within the range where the flow rate of the organic carbon source gas is 75 - 105 L / h, the flow rate ratio of the carrier gas to the organic carbon source gas is 1.3 - 1.7:1, and the reaction temperature is 750 - 850 °C, the reaction conditions are regulated, and the reaction is carried out for 3 h. During this period, C in the gas discharged from the tail end of the kiln 6 H 6 :C 2 H 2 The volume ratio is between 0.5 - 4, obtaining a surface carbon-coated silicon monoxide negative electrode material with a morphology similar to "burr-like".

[0088] Comparative Example 3

[0089] Referring to the method of Example 3, the only difference is that: within the range where the flow rate of the organic carbon source gas is 50 - 80 L / h, the flow rate ratio of the carrier gas to the organic carbon source gas is 0.2 - 0.5:1, and the reaction temperature is 600 - 700 °C, the reaction conditions are regulated, and the reaction is carried out for 5 h. During this period, C in the gas discharged from the tail end of the furnace 6 H 6 :C 2 H 2 The volume ratio is between 0.5 - 4, obtaining a surface carbon-coated graphite negative electrode material with a morphology similar to "burr-like".

[0090] Prepare lithium-ion batteries containing the anode materials prepared in the above Examples 1-4 and Comparative Examples 1-3, and conduct electrochemical performance tests on the lithium-ion batteries. Refer to the existing method: During the preparation of the anode electrode, use this anode material as the active substance, use polyacrylic acid as the binder, and add conductive acetylene black. The ratio is: active substance: acetylene black: polyacrylic acid = 8:1:1. Add an appropriate amount of deionized water into the grinding tank, grind and disperse evenly to make a slurry, then evenly coat the slurry on the copper foil, put the coated electrode into the oven and dry it at 60 °C for 12 h. After drying, roll and cut it into circular pieces with a diameter of 12 mm. The average loading of this composite anode material is about 0.8-1.2 mg·cm -2 .

[0091] Assemble the prepared anode electrode into a button cell:

[0092] Use a lithium sheet as the counter electrode, a polypropylene microporous membrane as the separator, and the electrolyte is 1 mol / L LiPF 6 dissolved in ethylene carbonate (EC) + dimethyl carbonate (DMC) (volume ratio 1:1). Assemble it into a button half-cell in a glove box filled with an argon atmosphere (O2 < 0.1 ppm, H 2 2O < 0.1 ppm). After assembly, let it stand at room temperature for 24 h to obtain a lithium-ion battery with the anode material. Conduct charge-discharge cycle tests on this button cell: The charge-discharge cut-off voltage is 0.01-1.50 V. Before the charge-discharge cycle test, activate the battery at a current density of 0.1 C for the first 3 cycles, and then conduct long-cycle tests at a current density of 0.2 C, or conduct rate tests at current densities of 0.5 C and 1 C.

[0093] The relevant test results of its electrochemical performance are shown in Table 1. The performance test parameters and corresponding test methods are as follows:

[0094] Battery rate: The performance level is reflected by the deviation of the 0.5C and 1C charge specific capacities of the button half-cell.

[0095] Battery cycle stability: The performance level is reflected by the deviation of the 0.2C capacity attenuation rate of the button cell.

[0096] Table 1

[0097]

[0098]

[0099] It can be obtained from Table 1 that the battery rate performance of the battery made of the anode material with a burr-like surface carbon layer morphology is better; while the battery cycle stability of the battery made of the anode material with an onion-like surface carbon layer morphology is higher.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the various embodiments of the present application.

[0101] In addition, those skilled in the art can understand that although some of the embodiments herein include certain features included in other embodiments rather than other features, the combination of the features of different embodiments means that it is within the scope of the present application and forms different embodiments. For example, in the above claims, any one of the claimed embodiments can be used in any combination. The information disclosed in this background art section is only intended to deepen the understanding of the overall background art of the present application, and should not be regarded as an admission or any form of implication that this information constitutes prior art already known to those skilled in the art.

Claims

1. A preparation method of a negative electrode material with a controllable surface carbon coating morphology, characterized in that the steps include: Put the negative electrode material precursor into a gas-phase reaction furnace, introduce an organic carbon source gas and a carrier gas, and raise the temperature for reaction to carry out gas-phase carbon coating treatment; Controlling C in the tail gas of the gas-phase reaction furnace during the reaction 6 H 6 gas and C 2 H 2 volume ratio of the gas to obtain a negative electrode material with a controllable morphology of the surface carbon coating layer, wherein If C 6 H 6 : The volume ratio of C 2 H 2 is > 2 and ≤ 8, preferably ≥ 3 and ≤ 5, and the morphology of the carbon coating layer is "onion-like"; If C 6 H 6 : The volume ratio of C 2 H 2 is between 0.5 and 2, preferably between 1 and 2, and the morphology of the carbon coating layer is "burr-like".

2. The preparation method according to claim 1, characterized in that The negative electrode material precursor is selected from at least one of graphite negative electrode materials, silicon oxide negative electrode materials, and silicon-carbon negative electrode materials, preferably a silicon monoxide negative electrode material.

3. The preparation method according to claim 1, characterized in that The organic carbon source gas is selected from at least one of C1-C4 alkanes, C1-C4 alkenes, and C1-C4 alkynes.

4. The preparation method according to claim 1, characterized in that The carrier gas is selected from at least one of nitrogen and inert gases, preferably at least one of nitrogen, argon, and helium.

5. The preparation method according to claim 1, characterized in that The gas-phase reaction furnace is selected from any one of a continuous rotary kiln and a fluidized bed gas-phase reaction furnace; Preferably, a tail gas monitoring device is provided at the exhaust end of the gas-phase reaction furnace for detecting the content of C 6 H 6 gas and C 2 H 2 gas in the tail gas of the gas-phase reaction furnace during the treatment process; Preferably, the exhaust gas monitoring device is provided as follows: a gas detection interface is reserved at the exhaust end of the gas-phase reaction furnace, and the discharged gas is led to a gas chromatograph analyzer through a pipeline to analyze in real time the contents of C 6 H 6 and C 2 H 2 in the exhaust gas.

6. The preparation method according to claim 1, characterized in that The flow rate of the organic carbon source gas introduced into the gas-phase reaction furnace is 50-150 L / h, preferably 60-90 L / h.

7. The preparation method according to claim 1, characterized in that The flow rate ratio of the carrier gas to the organic carbon source gas introduced into the gas-phase reaction furnace is 0.1-10:1, preferably 0.2-3:

1.

8. The preparation method according to claim 1, characterized in that During the gas-phase carbon coating treatment process, the reaction temperature is 600-1000 °C, preferably 800-900 °C; the reaction time is 1-5 h, preferably 2-3 h; the reaction pressure is 10-1000 PaG, preferably 20-200 PaG.

9. A negative electrode material with a controllable surface carbon coating morphology prepared by the method according to any one of claims 1-8.

10. A lithium-ion battery, comprising a negative electrode material with a controllable surface carbon coating morphology prepared by the method according to any one of claims 1-8, or comprising the negative electrode material with a controllable surface carbon coating morphology according to claim 9.

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