Composite negative electrode material and preparation method therefor, and battery

Abstract

A composite negative electrode material and a preparation method therefor, and a battery. The composite negative electrode material comprises a carbon material and a silicon-based material; pores are formed in the composite negative electrode material; for three pores which are not on a same straight line, the pore sizes of the three pores are respectively D1, D2, and D3, and pore distances are respectively L1, L2, and L3; A1 is defined as the minimum value among L1 2-(L2 / 2)2, L1 2-(L3 / 2)2, L2 2-(L1 / 2)2, L2 2-(L3 / 2)2, L3 2-(L1 / 2)2, and L3 2-(L2 / 2)2; B1 is D1+D2+D3; and 0.4<A1 / B1<50. In the composite negative electrode material, A1 / B1 satisfies the range of 0.4-50, which means pores in the material are distributed in a reasonable range. This indicates that, on the one hand, most pores of the original carbon material are effectively filled with a silicon-based material, i.e., the interior of the sample is relatively compact, which means the proportion of silicon and carbon in the sample is controlled to be within a reasonable range, and the specific capacity and initial efficiency of the composite negative electrode material are relatively high. On the other hand, the interior of the sample is not of a completely compact structure, thereby reducing the problem of excessive local stress in the material due to no pores or few pores being present, guaranteeing the integrity of the structure of the composite negative electrode material, and improving the cycle performance.

Description

Composite negative electrode material and preparation method thereof, and battery

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office on June 29, 2023, with application number 202310784881X and application name “Composite negative electrode material, preparation method thereof, and battery”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of negative electrode materials, and in particular to composite negative electrode materials, preparation methods thereof, and batteries. Background Art

[0003] Lithium-ion batteries are widely used in electric vehicles and consumer electronics due to their high energy density, long cycle life, low environmental pollution, and lack of memory effect. However, the low theoretical specific capacity (372 mAh / g) of traditional carbon anode materials has limited their widespread use. To increase the energy density of lithium-ion batteries, researchers have begun to search for high-capacity anode materials. Silicon-based anode materials, with their theoretical specific capacity reaching 4200 mAh / g, have gradually become a research hotspot. However, silicon-based anode materials experience significant volume expansion during alloying with lithium. Furthermore, as cycling progresses, silicon-based anode materials experience attenuation mechanisms such as pulverization, loss of contact with the conductive agent and current collector, and formation of an unstable solid electrolyte interface (SEI), which degrades the electrochemical performance of the anode materials.

[0004] Carbon materials have rich pore structures. When prepared as composite negative electrode materials with silicon-based materials, carbon materials can provide a large amount of embedding space for silicon-based materials, reduce the expansion effect of silicon-based materials, and improve their pulverization or formation of unstable solid electrolyte interfaces. During the silicon-based material filling process, the filling amount of silicon-based materials will affect the pore distribution of the composite negative electrode material, thereby affecting the electrochemical performance of the composite negative electrode material. It is understandable that if the filling amount of silicon-based materials is too small, the pore distribution of the composite negative electrode material will be sparse, and the silicon-based material will have enough space for expansion, but it cannot fully utilize the high capacity advantage of silicon; if the filling amount of silicon-based materials is too much, the high capacity advantage of silicon-based materials can be utilized, but the composite negative electrode material will have no pores or fewer pores. The composite negative electrode material will cause stress concentration due to the expansion effect of the silicon-based material, affecting the structural stability.

[0005] Therefore, controlling the pore distribution of the composite negative electrode material after filling with silicon-based materials is crucial to improving the electrochemical performance of batteries prepared with the composite negative electrode material.

[0006] Application Contents

[0007] The purpose of this application is to provide a composite negative electrode material, a preparation method thereof, and a battery. After the silicon-based material is filled in the carbon material to form a composite negative electrode material, the pore distribution of the composite negative electrode material is within a reasonable range, thereby obtaining a composite negative electrode material with excellent initial effect and cycle performance.

[0008] In a first aspect, the present application provides a composite negative electrode material, comprising a carbon material and a silicon-based material, wherein the carbon material has pores, and at least a portion of the silicon-based material is distributed in the pores of the carbon material;

[0009] The composite negative electrode material has pores. For any three adjacent pores that are not on the same straight line, the pore diameters of the three pores are D1, D2, and D3 respectively, and the pore distances are L1, L2, and L3 respectively. A1 is defined as L1 2 -(L2 / 2) 2 、L1 2 -(L3 / 2) 2 、L2 2 -(L1 / 2) 2 、L2 2 -(L3 / 2) 2 、L3 2 -(L1 / 2) 2 or L3 2 -(L2 / 2) 2 The minimum value in , B1 is D1+D2+D3, and 0.4<A1 / B1<50.

[0010] In a second aspect, the present application provides a method for preparing a composite negative electrode material, comprising the following steps:

[0011] Providing a carbon material having pores, introducing a reaction gas containing a silicon source gas and hydrogen under a negative pressure environment, and performing vapor deposition on the carbon material to obtain a composite negative electrode material; wherein the composite negative electrode material comprises a carbon material and a silicon-based material, and the composite negative electrode material has pores;

[0012] In the composite negative electrode material, for the three holes that are not on the same straight line, the pore diameters of the three holes are D1, D2, and D3 respectively, and the pore distances are L1, L2, and L3 respectively. A1 is defined as L1 2 -(L2 / 2) 2 、L1 2 -(L3 / 2) 2 、L2 2 -(L1 / 2) 2 、L2 2 -(L3 / 2) 2 、L3 2 -(L1 / 2) 2 or L3 2 -(L2 / 2) 2The minimum value in , B1 is D1+D2+D3, and 0.4<A1 / B1<50;

[0013] In the carbon material, for any three adjacent pores that are not on the same straight line, the pore diameters of the three pores are d'1, d'2, and d'3, and the pore distances are l'1, l'2, and l'3, respectively. A'2 is defined as l'2 2 -(l'1 / 2) 2 , l'2 2 -(l'3 / 2) 2 、l'3 2 -(l'1 / 2) 2 、l'3 2 -(l'2 / 2) 2 、l'1 2 -(l'2 / 2) 2 or l'1 2 -(l'3 / 2) 2 The minimum value in, B'2 is d'1+d'2+d'3, C'1 is l'2 2 -(l'1 / 2) 2 , l'2 2 -(l'3 / 2) 2 、l'3 2 -(l'1 / 2) 2 、l'3 2 -(l'2 / 2) 2 、l'1 2 -(l'2 / 2) 2 or l'1 2 -(l'3 / 2) 2 The maximum value among them, B'2 / C'1>1, and B'2 / A'2≤4.

[0014] In a third aspect, the present application provides a battery, comprising the composite negative electrode material described in any one of the first aspects or the composite negative electrode material prepared by the preparation method described in any one of the second aspects.

[0015] Compared with the prior art, this application has at least the following beneficial effects:

[0016] The composite negative electrode material of the present application includes a carbon material and a silicon-based material. At least part of the silicon-based material is located in the pores of the carbon material to form a composite negative electrode material with a reasonable pore distribution. At this time, for any three adjacent pores of the composite negative electrode material that are not on the same straight line, the pore diameters of the three pores are D1, D2, and D3 respectively, and the pore distances are L1, L2, and L3 respectively. A1 is defined as L1 2 -(L2 / 2) 2 、L1 2 -(L3 / 2) 2 、L22 -(L1 / 2) 2 、L2 2 -(L3 / 2) 2 、L3 2 -(L1 / 2) 2 or L3 2 -(L2 / 2) 2 The minimum value in , B1 is D1+D2+D3, and the relationship between A1 and B1 satisfies 0.4<A1 / B1<50. It can be understood that A1 represents the compactness of the three adjacent pores, and B1 represents the pore size of the three pores. When A1 / B1 is within the above range, it means that the compactness and pore size of the three pores that are not on the same straight line in the composite negative electrode material obtained after the silicon-based material is filled with the carbon material are moderate, that is, the pore distribution is moderate and not too sparse or dense. On the one hand, it means that most of the pores of the carbon material are effectively filled with the silicon-based material, that is, the interior of the composite negative electrode material is relatively dense, and the silicon-based material with high stability can provide abundant lithium storage sites, thereby improving the specific capacity and first efficiency of the composite negative electrode material; on the other hand, the applicant found that if the filling amount of the silicon-based material is too large, the silicon-based materials are stacked more tightly, and the distance between the three pores that are not on the same straight line in the pores of the composite negative electrode material formed after filling is too far, And the pore size is too small, making A1 / B1 too small, which will cause the composite negative electrode material to have no pores or fewer pores. The above situation will make it difficult to effectively relieve the stress of the silicon-based material during charging and discharging, and there will be problems of excessive local stress inside the composite negative electrode material, causing the internal structure of the composite negative electrode material to be damaged or collapsed. At this time, if the electrolyte continues to infiltrate, the SEI film thickens, and the cycle performance of the battery prepared by the composite negative electrode material deteriorates. When the A1 / B1 of the composite negative electrode material in this application is within the above range, the internal structure of the composite negative electrode material is not a completely dense structure, the pore distribution is appropriate, and the silicon-based material has a certain expansion space, which can ensure the structural stability of the composite negative electrode material during the cycle, thereby improving the cycle performance of the battery prepared by the composite negative electrode material.

[0017] The preparation method of the negative electrode material provided in the present application utilizes a vapor deposition process to deposit a silicon-based material onto a carbon material with a reasonable pore distribution, thereby preparing a composite negative electrode material of the present application having excellent specific capacity, first efficiency and cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG1 is a schematic diagram showing the relationship between the pore diameter and pore spacing of three pores that are not on the same straight line in a composite negative electrode material provided in an embodiment of the present application;

[0019] FIG2 is a schematic diagram showing the relationship between the pore diameter and pore spacing of three pores that are not on the same straight line in the carbon material of the composite negative electrode material provided in an embodiment of the present application;

[0020] FIG3 is a schematic flow chart of a method for preparing a composite negative electrode material according to an embodiment of the present application;

[0021] FIG4 is a comparison diagram of the adsorption curves of the carbon material raw material provided in Example 1 of the present application and the composite negative electrode material after depositing the silicon-based material. DETAILED DESCRIPTION

[0022] In order to better understand the technical solution of the present application, the embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0023] It should be clear that the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0024] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "an", "the" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0025] It should be understood that the term "and / or" as used herein is merely a description of the relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, or B exists alone. Furthermore, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0026] The present application provides a composite negative electrode material, which includes a carbon material and a silicon-based material. The carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material. As shown in FIG1 , the composite negative electrode material has pores. For any three adjacent pores that are not on the same straight line, the pore diameters of the three pores are D1, D2, and D3, respectively, and the pore spacings are L1, L2, and L3, respectively. A1 is defined as L1. 2 -(L2 / 2) 2 、L1 2 -(L3 / 2) 2 、L2 2 -(L1 / 2) 2 、L2 2 -(L3 / 2) 2 、L3 2 -(L1 / 2) 2 or L3 2 -(L2 / 2) 2 The minimum value in , B1 is D1+D2+D3, and 0.4<A1 / B1<50.

[0027] In the particle structure of the composite negative electrode material provided in this embodiment, A1 represents the compactness of three adjacent pores, and B1 represents the pore size of the three pores. It can be understood that when A1 / B1 is within the above range, it indicates that the compactness and pore size of the three pores that are not on the same straight line in the composite negative electrode material obtained after the silicon-based material is filled with the carbon material are moderate, that is, the pore distribution is not too sparse or dense. On the one hand, it shows that most of the pores of the carbon material are effectively filled with the silicon-based material, that is, the interior of the composite negative electrode material is relatively dense, and the silicon-based material with high stability can provide rich lithium storage sites, thereby improving the specific capacity and first efficiency of the composite negative electrode material; on the other hand, the applicant found that if the filling amount of the silicon-based material is too large, the silicon-based materials are stacked more tightly, and the pores of the composite negative electrode material formed after filling are not on the same straight line. The distance between the three holes on the upper surface is too far, and the pore size is too small, making A1 / B1 too small. At this time, the composite negative electrode material has no pores or fewer pores. The above situation will make it difficult to effectively relieve the stress of the silicon-based material during charging and discharging. There will be a problem of excessive local stress inside the composite negative electrode material, which will cause the internal structure of the composite negative electrode material to be damaged or collapsed. At this time, if the electrolyte continues to infiltrate, the SEI film thickens, and the cycle performance of the battery prepared by the composite negative electrode material deteriorates. When A1 / B1 of the composite negative electrode material in this application is within the above range, the interior of the composite negative electrode material is not a completely dense structure, the pore distribution is appropriate, and the silicon-based material has a certain expansion space, which can ensure the structural stability of the composite negative electrode material during the cycle, thereby improving the cycle performance of the battery prepared by the composite negative electrode material.

[0028] In some embodiments, the specific surface area of ​​the carbon material after removing the silicon-based material from the composite negative electrode material is 300 m 2 / g~2500m 2 / g. Specifically, the specific surface area can be 300m 2 / g、500m 2 / g、1000m 2 / g、1500m 2 / g、2000m 2 / g、2100m 2 / g、2200m 2 / g、2300m 2 / g、2400m 2 / g and 2500m 2 / g, etc., and of course, it can also be other values ​​within the above range, which is not limited here.

[0029] In some embodiments, the carbon material after removing the silicon-based material from the composite negative electrode material has pores, and at least a portion of the silicon-based material is filled in the pores. It is understood that the carbon material can serve as a supporting skeleton and also has good electrical conductivity, which can ensure the powder conductivity of the prepared composite negative electrode material. In this case, when the silicon-based material is filled in the pores of the carbon material, on the one hand, the specific capacity of the composite negative electrode material can be increased. On the other hand, the pores after the carbon material is filled with the silicon-based material are reduced, which can increase the density of the composite negative electrode material and improve the structural stability of the composite negative electrode material particles.

[0030] In some embodiments, the pore volume of all pores in the carbon material after removing the silicon-based material from the composite negative electrode material is 0.4 cm 3 / g~2m 3 / g. Specifically, the pore volume can be 0.4cm 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, 0.7cm 3 / g, 0.8cm 3 / g, 0.9cm 3 / g, 1.0cm 3 / g, 1.1cm 3 / g, 1.2cm 3 / g, 1.3cm 3 / g, 1.4cm 3 / g, 1.5cm 3 / g, 1.6cm 3 / g, 1.7cm 3 / g, 1.8cm 3 / g, 1.9cm 3 / g and 2cm 3 / g, etc., of course it can also be 0.4cm 3 / g~2cm 3 There is no limitation on other values ​​between / g.

[0031] In some embodiments, in the carbon material after the silicon-based material is removed from the composite negative electrode material, the pore size of at least part of the pores gradually decreases from the surface to the interior of the carbon material, wherein the average pore size change of each 1 μm extended from the surface to the interior of the carbon material is ≥0.1 nm, and optionally, the average pore size change per 1 μm extended can be specifically 0.1 nm, 0.15 nm, 0.2 nm, 0.25 nm, 0.3 nm, 0.35 nm, 0.4 nm, 0.45 nm and 0.5 nm, etc., of course, it can also be other values ​​within the above range, which is not limited here. It can be understood that the average pore size change per 1 μm extended is within the above range, which is conducive to the diffusion of gas into the interior of the carbon material, and can make the silicon-based material uniformly and effectively filled in the pores of the carbon material, thereby ensuring that the open porosity of the pores in the composite negative electrode material is within an appropriate range.

[0032] In some embodiments, the cross-section of the pores in the carbon material after the silicon-based material is removed from the composite negative electrode material is funnel-shaped or inverted-conical. It is understood that the funnel-shaped or inverted-conical pores have a large gas inlet, which allows the silicon-containing source gas and hydrogen-containing reaction gases to be introduced deeply into the pores of the carbon material, thereby facilitating the deposition of the silicon-based material within the pores of the carbon material. It can also reduce the reaction gas from decomposing too quickly on the surface of the carbon material and depositing on the surface of the carbon material, resulting in pore closure, which in turn leads to insufficient deposition of the silicon-based material within the pores of the carbon material and affects the structural stability of the composite negative electrode material.

[0033] In some embodiments, the density of the carbon material after removing the silicon-based material from the composite negative electrode material is ≤1.50 g / cm 3 , specifically 0.1g / cm 3 , 0.2g / cm 3 , 0.3g / cm 3 , 0.4g / cm 3 , 0.5g / cm 3 , 0.6g / cm 3 , 0.7g / cm 3 , 0.8g / cm 3 , 0.9g / cm 3 , 1.0g / cm 3 , 1.10g / cm 3 , 1.20g / cm 3 , 1.30g / cm 3 , 1.40g / cm 3 and 1.50g / cm 3 Of course, other values ​​within the above range are also possible and are not limited here. It can be understood that the carbon material has a large number of pores, the presence of which reduces the density of the carbon material, and sufficient pores are conducive to the deposition of silicon-based materials.

[0034] In some embodiments, the distribution density of the pores in the carbon material after the silicon-based material is removed from the composite negative electrode material is 1 / μm 2 ~1000 / μm 2 Specifically, the distribution density of pores in the carbon material can be 1 / μm 2 , 5 / μm 2 , 10 / μm 2 , 20 / μm 2 , 50 / μm 2 , 100 / μm 2 , 150 / μm 2 , 200 / μm 2 , 300 / μm 2 , 500 / μm 2 , 600 / μm 2 , 700 / μm 2 , 800 / μm 2 , 900 / μm 2 and 1000 / μm 2 Of course, it can also be other values ​​within the above range, which is not limited here.

[0035] In some embodiments, the average pore size of the carbon material after removing the silicon-based material from the composite negative electrode material is 0.1nm to 50nm, specifically 0.1nm, 0.5nm, 1nm, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm and 50nm, etc., of course, it can also be other values ​​within the above range, which is not limited here. It is understandable that the pore size distribution of the carbon material will directly affect the deposition of the silicon-based material. When the pore size of the carbon material is too small, it is difficult to introduce the reaction gas containing silicon source gas and hydrogen deeply into the pores of the carbon material. The silicon-based material is more likely to be deposited on the surface of the carbon material rather than in the pores, which can easily lead to the pores on the surface of the composite negative electrode material being closed prematurely, and the content of silicon-based material filled in the composite negative electrode material is too little, resulting in the degradation of the electrochemical performance of the material; and when the pore size of the carbon material is too large, its mechanical strength will be degraded, and at the same time, the segregation problem of the silicon-based material will occur. When the pore size exceeds a certain value, there will be no real improvement in the entry of the reaction gas containing silicon source gas and hydrogen, which will also lead to poor electrochemical performance of the material.

[0036] In some embodiments, the porosity of the carbon material after removing the silicon-based material from the composite negative electrode material is 45% to 75%. Specifically, the porosity of the carbon material can be 45%, 48%, 50%, 55%, 57%, 60%, 65%, 68%, 70%, 71%, 72%, 73%, 74%, and 75%, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0037] In some embodiments, in the carbon material after the silicon-based material is removed from the composite negative electrode material, as shown in FIG2 , for any three adjacent pores that are not on the same straight line, the pore diameters of the three pores are d1, d2, and d3, and the pore distances are l1, l2, and l3, respectively. A2 is defined as l2 2 -(l1 / 2) 2 、l2 2 -(l3 / 2) 2 、l3 2 -(l1 / 2) 2 、l3 2 -(l2 / 2) 2 、l1 2 -(l2 / 2) 2 or l1 2 -(l3 / 2) 2 The minimum value in, B2 is d1+d2+d3, C1 is l2 2 -(l1 / 2) 2 、l2 2 -(l3 / 2) 2 、l3 2 -(l1 / 2) 2 、l3 2 -(l2 / 2) 2 、l1 2 -(l2 / 2) 2 or l1 2 -(l3 / 2) 2 The maximum value among them, B2 / C1>1, and B2 / A2≤4.

[0038] Understandably, when B2 / C1>1 and B2 / A2≤4 are present in the carbon material after the silicon-based material is removed from the composite negative electrode material, this indicates that the pore distribution in the carbon material is neither too concentrated nor too distant, thereby facilitating the deposition of the silicon-based material within the pores of the carbon material. Controlling B2 / C1>1 and B2 / A2≤4 in the carbon material can, on the one hand, ensure that the silicon-based material is fully deposited within the pores of the carbon material, thereby facilitating the improvement of the specific capacity of the composite negative electrode material; on the other hand, it can reduce the excessive deposition of the silicon-based material within the pores of the carbon material, thereby reserving a certain buffer space for the volume expansion of the silicon-based material and alleviating the stress release of the composite negative electrode material, thereby facilitating the improvement of the cycle performance of the composite negative electrode material.

[0039] In some embodiments, the pores in the carbon material after removing the silicon-based material from the composite negative electrode material include micropores, mesopores and macropores, wherein the volume proportion of micropores in all pores is 30% to 99%, the volume proportion of mesopores in all pores is 5% to 70%, and the volume proportion of macropores in all pores is 0 to 5%.

[0040] Specifically, the volume proportion of micropores in all pores can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% and 99%, etc. Of course, it can also be other values ​​between 30% and 99%, which are not limited here.

[0041] The volume proportion of mesopores in all pores can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% and 70%, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0042] Specifically, the volume proportion of macropores in all pores can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% and 5%, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0043] In some embodiments, the pores in the carbon material after the silicon-based material is removed from the composite negative electrode material include mesopores, wherein the volume proportion of pores with a pore diameter of 2 nm to 20 nm in the mesopores is >90%, specifically 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% and 99%, etc., and of course it can also be other values ​​within the above range, which is not limited here.

[0044] In some embodiments, the pores in the carbon material after the silicon-based material is removed from the composite negative electrode material include mesopores, wherein the volume of the mesopores with a pore diameter of 5 nm to 20 nm accounts for 10% to 50% of all mesopores, specifically 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 46%, 47%, 48%, 49% and 50%, etc., of course, it can also be other values ​​between 10% and 50%, which are not limited here.

[0045] It can be understood that the pore size distribution of the carbon material after the silicon-based material is removed from the composite negative electrode material is appropriate, which helps to form gas-phase mass transfer channels inside the carbon material during the deposition process, improve the internal diffusion environment of the carbon material, reduce the density gradient of the carbon material, and thus improve the density of the composite negative electrode material.

[0046] In some embodiments, the pore filling rate of the composite negative electrode material is ≥70%. Specifically, the pore filling rate can be 70%, 71%, 72%, 73%, 74%, 75%, 80%, 83%, 85%, 87%, 90%, 91%, 93%, 95%, 96%, 97% and 99%, etc., of course, it can also be other values ​​within the above range, which is not limited here. Preferably, the pore filling rate is 80% to 90%. It can be understood that the pore filling rate within the above range is beneficial to improving the specific capacity of the composite negative electrode material on the one hand, and on the other hand, it is beneficial to improving the structural stability of the composite negative electrode material, thereby reducing the structural collapse of the composite negative electrode material during the cycle.

[0047] In some embodiments, the mass proportion of silicon-based materials in the composite negative electrode material is 15% to 60%, specifically 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55% and 60%, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0048] In some embodiments, the average particle size of the silicon-based material is less than 50 nm. Specifically, the average particle size of the silicon-based material can be 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 46 nm, 47 nm, 48 nm, 49 nm, and 50 nm, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0049] In some embodiments, the silicon-based material includes at least one of amorphous silicon, crystalline silicon, silicon oxide, silicon alloy, and a composite of crystalline silicon and amorphous silicon; specifically, the silicon alloy can be a silicon-lithium alloy, a silicon-magnesium alloy, etc. Of course, it should be noted that in some cases, the silicon alloy includes elemental particles and alloys.

[0050] In some embodiments, the silicon-based material includes amorphous silicon. It is understood that the silicon-based material in the composite negative electrode material includes amorphous silicon, which expands isotropically during the lithium insertion process, which can reduce the collapse of the pore structure, inhibit the rapid decay of the specific capacity, and improve the lithium insertion cycle performance.

[0051] In some embodiments, the specific surface area of ​​the composite negative electrode material is 1 m 2 / g~500m 2 / g. Specifically, the specific surface area of ​​the composite negative electrode material can be 1m 2 / g、5m 2 / g、10m 2 / g, 50m 2 / g、100m 2 / g, 150m 2 / g, 200m 2 / g, 250m 2 / g、300m 2 / g、350m 2 / g, 400m 2 / g, 450m 2 / g and 500m 2 / g, etc., and of course, it can also be other values ​​within the above range, which is not limited here.

[0052] In some embodiments, the pore volume of the pores in the composite negative electrode material is 0.001 cm 3 / g~0.6cm 3 / g, specifically 0.001cm 3 / g, 0.005cm 3 / g, 0.01cm 3 / g, 0.05cm 3 / g, 0.1cm 3 / g, 0.15cm 3 / g, 0.2cm 3 / g, 0.25cm 3 / g, 0.3cm 3 / g, 0.35cm 3 / g, 0.4cm 3 / g, 0.45cm 3 / g, 0.5cm 3 / g, 0.55cm 3 / g and 0.6cm 3 / g, etc., of course, it can also be other values ​​within the above range, which is not limited here. Compared with the pore volume of carbon materials, the pore volume of the composite negative electrode material after the composite silicon-based material is significantly reduced, the density of the composite negative electrode material is increased, and the composite negative electrode material also reserves an appropriate amount of pores to alleviate the volume expansion caused by the lithium insertion and removal process of the silicon-based material, which is beneficial to improve the cycle performance of the material. Preferably, the pore volume of the pores in the composite negative electrode material is 0.05cm 3 / g~0.5cm 3 / g.

[0053] In some embodiments, the volume percentage of pores in the composite negative electrode material is ≤20%. Specifically, the volume percentage of pores in the composite negative electrode material can be 1%, 3%, 5%, 7%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, and 20%, etc., and of course other values ​​within the above range are also possible and are not limited here. Preferably, the volume percentage of pores in the composite negative electrode material is 5% to 15%.

[0054] In some embodiments, the density of the composite negative electrode material is 1.9 g / cm 3 ~2.3g / cm 3 , specifically 1.9g / cm 3 , 1.95g / cm 3 , 2.0g / cm 3 , 2.1g / cm 3 , 2.15g / cm 3 , 2.2g / cm 3 , 2.25g / cm 3 and 2.3 g / cm 3 Of course, other values ​​within the above range are also possible and are not limited here. It can be seen that because the silicon-based material fills the pores of the carbon material, the density of the carbon material is increased, so that the overall density of the composite negative electrode material increases by 80% to 120% compared to the initial carbon material.

[0055] In some embodiments, the porosity of the composite negative electrode material is 5% to 20%. Specifically, the porosity of the composite negative electrode material can be 5%, 6%, 7%, 10%, 12%, 15%, 16%, 17%, 18%, 19% and 20%, etc. Of course, it can also be other values ​​between 5% and 20%, which are not limited here. It is understandable that due to factors such as diffusion limitations, it is impossible for silicon-based materials to be deposited in the pores of carbon materials to achieve 100% pore filling. When the porosity is lower than 5%, the composite negative electrode material does not have enough pores to withstand the volume expansion during the charge and discharge process; when the porosity is higher than 20%, on the one hand, the composite negative electrode material has a low specific capacity due to too little Si filling; on the other hand, due to the large number of pores in the composite negative electrode material, its overall stability is poor. During the preparation of the electrode sheet, the material structure is prone to collapse due to the extremely high pressure generated by the rolling process.

[0056] In some embodiments, the open pores of the pores in the composite negative electrode material account for 2% to 20% of the total pores, specifically 2%, 3%, 4%, 5%, 8%, 10%, 12%, 15%, 16%, 17%, 18%, 19% and 20%, etc., of course, it can also be other values ​​within the above range, which are not limited here. It should be noted that the open porosity of the pores in the composite negative electrode material refers to the volume ratio of the open pore volume to the pore volume of all pores in the composite negative electrode material, and all pores here include open pores and closed pores. When the open porosity is too large, it means that most of the pores in the carbon material are not effectively filled, and the deposition efficiency of the silicon-based material is insufficient. When the open porosity is too small, it means that the filling rate of the pores in the carbon material is high, and there is not enough pore space in the composite negative electrode material to buffer the volume expansion of the silicon-based material during the lithium insertion and extraction process. In this way, when lithium is inserted and extracted, the volume expansion of the silicon-based material causes the expansion pressure in the material structure to be too large, resulting in structural instability of the composite negative electrode material and deterioration of the electrochemical performance. Therefore, controlling the open porosity of the pores in the composite negative electrode material within the above range is beneficial for improving the specific capacity of the composite negative electrode material. On the other hand, the pores after the carbon material is filled into the silicon-based material are reduced, which can increase the density of the composite negative electrode material and improve the structural stability of the particles. The open porosity within the appropriate range also provides expansion space for the silicon-based material, reducing the collapse of the material structure caused by volume expansion during the lithium insertion and extraction process, effectively reducing the occurrence of side reactions, and thus improving the cycling performance of the material. Furthermore, a balance is found between volumetric energy density, rolled particle strength, and particle stability during the cycle, comprehensively improving all aspects of the negative electrode material performance.

[0057] In some embodiments, the pores in the composite negative electrode material have a pore diameter of D nm, where D ranges from 0.1 to 100. Specifically, the pore diameter of the composite negative electrode material can be 0.1 mm, 0.5 nm, 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, and 100 nm, etc. Of course, other values ​​within the above range are also possible, and are not limited here.

[0058] In some embodiments, in the composite negative electrode material, the average pore distance between any two adjacent pores is L nm, and the value of L ranges from 1 to 300. Specifically, the average pore distance between any two adjacent pores in the composite negative electrode material can be 1 nm, 5 nm, 10 nm, 50 nm, 70 nm, 100 nm, 110 nm, 150 nm, 180 nm, 200 nm, 230 nm, 250 nm, 280 nm, 290 nm, and 300 nm, etc., and of course, it can also be other values ​​between 1 nm and 300 nm, which is not limited here.

[0059] In some embodiments, the pores in the composite negative electrode material have a pore diameter of D nm, an average pore distance between any two adjacent pores of L nm, and L ≥ 4 × D. Specifically, L can be 4 × D, 5 × D, 6 × D, 7 × D, 8 × D, and 10 × D, etc., and of course, other values ​​within the above range are also possible and are not limited here.

[0060] In some embodiments, as a preferred technical solution of the present application, in the composite negative electrode material, for any three adjacent pores that are not on the same straight line, the pore diameters of the three pores are D1, D2, and D3, and the pore distances are L1, L2, and L3, respectively. A1 is defined as L1. 2 -(L2 / 2) 2 、L1 2 -(L3 / 2) 2 、L2 2 -(L1 / 2) 2 、L2 2 -(L3 / 2) 2 、L3 2 -(L1 / 2) 2 or L3 2 -(L2 / 2) 2 The minimum value of B1 is D1+D2+D3, and 3<A1 / B1<50. More preferably, 10<A1 / B1<30. It can be understood that when A1 / B1 is within the above range, on the one hand, the silicon-based material can be fully deposited within the pores of the carbon material, which is beneficial to improving the specific capacity of the composite negative electrode material; on the other hand, after the silicon-based material is deposited, the composite negative electrode material will leave a suitable amount of pores within the material to buffer the volume expansion of silicon, thereby improving the material's cycling performance.

[0061] In some embodiments, the carbon material after removing the silicon-based material from the composite negative electrode material is tested using the N2 adsorption-desorption method, and the carbon material has a peak Q1 in the range of 2nm to 50nm; the composite negative electrode material is tested using the N2 adsorption-desorption method, and the composite negative electrode material has a peak Q2 in the range of 2nm to 50nm, and the following relationship Q2 / Q1≤0.6 is satisfied. It can be understood that Q2 / Q1 can be 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, and 0.6, etc.

[0062] It should be noted that the N2 adsorption-desorption method tests the amount of silicon-based material filling in the composite negative electrode material before and after deposition. That is, the composite negative electrode material here refers to the carbon material after the silicon-based material is deposited. When the peak values ​​of the carbon material before and after the silicon-based material is deposited, as tested by the N2 adsorption-desorption method, within the range of 2nm to 50nm, satisfy the above relationship, the silicon-based material can be evenly filled in the pores of the carbon material. At this time, a large number of pores in the composite negative electrode material are filled. On the one hand, this can ensure the structural stability of the material during the charge and discharge process. On the other hand, the incompletely filled pores in the composite negative electrode material can effectively provide expansion space for the surrounding silicon-based material.

[0063] In some embodiments, the differential specific capacity curve (dQ / dV) of the composite negative electrode material does not have a crystalline Li 15 The characteristic peak of the Si4 alloy phase indicates that the Si in the alloy remains amorphous when it is lithiated into lithiated silicon, and basically no crystalline Li is generated. 15 Si4.

[0064] In some embodiments, the mass proportion of oxygen elements in the composite negative electrode material is ≤10wt%. Specifically, the mass proportion of oxygen elements in the composite negative electrode material can be 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt% and 10wt%, which are not limited here. It can be understood that if the mass proportion of oxygen elements is too high, the silicon-based material in the composite negative electrode material will be partially oxidized, and the pores will be at least partially destroyed, thereby affecting the cycle stability of the material. Controlling the mass proportion of oxygen elements in the composite negative electrode material within the above range can ensure that a large amount of inactive SiO2 will not be generated in the material, thereby reducing the cycle performance of the composite negative electrode material.

[0065] In a second aspect, the present application also provides a method for preparing a composite negative electrode material, as shown in FIG3 , comprising the following steps:

[0066] Providing a carbon material having pores, introducing a reaction gas containing a silicon source gas and hydrogen under a negative pressure environment, and performing vapor deposition on the carbon material to obtain a composite negative electrode material; wherein the composite negative electrode material includes a carbon material and a silicon-based material, and the composite negative electrode material has pores;

[0067] In the composite negative electrode material, for any three adjacent pores that are not on the same straight line, the pore diameters of the three pores are D1, D2, and D3, and the pore distances are L1, L2, and L3, respectively. A1 is defined as L1 2 -(L2 / 2) 2 、L1 2 -(L3 / 2) 2 、L2 2-(L1 / 2) 2 、L2 2 -(L3 / 2) 2 、L3 2 -(L1 / 2) 2 or L3 2 -(L2 / 2) 2 The minimum value in , B1 is D1+D2+D3, and 0.4<A1 / B1<50;

[0068] In carbon materials, for any three adjacent pores that are not on the same straight line, the pore diameters of the three pores are d'1, d'2, and d'3, and the pore spacings are l'1, l'2, and l'3, respectively. A'2 is defined as l'2 2 -(l'1 / 2) 2 , l'2 2 -(l'3 / 2) 2 、l'3 2 -(l'1 / 2) 2 、l'3 2 -(l'2 / 2) 2 、l'1 2 -(l'2 / 2) 2 or l'1 2 -(l'3 / 2) 2 The minimum value in, B'2 is d'1+d'2+d'3, C'1 is l'2 2 -(l'1 / 2) 2 , l'2 2 -(l'3 / 2) 2 、l'3 2 -(l'1 / 2) 2 、l'3 2 -(l'2 / 2) 2 、l'1 2 -(l'2 / 2) 2 or l'1 2 -(l'3 / 2) 2 The maximum value among them, B'2 / C'1>1, and B'2 / A'2≤4.

[0069] In the above scheme, the preparation method of the negative electrode material provided in this application utilizes a vapor deposition process to fully fill the silicon-based material into the pores of the carbon material, so as to prepare the composite negative electrode material of this application having excellent specific capacity, first efficiency and cycle performance.

[0070] The above technical solution is explained below with reference to specific embodiments:

[0071] Step S101: providing a carbon material having pores.

[0072] In some embodiments, the porous carbon material can be obtained commercially or by the following preparation method, which comprises:

[0073] Step S1011, dissolving the phenolic small molecule in a deionized water solution containing NaOH to obtain a mixed solution, wherein the molar ratio of NaOH to the phenolic small molecule is 4:1;

[0074] Step S1012: adding zinc acetate to the mixed solution, stirring at room temperature for 24 hours to obtain a precipitate, washing with deionized water and drying to obtain a metal coordination compound powder, wherein the molar ratio of zinc acetate to phenolic small molecules is 4:1.

[0075] In step S1013, the metal coordination compound powder is finally placed in a quartz tube. After being purged with high-purity nitrogen for 10 minutes to remove the air inside the quartz tube, the temperature is raised to 1000°C at a rate of 5°C / min, kept at this temperature for 3 hours, and then cooled to obtain a porous carbon material.

[0076] The main reason why the carbon materials derived from the metal coordination compounds have porous structures is the template effect of nano ZnO and carbon thermal activation. 2+ The ZnO nanoparticles, formed in situ within the carbonaceous structure, thermally evolve into ZnO particles. These ZnO nanoparticles act as templates, creating a space-occupying effect that favors the formation of micropores and mesopores. Simultaneously, ZnO undergoes a carbothermal reduction reaction with carbon atoms, etching the carbonaceous matrix to create pores. The generated gases and the evaporation of elemental Zn can further expand the pore size or create additional micro / mesopores. The subsequent high-temperature carbothermal reduction plays a significant role in pore formation. High zinc content leads to a more pronounced nanoparticle template effect and thermal activation during pyrolysis, resulting in a carbon material with a high specific surface area.

[0077] As an optional solution of the present application, the phenolic small molecule in step S1011 can be catechol. Catechol is a phenolic molecule with the simplest structural composition and a single chelating site (a chelating phenol group). The catechol is mixed with zinc salts such as zinc acetate in step S1012 in an alkaline aqueous solution to prepare a metal coordination compound at room temperature. During the mixing process, NaOH is added to the deionized water solution to promote the rapid deprotonation of the phenolic hydroxyl group in the catechol through an acid-base reaction, and then reacts with Zn 2+ A coordination reaction occurs to form an insoluble metal complex precipitate, and finally the dried metal coordination compound is subjected to a high temperature treatment of 1000° C. in an inert nitrogen atmosphere to obtain a carbon material.

[0078] As another optional scheme of the present application, the phenolic small molecule in step S1011 can also be methyl gallate. The aromatic ring of methyl gallate contains at least one single chelating group. The single chelating group is the key to forming a thermally stable metal coordination compound. Only when the coordination compound has sufficiently high thermal stability can it be converted into a carbon material through subsequent heat treatment.

[0079] In addition to the above special instructions, other types of phenolic small molecules can also be used, such as 4-methylcatechol, 2,3-dihydroxynaphthalene, 3,4-dihydroxybenzonitrile, 3-hydroxyaminobenzoic acid, pyrogallol and Baicalin, etc., which can be selected according to actual needs and are not limited here.

[0080] In some embodiments, the carbon material has a specific surface area of ​​300 m 2 / g~2500m 2 / g. Specifically, the specific surface area of ​​the carbon material can be 300m 2 / g、500m 2 / g、1000m 2 / g、1500m 2 / g、2000m 2 / g、2100m 2 / g、2200m 2 / g、2300m 2 / g、2400m 2 / g and 2500m 2 / g, etc., and of course, it can also be other values ​​within the above range, which is not limited here.

[0081] In some embodiments, the pore volume of all pores in the carbon material is 0.4 cm 3 / g~2cm 3 Specifically, the pore volume of all pores in the carbon material can be 0.4 cm 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, 0.7cm 3 / g, 0.8cm 3 / g, 0.9cm 3 / g, 1.0cm 3 / g, 1.1cm 3 / g, 1.2cm 3 / g, 1.3cm 3 / g, 1.4cm 3 / g, 1.5cm 3 / g, 1.6cm 3 / g, 1.7cm 3 / g, 1.8cm 3 / g, 1.9cm3 / g and 2cm 3 / g, etc., of course it can also be 0.4cm 3 / g~1.8cm 3 There is no limitation on other values ​​between / g.

[0082] In some embodiments, the pore size of at least part of the pores gradually decreases from the surface to the interior of the carbon material. It can be understood that the pore structure with the above-mentioned pore size change is conducive to the diffusion of gas into the interior of the carbon material, and can make the silicon-based material uniformly and effectively filled in the pores of the carbon material, thereby ensuring that the opening porosity of the pores in the composite negative electrode material is within an appropriate range.

[0083] In some embodiments, the density of the carbon material is ≤1.50 g / cm 3 , specifically 0.1g / cm 3 , 0.2g / cm 3 , 0.3g / cm 3 , 0.4g / cm 3 , 0.5g / cm 3 , 0.6g / cm 3 , 0.7g / cm 3 , 0.8g / cm 3 , 0.9g / cm 3 , 1.0g / cm 3 , 1.10g / cm 3 , 1.20g / cm 3 , 1.30g / cm 3 , 1.40g / cm 3 and 1.50g / cm 3 Of course, other values ​​within the above range are also possible and are not limited here. It can be understood that the carbon material has a large number of pores. The presence of pores reduces the density of the carbon material, and sufficient pores are conducive to the deposition of silicon-based materials. When the density of the carbon material is too high, the pores become less, Si deposition is likely to be insufficient, and the specific capacity of the composite negative electrode material cannot be effectively improved.

[0084] In some embodiments, the pore density in the carbon material is 1 / μm 2 ~1000 / μm 2 Specifically, the distribution density of pores in the carbon material can be 1 / μm 2 , 5 / μm 2 , 10 / μm 2 , 20 / μm 2 , 50 / μm 2 , 100 / μm 2 , 150 / μm 2 , 200 / μm2 , 300 / μm 2 , 500 / μm 2 , 600 / μm 2 , 700 / μm 2 , 800 / μm 2 , 900 / μm 2 and 1000 / μm 2 Of course, it can also be other values ​​within the above range, which is not limited here.

[0085] In some embodiments, the average pore size of the carbon material is 0.1 nm to 50 nm, specifically 0.1 nm, 0.5 nm, 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm and 50 nm, etc. Of course, it can also be other values ​​of 0.1 nm to 50 nm, which are not limited here. It is understandable that the pore size distribution of the carbon material will directly affect the deposition of the silicon-based material. When the pore size of the carbon material is too small, it is difficult to introduce the reaction gas containing the silicon source gas deeply into the pores of the carbon material. The silicon-based material is more likely to be deposited on the surface of the carbon material rather than in the pores, which can easily lead to the pores on the surface of the composite negative electrode material being closed prematurely, and the content of the silicon-based material filled in the composite negative electrode material is too small, thereby causing the electrochemical performance of the material to deteriorate. If the pore size of the carbon material is too large, its mechanical strength will deteriorate, and the problem of segregation of the silicon-based material will occur. When the pore size exceeds a certain value, the pressure difference effect decreases, which is not conducive to the reaction gas containing the silicon source gas and hydrogen entering the pores of the carbon material, resulting in no obvious improvement in the electrochemical performance of the material.

[0086] In some embodiments, the porosity of the carbon material is 45% to 75%. Specifically, the porosity of the carbon material can be 45%, 48%, 50%, 55%, 57%, 60%, 65%, 68%, 70%, 71%, 72%, 73%, 74%, and 75%, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0087] In some embodiments, the pore filling rate of the composite negative electrode material is ≥70%. Specifically, the pore filling rate can be 70%, 71%, 72%, 73%, 74%, 75%, 80%, 83%, 85%, 87%, 90%, 91%, 93%, 95%, 96%, 97% and 99%, etc., of course, it can also be other values ​​within the above range, which is not limited here. Preferably, the pore filling rate is 80% to 90%. It can be understood that the pore filling rate within the above range is beneficial to improving the specific capacity of the composite negative electrode material on the one hand, and on the other hand, it is beneficial to improving the structural stability of the composite negative electrode material, thereby reducing the structural collapse of the composite negative electrode material during the cycle.

[0088] In some embodiments, in the carbon material, as shown in FIG2 , for any three adjacent pores that are not on the same straight line, the pore diameters of the three pores are d'1, d'2, and d'3, and the pore distances are l'1, l'2, and l'3, respectively. A'2 is defined as l'2 2 -(l'1 / 2) 2 , l'2 2 -(l'3 / 2) 2 、l'3 2 -(l'1 / 2) 2 、l'3 2 -(l'2 / 2) 2 、l'1 2 -(l'2 / 2) 2 or l'1 2 -(l'3 / 2) 2 The minimum value in, B'2 is d'1+d'2+d'3, C'1 is l'2 2 -(l'1 / 2) 2 , l'2 2 -(l'3 / 2) 2 、l'3 2 -(l'1 / 2) 2 、l'3 2 -(l'2 / 2) 2 、l'1 2 -(l'2 / 2) 2 or l'1 2 -(l'3 / 2) 2 The maximum value among them, B'2 / C'1>1, and B'2 / A'2≤4.

[0089] Understandably, when B'2 / C'1>1 and B'2 / A'2≤4 in the carbon material, it indicates that the pore distribution in the carbon material is uniform, with no overly concentrated or overly dispersed pores, thus facilitating the deposition of silicon-based materials within the pores of the carbon material. Controlling B'2 / C'1>1 and B'2 / A'2≤4 in the carbon material can, on the one hand, ensure that the silicon-based material is fully deposited within the pores of the carbon material, which is beneficial for improving the specific capacity of the composite negative electrode material; on the other hand, it can reduce excessive deposition of silicon-based materials within the pores of the carbon material, reserving a certain buffer space for the volume expansion of the silicon-based material, alleviating the stress release of the composite negative electrode material, and thus improving the cycle performance of the composite negative electrode material.

[0090] In some embodiments, the pores in the carbon material include micropores, mesopores and macropores, wherein the volume of micropores accounts for 30% to 99% of all pores, the volume of mesopores accounts for 5% to 70% of all pores, and the volume of macropores accounts for 0 to 5% of all pores.

[0091] Specifically, the volume proportion of micropores in all pores can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% and 99%, etc. Of course, it can also be other values ​​between 30% and 99%, which are not limited here.

[0092] The volume proportion of mesopores in all pores can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% and 70%, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0093] Specifically, the volume proportion of macropores in all pores may be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0094] In some embodiments, the pores in the carbon material include mesopores, wherein the volume proportion of pores with a pore diameter of 2 nm to 20 nm in the mesopores is >90%, specifically 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% and 99%, etc., and of course it can also be other values ​​within the above range, which is not limited here.

[0095] In some embodiments, the pores in the carbon material include mesopores, wherein the volume of the mesopores with a pore diameter of 5 nm to 20 nm accounts for 10% to 50% of all mesopores, specifically 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 46%, 47%, 48%, 49% and 50%, etc., and of course it can also be other values ​​between 10% and 50%, which are not limited here.

[0096] It can be understood that the appropriate pore size distribution of the carbon material helps to form gas-phase mass transfer channels inside the carbon material during the deposition process, improve the internal diffusion environment of the carbon material, reduce the density gradient of the carbon material, and thus improve the density of the composite negative electrode material.

[0097] In some embodiments, the cross-section of the pores is funnel-shaped or inverted-conical. It is understood that the large gas inlet of the funnel-shaped or inverted-conical pores allows the reactant gas containing the silicon source gas to be introduced deeply into the pores of the carbon material, thereby facilitating the deposition of the silicon-based material within the pores of the carbon material. It also reduces the rapid decomposition of the reactant gas on the surface of the carbon material, which can lead to deposition on the surface of the carbon material, resulting in pore closure and insufficient deposition of the silicon-based material within the pores of the carbon material, thereby affecting the structural stability of the composite negative electrode material.

[0098] In some embodiments, the carbon material includes a catalyst, which is located within the pores. It is understood that the catalyst located within the pores provides sites for the reaction gas containing the silicon source gas to deposit and decompose the silicon-based material to form a silicon-carbon composite. The presence of the catalyst in the carbon material facilitates the deposition of the silicon-based material within the pores, and can encourage the silicon-based material to deposit within the pores of the carbon material rather than on the surface of the carbon material.

[0099] In some embodiments, the catalyst and the carbon material may be doped in liquid phase or solid phase. For example, carbon particles may be suspended in a doping solution containing the catalyst, followed by solid-liquid separation and drying to obtain a catalyst-containing carbon material. Alternatively, the catalyst may be mixed with a solution containing a polymer monomer, and then polymerized to obtain a catalyst-containing polymer, which may then be carbonized to obtain a catalyst-containing carbon material. In the actual preparation process, the carbon material may also be prepared by other methods, which are not limited here.

[0100] In some embodiments, the carbon material includes a catalyst, and the catalyst includes at least one of Ni, Cu, Fe, Mn, Au, Al, Sn, Pd, Pt, Ru, and Ir. It is understood that the metal catalyst in the carbon material undergoes a eutectic reaction with the silicon source gas, and the silicon source gas reacts with the metal catalyst to form a liquid alloy. At a certain deposition temperature, the liquid alloy crystallizes to precipitate the silicon-based material and the metal catalyst. The presence of the metal catalyst can accelerate the rate of the hydrosilation reaction, making the reaction of the Si-H bond with the unsaturated organic compound more likely to proceed. The hydrosilation reaction refers to the addition reaction of the Si-H group to the unsaturated carbon-carbon bond when a hydride is added to an unsaturated organic compound. Here, the presence of the metal catalyst significantly reduces the activation energy of the reaction, making the hydrogenation reaction more likely to proceed.

[0101] In some embodiments, the catalyst accounts for 0.1% to 20% by weight of the carbon material, and specifically may be 0.1%, 0.5%, 1%, 3%, 5%, 7%, 10%, 11%, 15%, 16%, 17%, 18%, 19%, and 20%, etc., and of course other values ​​between 0.1% and 20% are also possible, without limitation herein. An appropriate amount of catalyst can serve as an active site for silicon deposition, facilitating the deposition of silicon-based materials within the pores of the carbon material.

[0102] In some embodiments, the carbon material may further include a catalyst precursor, the catalyst precursor including a metal salt and / or a metal oxide, and the metal includes at least one of Ni, Cu, Fe, Mn, Au, Al, Sn, Pd, Pt, Ru, and Ir.

[0103] In some embodiments, the metal salt includes at least one of a halide salt, a nitrate salt, a carbonate salt, a carboxylate salt, and a sulfate salt.

[0104] In some embodiments, the mass proportion of the catalyst precursor in the carbon material is 0.1% to 10%. Specifically, the mass proportion of the catalyst precursor can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, and 10%, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0105] In some embodiments, before introducing the reaction gas containing silicon source gas under a negative pressure environment, the method further includes the following steps: vacuuming, and stopping vacuuming when the deposition pressure of the vapor deposition reaches 0.1kPa to 50kPa; then introducing a protective atmosphere to control the oxygen content in the vapor deposition reaction chamber to be less than 5%.

[0106] It can be understood that before the reaction gas containing silicon source gas is introduced, a vacuum step is performed first, so that there is a certain pressure difference between the inner and outer surfaces of the carbon material particles when the reaction gas containing silicon source gas is introduced, which is conducive to the penetration of the reaction gas containing silicon source gas into the interior of the carbon material particles; a protective atmosphere is introduced to control the oxygen content in the vapor deposition reaction chamber to be less than 5%, specifically 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% and 4.7%, etc., which can reduce the oxidation of silicon-based materials in the material to generate SiO2, and the synergistic effect of the protective atmosphere and hydrogen can better control the gas reaction rate during the deposition process, thereby controlling the deposition rate of the silicon-based material, so that the silicon-based material can be evenly filled in the pores of the carbon material instead of being deposited on the surface of the carbon material.

[0107] In some embodiments, the steps of evacuating the chamber and applying a protective atmosphere may be repeated multiple times to ensure that the pressure in the reaction chamber reaches 0.1 kPa to 50 kPa and the oxygen content is less than 5%.

[0108] S102, introducing a reaction gas containing a silicon source gas and hydrogen under a negative pressure environment, and performing vapor deposition on the carbon material to obtain a composite negative electrode material.

[0109] In some embodiments, the deposition temperature of the vapor deposition is 400° C. to 650° C. Specifically, the deposition temperature can be 400° C., 420° C., 450° C., 470° C., 490° C., 500° C., 530° C., 550° C., 580° C., 600° C., 610° C., 620° C., 630° C., 640° C., and 640° C., etc. Of course, other values ​​between 400° C. and 650° C. are also possible, and are not limited here.

[0110] In some embodiments, the heating rate of vapor deposition is 2°C / min to 20°C / min, specifically 2°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, 13°C / min, 15°C / min, 16°C / min, 17°C / min, 18°C / min, 19°C / min and 20°C / min, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0111] In some embodiments, the deposition pressure of the vapor deposition is 0.1 kPa to 50 kPa. Specifically, the deposition pressure can be 0.1 kPa, 0.5 kPa, 1 kPa, 5 kPa, 10 kPa, 15 kPa, 20 kPa, 25 kPa, 30 kPa, 35 kPa, 40 kPa, 45 kPa, and 50 kPa, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0112] In some embodiments, the deposition time of vapor deposition is 2 hours to 1000 hours. Specifically, the deposition time can be 2 hours, 5 hours, 10 hours, 50 hours, 100 hours, 150 hours, 200 hours, 250 hours, 300 hours, 350 hours, 400 hours, 500 hours, 600 hours, 650 hours, 700 hours, 800 hours, 900 hours, and 1000 hours, etc. Of course, other values ​​between 2 hours and 1000 hours are also possible, and are not limited here.

[0113] It can be understood that the process conditions of vapor deposition (such as deposition temperature, deposition pressure and deposition time) will affect the deposition of silicon-based materials in the pores of carbon materials. Controlling the temperature, pressure and time of vapor deposition within the above range can ensure that the reaction gas containing silicon source gas does not decompose and deposit before entering the pores of carbon material, but quickly decomposes and deposits after entering the pores.

[0114] In some embodiments, vapor deposition is performed under a protective atmosphere.

[0115] In some embodiments, the protective atmosphere includes at least one of nitrogen, argon, helium, neon, krypton, and xenon.

[0116] In some embodiments, the volume ratio of the protective atmosphere to the reaction gas is 1:10 to 10:1. Specifically, the volume ratio of the protective atmosphere to the reaction gas can be 1:1, 1:2, 1:5, 1:7, 1:8, 1:10, 10:1, 9:1, 6:1, 5:1, 4:1, and 2:1, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0117] In some embodiments, the raw material of the silicon source gas includes at least one of monosilane, disilane, monochlorosilane, dichlorosilane, trichlorosilane, and tetrachlorosilane. It should be noted that when the raw material of the silicon source gas is monosilane, disilane, monochlorosilane, or dichlorosilane, it is gaseous at room temperature; when the raw material of the silicon source gas is trichlorosilane or tetrachlorosilane, it is liquid at room temperature. During the vapor deposition process, the liquid silicon source gas vaporizes and becomes a gaseous silicon source.

[0118] In some embodiments, the volume percentage of hydrogen in the reaction gas containing silicon source gas and hydrogen is 50% to 98%, specifically 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, and 98%. Of course, other values ​​within the above range are also possible and are not limited here. If the mass percentage of hydrogen is too low, the gaseous silicon source will decompose too quickly, easily decomposing and depositing quickly on the surface of the carbon material, thereby causing pore sealing problems. If the volume percentage of hydrogen is too high, although the reaction process can be well controlled, the decomposition rate of the gaseous silicon source will be too slow, thereby affecting the deposition efficiency. Therefore, by controlling the volume proportion of hydrogen at 50% to 98%, under the synergistic effect of the protective atmosphere and hydrogen, the decomposition rate of the gaseous silicon source can be controlled, thereby controlling the deposition rate of the silicon-based material, so that the silicon-based material can be evenly and effectively filled in the pores of the carbon material, reducing the problem of the gaseous silicon source decomposing too quickly and depositing on the surface of the carbon material, thereby causing the pores in the carbon material to be closed.

[0119] In some embodiments, the method further comprises: cooling, washing, and drying the vapor-deposited reaction product to obtain a composite negative electrode material.

[0120] In some embodiments, the washing method comprises ultrasonic cleaning.

[0121] In some embodiments, the washing solvent comprises anhydrous ethanol.

[0122] In some embodiments, the washing time is 30 min to 60 min, specifically 30 min, 35 min, 40 min, 45 min, 50 min, 51 min, 53 min, 55 min 56 min, 57 min, 58 min, 59 min and 60 min. Of course, it can also be other values ​​within the above range, which is not limited here.

[0123] In some embodiments, the drying time is 20 min to 100 min. Specifically, the drying time can be 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, 65 min, 70 min, 75 min, 80 min, 85 min, 90 min, 95 min, and 100 min, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0124] In some embodiments, the drying temperature is 70°C to 90°C, specifically 70°C, 75°C, 80°C, 81°C, 83°C, 84°C, 85°C, 86°C, 87°C, 88°C, 89°C and 90°C. Of course, it can also be other values ​​between 70°C and 90°C, which are not limited here.

[0125] The open pores in the composite negative electrode material prepared in this embodiment account for 2% to 20% of the total pores, and can specifically be 2%, 3%, 4%, 5%, 8%, 10%, 12%, 15%, 16%, 17%, 18%, 19% and 20%, etc. Of course, it can also be other values ​​within the above range, which are not limited here. If the open porosity is too large, it means that the amount of silicon-based material filled in the carbon material is too small, resulting in a low specific capacity of the composite negative electrode material, and too many pores in the composite negative electrode material are likely to affect the overall structural stability of the material; if the open porosity is too small, it means that the silicon-based material is filled in the carbon material too much, resulting in too little pore space for buffering volume expansion, and there is not enough pore space in the composite negative electrode material to withstand the volume expansion during the charge and discharge process. In addition, due to factors such as diffusion limitations, it is impossible for the open pores of the carbon material to be 100% filled with Si. Therefore, the open porosity of the pores in the composite negative electrode material is controlled between 2% and 20% of the total pores. On the one hand, the silicon-based material can be fully filled in the pores of the carbon material, thereby improving the specific capacity of the material; on the other hand, a certain amount of pore space is retained to buffer the volume expansion without causing a significant decrease in the structural stability of the material, thereby making the overall performance of the material better.

[0126] In some embodiments, the method further comprises: performing a surface coating treatment on the composite negative electrode material obtained above to form a coating layer on the surface of the composite negative electrode material to obtain a composite negative electrode material having a coating layer on the surface.

[0127] It can be understood that during the above-mentioned surface coating treatment, the coating material is coated on the surface of the composite negative electrode material so that part of the open pores on the surface of the composite negative electrode material are covered by the coating material, and the remaining pores can alleviate the volume expansion of silicon; and in the process of vapor deposition, it is difficult to ensure that all silicon-based materials are deposited inside the composite negative electrode material. Therefore, the coating layer can also cover and protect a small amount of Si particles exposed on the surface of the composite negative electrode material, while reducing the direct contact between the Si particles and the electrolyte without affecting the transmission of lithium ions, which is conducive to the formation of a thinner SEI film when the material contacts the electrolyte, so that it consumes less electrolyte, has a better cycle retention rate and lower volume expansion, and can also improve the specific capacity of the material.

[0128] In some embodiments, the coating material includes at least one of a carbon material, a metal oxide material, a polymer material, and a nitride material.

[0129] In some embodiments, the carbon material includes at least one of soft carbon, hard carbon, crystalline carbon, and amorphous carbon.

[0130] In some embodiments, the metal oxide material includes at least one of oxides of Sn, Ge, Fe, Si, Cu, Ti, Na, Mg, Al, Ca, and Zn.

[0131] In some embodiments, the nitride material includes at least one of silicon nitride, aluminum nitride, titanium nitride, and tantalum nitride.

[0132] In some embodiments, the polymer material includes at least one of polyaniline, polyacrylic acid, polyurethane, polydopamine, polyacrylamide, sodium carboxymethylcellulose, polyimide, and polyvinyl alcohol.

[0133] In some embodiments, the composite negative electrode material having a carbon coating layer on the surface is tested by N2 adsorption-desorption method. The composite negative electrode material having a carbon coating layer on the surface has a peak Q3 in the range of 2nm to 50nm and satisfies the following relationship Q3 / Q2≤0.3. Specifically, Q3 / Q2 can be 0.1, 0.15, 0.2, 0.21, 0.2 2 , 0.23, 0.25, 0.26, 0.26, 0.28, 0.29 and 0.3, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0134] It should be noted that when the peak values ​​of the carbon material after depositing the silicon-based material and the negative electrode material after being coated with the carbon coating layer tested by the N2 adsorption-desorption method in the range of 2nm to 50nm meet the above relationship, the part of the silicon-based material exposed on the surface of the carbon material after depositing the silicon-based material can be coated by the carbon coating layer, which can reduce the direct contact between the part of the exposed silicon-based material and the electrolyte, reduce the occurrence of side reactions of the negative electrode material, and the negative electrode material coated with the carbon coating layer can improve the structural stability during the charging and discharging process.

[0135] The present application also provides a battery comprising the above-mentioned composite negative electrode material.

[0136] The above are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application should be included in the scope of protection of the present application.

[0137] Example 1

[0138] (1) Dissolve catechol in deionized water containing NaOH to obtain a mixed solution, wherein the molar ratio of NaOH to catechol is 2:1; add zinc acetate to the mixed solution, stir at room temperature for 24 hours to obtain a precipitate, wash with deionized water and dry to obtain a metal coordination compound powder, wherein the molar ratio of zinc acetate to catechol is 4:1; finally, place the metal coordination compound powder in a quartz tube, purge with high-purity nitrogen for 10 minutes to remove the air inside the quartz tube, heat the tube to 1000°C at a rate of 5°C / min, keep the temperature for 3 hours, and cool the tube to obtain a porous carbon material.

[0139] The porous carbon material is loaded into a CVD furnace, and the CVD furnace is evacuated to exhaust the air in the CVD furnace. The evacuation is stopped when the deposition pressure reaches 2 kPa. The CVD furnace is powered on and argon gas is introduced at a rate of 10 L / min to purify the CVD furnace. At this time, the oxygen content in the furnace is ≤5%.

[0140] (2) The furnace temperature was raised to 400°C at a heating rate of 10°C / min, and the vacuum system was reopened and evacuated to 2 kPa. At this time, the oxygen content in the furnace was ≤0.5%. Then, the reaction gas was introduced at a rate of 3 L / min for chemical vapor deposition for 50 hours to obtain a reaction product. The reaction gas was a mixture of monosilane and hydrogen, and the volume proportion of hydrogen in the reaction gas was 55%.

[0141] (3) Argon was introduced at a rate of 10 L / min, the argon partial pressure was controlled at 0.1 kPa, the vacuum pump speed was adjusted, and the deposition pressure in the CVD furnace was controlled at 2 kPa.

[0142] (4) Turn off the power and close the vacuum system, and introduce argon into the CVD furnace until the pressure inside the CVD furnace reaches normal pressure, then open the vent valve. After the temperature inside the CVD furnace cools to room temperature, stop introducing argon, take out the reaction product, ultrasonically clean it with anhydrous ethanol for 20 minutes, and then dry it in an oven at 70°C for 60 minutes to obtain a composite negative electrode material.

[0143] The composite negative electrode material prepared in this embodiment includes a carbon material and a silicon-based material. The carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material. The composite negative electrode material has pores, and has three pores that are not on the same straight line.

[0144] Figure 4 is a comparison diagram of the adsorption curves of the composite negative electrode material and the carbon material provided in Example 1 of the present application. As shown in Figure 4, the carbon material after removing the silicon-based material from the composite negative electrode material is tested by the N2 adsorption-desorption method, and has a peak value Q1 in the range of 2nm to 50nm, Q1=0.82; the composite negative electrode material is tested by the N2 adsorption-desorption method, and has a peak value Q2 in the range of 2nm to 50nm, Q2=0.46, Q2 / Q1=0.56.

[0145] The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

[0146] Example 2:

[0147] (1) Dissolve catechol in deionized water containing NaOH to obtain a mixed solution, wherein the molar ratio of NaOH to catechol is 6:1; add zinc acetate to the mixed solution, stir at room temperature for 24 hours to obtain a precipitate, wash with deionized water and dry to obtain a metal coordination compound powder, wherein the molar ratio of zinc acetate to catechol is 4:1; finally, place the metal coordination compound powder in a quartz tube, purge with high-purity nitrogen for 10 minutes to remove the air inside the quartz tube, heat the tube to 1000°C at a rate of 5°C / min, keep the temperature for 3 hours, and cool the tube to obtain a porous carbon material.

[0148] The porous carbon material is loaded into a CVD furnace, and the CVD furnace is evacuated to exhaust the air in the CVD furnace. When the pressure in the CVD furnace reaches 6 kPa, the evacuation is stopped. The CVD furnace is powered on and nitrogen is introduced at a rate of 2 L / min. At this time, the oxygen content in the furnace is ≤5%.

[0149] (2) The furnace temperature was raised to 500°C at a heating rate of 5°C / min, and the vacuum system was reopened and evacuated to 6 kPa. At this time, the oxygen content in the furnace was ≤0.5%; then, the reaction gas was introduced at a rate of 50 L / min for chemical vapor deposition for 20 hours to obtain a reaction product; wherein, the reaction gas was monosilane and hydrogen, and the volume proportion of hydrogen in the reaction gas was 75%.

[0150] (3) Nitrogen was introduced at a rate of 2 L / min, the nitrogen partial pressure was controlled at 0.2 kPa, the vacuum pump speed was adjusted, and the deposition pressure in the CVD furnace was controlled at 8 kPa.

[0151] (4) Turn off the power and close the vacuum system, and introduce nitrogen into the CVD furnace until the pressure inside the CVD furnace reaches normal pressure, then open the vent valve. After the temperature inside the CVD furnace cools to room temperature, stop introducing nitrogen, take out the reaction product, ultrasonically clean it with anhydrous ethanol for 40 minutes, and then dry it in an oven at 80°C for 90 minutes to obtain a composite negative electrode material.

[0152] The composite negative electrode material prepared in this embodiment includes a carbon material and a silicon-based material. The carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material. The composite negative electrode material has pores, and has three pores that are not on the same straight line.

[0153] The carbon material after removing the silicon-based material from the composite negative electrode material was tested using the N2 adsorption-desorption method, and the peak value Q1 was found to be 0.28 in the range of 2nm to 50nm. The composite negative electrode material was tested using the N2 adsorption-desorption method, and the peak value Q2 was found to be 0.05 in the range of 2nm to 50nm, and Q2 / Q1 was found to be 0.18.

[0154] The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

[0155] Example 3

[0156] (1) Dissolve catechol in deionized water containing NaOH to obtain a mixed solution, wherein the molar ratio of NaOH to catechol is 4:1; add zinc acetate to the mixed solution, stir at room temperature for 24 hours to obtain a precipitate, wash with deionized water and dry to obtain a metal coordination compound powder, wherein the molar ratio of zinc acetate to catechol is 4:1; finally, place the metal coordination compound powder in a quartz tube, purge with high-purity nitrogen for 10 minutes to remove the air inside the quartz tube, heat to 1000°C at a rate of 5°C / min, keep warm for 3 hours, and cool to obtain a porous carbon material.

[0157] The porous carbon material is loaded into a CVD furnace, and the CVD furnace is evacuated to exhaust the air in the CVD furnace. When the pressure in the CVD furnace reaches 10 kPa, the evacuation is stopped. The CVD furnace is powered on and argon gas is introduced at a rate of 16 L / min. At this time, the oxygen content in the furnace is ≤5%.

[0158] (2) The furnace temperature was raised to 450°C at a heating rate of 15°C / min, and the vacuum system was reopened and evacuated to 10 kPa. At this time, the oxygen content in the furnace was ≤0.5%. Then, the reaction gas was introduced at a rate of 5 L / min for chemical vapor deposition for 6 hours to obtain a reaction product, wherein the reaction gas was methane silicon and hydrogen, and the volume proportion of hydrogen in the reaction gas was 95%.

[0159] (3) Argon was introduced at a rate of 16 L / min, the argon partial pressure was controlled at 0.15 kPa, the vacuum pump speed was adjusted, and the deposition pressure in the CVD furnace was controlled at 2 kPa.

[0160] (4) Turn off the power and close the vacuum system, and open the vent valve when argon is introduced into the CVD furnace until the pressure inside the CVD furnace reaches normal pressure. After the temperature inside the CVD furnace cools to room temperature, stop introducing argon, take out the reaction product, ultrasonically clean it with anhydrous ethanol for 30 minutes, and then dry it in an oven at 80°C for 30 minutes to obtain a composite negative electrode material.

[0161] The composite negative electrode material prepared in this embodiment includes a carbon material and a silicon-based material. The carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material. The composite negative electrode material has pores, and has three pores that are not on the same straight line.

[0162] The carbon material after removing the silicon-based material from the composite negative electrode material was tested using the N2 adsorption-desorption method, and the peak value Q1 was found to be 0.59 in the range of 2nm to 50nm. The composite negative electrode material was tested using the N2 adsorption-desorption method, and the peak value Q2 was found to be 0.35 in the range of 2nm to 50nm, and Q2 / Q1 was found to be 0.59.

[0163] The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

[0164] Example 4

[0165] (1) Dissolve catechol in deionized water containing NaOH to obtain a mixed solution, wherein the molar ratio of NaOH to catechol is 8:1; add zinc acetate to the mixed solution, stir at room temperature for 24 hours to obtain a precipitate, wash with deionized water and dry to obtain a metal coordination compound powder, wherein the molar ratio of zinc acetate to catechol is 4:1; finally, place the metal coordination compound powder in a quartz tube, purge with high-purity nitrogen for 10 minutes to remove the air inside the quartz tube, heat the tube to 1000°C at a rate of 5°C / min, keep the temperature for 3 hours, and cool the tube to obtain a porous carbon material.

[0166] The porous carbon material is loaded into a CVD furnace, and the CVD furnace is evacuated to exhaust the air in the CVD furnace. When the pressure in the CVD furnace reaches 5kPa, the evacuation is stopped. The CVD furnace is powered on, and nitrogen is introduced at a rate of 15L / min to purify the CVD furnace. At this time, the oxygen content in the furnace is ≤5%.

[0167] (2) The furnace temperature was raised to 650°C at a heating rate of 10°C / min, and the vacuum system was reopened and evacuated to 5 kPa. At this time, the oxygen content in the furnace was ≤0.5%. Then, the reaction gas was introduced at a rate of 20 L / min for chemical vapor deposition for 5 hours to obtain a reaction product, wherein the reaction gas was methane silicon and hydrogen, and the volume proportion of hydrogen in the reaction gas was 60%.

[0168] (3) Nitrogen was introduced at a rate of 12 L / min, the partial pressure of nitrogen was controlled at 0.08 kPa, and the vacuum pump speed was adjusted to control the deposition pressure in the CVD furnace at 1 kPa.

[0169] (4) Turn off the power and close the vacuum system, and introduce nitrogen into the CVD furnace until the pressure inside the CVD furnace reaches normal pressure, then open the vent valve. After the temperature inside the CVD furnace cools to room temperature, stop introducing nitrogen, take out the reaction product, ultrasonically clean it with anhydrous ethanol for 35 minutes, and then dry it in an oven at 90°C for 80 minutes to obtain a composite negative electrode material.

[0170] The composite negative electrode material prepared in this embodiment includes a carbon material and a silicon-based material. The carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material. The composite negative electrode material has pores, and has three pores that are not on the same straight line.

[0171] The carbon material after removing the silicon-based material from the composite negative electrode material was tested using the N2 adsorption-desorption method, and the peak value Q1 was found to be 0.62 in the range of 2nm to 50nm. The composite negative electrode material was tested using the N2 adsorption-desorption method, and the peak value Q2 was found to be 0.23 in the range of 2nm to 50nm, and Q2 / Q1 was found to be 0.37.

[0172] The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

[0173] Example 5

[0174] The difference from Example 3 is that:

[0175] 4-Methylcatechol was dissolved in deionized water containing NaOH to obtain a mixed solution, wherein the molar ratio of NaOH to catechol was 4:1; zinc acetate was added to the mixed solution, and the mixture was stirred at room temperature for 24 hours to obtain a precipitate, which was washed with deionized water and dried to obtain a metal coordination compound powder, wherein the molar ratio of zinc acetate to 4-methylcatechol was 4:1; finally, the metal coordination compound powder was placed in a quartz tube, purged with high-purity nitrogen for 10 minutes to remove the air inside the quartz tube, and then heated to 1000°C at a rate of 5°C / min, kept warm for 3 hours, and then cooled to obtain a porous carbon material.

[0176] A carbon material with pores is selected, and the specific parameters of the pore structure of the carbon material are shown in Table 1.

[0177] The composite negative electrode material prepared in this embodiment includes a carbon material and a silicon-based material. The carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material. The composite negative electrode material has pores, and has three pores that are not on the same straight line.

[0178] The carbon material after removing the silicon-based material from the composite negative electrode material was tested using the N2 adsorption-desorption method, and the peak value Q1 was found to be 0.78 in the range of 2nm to 50nm. The composite negative electrode material was tested using the N2 adsorption-desorption method, and the peak value Q2 was found to be 0.34 in the range of 2nm to 50nm, and Q2 / Q1 was found to be 0.43.

[0179] The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

[0180] Example 6

[0181] The difference from Example 3 is that:

[0182] 2,3-dihydroxynaphthalene is dissolved in deionized water containing NaOH to obtain a mixed solution, wherein the molar ratio of NaOH to 2,3-dihydroxynaphthalene is 4:1; zinc acetate is added to the mixed solution, and the mixture is stirred at room temperature for 24 hours to obtain a precipitate, which is washed with deionized water and dried to obtain a metal coordination compound powder, wherein the molar ratio of zinc acetate to 2,3-dihydroxynaphthalene is 4:1; finally, the metal coordination compound powder is placed in a quartz tube, purged with high-purity nitrogen for 10 minutes to remove the air inside the quartz tube, and then heated to 1000°C at a rate of 5°C / min, kept warm for 3 hours, and then cooled to obtain a porous carbon material.

[0183] A carbon material with pores is selected, and the specific parameters of the pore structure of the carbon material are shown in Table 1.

[0184] The composite negative electrode material prepared in this embodiment includes a carbon material and a silicon-based material. The carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material. The composite negative electrode material has pores, and has three pores that are not on the same straight line.

[0185] The carbon material after removing the silicon-based material from the composite negative electrode material was tested using the N2 adsorption-desorption method, and a peak Q1 was found in the range of 2nm to 50nm, with Q1 = 0.50; the composite negative electrode material was tested using the N2 adsorption-desorption method, and a peak Q2 was found in the range of 2nm to 50nm, with Q2 = 0.2 and Q2 / Q1 = 0.40.

[0186] The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

[0187] Example 7

[0188] The difference from Example 3 is that:

[0189] 3,4-dihydroxybenzonitrile was dissolved in deionized water containing NaOH to obtain a mixed solution, wherein the molar ratio of NaOH to 3,4-dihydroxybenzonitrile was 4:1; zinc acetate was added to the mixed solution, and the mixture was stirred at room temperature for 24 hours to obtain a precipitate, which was washed with deionized water and dried to obtain a metal coordination compound powder, wherein the molar ratio of zinc acetate to 3,4-dihydroxybenzonitrile was 4:1; finally, the metal coordination compound powder was placed in a quartz tube, purged with high-purity nitrogen for 10 minutes to remove the air inside the quartz tube, and then heated to 1000°C at a rate of 5°C / min, maintained for 3 hours, and then cooled to obtain a porous carbon material.

[0190] A carbon material with pores is selected, and the specific parameters of the pore structure of the carbon material are shown in Table 1.

[0191] The composite negative electrode material prepared in this embodiment includes a carbon material and a silicon-based material. The carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material. The composite negative electrode material has pores, and has three pores that are not on the same straight line.

[0192] The carbon material after removing the silicon-based material from the composite negative electrode material was tested using the N2 adsorption-desorption method, and the peak value Q1 was found to be 0.67 in the range of 2nm to 50nm. The composite negative electrode material was tested using the N2 adsorption-desorption method, and the peak value Q2 was found to be 0.17 in the range of 2nm to 50nm, and Q2 / Q1 was found to be 0.25.

[0193] The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

[0194] Example 8

[0195] The difference from Example 3 is that:

[0196] 3-Hydroxyamine benzoate is dissolved in deionized water containing NaOH to obtain a mixed solution, wherein the molar ratio of NaOH to 3-hydroxyamine benzoate is 4:1; zinc acetate is added to the mixed solution, and the mixture is stirred at room temperature for 24 hours to obtain a precipitate, which is washed with deionized water and dried to obtain a metal coordination compound powder, wherein the molar ratio of zinc acetate to 3-hydroxyamine benzoate is 4:1; finally, the metal coordination compound powder is placed in a quartz tube, purged with high-purity nitrogen for 10 minutes to remove the air inside the quartz tube, and then heated to 1000°C at a rate of 5°C / min, kept warm for 3 hours, and then cooled to obtain a porous carbon material.

[0197] A carbon material with pores is selected, and the specific parameters of the pore structure of the carbon material are shown in Table 1.

[0198] The composite negative electrode material prepared in this embodiment includes a carbon material and a silicon-based material. The carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material. The composite negative electrode material has pores, and has three pores that are not on the same straight line.

[0199] The carbon material after removing the silicon-based material from the composite negative electrode material was tested using the N2 adsorption-desorption method, and the peak value Q1 was found to be 0.75 in the range of 2nm to 50nm. The peak value Q2 was found to be 0.33 and Q2 / Q1 was found to be 0.44 in the range of 2nm to 50nm when the composite negative electrode material was tested using the N2 adsorption-desorption method.

[0200] The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

[0201] Example 9

[0202] The difference from Example 3 is that:

[0203] Pyrogallol is dissolved in deionized water containing NaOH to obtain a mixed solution, wherein the molar ratio of NaOH to pyrogallol is 4:1; zinc acetate is added to the mixed solution, and the mixture is stirred at room temperature for 24 hours to obtain a precipitate, which is washed with deionized water and dried to obtain a metal coordination compound powder, wherein the molar ratio of zinc acetate to pyrogallol is 4:1; finally, the metal coordination compound powder is placed in a quartz tube, purged with high-purity nitrogen for 10 minutes to remove the air inside the quartz tube, and then heated to 1000°C at a rate of 5°C / min, kept warm for 3 hours, and then cooled to obtain a porous carbon material.

[0204] A carbon material with pores is selected, and the specific parameters of the pore structure of the carbon material are shown in Table 1.

[0205] The composite negative electrode material prepared in this embodiment includes a carbon material and a silicon-based material. The carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material. The composite negative electrode material has pores, and has three pores that are not on the same straight line.

[0206] The carbon material after removing the silicon-based material from the composite negative electrode material was tested using the N2 adsorption-desorption method, and the peak value Q1 was found to be 2nm to 50nm, with Q1=0.80. The composite negative electrode material was tested using the N2 adsorption-desorption method, and the peak value Q2 was found to be 2nm to 50nm, with Q2=0.25 and Q2 / Q1=0.31.

[0207] The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

[0208] Example 10

[0209] The difference from Example 1 is that:

[0210] (3) Argon was introduced at a rate of 50 L / min, the partial pressure of argon was controlled at 10 kPa, and the vacuum pump speed was adjusted to control the deposition pressure in the CVD furnace at 50 kPa.

[0211] The composite negative electrode material prepared in this embodiment includes a carbon material and a silicon-based material. The carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material. The composite negative electrode material has pores, and has three pores that are not on the same straight line.

[0212] The carbon material after removing the silicon-based material from the composite negative electrode material was tested using the N2 adsorption-desorption method, and the peak value Q1 was found to be 0.83 in the range of 2nm to 50nm. The composite negative electrode material was tested using the N2 adsorption-desorption method, and the peak value Q2 was found to be 0.17 in the range of 2nm to 50nm, and Q2 / Q1 was found to be 0.20.

[0213] The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

[0214] Example 11

[0215] The difference from Example 1 is that:

[0216] After step (4), the prepared composite negative electrode material is subjected to surface coating treatment to obtain a composite negative electrode material having a coating layer on the surface.

[0217] The composite negative electrode material prepared in this embodiment includes a carbon material and a silicon-based material. The carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material. The composite negative electrode material has pores, and has three pores that are not on the same straight line.

[0218] The carbon material after removing the silicon-based material from the composite negative electrode material was tested using the N2 adsorption-desorption method, and the peak value Q1 was found to be 0.86 in the range of 2nm to 50nm. The composite negative electrode material was tested using the N2 adsorption-desorption method, and the peak value Q2 was found to be 0.5 in the range of 2nm to 50nm, and Q2 / Q1 was found to be 0.58.

[0219] The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

[0220] Example 12

[0221] The difference from Example 1 is that:

[0222] (2) The furnace temperature was raised to 700°C at a heating rate of 10°C / min, and the vacuum system was reopened and evacuated to 2 kPa. At this time, the oxygen content in the furnace was ≤0.5%; then, the reaction gas was introduced at a rate of 3 L / min for chemical vapor deposition for 50 hours to obtain a reaction product; wherein, the reaction gas was a mixture of monosilane and hydrogen, and the volume proportion of hydrogen in the reaction gas was 55%.

[0223] In the composite negative electrode material prepared in this embodiment, the carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material; the composite negative electrode material has pores, and has three pores that are not on the same straight line.

[0224] The carbon material after removing the silicon-based material from the composite negative electrode material was tested using the N2 adsorption-desorption method, and the peak value Q1 was found to be 0.43 in the range of 2nm to 50nm. The composite negative electrode material was tested using the N2 adsorption-desorption method, and the peak value Q2 was found to be 0.14 in the range of 2nm to 50nm, and Q2 / Q1 was found to be 0.33.

[0225] The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

[0226] Example 13

[0227] The difference from Example 3 is that:

[0228] Baicalein was dissolved in deionized water containing NaOH to obtain a mixed solution, wherein the molar ratio of NaOH to baicalein was 4:1; zinc acetate was added to the mixed solution, and the mixture was stirred at room temperature for 24 hours to obtain a precipitate, which was washed with deionized water and dried to obtain a metal coordination compound powder, wherein the molar ratio of zinc acetate to baicalein was 4:1; finally, the metal coordination compound powder was placed in a quartz tube, purged with high-purity nitrogen for 10 minutes to remove the air inside the quartz tube, and then heated to 1000°C at a rate of 5°C / min, kept warm for 3 hours, and then cooled to obtain a porous carbon material.

[0229] The porous carbon material is loaded into a CVD furnace, and the CVD furnace is evacuated to exhaust the air in the CVD furnace. The evacuation is stopped when the deposition pressure reaches 2 kPa. The CVD furnace is powered on and argon gas is introduced into the CVD furnace at a rate of 10 L / min to purify the CVD furnace. At this time, the oxygen content in the furnace is ≤5%.

[0230] (2) The CVD furnace is connected in series with an evaporation furnace to deposit SiO 1.5 The particles were placed in an evaporation furnace and the furnace temperature was raised to 1400°C at a heating rate of 10°C / min to make SiO 1.5 The particles evaporate into a gaseous state.

[0231] (3) At the same time, the CVD furnace temperature was raised to 650°C at a heating rate of 10°C / min, and the vacuum system was reopened and evacuated to 2 kPa. At this time, the oxygen content in the furnace was ≤0.5%.

[0232] (4) Turn off the power and close the vacuum system, and introduce argon into the CVD furnace until the pressure inside the CVD furnace reaches normal pressure, then open the vent valve. After the temperature inside the CVD furnace cools to room temperature, stop introducing argon, take out the reaction product, ultrasonically clean it with anhydrous ethanol for 20 minutes, and then dry it in an oven at 70°C for 60 minutes to obtain a composite negative electrode material.

[0233] The composite negative electrode material prepared in this embodiment includes a carbon material and a silicon-based material. The carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material. The composite negative electrode material has pores, and has three pores that are not on the same straight line.

[0234] The carbon material after removing the silicon-based material from the composite negative electrode material was tested using the N2 adsorption-desorption method, and the peak value Q1 was found to be 0.45 in the range of 2nm to 50nm. The peak value Q2 was found to be 0.22 and Q2 / Q1 was found to be 0.50 in the range of 2nm to 50nm when the composite negative electrode material was tested using the N2 adsorption-desorption method.

[0235] The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

[0236] Example 14

[0237] (1) The difference from Example 3 is that:

[0238] Methyl gallate is dissolved in deionized water containing NaOH to obtain a mixed solution, wherein the molar ratio of NaOH to methyl gallate is 4:1; zinc acetate is added to the mixed solution, and the mixture is stirred at room temperature for 24 hours to obtain a precipitate, which is washed with deionized water and dried to obtain a metal coordination compound powder, wherein the molar ratio of zinc acetate to methyl gallate is 4:1; finally, the metal coordination compound powder is placed in a quartz tube, purged with high-purity nitrogen for 10 minutes to remove the air inside the quartz tube, and then heated to 1000°C at a rate of 5°C / min, kept warm for 3 hours, and then cooled to obtain a porous carbon material.

[0239] In the above preparation process, the presence of at least one single chelate group in the aromatic ring is the key to forming a thermally stable metal coordination compound. Only when the coordination compound has sufficiently high thermal stability can it be converted into a carbon material through heat treatment.

[0240] The porous carbon material is loaded into a CVD furnace, and the CVD furnace is evacuated to exhaust the air in the CVD furnace. The evacuation is stopped when the deposition pressure reaches 2 kPa. The CVD furnace is powered on and argon gas is introduced into the CVD furnace at a rate of 10 L / min to purify the CVD furnace. At this time, the oxygen content in the furnace is ≤5%.

[0241] (2) The CVD furnace is connected in series with an evaporation furnace. Al particles are first placed in the evaporation furnace, and the furnace temperature is raised to 1200°C at a heating rate of 10°C / min, so that the Al particles evaporate into gas.

[0242] (3) At the same time, the CVD furnace temperature was raised to 500°C at a heating rate of 10°C / min, and the vacuum system was reopened and evacuated to 2 kPa. At this time, the oxygen content in the furnace was ≤0.5%.

[0243] (4) The CVD furnace is connected in series with an evaporation furnace, and the Si particles are placed in the evaporation furnace. The furnace temperature is raised to 2700°C at a heating rate of 10°C / min, so that the Si particles evaporate into gas.

[0244] (5) At the same time, the CVD furnace temperature was raised to 500°C at a heating rate of 10°C / min, and the vacuum system was reopened and evacuated to 2 kPa. At this time, the oxygen content in the furnace was ≤0.5%.

[0245] (6) The CVD furnace temperature was further increased to 700°C at a heating rate of 10°C / min, and the vacuum system was reopened and evacuated to 2 kPa. At this time, the oxygen content in the furnace was ≤0.5%, allowing Si and Al to react to form Al-Si alloy.

[0246] (7) Stop the power supply and close the vacuum system, and introduce argon into the CVD furnace until the pressure inside the CVD furnace reaches normal pressure, then open the vent valve. After the temperature inside the CVD furnace cools to room temperature, stop introducing argon, take out the reaction product, ultrasonically clean it with anhydrous ethanol for 20 minutes, and then dry it in an oven at 70°C for 60 minutes to obtain a composite negative electrode material.

[0247] The composite negative electrode material prepared in this embodiment includes a carbon material and a silicon-based material. The carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material. The composite negative electrode material has pores, and has three pores that are not on the same straight line.

[0248] The carbon material after removing the silicon-based material from the composite negative electrode material was tested using the N2 adsorption-desorption method, and the peak value Q1 was found to be 0.45 in the range of 2nm to 50nm. The peak value Q2 was found to be 0.18 and Q2 / Q1 was found to be 0.40 in the range of 2nm to 50nm when the composite negative electrode material was tested using the N2 adsorption-desorption method.

[0249] The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

[0250] Comparative Example 1

[0251] The difference from Example 1 is that:

[0252] The reaction gas introduced in step (2) contains only monosilane and no hydrogen.

[0253] The composite negative electrode material obtained in this comparative example includes a carbon material, a silicon-based material, and a carbon coating layer, and the carbon material has pores.

[0254] The carbon material after removing the silicon-based material from the composite negative electrode material was tested using the N2 adsorption-desorption method, and the peak value Q1 was found to be 0.82 in the range of 2nm to 50nm. The composite negative electrode material was tested using the N2 adsorption-desorption method, and the peak value Q2 was found to be 0.54 in the range of 2nm to 50nm, and Q2 / Q1 was found to be 0.66.

[0255] Comparative Example 2

[0256] The difference from Example 1 is that:

[0257] No vacuuming is performed in step (1).

[0258] The composite negative electrode material obtained in this comparative example includes a carbon material, a silicon-based material, and a carbon coating layer, and the carbon material has pores.

[0259] The carbon material after removing the silicon-based material from the composite negative electrode material was tested using the N2 adsorption-desorption method, and the peak value Q1 was found to be 0.82 in the range of 2nm to 50nm. The composite negative electrode material was tested using the N2 adsorption-desorption method, and the peak value Q2 was found to be 0.59 in the range of 2nm to 50nm, and Q2 / Q1 was found to be 0.72.

[0260] Comparative Example 3

[0261] The difference from Example 1 is that:

[0262] In step (2), the furnace temperature is raised to 400°C at a heating rate of 10°C / min, and the vacuum system is reopened and evacuated to 2 kPa. At this time, the oxygen content in the furnace is ≤0.5%; then, the reaction gas is introduced at a rate of 5 L / min for chemical vapor deposition for 100 hours to obtain a reaction product; wherein the reaction gas is a mixed gas of monosilane and hydrogen, and the volume proportion of hydrogen in the reaction gas is 55%.

[0263] The carbon material after removing the silicon-based material from the composite negative electrode material was tested using the N2 adsorption-desorption method, and the peak value Q1 was found to be 0.82 in the range of 2nm to 50nm. The composite negative electrode material was tested using the N2 adsorption-desorption method, and the peak value Q2 was found to be 0.62 in the range of 2nm to 50nm, and Q2 / Q1 was found to be 0.76.

[0264] Performance Testing

[0265] (1) Test method for specific surface area of ​​composite negative electrode materials or carbon materials:

[0266] The specific surface area was measured using a Micromeritics TriStar 3000 surface area and pore size analyzer.

[0267] (2) Test method for density of composite negative electrode material or carbon material:

[0268] The powder is placed in an environment filled with N2, and the nitrogen gas replacement amount is measured to calculate the density.

[0269] (3) Testing method for pore volume of composite negative electrode materials or carbon materials:

[0270] The test was conducted using the ASAP2460 equipment from American Micromeritics. The pore volume V was calculated using the BJHDesorption cumulative volume of pores model. Calculated within the pore size range.

[0271] Micropore and mesopore analysis was performed using the Micromeretics ASAP 2460. At liquid nitrogen temperature, the equilibrium amount of nitrogen adsorbed on a surface is correlated with properties such as pore size. By combining the relationship between the amount adsorbed and relative pressure during adsorption, various models can be fitted to calculate pore size. The software generates reports using density functional theory (DFT) to calculate pore size distribution, total pore volume, and pore volume within a specific range.

[0272] The true density P of the negative electrode material is tested, and the porosity of the negative electrode material is calculated to be V / (V+1 / P).

[0273] (4) Pore diameter of composite negative electrode materials or carbon materials and pore diameter testing method:

[0274] Take an appropriate amount of sample particles and measure the pore diameter and the pore diameter change from the surface to the center of the particle under a transmission electron microscope (SEM can also be used). Select three holes in the sample that are not on the same straight line. The pore diameters of the three holes are D1, D2, and D3, and the pore distances are L1, L2, and L3 respectively. Define A1 as L1 2 -(L2 / 2) 2 、L1 2 -(L3 / 2) 2 、L2 2 -(L1 / 2) 2 、L2 2 -(L3 / 2) 2 、L3 2 -(L1 / 2) 2 or L3 2 -(L2 / 2) 2 The minimum value in , B1 is D1+D2+D3, find the value of A1 / B1.

[0275] (5) Test method for the distribution density of pores in carbon materials:

[0276] After a proper amount of sample particles are cut and processed, the number of pores per unit area on the cut surface of the carbon material is measured to obtain the distribution density of pores in the carbon material.

[0277] (6) Test method for the mass content of silicon-based materials in composite negative electrode materials:

[0278] Weigh the mass of the composite negative electrode material as M1, and the mass of the material tested after etching the silicon-based material as m 2 ,(M1-m 2 ) / M1 is the mass content of silicon-based materials in the composite negative electrode material.

[0279] (7) Testing method for filling rate of carbon material pores:

[0280] The volume of the pores in the composite negative electrode material before etching the active material is measured as V1, and the volume of the pores after etching the silicon-based material is measured as V2. (V2-V1) / V2 is the filling rate of the silicon-based material in the pores of the carbon material.

[0281] (8) Electrochemical performance test

[0282] 1) The initial discharge capacity and initial coulombic efficiency (ICE) were measured using the following method: a negative electrode slurry was prepared using a composite negative electrode material, conductive carbon black, and polyacrylic acid (PPA) in a mass ratio of 75:15:10. This slurry was then coated onto copper foil and dried to form a negative electrode sheet. A lithium metal sheet was used as the counter electrode, and button cells were assembled in an argon-filled glove box. The cells were charged and discharged at a current density of 0.1C over the 0.01V-5V range to determine their initial discharge capacity and initial coulombic efficiency (ICE).

[0283] 2) The test method for the capacity retention rate and the electrode thickness expansion rate after 50 cycles is as follows: a negative electrode slurry is prepared according to a mass ratio of 92:2:2:2:2 of the composite negative electrode material, conductive carbon black (Super-P), conductive graphite (KS-6), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR), which is coated on copper foil and dried to form a negative electrode electrode. The proportion of Si-C and graphite in the mixture of the composite negative electrode material with a carbon coating layer and graphite is determined by the initial reversible specific capacity of the two and the capacity required for the two to be combined. A button cell is assembled in an argon-filled glove box using a metal lithium sheet as the counter electrode. The button cell is subjected to 50 repeated charge and discharge tests in the charge and discharge range of 0.01V-5V at a current density of 1C to obtain the capacity retention rate and the electrode thickness expansion rate after 50 cycles of the battery.

[0284] (9) Test method for porosity of composite negative electrode materials or carbon materials:

[0285] a. First use an electronic balance to measure the mass M1 (g) of the sample in air;

[0286] b. Place the sample in molten paraffin under vacuum, allowing the wax to fully fill the pores of the sample. After soaking for 1 hour until fully saturated, remove the sample and carefully wipe off the wax on the surface of the sample. Then use an electronic balance to measure the mass of the sample in air, M2 (g);

[0287] c. Place the paraffin-filled sample on a sling and immerse it in water and weigh it, mass M3 (g);

[0288] d. Immerse the spreader without the sample in water and weigh it, the mass is M4 (g).

[0289] The porosity of the sample was calculated according to the following formula:

[0290] At the same time, the open porosity of the sample can be calculated according to the following formula:

[0291] Where, ρ s is the density of the carbon material corresponding to the dense solid (g / cm 3 ), ρ L is the density of water (g / cm 3 ), ρ ME is the density of paraffin wax (g / cm 3 ).

[0292] (10) Removing the silicon-based material from the composite negative electrode material by etching:

[0293] Add a 1M nitric acid solution to the composite negative electrode material and soak it for 4 hours. Then, add a 20% mass fraction HF acid solution drop by drop into the composite negative electrode material, which will produce yellow smoke. Repeat the addition until no yellow smoke is produced in the solution. Finally, use a 1M nitric acid solution to digest the residue, then wash and dry it to obtain the composite negative electrode material after removing the silicon-based material.

[0294] (10) Test on the change of average pore size of carbon material after removing silicon-based material from composite negative electrode material:

[0295] Magnetron sputtering or focused ion beam (FIB) technology is used to gradually remove the surface layer of the carbon material. Imaging technology is then used to observe and record the changes in the internal pore size of the carbon material with depth, thereby obtaining the internal pore size change trend. Alternatively, FIB technology is used to cut particles. The carbon material particles are cut using FIB technology, and then the cut surface is imaged to obtain pore size information. By performing probabilistic statistical analysis on this data, the pore size changes of the carbon material can be statistically analyzed.

[0296] Table 1 Parameters of carbon materials

[0297] Table 2 Parameters of composite negative electrode materials

[0298] Table 3 Performance test results of examples and comparative examples

[0299] According to the results shown in Tables 1 to 3, the composite negative electrode material prepared in the embodiment of the present application has a high initial discharge specific capacity, initial coulombic efficiency, and capacity retention rate after 50 cycles, and the electrode thickness expansion rate after 50 cycles is low. This is because in the particle structure of the composite negative electrode material prepared in this embodiment, any three adjacent holes that are not on the same straight line are taken, and the pore diameters of the three holes are D1, D2, and D3, and the pore spacings are L1, L2, and L3, respectively. A1 is defined as L1. 2 -(L2 / 2) 2 、L1 2 -(L3 / 2) 2 、L2 2 -(L1 / 2) 2 、L2 2 -(L3 / 2) 2 、L3 2 -(L1 / 2) 2 or L3 2 -(L2 / 2) 2 The minimum value in , B1 is D1+D2+D3, and the relationship between A1 and B1 satisfies 0.4<A1 / B1<50. At this time, A1 / B1 is within the above range, and the pore distribution inside the composite negative electrode material is within a reasonable range, that is, the pore distribution is moderate and not too sparse or dense. On the one hand, it shows that most of the pores of the composite material are effectively filled with silicon-based materials, that is, the interior of the composite negative electrode material is relatively dense, and the silicon-based material with high stability can provide abundant lithium storage sites, thereby improving the specific capacity and first efficiency of the composite negative electrode material; on the other hand, the interior of the composite negative electrode material is not a completely dense structure, and the silicon-based material has a certain expansion space, which can ensure the structural stability of the composite negative electrode material during the cycle, alleviate the expansion of the electrode sheet, and improve the cycle performance of the battery prepared with the composite negative electrode material.

[0300] As can be seen from the table, compared with Example 1, although the capacity retention rate of the composite negative electrode material of Example 10 is higher after 50 cycles, the initial discharge specific capacity is lower. This is because the air flow of argon introduced during the preparation process is too large, resulting in an excessively large argon partial pressure, which causes the deposition rate of the silicon-based material to be too slow. At the same deposition time, the deposition rate of the silicon-based material in the carbon material is too slow, resulting in a low filling rate of the pores in the carbon material, and too little deposition of the silicon-based material in the pores. The high capacity advantage of silicon cannot be fully utilized, making it difficult to improve the specific capacity of the composite negative electrode material, resulting in a low initial discharge specific capacity of the composite negative electrode material.

[0301] Compared with Example 1, although the composite negative electrode material in Example 14 has higher initial coulombic efficiency and capacity retention rate after 50 cycles, and lower electrode thickness expansion rate after 50 cycles, its initial discharge specific capacity is poor. This is because the silicon-based material deposited in Example 14 is a silicon alloy, and the mass percentage of silicon in the silicon alloy is lower than that of pure crystalline silicon, which results in too little deposited silicon content in the pores, and the high capacity advantage of silicon cannot be fully utilized, making it difficult to improve the specific capacity of the composite negative electrode material, resulting in a low initial discharge specific capacity of the composite negative electrode material.

[0302] Compared with Example 1, in the composite negative electrode material of Comparative Example 1, only monosilane is introduced into the reaction gas during the preparation process, which does not contain hydrogen. Therefore, the decomposition rate of monosilane is too fast and deposited on the surface of the carbon material, resulting in the pores on the surface of the carbon material being closed, and the open porosity is only 0.5%. It is difficult for the silicon-based material to deposit and fill the pores of the carbon material. The filling rate of the pores in the carbon material is too low, and the amount of silicon-based material deposited in the pores is too small, which cannot fully utilize the high capacity advantage of silicon, making it difficult to improve the specific capacity of the composite negative electrode material, thereby resulting in a low first discharge specific capacity of the material.

[0303] Compared with Example 1, the composite negative electrode material of Comparative Example 2 does not undergo a vacuuming step during the preparation process, which is not conducive to the deposition of silicon-based materials in the carbon material. The open porosity is only 0.8%. The silicon-based material is deposited on the surface of the carbon material, resulting in the pores on the surface of the carbon material being closed, making it difficult to deposit into the pores of the carbon material. The filling rate of the pores in the carbon material is low, and the amount of silicon-based material deposited in the pores is too small, which cannot fully utilize the high capacity advantage of silicon, making it difficult to improve the specific capacity of the composite negative electrode material, thereby resulting in a low first discharge specific capacity of the material.

[0304] Compared with Example 1, the content of monosilane in the reaction gas introduced in Comparative Example 3 increases, the amount of silicon-based material deposited in the pores is too much, and there are no pores or fewer pores inside the composite negative electrode material. Although the first discharge specific capacity and the first coulombic efficiency of the composite negative electrode material are increased, the excessive silicon-based material makes it difficult to effectively relieve the stress of the silicon-based material during the cycle, and the composite negative electrode material will have the problem of excessive local stress. The electrode thickness expansion rate increases after 50 cycles, and the composite negative electrode material suffers from pulverization, contact loss with the conductive agent and the current collector, etc., resulting in a decrease in the capacity retention rate after 50 cycles.

Claims

1. A composite negative electrode material, characterized in that: The composite negative electrode material comprises a carbon material and a silicon-based material, the carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material; The composite negative electrode material has holes. For any three adjacent holes that are not on the same straight line, the diameters of the three holes are D1, D2, and D3, respectively, and the hole distances are L1, L2, and L3, respectively. A1 is defined as L1 2 -(L2 / 2) 2 、L1 2 -(L3 / 2) 2 、L2 2 -(L1 / 2) 2 、L2 2 -(L3 / 2) 2 、L3 2 -(L1 / 2) 2 or L3 2 -(L2 / 2) 2 The minimum value of B1 is D1+D2+D3, and 0.4<A1 / B1<50.

2. The composite negative electrode material according to claim 1, characterized in that: In the carbon material after the silicon-based material is removed from the composite negative electrode material, for any three adjacent holes that are not on the same straight line, the pore sizes of the three holes are d1, d2, and d3, respectively, and the pore distances are l1, l2, and l3, respectively, and A2 is defined as l2 2 -(l1 / 2) 2 、l2 2 -(l3 / 2) 2 、l3 2 -(l1 / 2) 2 、l3 2 -(l2 / 2) 2 、l1 2 -(l2 / 2) 2 or l1 2 -(l3 / 2) 2 The minimum value in, B2 is d1+d2+d3, C1 is l2 2 -(l1 / 2) 2 、l2 2 -(l3 / 2) 2 、l3 2 -(l1 / 2) 2 、l3 2 -(l2 / 2) 2 、l1 2 -(l2 / 2) 2 or l1 2 -(l3 / 2) 2 The maximum value among them, and B2 / C1>1, B2 / A2≤4.

3. The composite negative electrode material according to claim 1, characterized in that: The average pore size of the pores in the composite negative electrode material is Dnm, and the value range of D is 0.1-100.

4. The composite negative electrode material according to claim 1, characterized in that In the composite negative electrode material, the average pore distance between any two adjacent pores is Lnm, and the value range of L is 1-300.

5. The composite negative electrode material according to claim 1, characterized in that: The average pore diameter of the pores in the composite negative electrode material is Dnm, and the average pore distance between any two adjacent pores is Lnm, where L≥4×D.

6. The composite negative electrode material according to claim 1, characterized in that: The pore volume of the pores in the composite negative electrode material is 0.001 cm 3 / g~0.6cm 3 / g.

7. The composite negative electrode material according to claim 1, characterized in that: The open pores in the composite negative electrode material account for 2% to 20% of the total pores.

8. The composite negative electrode material according to claim 1, characterized in that: The pores in the carbon material after removing the silicon-based material from the composite negative electrode material include micropores, mesopores and macropores; wherein the volume proportion of the micropores in all pores is 30% to 99%, the volume proportion of the mesopores in all pores is 5% to 70%, and the volume proportion of the macropores in all pores is 0 to 5%.

9. The composite negative electrode material according to claim 8, characterized in that: The pores in the carbon material after the silicon-based material is removed from the composite negative electrode material include mesopores, wherein the volume proportion of pores with a pore size of 2nm to 20nm in the mesopores is >90% of all mesopores; the volume proportion of pores with a pore size of 5nm to 20nm in the mesopores is 10% to 50% of all mesopores.

10. The composite negative electrode material according to claim 1, characterized in that: In the carbon material after the silicon-based material is removed from the composite negative electrode material, the pore size of at least part of the pores gradually decreases from the surface to the inside of the carbon material, wherein the average pore size changes by ≥0.1 nm for every 1 μm of extension from the surface to the inside of the carbon material.

11. The composite negative electrode material according to claim 1, characterized in that: The mass proportion of the silicon-based material in the composite negative electrode material is 15% to 60%.

12. The composite negative electrode material according to claim 1, characterized in that: The carbon material after removing the silicon-based material from the composite negative electrode material is tested by the N2 adsorption-desorption method, and has a peak value Q1 in the range of 2nm to 50nm; the composite negative electrode material is tested by the N2 adsorption-desorption method, and has a peak value Q2 in the range of 2nm to 50nm, and satisfies the following relationship Q2 / Q1≤0.

6.

13. The composite negative electrode material according to claim 1, characterized in that: The mass percentage of oxygen in the composite negative electrode material is ≤10wt%.

14. A method for preparing a composite negative electrode material, characterized in that: The following steps are involved: Providing a carbon material with pores, introducing a reaction gas containing a silicon source gas and hydrogen under a negative pressure environment, and performing vapor deposition on the carbon material to obtain a composite negative electrode material; wherein the composite negative electrode material comprises a carbon material and a silicon-based material, and the composite negative electrode material has pores; In the composite negative electrode material, for any three adjacent holes that are not on the same straight line, the pore sizes of the three holes are D1, D2, and D3, respectively, and the pore distances are L1, L2, and L3, respectively. A1 is defined as L1 2 -(L2 / 2) 2 、L1 2 -(L3 / 2) 2 、L2 2 -(L1 / 2) 2 、L2 2 -(L3 / 2) 2 、L3 2 -(L1 / 2) 2 or L3 2 -(L2 / 2) 2 The minimum value of , B1 is D1+D2+D3, and 0.4<A1 / B1<50; In the carbon material, for any three adjacent holes that are not on the same straight line, the diameters of the three holes are d'1, d'2, and d'3, respectively, and the hole spacings are l'1, l'2, and l'3, respectively. A'2 is defined as l'2 2 -(l'1 / 2) 2 ,l'2 2 -(l'3 / 2) 2 ,l'3 2 -(l'1 / 2) 2 ,l'3 2 -(l'2 / 2) 2 ,l'1 2 -(l'2 / 2) 2 or l'1 2 -(l'3 / 2) 2 The minimum value among them, B'2 is d'1+d'2+d'3, C'1 is l'2 2 -(l'1 / 2) 2 ,l'2 2 -(l'3 / 2) 2 ,l'3 2 -(l'1 / 2) 2 ,l'3 2 -(l'2 / 2) 2 ,l'1 2 -(l'2 / 2) 2 or l'1 2 -(l'3 / 2) 2 The maximum value among them, B'2 / C'1>1, and B'2 / A'2≤4.

15. A battery, characterized in that: The battery comprises the composite negative electrode material according to any one of claims 1 to 13 or the composite negative electrode material prepared by the method for preparing the composite negative electrode material according to claim 14.

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