WO2019047713A1

WO2019047713A1 - Composite negative electrode active material, preparation method therefor and lithium battery

Info

Publication number: WO2019047713A1
Application number: PCT/CN2018/101673
Authority: WO
Inventors: 江正福
Original assignee: 比亚迪股份有限公司
Priority date: 2017-09-05
Filing date: 2018-08-22
Publication date: 2019-03-14
Also published as: CN109428071A

Abstract

Disclosed are a composite negative electrode active material, a preparation method therefor and a lithium battery. The composite negative electrode active material comprises a graphite core, a first coating layer coated on the surface of the graphite core and a second coating layer coated on the first coating layer, the first coating layer comprising carbon and a mixture of a nano-silicon oxide and nano-silicon, and the second coating layer comprising nano-silicon and carbon.

Description

Composite anode active material, preparation method thereof and lithium battery

Technical field

The present disclosure relates to the field of battery materials, and in particular to a composite anode active material, a preparation method thereof and a lithium battery.

Background technique

Graphite is soft, is a non-metallic mineral, has high temperature resistance, oxidation resistance, corrosion resistance, etc. It also has good thermal conductivity and electrical conductivity, so it has attracted attention in the field of electrochemistry and has been widely used. Graphite has good conductivity, high degree of crystallization and good layered structure, so it is very suitable for repeated insertion-deintercalation of lithium ions. It is the most widely used anode material. The silicon-containing substance is also a negative electrode material, which has a function of increasing the theoretical capacity and is often combined with graphite.

CN106532017A discloses a preparation method of SiOx/C surface coated graphite anode material, wherein the specific step is to first prepare SiOx/C material precursor by using SiOx, asphalt and organic acid solution as raw materials. Then, graphite was further added, and samples were prepared by means of spray granulation and high temperature pyrolysis through additives, resins and curing agents. The disclosure can effectively alleviate the volume effect of the silicon material during the charging and discharging process, thereby improving the cycle stability; at the rate of 0.1 C, the first charge and discharge efficiency is 82.42%, the reversible specific capacity is 488.2 mAh/g, and the resin is utilized at the same time. The skeleton formed after solidification can effectively avoid the phenomenon of blocking and agglomeration between the particles during the carbonization process of the additive, so that the prepared material has the characteristics of good dispersibility and uniformity, easy mass production, and low cost.

However, the product prepared by the above method has the following disadvantages: firstly, due to the use of silicon oxide, in the process of lithium intercalation, oxygen must consume a part of the lithium source to form an oxide of lithium which does not have reversible lithium intercalation. The performance in electrochemical performance is the first charge and discharge efficiency. Now the first charge and discharge efficiency of graphite is between 93% and 95%, and according to the above application, the best first charge and discharge efficiency is about 82%; Secondly, the material specific capacity of SiOx is too low compared to Si. Therefore, in order to obtain the same specific capacity, more SiOx must be added, which also makes it difficult to further improve the first charge and discharge efficiency, and add more SiOx. In terms of cost increase, on the other hand, the coating difficulty is further improved, and the uniformity of the surface of the graphite coating is not guaranteed, and the electrochemical performance is poor cycle performance.

Public content

The purpose of the present disclosure is to overcome the problems of low specific capacity, low initial charge and discharge efficiency, and poor cycle performance of carbon and silicon oxide composite anode active materials in the prior art, and a composite anode active material, a preparation method thereof and lithium The battery, the composite anode active material has high specific capacity and first charge and discharge efficiency and good cycle performance; in addition, the preparation method of the present disclosure adopts a secondary coating method, which can avoid difficulty in completely coating the primary coating method. The coating method of the present disclosure is more reasonable and advanced, and the side reaction of the material surface and the electrolyte can be further reduced.

In order to achieve the above object, in a first aspect of the present disclosure, the present disclosure provides a composite anode active material including a graphite core, a first cladding layer coated on a surface of the graphite core, and a second cladding layer coated on the surface of the first cladding layer, wherein the first cladding layer comprises a mixture of oxides of nano-silicon and nano-silicon and carbon, and the second cladding layer comprises nano-silicon And carbon.

In a second aspect of the present disclosure, the present disclosure also provides a method of preparing a composite anode active material, the method comprising the steps of:

(1) mixing and mixing a mixture of nano-silicon oxide and nano-silicon with a first carbon source to obtain a first cladding material; (2) kneading the first cladding material with graphite to make the first package Coating the graphite to coat the graphite, and then performing the first calcination to obtain primary particles;

(3) mixing and grinding the nano silicon with the second carbon source to obtain a second cladding material;

(4) kneading the second cladding material with the primary particles such that the second cladding material coats the primary particles, and then performing a second calcination to obtain a composite negative electrode active material.

In a third aspect of the present disclosure, the present disclosure also provides a composite anode active material prepared by the above-described production method.

In a fourth aspect of the present disclosure, the present disclosure also provides a lithium battery comprising the composite anode active material described above in the present disclosure.

According to the above technical solution, the present disclosure mainly has the following beneficial effects:

(1) In the present disclosure, the first layer of coated SiO is subjected to high temperature calcination and then ball milling and recoating, so that the first layer of coated material is a disproportionation product of nano SiO: nano silicon and nano SiO ₂ The mixture, which allows the subsequent coating to completely coat the surface of the graphite core with nano-silicon and nano-SiO ₂ using a small amount of carbon precursor, greatly improves the material's first charge and discharge efficiency. At the same time, when the second layer of nano-silicon coating is carried out, the coating effect can be further improved, so that the overall first charge and discharge efficiency of the material is greatly improved compared with the single layer coating alone, and the SiOx is completely packaged. Under the condition of the first charge and discharge efficiency of the graphite surface, the first charge and discharge efficiency of the composite material can reach more than 95%, close to the graphite level.

(2) In the present disclosure, the second layer coating is performed on the basis of the disproportionation product coated with SiO, mainly by coating the nano silicon on the composite material (ie, the surface of the graphite core is coated with the first cladding layer). The surface further enhances the overall specific capacity of the composite; due to the limited specific capacity of SiO, the highest specific capacity is only 1500mAh/g-1700mAh/g, which is much lower than that of nano silicon of 3200mAh/g-3500mAh/g. Specific capacity, so the use of a second layer of cladding to coat the nano-silicon particles on the surface of the composite material can achieve a higher specific capacity than the coating of SiO alone.

(3) The disproportionation product of the first layer of SiO coated in the present disclosure is subjected to ball milling nano-treatment, so that the particle size of the nano-silicon particles in the coated disproportionation product is smaller than that of the particle-coated nano-sized SiO alone. The absolute expansion volume of the material is reduced, and the SiO ₂ in the disproportionation product after SiO calcination can play a buffering effect on the volume expansion of the nano silicon after lithium insertion, so that the volume expansion of the whole composite material during the lithium insertion process is very Small, this ensures that the composite material of the present disclosure has good cycle performance.

The additional aspects and advantages of the present disclosure will be set forth in part in the description which follows.

DRAWINGS

The drawings are intended to provide a further understanding of the disclosure, and are in the In the drawing:

1 is an SEM image of a sample S1 prepared in Example 1, the magnification is 3000 times;

2 is an SEM image of the sample S4 prepared in Example 4, the magnification is 3000 times;

3 is an SEM image of the sample DS1 prepared in Comparative Example 1, the magnification is 1000 times;

4 is an SEM image of the sample DS2 prepared in Comparative Example 2, the magnification is 1000 times;

Figure 5 is an SEM image of the sample DS3 prepared in Comparative Example 3, the magnification is 1000 times;

6 is a graph showing the charge and discharge performance of a lithium battery fabricated using the composite negative electrode active material prepared in Example 1;

7 is a cycle performance diagram of a lithium battery fabricated using the composite anode active material prepared in Example 1;

Fig. 8 is a graph showing the cycle performance of a lithium battery fabricated using the composite negative electrode active material prepared in Comparative Example 1.

Public detailed description

The embodiments of the present disclosure are described in detail below, and the examples of the embodiments are illustrated in the drawings, wherein the same or similar reference numerals are used to refer to the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the drawings are illustrative, and are not intended to be construed as limiting.

In the description of the present disclosure, it is to be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", " Rear, Left, Right, Vertical, Horizontal, Top, Bottom, Inner, Out, Clockwise, Counterclockwise, Axial The orientation or positional relationship of the "radial", "circumferential" and the like is based on the orientation or positional relationship shown in the drawings, and is merely for the convenience of describing the present disclosure and the simplified description, and does not indicate or imply the indicated device or The elements must have a particular orientation, are constructed and operated in a particular orientation, and thus are not to be construed as limiting the disclosure.

Moreover, the terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, features defining "first" and "second" may include at least one of the features, either explicitly or implicitly. In the description of the present disclosure, the meaning of "a plurality" is at least two, such as two, three, etc., unless specifically defined otherwise.

In the present disclosure, the first feature "on" or "under" the second feature may be a direct contact of the first and second features, or the first and second features may be indirectly through an intermediate medium, unless otherwise explicitly stated and defined. contact. Moreover, the first feature "above", "above" and "above" the second feature may be that the first feature is directly above or above the second feature, or merely that the first feature level is higher than the second feature. The first feature "below", "below" and "below" the second feature may be that the first feature is directly below or obliquely below the second feature, or merely that the first feature level is less than the second feature.

The endpoints and any values of the ranges disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to include values that are close to the ranges or values. For numerical ranges, the endpoint values of the various ranges, the endpoint values of the various ranges and the individual point values, and the individual point values can be combined with one another to yield one or more new ranges of values. The scope should be considered as specifically disclosed herein.

A first aspect of the present disclosure provides a composite anode active material comprising a graphite core, a first cladding layer coated on a surface of the graphite core, and a surface coated on the first cladding layer a second cladding layer, wherein the first cladding layer comprises a mixture of oxides of nano-silicon and nano-silicon and carbon, and the second cladding layer comprises nano-silicon and carbon.

According to an embodiment of the present disclosure, the nano-silicon coated in the first cladding layer is mainly for improving the overall specific capacity of the material, but in order to reduce the volume expansion effect of the nano-silicon during charging and discharging, on the one hand, the granular particles are selected. Nano-silicon with small diameter, which ensures that more nano-silicon particles can be uniformly dispersed on the graphite surface when coated with the same amount of nano-silicon; on the other hand, porous nano-silicon particles with pores are selected, and the existence of their own pores Can further alleviate its volume change. The size of the specific nano-silicon is required to be <200 nm, and further, the particle size is 30-100 nm. According to an embodiment of the present disclosure, in the second cladding layer, the nano silicon may be at least one of porous nano silicon and ordinary nano silicon, and further, the nano silicon is porous nano silicon. Porous nano-silicon has the high specific capacity characteristic of ordinary nano-silicon, and its expansion effect after lithium insertion is significantly lower than that of ordinary nano-silicon, so it can meet the requirements of battery cycle performance, and is particularly suitable for use as the second in the present disclosure. Coating composition.

According to an embodiment of the present disclosure, the first cladding layer is a SiO disproportionation product, and the SiO disproportionation product has two main functions:

First, it is possible to increase the specific capacity of the material. More importantly, SiO ₂ in the SiO disproportionation product can buffer the volume change of the material during charge and discharge, and improve the cycle performance of the material. The second cladding layer contains nano-silicon, which also has two functions. One is to make it difficult to obtain a smooth surface by one coating (that is, to reduce the specific surface area of the anode active material to some extent), and the other is to solve the problem of separately coating SiO. Increase the problem of limited specific capacity. Therefore, in order to achieve high specific capacity and good cycle performance, the amount of each cladding layer is balanced between the most important properties of the two battery materials; as one embodiment of the present disclosure, the graphite core, the first The weight ratio of the content of a coating layer and the second coating layer is (20-25):1:(0.7-0.9). The weight ratio of the content of the graphite core, the first cladding layer and the second cladding layer may be a combination of any one of the range end values in the above ratio, for example, may be (20:1) :0.7), (21:1:0.7), (22:1:0.7), (23:1:0.7), (24:1:0.7), (25:1:0.7), (20:1:0.8) ), (20:1:0.9), (21:1:0.8), (21:1:0.9), (22:1:0.8), (22:1:0.9), (23:1:0.8), (23:1:0.9), (24:1:0.8), (24:1:0.9), (25:1:0.8), and (25:1:0.9).

According to an embodiment of the present disclosure, the content of the carbon and the mixture of the oxide of the nano silicon and the nano silicon in the first cladding layer is not particularly limited. In order to further increase the specific capacity and the first charge and discharge efficiency of the composite negative electrode active material, and improve the cycle performance, the carbon content may be 30 to 70% by weight based on the total amount of the first cladding layer, further 40-60% by weight, still more preferably 45-55% by weight. The content of the mixture of the nano-silicon oxide and the nano-silicon may be from 30 to 70% by weight, further from 40 to 60% by weight, and further from 45 to 55% by weight.

According to an embodiment of the present disclosure, in order to further increase the specific capacity and first charge and discharge efficiency of the composite anode active material, and improve cycle performance, the carbon content may be 50 based on the total amount of the second cladding layer. 80% by weight, further 60-70% by weight, further further 62-68% by weight. The content of the nano-silicon may be 20-50% by weight, further 30-40% by weight, and further 32-38% by weight.

According to an embodiment of the present disclosure, the percentage of each component is based on the total weight of the composite anode active material: the content of the nano-silicon is 1.5-4.5% by weight; the oxide of the nano-silicon and The content of the mixture of nano-silicon is from 1 to 3% by weight; the content of the carbon is from 3 to 7% by weight; and the content of the graphite is from 88 to 93% by weight.

According to an embodiment of the present disclosure, the carbon is amorphous carbon.

According to an embodiment of the present disclosure, the nano silicon oxide is required to have a size of <200 nm, and further, a particle size of 30 to 100 nm. The nano silicon oxide may be selected from one or more of silicon oxide SiOx in any oxidation state, wherein x≤2; for example, the silicon oxide SiOx may be SiO, SiO ₂ , SiO _0.9 , SiO _1.3 , SiO _1.6 , SiO _0.3, etc., that is, x may be any number less than or equal to 2, including integers and fractions (decimal), that is, x may be _0.1 , _0.2 , _0.3 , _0.4 , _0.5 , 0.6, _0.7 , 0.8, 0.9 Any one of 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, and 2, 0 < x ≤ 2.

The above-mentioned nano silicon oxide may be a disproportionation product obtained by purchase or a disproportionation reaction of SiO.

In a second aspect of the present disclosure, there is provided a method of preparing a composite anode active material, the method comprising the steps of:

(1) mixing and grinding a mixture of nano-silicon oxide and nano-silicon with a first carbon source to obtain a first cladding material;

(2) kneading the first cladding material with graphite such that the first cladding material coats the graphite, and then performing the first calcination to obtain primary particles;

According to the preparation method of the embodiment of the present disclosure, the mixture of the oxide of the nano silicon and the nano silicon may be obtained by purchase or may be prepared. In the present disclosure, the preparation method of the mixture of the nano silicon oxide and the nano silicon may be As follows: a high-temperature calcination under an inert atmosphere using SiO2 as a raw material, and a disproportionation reaction occurs to obtain a mixture of nano-silicon oxide and nano-silicon. Nano-silicon and nano-SiO ₂ are disproportionation products obtained by disproportionation of SiO. Nano-SiO ₂ and nano-silicon are uniformly dispersed. The nano-SiO ₂ and nano-silicon are uniformly coated on the graphite surface by kneading. On the one hand, it is beneficial to the negative active material. Uniform expansion during use improves cycle performance; on the other hand, the uniform dispersion of nano-silicon in the coating can effectively increase the specific capacity of the material.

According to the preparation method of the embodiment of the present disclosure, in the present disclosure, the grinding is not particularly limited, and may be, for example, ball milling, flat grinding or round grinding; the grinding is ball milling according to an embodiment of the present disclosure.

According to the preparation method of the embodiment of the present disclosure, the graphite core is coated by the method of secondary coating, and on the one hand, the prepared product has the advantages of the combination of the nano silicon oxide and the nano silicon particle, and the other is superior. On the one hand, from the coating itself, since the primary coating is either difficult to completely coat, or it is necessary to increase the amount of carbon source to ensure the completely covered crucible, secondary coating can avoid this situation. This will further reduce the side reaction of the material surface and the electrolyte.

According to the preparation method of the embodiment of the present disclosure, the mixture of the nano-silicon oxide and the nano-silicon in the present disclosure may be a mixture of oxide SiOx and nano-scale silicon of various oxidation states of nano-scale silicon in an arbitrary ratio.

Among them, the size of the nano silicon is required to be <200 nm, and further, the particle size is 30-100 nm.

Wherein, the size of the nano-silicon oxide is required to be <200 nm, and further, the particle size is 30-100 nm, and the nano-silicon oxide may be selected from one or more of silicon oxide SiOx in any oxidation state. Wherein x ≤ 2; for example, in an embodiment of the present disclosure, the silicon oxide SiOx may be SiO, SiO ₂ , SiO _0.9 , SiO _1.3 , SiO _1.6 , SiO _0.3 , or the like, that is, wherein x may be less than Any number equal to 2, including integers and fractions (decimal), ie, x can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6 Any one of 1.7, 1.8, 1.9, and 2, further, 0 < x ≤ 2; further, may include at least at least a common nano silicon oxide such as SiO and SiO ₂ ; and further, the nano The mixture of silicon oxide and nano-silicon is a mixture of nano-silicon particles and nano-SiO ₂ .

According to the preparation method of the embodiment of the present disclosure, the mixture of the nano-silicon oxide and the nano-silicon can be obtained by ball milling the silicon source to a nano-sized size and then performing calcination. The nanometer size is not particularly limited and may be, for example, 1-100 nm.

According to the preparation method of the embodiment of the present disclosure, the silicon source may be a large particle silicon source conventional in the art, for example, in the present disclosure, the silicon source is SiO.

According to the production method of the embodiment of the present disclosure, the calcination conditions may include a temperature of 600 to 1200 ° C and a time of 1 to 10 hours.

According to the production method of the embodiment of the present disclosure, the calcination process is carried out under an inert atmosphere, for example, under an argon or nitrogen atmosphere.

According to the preparation method of the embodiment of the present disclosure, in the step (1), the process of mixing and grinding the mixture of the nano-silicon oxide and the nano-silicon and the first carbon source may be carried out by a ball milling method conventional in the art. The ball milling time can be from 1 to 20 hours, further from 5 to 15 hours.

According to the preparation method of the embodiment of the present disclosure, in the step (1), the first carbon source may be a conventional selection in the art. As one embodiment of the present disclosure, the first carbon source may be selected from one or more of the group consisting of glucose, sucrose, phenolic resin, asphalt, and citric acid.

According to the preparation method of the embodiment of the present disclosure, in the step (1), the weight ratio of the mixture of the nano-silicon oxide and the nano-silicon and the first carbon source may be (0.5-1.5): 1, Further (0.8-1.2): 1, more preferably 1:1;

According to the preparation method of the embodiment of the present disclosure, in the step (2), the weight ratio of the first coating material to the amount of graphite may be 1: (20-25), further 1: (22-24).

According to the production method of the embodiment of the present disclosure, in the step (2), the kneading process can be carried out in a kneader conventional in the art. The kneading operating conditions may include a temperature of 50 to 300 ° C and a time of 1 to 10 hours.

According to the preparation method of the embodiment of the present disclosure, in the step (2), the conditions of the primary calcination may include a temperature of 600 to 1200 ° C and a time of 1 to 10 h.

According to the production method of the embodiment of the present disclosure, in the step (2), the process of the primary calcination is carried out under an inert atmosphere. The inert atmosphere may be provided by nitrogen, helium, argon or the like.

According to the preparation method of the embodiment of the present disclosure, in the step (3), the introduction of the nano-silicon particles can reduce the decrease in the first charge and discharge efficiency due to the single cladding of the silicon oxide, and since the nano-silicon particles have an oxidation relative to the silicon The better specific capacity, the introduction of nano-silicon particles can also increase the specific capacity of the product. Further, the nano-silicon may be porous nano-silicon particles. Compared with ordinary nano-silicon particles, porous nano-silicon has less volume expansion when intercalating lithium, so the porous nano-silicon particles are introduced for secondary coating, so that the composite negative active material prepared by the present disclosure can not only obtain a higher first charge. Discharge efficiency and specific capacity, but also significantly improved cycle performance.

According to the preparation method of the embodiment of the present disclosure, in the step (3), the porous nano-silicon particles may have a particle size of 30 to 100 nm. The porous nano-silicon particles refer to nanoparticles having a porosity of 5% to 30%.

According to the preparation method of the embodiment of the present disclosure, in the step (3), the weight ratio of the amount of the nano silicon to the second carbon source may be 1: (1.5 - 2.5), preferably 1: (1.8 - 2.2), more preferably It is 1:2.

According to the preparation method of the embodiment of the present disclosure, in the step (3), the second carbon source may be a conventional selection in the art. According to an embodiment of the present disclosure, the second carbon source is one or more of asphalt, glucose, and sucrose. In the present disclosure, the first carbon source is different from the second carbon source, mainly because in the present disclosure, the first carbon source mainly functions as conductivity, and the second carbon source mainly functions as The castability is relatively good, and the surface of the formed product is smooth, and the specific surface area is small, specifically less than 3 m ² /g. In the present disclosure, when the first carbon source and the second carbon source are selected from the components specifically defined above, a better effect can be obtained.

According to the preparation method of the embodiment of the present disclosure, in the step (3), the ball milling process can be carried out by a ball milling method conventional in the art. The ball milling time can be from 10 to 40 hours, further from 15 to 30 hours.

According to the preparation method of the embodiment of the present disclosure, in the step (4), the weight ratio of the second cladding material to the primary particles may be 1: (25-35), further 1: (28- 32).

According to the production method of the embodiment of the present disclosure, in the step (4), the kneading process can be carried out in a kneading machine conventional in the art. The kneading time may be from 12 to 36 hours.

According to the preparation method of the embodiment of the present disclosure, in the step (4), the conditions of the secondary calcination may include a temperature of 600 to 1200 ° C and a time of 1 to 10 h.

According to the production method of the embodiment of the present disclosure, in the step (4), the secondary calcination process is performed under an inert atmosphere. The inert atmosphere may be provided by nitrogen, helium, argon or the like.

According to the preparation method of the embodiment of the present disclosure, the first cladding material, the second cladding material, and the graphite are used in an amount such that the graphite core in the prepared composite anode active material is coated on the surface of the graphite core. The weight ratio of a cladding layer and a second cladding layer coated on the surface of the first cladding layer is (20-25):1:(0.7-0.9). The weight ratio of the graphite core, the first cladding layer and the second cladding layer may be a combination of any one of the range end values in the above ratios, for example, may be (20:1:0.7), (21:1:0.7), (22:1:0.7), (23:1:0.7), (24:1:0.7), (25:1:0.7), (20:1:0.8), (20 :1:0.9), (21:1:0.8), (21:1:0.9), (22:1:0.8), (22:1:0.9), (23:1:0.8), (23:1) : 0.9), (24:1:0.8), (24:1:0.9), (25:1:0.8), and (25:1:0.9). The weight ratio of the cladding layer to the graphite core can be adjusted according to actual needs. By this adjustment, the amount of the nano silicon particles and the nano silicon oxide can be adjusted to achieve the balance of the first effect, the cycle performance and the capacity, and the other. It is also possible to adjust the ratio of the amount of amorphous carbon to nano-silicon and silicon oxide to achieve uniform coating.

In a third aspect of the present disclosure, the present disclosure also provides a composite anode active material prepared by the above-described production method. The composite anode active material has two coating layers, so that the composite anode active material has high first charge and discharge efficiency and specific capacity, and has good cycle performance.

In a fourth aspect of the present disclosure, the present disclosure also provides a lithium battery containing the composite anode active material of the present disclosure.

The composite anode active material of the present disclosure has a coating layer added to the core-shell material of the prior art, and the nano-silicon is coated on the composite material by secondary coating (ie, the graphite core surface package) The surface of the first cladding composite). Therefore, by adjusting the ratio of the oxide of the nano-silicon and the nano-silicon, on the one hand, the adverse effect on the first charge and discharge efficiency due to the SiOx coating alone can be reduced; on the other hand, due to the use of the two-layered structure, the material The surface and electrolyte side reactions are reduced, so the first charge and discharge efficiency can be close to the level of graphite. In addition, ordinary nano-silicon oxides have a specific capacity of about 1600 mAh/g at the current level, and nano-silicon particles generally have a specific capacity of about 2700-3200 mAh/g, which is nearly double that of silicon oxide. The disclosed negative electrode material has a large specific capacity compared with the prior art due to the introduction of nano-silicon on the second cladding layer. Furthermore, since the nano-silicon is required to have a large expansion space after lithium intercalation, the silicon oxide is intercalated with lithium. After the required expansion space is small, the use of the two solves the problem of material cracking caused by excessive volume expansion after lithium intercalation by the nano-silicon, so that better cycle performance can be obtained during the cycle of the battery.

The present disclosure is further illustrated by the following examples, but does not limit the disclosure.

SiO, SiO _0.3 , SiO _0.9 , SiO _1.3 , SiO _1.6 , porous nano-silicon and nano-silicon were all purchased from TBEA.

Asphalt was purchased from Jiangxi Zhengtuo New Energy Co., Ltd.

Sucrose was purchased from Guangdong Guanghua Chemical Factory Co., Ltd.

Citric acid was purchased from Guangdong Guanghua Chemical Factory Co., Ltd.

Example 1

This embodiment is intended to illustrate a composite negative electrode active material prepared by the production method of the present disclosure.

(1) 50 g of large particles of SiO were ball-milled for 5 hours to obtain nano-sized SiO, and then calcined at 800 ° C for 2 hours under argon atmosphere to obtain a mixture of nano-silicon oxide SiO ₂ and nano-silicon; the calcined product and The sucrose was mixed at a weight ratio of 1:1.2 and ball-milled for 10 hours to obtain a first coating material;

(2) mixing the first cladding material and graphite in a ratio of 1:23 by weight, and kneading in a kneader at 200 ° C for 24 hours, and then kneading the product under an argon atmosphere at 800 ° C Calcination for 3 hours to obtain primary particles;

(3) Ball-milling 35 g of porous nano-silicon (particle size of 100 nm) and pitch at a weight ratio of 1:1.5 for 24 hours to obtain a second cladding material:

(4) mixing the second cladding material with the primary particles in a ratio of 1:30 by weight, and kneading at 150 ° C for 30 hours, and then calcining the kneaded product in an argon atmosphere at 1000 ° C for 5 hours. A composite negative electrode active material S1 was obtained.

Example 2

(1) 50 g of large particles of SiO were ball-milled for 5 hours to obtain nano-sized SiO, and then calcined under an argon atmosphere at 700 ° C for 3 hours to obtain a mixture of nano-silicon oxide SiO ₂ and nano-silicon, and the calcined product was Glucose is mixed at a weight ratio of 1:1 and ball milled for 10 hours to obtain a first coating material;

(2) mixing the first cladding material and graphite in a ratio of 1:25 by weight, and kneading in a kneader at 150 ° C for 30 hours, and then kneading the product under an argon atmosphere at 1200 ° C Calcination for 1 hour to obtain primary particles;

(3) 45 g of nano silicon (particle size of 100 nm) and pitch were ball milled at a weight ratio of 1:2 for 24 hours to obtain a second coating material;

(4) mixing the second cladding material with the primary particles in a ratio of 1:32 by weight, and kneading at 150 ° C for 24 hours, and then calcining the kneaded product in an argon atmosphere at 1000 ° C for 5 hours. A composite negative electrode active material S2 was obtained.

Example 3

(1) 50 g of large particles of SiO were ball-milled for 5 hours to obtain nano-sized SiO, and then calcined at 800 ° C for 2 hours under argon atmosphere to obtain a mixture of nano-silicon oxide SiO ₂ and nano-silicon, and the calcined product was The citric acid was mixed at a weight ratio of 1:0.8 and ball-milled for 10 hours to obtain a first coating material;

(2) mixing the first cladding material and graphite in a ratio of 1:20 by weight, and kneading in a kneader at 200 ° C for 24 hours, and then kneading the product under an argon atmosphere at 1200 ° C Calcination for 1 hour to obtain primary particles;

(3) 40 g of nano-silicon (particle size of 100 nm) and asphalt were ball milled at a ratio of 1:2 by weight for 24 hours to obtain a second coating material;

(4) mixing the second cladding material with the primary particles in a ratio of 1:28 by weight, and kneading at 250 ° C for 20 hours, and then calcining the kneaded product in an argon atmosphere at 1000 ° C for 5 hours. A composite negative electrode active material S3 was obtained.

Example 4

The composite anode active material was prepared according to the preparation method in Example 1, except that the weight ratio of the calcined product to the sucrose was 2:1 in the preparation of the first coating material. A composite negative electrode active material S4 was obtained.

Example 5

The composite anode active material was prepared in accordance with the production method of Example 1, except that the weight ratio of the primary particles to the second coating material was 35:1, and the composite anode active material S5 was obtained.

Example 6

This embodiment is intended to illustrate a composite negative electrode active material prepared by the production method of the present disclosure. The composite anode active material was prepared according to the preparation method in Example 1, except that in the step (1), a mixture of nano-silicon oxide SiO and nano-silicon was used to obtain a composite anode active material S6.

Example 7

A composite anode active material was prepared according to the preparation method in Example 1, except that in the step (1), a mixture of nano-silicon oxide SiO _0.9 and nano-silicon was used to obtain a composite anode active material S7.

Example 8

A composite anode active material was prepared according to the preparation method in Example 1, except that in the step (1), a mixture of nano-silicon oxide SiO _1.3 and nano-silicon was used to obtain a composite anode active material S8.

Example 9

A composite anode active material was prepared according to the preparation method in Example 1, except that in the step (1), a mixture of nano-silicon oxide SiO _1.6 and nano-silicon was used to obtain a composite anode active material S9.

Comparative example 1

The composite anode active material was prepared in accordance with the preparation method in Example 1, except that the second anode coating was not carried out to obtain a composite anode active material DS1.

Comparative example 2

The composite anode active material was prepared according to the preparation method in Example 1, except that the graphite was coated directly with the second cladding material to obtain a composite anode active material DS2.

Comparative example 3

50 g of SiO particles, 50 g of pitch and 450 g of graphite were uniformly mixed, and kneaded at 200 ° C for 24 hours, and then the kneaded product was calcined at 1000 ° C for 5 hours under an argon atmosphere to obtain a composite negative electrode active material DS3.

Experimental example 1

SEM scan test

Test instrument: (JSM-5610LV model, JEOL manufacturer, etc.) scanning electron microscope;

Test method: The microstructure of the sample was observed by a scanning electron microscope.

1 is an SEM image of the sample S1 prepared in Example 1, the magnification is 3000 times, and it can be seen from the figure that the surface of the sample is smooth and uniform, indicating that the secondary coating effect in the present disclosure is remarkable;

2 is an SEM image of the sample S4 prepared in Example 4, the magnification is 3000 times, and it can be seen from the figure that although the surface of the sample is slightly rougher than that of FIG. 1, the overall coating effect is still good;

3 is an SEM image of the sample DS1 prepared in Comparative Example 1, the magnification is 1000 times, as can be seen from the figure, the surface of the sample is rough and the coating is incomplete;

4 is an SEM image of the sample DS2 prepared in Comparative Example 2, the magnification is 1000 times, as can be seen from the figure, the surface of the sample is rough, there are many crumbs, and the coating is incomplete;

Figure 5 is an SEM image of the sample DS3 prepared in Comparative Example 3, with a magnification of 1000 times. As can be seen from the figure, the sample surface is rough, has a lot of debris, and the coating is incomplete.

It can be seen from the above comparison that the composite anode active material prepared by the method of the present disclosure has a good coating effect and a uniform surface, and the coating effect is poor and the surface is rough by other prior art methods.

Experimental example 2

Charge and discharge performance test

experimental method:

The composite anode active material prepared in each of the examples and the comparative examples was made into a button lithium battery;

Adopt LB30 electrolyte of Xinzhoubang Co., Ltd.;

The counter electrode is lithium sheet (Shanghai Senyu Fine Chemical Co., Ltd.;

The first charge and discharge efficiency and specific capacity of the test materials were tested using the BK-6016 battery detection system of Guangzhou Lanqi Electronic Industry Co., Ltd.;

The specific charge and discharge system is: three-stage lithium intercalation for a period of lithium de-lithium, with lithium constant current of 0.2C to 5mV, then lithium with a constant current of 0.1C to 5mV, and then with lithium constant current of 0.05C to 5mV, put on for 5min, 0.2C constant current delithiation to 1.5V, the first charge and discharge efficiency is the ratio of delithiation specific capacity and lithium intercalation specific capacity;

The specific capacity is the delithiation specific capacity (mAh/g);

The capacity retention of the battery after 100 cycles was the ratio of the 100th delithiation capacity of the battery to the first delithiation ratio.

6 is a graph showing the charge and discharge performance of the button battery made of the sample S1 in Example 1;

The data obtained from the charge and discharge performance experiments are given in Table 1.

Table 1

样品\项目Sample\project	比容量(mAh/g)Specific capacity (mAh/g)	首次充放电效率First charge and discharge efficiency	循环100次后电池的容量保持率Capacity retention rate of battery after 100 cycles
S1S1	421421	94.5％94.5%	95.01％95.01%
S2S2	414414	93.8％93.8%	95.90％95.90%
S3S3	428428	95.0％95.0%	94.61％94.61%
S4S4	421421	92.1％92.1%	93.27％93.27%
S5S5	416416	92.7％92.7%	93.83％93.83%
S6S6	436436	94.9％94.9%	90.08％90.08%
S7S7	425425	94.5％94.5%	94.27％94.27%
S8S8	417417	93.2％93.2%	95.62％95.62%
S9S9	395395	88.4％88.4%	95.37％95.37%
DS1DS1	384384	85.4％85.4%	47.88％47.88%
DS2DS2	415415	83.1％83.1%	36.29％36.29%
DS3DS3	498498	76.5％76.5%	25.31％25.31%

Experimental example 3

Cycle performance test

experimental method:

The composite anode active materials prepared in Example 1 and Comparative Example 1 were made into a button lithium battery;

Adopt LB30 electrolyte of Xinzhoubang Co., Ltd.;

The counter electrode is lithium sheet (Shanghai Senyu Fine Chemical Co., Ltd.);

The cycle performance of the half-cell was tested using the BK-6016 battery detection system of Guangzhou Lanqi Electronic Industry Co., Ltd.;

The specific test system is: using 0.1C constant current embedded lithium to 5mV, shelving for 5min, 0.1C constant current de-lithium to 1.5V, the test results are shown in Figure 7, Figure 8, respectively, for Figure 7 need to be explained, due to the cycle Good performance leads to overlap of re-discharge data, which is normal.

As can be seen from the figure, the specific capacity retention rate after the 100 cycles of the material in Example 1 was 94%; and the specific capacity retention ratio after the 27 cycles of the material in Comparative Example 1 was 58%.

The preferred embodiments of the present disclosure have been described in detail above, but the present disclosure is not limited to the specific details in the above-described embodiments, and various simple modifications can be made to the technical solutions of the present disclosure within the scope of the technical idea of the present disclosure. All fall within the scope of protection of the present disclosure.

It should be further noted that the specific technical features described in the above specific embodiments may be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present disclosure is applicable to various possibilities. The combination method will not be described separately.

In addition, any combination of various embodiments of the present disclosure may be made as long as it does not deviate from the idea of the present disclosure, and should also be regarded as the disclosure of the present disclosure.

In the description of the present specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" and the like means a specific feature described in connection with the embodiment or example. A structure, material, or feature is included in at least one embodiment or example of the present disclosure. In the present specification, the schematic representation of the above terms is not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. In addition, various embodiments or examples described in the specification and features of various embodiments or examples may be combined and combined without departing from the scope of the invention.

While the embodiments of the present disclosure have been shown and described above, it is understood that the foregoing embodiments are illustrative and are not to be construed as limiting the scope of the disclosure The embodiments are subject to variations, modifications, substitutions and variations.

Claims

A composite anode active material, wherein the composite anode active material comprises a graphite core, a first cladding layer coated on a surface of the graphite core, and a second coating layer coated on a surface of the first cladding layer a cladding layer, wherein the first cladding layer comprises a mixture of an oxide of nano-silicon and nano-silicon, and the second cladding layer comprises nano-silicon and carbon.
The composite anode active material according to claim 1, wherein a weight ratio of the graphite core, the first cladding layer and the second cladding layer is (20-25):1:(0.7 -0.9).
The composite anode active material according to claim 1 or 2, wherein the content of carbon is from 30 to 70% by weight based on the total amount of the first cladding layer, and the oxide of the nano-silicon and The content of the mixture of nano-silicon is from 30 to 70% by weight.
The composite anode active material according to any one of claims 1 to 3, wherein the carbon content is 50 to 80% by weight based on the total amount of the second cladding layer, the nano-silicon The content is 20-50% by weight.
The composite anode active material according to any one of claims 1 to 4, wherein the oxide of silicon is SiOx, wherein X ≤ 2.
The composite anode active material according to any one of claims 1 to 5, wherein the nano-silicon is porous nano-silicon particles.
The composite anode active material according to any one of claims 1 to 6, wherein the carbon is amorphous carbon.
A method of preparing a composite anode active material, wherein the method comprises the following steps:

(1) mixing and grinding a mixture of nano-silicon oxide and nano-silicon with a first carbon source to obtain a first cladding material;

(2) kneading the first cladding material with graphite such that the first cladding material coats the graphite, and then performing the first calcination to obtain primary particles;

(3) mixing and grinding the nano silicon with the second carbon source to obtain a second cladding material;

(4) kneading the second cladding material with the primary particles such that the second cladding material coats the primary particles, and then performing a second calcination to obtain a composite negative electrode active material.
The method according to claim 8, wherein the mixture of the nano-silicon oxide and the nano-silicon is obtained by grinding a silicon source to a nano-sized size and then performing calcination.
The method according to claim 8 or 9, wherein the calcination is carried out under an inert atmosphere, and the conditions of the calcination include a temperature of 600 to 1200 ° C and a time of 1 to 10 h.
The method according to any one of claims 8 to 10, wherein the oxide of silicon is SiOx, wherein X ≤ 2.
The method of any of claims 8-11, wherein the nano-silicon is porous nano-silicon particles.
The method according to any one of claims 8 to 12, wherein the first calcination and the second calcination are both carried out under an inert atmosphere, and the respective calcination conditions include: calcination temperature of 600-1200 °C, calcination time is 1-10h.
The method according to any one of claims 8 to 13, wherein the first carbon source is selected from one or more of glucose, sucrose, phenolic resin, pitch, and citric acid, the second carbon source One or more selected from the group consisting of asphalt, glucose, and sucrose.
The method according to any one of claims 8 to 14, wherein in step (1), the weight ratio of the mixture of the oxide of the nano-silicon and the nano-silicon and the amount of the first carbon source is ( 0.8-1.2): 1.
The method according to any one of claims 8 to 15, wherein, in the step (3), the nano silicon and the second carbon source are used in a weight ratio of 1: (1.8 - 2.2).
The method according to any one of claims 8 to 16, wherein the first cladding material, the second cladding material and the graphite are used in an amount such that the prepared composite anode active material has a graphite core The weight ratio of the first cladding layer coated on the surface of the graphite core and the second cladding layer coated on the surface of the first cladding layer is (20-25): 1: (0.7-0.9) .
A composite anode active material, wherein the composite anode active material is produced by the method according to any one of claims 8-17.
A lithium battery comprising the composite anode active material according to any one of claims 1 to 7 or the composite anode active material according to claim 18.