CN115458715A - Silicon carbon negative electrode material and its preparation method and lithium ion battery - Google Patents

Abstract

The invention discloses a silicon-carbon negative electrode material, a preparation method thereof and a lithium ion battery. The silicon-carbon anode material comprises carbon, composite silicon particles and a conductive agent, wherein the carbon, the composite silicon particles and the conductive agent form mixture particles, the composite silicon particles comprise a silicon-based core body and a carbon coating layer coating the silicon-based core body, and the carbon coating layer is doped with ceramic. Therefore, the silicon-carbon negative electrode material provided by the invention has the advantages that the mixture particles are formed by the carbon, the composite silicon particles and the conductive agent, so that the carbon, the composite silicon particles and the conductive agent have a synergistic effect, and the silicon-carbon negative electrode material is endowed with high charge-discharge efficiency, charge-discharge rate, specific capacity and cycle performance. The preparation method of the silicon-carbon cathode material can ensure that the prepared silicon-carbon cathode material has stable structure and electrochemical performance, is high in efficiency and saves the production cost. The lithium ion battery has excellent rate performance and cycle performance, long service life, strong quick charging capability and stable electrochemical performance.

Description

Silicon carbon negative electrode material and its preparation method and lithium ion battery

technical field

The invention belongs to the field of lithium-ion batteries, and in particular relates to a silicon-carbon negative electrode material, a preparation method thereof, and a lithium-ion battery.

Background technique

The development of lithium-ion batteries with high energy density, long cycle life and certain rate characteristics is the technical development trend of 3C batteries and power and energy storage batteries. As the next-generation negative electrode material of pure graphite negative electrode materials, silicon materials have a capacity of more than 4200mAh/g Theoretical specific capacity and a more suitable charge-discharge platform (0.4-0.5V); but its disadvantages are that it can produce a maximum volume expansion of 300% and poor conductivity during the alloying reaction, which will lead to powdering of the negative electrode material, negative electrode material and Current collector separation, rapid capacity decay, etc., which severely limit the use in lithium-ion batteries.

In view of this, the nanonization of silicon materials can effectively alleviate the huge volume change during charging and discharging, effectively improve its electrical conductivity by carbon coating and other means, and reduce the volume expansion rate by sacrificing theoretical specific capacity by preparing silicon-oxygen materials. To improve the performance of silicon-based anode materials is a current research hotspot. Although there are currently public reports on modified silicon materials, the energy density, charge and discharge efficiency, rate performance or/or cycle performance of the currently disclosed modified silicon materials are adversely affected, and many preparation methods cannot achieve industrialization. For example, in the publicly reported porous core silicon and its preparation method, it uses HF etching to form porous core silicon on the Si/SiO ₂ mixture, but this method cannot guarantee that all SiO ₂ is etched away; In the silicon carbon material, it turns nano-silicon particles into nano-silicon spheres through a series of treatments before carbon coating, which greatly increases the production cost of the material; in another silicon-carbon material disclosed, it uses SiC in High-temperature pyrolysis at 2200-2400 ° C into silicon materials, and requires a vacuum environment, making the cost higher. In a disclosed nano-silicon alloy material, the negative electrode material includes 40%-60% wt of nano-silicon alloy material, which greatly increases the cost of the material.

Therefore, it is a difficult problem that this field has been trying to overcome if improving the silicon carbon material, taking into account the charge and discharge efficiency, cycle life and charge and discharge rate and reducing its economic cost under the premise of ensuring energy density.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned deficiencies in the prior art, and provide a silicon-carbon negative electrode material and its preparation method to solve the problem of unsatisfactory or unsuitable cycle performance and high cost of existing silicon-carbon materials in terms of charging and discharging efficiency, fast charging ability and cycle performance technical issues.

Another object of the present invention is to provide a lithium-ion battery to solve the technical problems of the existing lithium-ion batteries containing silicon and carbon materials, such as unsatisfactory first effect, fast charging ability and cycle performance, and high cost.

In order to achieve the purpose of the above invention, one aspect of the present invention provides a silicon carbon negative electrode material. The silicon-carbon negative electrode material of the present invention includes carbon, composite silicon particles and conductive agent, and carbon, composite silicon particles and conductive agent form mixture particles, wherein the composite silicon particles include silicon-based nuclei and carbon-coated silicon-based nuclei layer, and the carbon coating layer is doped with ceramics. In this way, in the mixture particles of the silicon-carbon anode material in the embodiment of the present invention, the composite silicon particles use the silicon-based material as the nucleus to endow the silicon-carbon anode material with high specific capacity characteristics, and use the carbon material containing ceramics as the coating layer to impart the coating Excellent mechanical properties of the layer, constructing an anti-swelling functional layer with good mechanical properties, which can effectively resist the volume expansion effect of the silicon-based nuclei during charge and discharge, and endow the composite silicon particles with excellent volume and structural stability, thus endowing Composite silicon particles have excellent cycle performance. The carbon and conductive agent contained in the mixture particles and the carbon coating layer contained in the composite silicon particles build a good conductive system, endowing the silicon-carbon anode material with low resistance and high conductivity, thus endowing the silicon-carbon anode material with high charge and discharge efficiency and charge-discharge rate. Therefore, the silicon-carbon negative electrode material of the embodiment of the present invention forms mixture particles including carbon, composite silicon particles and conductive agent, so that carbon, composite silicon particles and conductive agent play a synergistic effect, endowing the silicon-carbon negative electrode material with high charge and discharge efficiency , charge-discharge rate, specific capacity and cycle performance.

Further, the mass ratio of carbon, composite silicon particles and conductive agent contained in the silicon-carbon negative electrode material is 85-70:(10):(5-20). By controlling and adjusting the ratio of carbon, composite silicon particles and conductive agent, the conductivity and specific capacity of silicon carbon negative electrode materials are improved, so that silicon carbon negative electrode materials have high charge and discharge efficiency, charge and discharge rate, specific capacity and other properties.

Further, carbon is used as a carrier, and the composite silicon particles and the conductive agent are dispersed in the carrier. The composite silicon particles and the conductive agent are dispersed in the carbon carrier, the composite silicon particles and the conductive agent can be dispersed more uniformly, and the contact area between the composite silicon particles and carbon can be increased, thereby improving the conductivity of the silicon-carbon negative electrode material.

Further, carbon is cracked carbon. In this way, the structural stability of the particles of the mixture comprising carbon, composite silicon particles, and conductive agent can be improved.

Further, the particle size of the composite silicon particles is in the nanometer range. By controlling the particle size of the composite silicon particles, its dispersibility in the mixture particles can be improved and the particle size of the silicon-carbon negative electrode material can be controlled.

Further, the conductive agent includes at least one of carbon nanotubes, super p, graphene, and graphite fine powder. These conductive agents have excellent electrical conductivity, and when they are carbon nanotubes, their one-bit structure can form a three-dimensional conductive network structure in the mixed particles or in the secondary particles constructed by the mixed particles, which improves the electrical conductivity on the one hand, On the other hand, the structural stability of the silicon-carbon negative electrode material particles is improved, and the cycle performance of the silicon-carbon negative electrode material is improved.

Further, the silicon-based core body is elemental silicon. The elemental silicon is used as a nucleus to improve the first effect and have low volume expansion, and can improve the first effect performance and cycle performance of the silicon-carbon negative electrode material.

Further, the ceramics include at least one of alumina, silicon carbide, and titanium dioxide. These ceramics have good mechanical properties, improve the anti-silicon-based nuclei volume expansion effect of the carbon coating, and can improve the role of the carbon coating in isolating the electrolyte, avoiding the direct contact of the electrolyte with the silicon-based nuclei, and improving the silicon-based nuclei. Electrochemical properties of carbon anode materials.

Further, the thickness of the carbon coating layer is 5-8nm. The carbon coating layer with this thickness has relatively excellent mechanical properties and the performance of blocking the contact between the electrolyte and the silicon-based nuclei.

Further, the silicon-carbon negative electrode material also includes a capacity extender, which is mixed with carbon, composite silicon particles, and a conductive agent. The presence of the capacity supplement can effectively fill the micropores that may exist in the carbon, thereby assisting the silicon-based nuclei to increase the capacity of the silicon-carbon anode material, increase the specific capacity of the silicon-carbon anode material, and assist carbon and the conductive agent to build a three-dimensional The conductive system improves the conductivity of silicon-carbon anode materials and improves their fast charging capabilities.

Furthermore, the content of the capacity extender in the silicon-carbon negative electrode material is 5%-10%.

Still further, the capacity extender includes graphite.

By controlling the content and type of the capacity supplement, the above-mentioned function of the capacity supplement is improved, thereby improving the conductivity of the silicon-carbon negative electrode material and improving its fast charging ability.

Another aspect of the present invention provides a method for preparing a silicon-carbon negative electrode material. The preparation method of silicon carbon negative electrode material comprises the following steps:

Composite silicon particles are provided; the composite silicon particles include a silicon-based core body and a carbon coating layer covering the silicon-based core body, and the carbon coating layer is doped with ceramics;

Mixing the composite silicon particles with the conductive agent and the first carbon source to obtain the mixed material;

The mixed material is subjected to the first carbonization treatment.

In this way, the preparation method of the silicon-carbon negative electrode material of the present invention can effectively ensure that the composite silicon particles, the conductive agent, and the carbon generated by carbonization are evenly dispersed, thereby ensuring that the carbon contained in the prepared silicon-carbon negative electrode material, the composite silicon particles, and the conductive agent play an enhanced role The effect can endow the prepared silicon carbon negative electrode material with high charge and discharge efficiency, charge and discharge rate, specific capacity and cycle performance, and at the same time, the particle structure of the material has good mechanical properties. In addition, the preparation method of the silicon-carbon negative electrode material can ensure that the prepared silicon-carbon negative electrode material has a stable structure and electrochemical performance, and has high efficiency and saves production costs.

Further, the composite silicon particles, the conductive agent and the first carbon source are mixed according to a mass ratio of 10:(5-20):(85-70). By controlling and optimizing the mixing ratio of the three, the mass ratio of composite silicon particles, conductive agent and carbon contained in the silicon-carbon negative electrode material can be controlled, thereby improving the charge-discharge efficiency, charge-discharge rate, and ratio of the prepared silicon-carbon negative electrode material. performance such as capacity.

Further, before the step of subjecting the mixed material to the first carbonization treatment, the mixed material is formulated into a mixture dispersion; then the mixture dispersion is spray-dried and granulated to obtain mixture particles; then the mixture particles are subjected to the first carbonization treatment . By spraying and granulating the mixed materials, on the one hand, the raw materials of each component can be mixed evenly, and the particle size of the formed precursor particles is complete and uniform.

Further, the composite silicon particles are prepared according to a method comprising the following steps:

Mixing the silicon-based particles with a second carbon source containing a ceramic precursor, so that the second carbon source containing a ceramic precursor forms a coating layer on the surface of the silicon-based particles to obtain a composite silicon particle precursor;

The composite silicon particle precursor is subjected to the second carbonization treatment to obtain the composite silicon particle.

The carbon coating layer contained in the composite silicon particles prepared by the method is complete, and has strong mechanical properties and uniform particles.

Furthermore, the silicon-based particles include at least one of elemental silicon, silicon carbide, and silicon oxide.

Furthermore, the second carbon source includes at least one of an organic aluminum source and an organic titanium source.

Furthermore, the temperature of the second carbonization treatment is 600-900°C.

Through the selection of raw materials for the composite silicon particles and the control of the carbonization temperature, ceramic components are uniformly dispersed in the generated carbon coating layer, which endows the generated carbon coating layer with good mechanical properties and electrolyte isolation properties, so that the prepared composite silicon particles It has high specific capacity and good particle mechanical properties.

Further, the first carbon source includes at least one of pitch, biochar, polyethylene glycol, PVP, citric acid, and phenolic resin; and/or

Further, the temperature of the first carbonization treatment is 600-900°C.

By controlling the type of the first carbon source and the carbonization treatment temperature, the related electrochemical performance of the silicon-carbon negative electrode material is improved.

Another aspect of the present invention provides a lithium ion battery, including a negative electrode, the negative electrode includes a current collector and a negative electrode active layer bonded to the surface of the current collector, the negative electrode active layer contains the above-mentioned silicon carbon negative electrode material of the present invention or by the above-mentioned present invention The silicon carbon negative electrode material prepared by the silicon carbon negative electrode material preparation method. In this way, since the lithium-ion battery of the present invention contains the silicon-carbon negative electrode material of the present invention, the negative electrode cycle performance is good and the internal resistance is low, thereby endowing the lithium-ion battery of the present invention with excellent rate performance and cycle performance, long life, and strong fast charging ability , stable electrochemical performance.

Description of drawings

In order to more clearly illustrate the specific implementation of the present invention or the technical solutions in the prior art, the following will briefly introduce the accompanying drawings that need to be used in the specific implementation or description of the prior art. Obviously, the accompanying drawings in the following description The drawings show some implementations of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any creative work.

Fig. 1 is the structural representation of silicon carbon negative electrode material of the embodiment of the present invention;

Fig. 2 is a schematic structural view of the composite silicon particles contained in the silicon-carbon negative electrode material of the embodiment of the present invention;

Fig. 3 is a schematic flowchart of a method for preparing a silicon-carbon anode material according to an embodiment of the present invention.

detailed description

In order to make the technical problems, technical solutions and beneficial effects to be solved in the present application clearer, the present application will be further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described here are only used to explain the present application, and are not intended to limit the present application.

In this application, the term "and/or" describes the association relationship of associated objects, indicating that there may be three relationships, for example, A and/or B may mean: A exists alone, A and B exist simultaneously, and B exists alone Condition. Among them, A and B can be singular or plural. The character "/" generally indicates that the contextual objects are an "or" relationship.

In this application, "at least one" means one or more, and "multiple" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one item (unit) of a, b, or c", or "at least one item (unit) of a, b, and c" can mean: a, b, c, a-b( That is, a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple.

It should be understood that in various embodiments of the present application, the sequence numbers of the above-mentioned processes do not mean the order of execution, and some or all steps may be executed in parallel or sequentially, and the execution order of each process shall be based on its functions and The internal logic is determined and should not constitute any limitation to the implementation process of the embodiment of the present application.

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", "said" and "the" used in the embodiments of this application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

The weight of the relevant components mentioned in the description of the embodiments of the present application can not only refer to the specific content of each component, but also represent the proportional relationship between the weights of the various components. The scaling up or down of the content of the fraction is within the scope disclosed in the description of the embodiments of the present application. Specifically, the mass described in the description of the embodiments of the present application may be μg, mg, g, kg and other well-known mass units in the chemical industry.

The terms "first" and "second" are only used for descriptive purposes to distinguish objects such as substances from each other, and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of indicated technical features. For example, without departing from the scope of the embodiments of the present application, the first XX can also be called the second XX, and similarly, the second XX can also be called the first XX. Thus, a feature defined as "first" and "second" may explicitly or implicitly include one or more of these features.

On the one hand, the embodiment of the present invention provides a silicon carbon negative electrode material. As shown in FIG. 1 and FIG. 2 , the silicon-carbon anode material of the embodiment of the present invention includes carbon 10 , composite silicon particles 20 and conductive agent 30 , and the carbon 10 , composite silicon particles 20 and conductive agent 30 form mixture particles.

Among them, the carbon 10 contained in the silicon-carbon negative electrode material of the embodiment of the present invention communicates with the conductive agent 30 to build a good conductive system, and the composite silicon particles 20 are dispersed in the conductive system, effectively improving the conductivity of the composite silicon particles 20 , endow the silicon carbon negative electrode material with low resistance and high conductivity, thereby endowing the silicon carbon negative electrode material with high charge and discharge efficiency and charge and discharge rate.

In the embodiment, carbon 10 is used as a carrier, that is, the content of carbon 10 is controlled so that it constitutes the carrier component of the mixture particles, so that the composite silicon particles 20 and the conductive agent 30 are dispersed in the carrier. Using carbon 10 as a carrier, the composite silicon particles 20 and the conductive agent 30 are dispersed in the carbon 10 carrier, on the one hand, it can make the composite silicon particles 20 and the conductive agent 30 more uniformly dispersed, and can increase the contact area between the composite silicon particles 20 and carbon , thereby improving the electrical conductivity of the silicon-carbon negative electrode material, and the carbon support can also improve the mechanical properties of the above-mentioned mixture particles.

In an embodiment, carbon 10 is cracked carbon. In this way, the cracked carbon can be fully filled between the composite silicon particles 20 and the conductive agent 30 to act as a carrier and a conductive bond, thereby improving the conductivity of the silicon-carbon negative electrode material and improving the structural stability of the mixture particles.

In an embodiment, the conductive agent 30 includes at least one of carbon nanotubes, super p, graphene, and graphite fine powder. These conductive agents have excellent conductive properties. And when the conductive agent 30 is carbon nanotubes, its one-dimensional structure can form a three-dimensional conductive network structure in the mixed particles or in the secondary particles constructed by the mixed particles, which improves the conductivity on the one hand, and improves the silicon-carbon carbon nanotube structure on the other hand. The structural stability of the negative electrode material particles improves the cycle performance of the silicon carbon negative electrode material.

The structure of the composite silicon particle 20 contained in the silicon-carbon negative electrode material of the embodiment of the present invention is shown in FIG. The cladding layer 22 is doped with ceramics. In this way, the composite silicon particle 20 uses the silicon-based material as the core body to endow the silicon-carbon negative electrode material with high specific capacity characteristics, and uses the carbon material containing ceramics as the coating layer to endow the coating layer 22 with excellent mechanical properties, and the structure has good mechanical properties. The anti-expansion functional layer can effectively resist the volume expansion effect of the silicon-based core body 21 during charging and discharging, endow the composite silicon particles with excellent volume and structural stability, and thus endow the composite silicon particles with excellent cycle performance. Also, the carbon contained in the carbon coating layer 22 imparts excellent electrical conductivity to the carbon coating layer 22 . Moreover, it forms a good conductive system with the carbon 10 and conductive agent 30 contained in the silicon-carbon negative electrode material, which plays a conductive synergistic role, endows the silicon-carbon negative electrode material with low resistance and high electrical conductivity, thereby endowing the silicon-carbon negative electrode material with high Charge and discharge efficiency and charge and discharge rate. Therefore, the silicon-carbon negative electrode material of the embodiment of the present invention forms mixture particles including carbon 10, composite silicon particles 20 and conductive agent 30, so that carbon 10, composite silicon particles 20 and conductive agent 30 play a synergistic effect, endowing the silicon-carbon negative electrode The material has high charge and discharge efficiency, charge and discharge rate, specific capacity and cycle performance.

The silicon-based nuclei 21, as the main material of the main specific capacity of the silicon-carbon negative electrode material, endows the silicon-carbon negative electrode material with high specific capacity characteristics. The material of the silicon-based nuclei 21 can be a conventional silicon-based material, such as silicon oxide, carbon At least one of silicon and elemental silicon. In the embodiment of the present invention, elemental silicon is ideally selected. These silicon-based materials have high specific capacity, among which elemental silicon not only has a high specific capacity, but also can improve the first effect, have low volume expansion, and can improve the first effect performance and cycle performance of the silicon-carbon negative electrode material.

In an embodiment, the particle size of the silicon-based nuclei 21 is in the micron range, and D90≤100nm. In addition, the silicon-based nuclei 21 may be primary particles or secondary particles formed from primary particles.

In an embodiment, the thickness of the carbon coating layer 22 is 5-8nm. In a specific embodiment, the thickness of the carbon coating layer 22 is 5nm, 5.5nm, 6nm, 6.5nm, 7nm, 7.5nm, 8nm and other typical and non-limiting Sexual thickness. The carbon coating layer 22 with this thickness has relatively excellent mechanical properties and the performance of blocking the contact between the electrolyte and the silicon-based nuclei.

Wherein, in some embodiments, the ceramic distributed in the carbon coating layer 22 includes at least one of aluminum oxide, silicon carbide, and titanium dioxide, and silicon oxide is further selected. These ceramics have good mechanical properties, improve the anti-silicon core body 21 volume expansion effect of the carbon coating layer 22, and can improve the effect of the carbon coating layer 22 isolating the electrolyte, and avoid the electrolyte directly contacting the silicon base core body 21. contact to improve the electrochemical performance of silicon-carbon anode materials.

In an embodiment, the particle size of the composite silicon particle 20 is in the nanometer range, such as D50 is 80-300nm, in a specific embodiment, D50 is 80nm, 100nm, 120nm, 140nm, 160nm, 180nm, 200nm, 220nm, 240nm, 260nm, 280nm , 300nm and other typical and non-limiting particle sizes. By controlling the particle size of the composite silicon particle 20, its dispersibility in the mixture particles can be improved and the particle size of the silicon-carbon negative electrode material can be controlled.

In addition, the composite silicon particles 20 may be primary particles or secondary particles formed from primary particles.

Based on the interaction relationship and effect of the carbon 10 contained in the silicon-carbon negative electrode material, the composite silicon particles 20 and the conductive agent 30, in the embodiment, the mass ratio of the carbon 10, the composite silicon particles 20 and the conductive agent 30 is composed of the composite silicon particles, The conductive agent and the first carbon source are mixed in a mass ratio of 10:(5-20):(85-70) and then subjected to carbonization treatment, specifically as the mixing ratio in the silicon-carbon negative electrode material preparation method below. By controlling and adjusting the ratio of carbon 10, composite silicon particles 20 and conductive agent 30, the conductivity and specific capacity of the silicon-carbon negative electrode material are improved, so that the silicon-carbon negative electrode material has high charge-discharge efficiency, charge-discharge rate, and specific capacity.

Based on the silicon-carbon negative electrode material in each of the above embodiments, in the embodiment, the silicon-carbon negative electrode material also includes a capacity supplement, as shown in Figure 1, the capacity supplement 40 is mixed with carbon 10, composite silicon particles 20 and conductive agent 30, That is, the capacity extender 40 forms a mixture with the carbon 10 , the composite silicon particles 20 and the conductive agent 30 . The presence of the capacity supplement 40 can effectively fill the micropores that may exist in the carbon 10, especially when the carbon 10 is sintered carbon, the capacity supplement 40 can effectively fill the micropores that exist in the sintered carbon, thereby assisting silicon The base core body 21 improves the capacity of the silicon-carbon negative electrode material, increases the specific capacity of the silicon-carbon negative electrode material, and at the same time assists the carbon 10 and the conductive agent 30 to build a three-dimensional conductive system, improves the conductivity of the silicon-carbon negative electrode material, and improves its fast charging ability.

In an embodiment, the content of the capacity supplement 40 in the silicon-carbon negative electrode material is 5-10%. In specific embodiments, the content of the capacity supplement 40 in the silicon-carbon negative electrode material is 5%, 6%, 7%, 8%. , 9%, 10% and other typical and non-limiting contents. In other embodiments, capacity extender 40 includes graphite. By controlling the content and type of the capacity supplement 40, the above-mentioned function of the capacity supplement can be improved, thereby improving the electrical conductivity of the silicon-carbon negative electrode material and improving its fast charging capability.

Based on the above, the silicon-carbon negative electrode material of the embodiment of the present invention forms a mixture particle including carbon 10, composite silicon particles 20 and conductive agent 30 to play a synergistic effect, and endows the silicon-carbon negative electrode material with high charge and discharge efficiency, charge and discharge rate, Specific capacity and cycle performance.

On the other hand, the embodiment of the present invention provides the preparation method of the silicon-carbon negative electrode material in the above embodiment of the present invention. The process flow of the preparation method of the silicon carbon negative electrode material of the embodiment of the present invention is shown in Figure 3, which includes the following steps:

S01: Provide composite silicon particles;

S02: Mixing the composite silicon particles with the conductive agent and the first carbon source to obtain a mixed material;

S03: performing the first carbonization treatment on the mixed material.

Wherein, in step S01 , the composite silicon particles are the composite silicon particles 20 described above and shown in FIG. 2 . Therefore, the composite silicon particle in step S01 includes a silicon-based core body 21 and a carbon coating layer 22 covering the silicon-based core body 21 , and the carbon coating layer 22 is doped with ceramics. In order to save space, the structure and composition of the composite silicon particles in step S01 will not be repeated here.

In the embodiment, the composite silicon particles are prepared according to a method comprising the following steps:

S011: Mixing silicon-based particles with a second carbon source containing a ceramic precursor, so that the second carbon source containing a ceramic precursor forms a coating layer on the surface of the silicon-based particles to obtain a composite silicon particle precursor;

S012: performing a second carbonization treatment on the composite silicon particle precursor to obtain composite silicon particles.

Wherein, in step S011, the silicon-based particles may be the silicon-based nuclei 21 contained in the composite silicon particles 20 above, and in an embodiment, they may be conventional silicon-based materials in the range of nanometer particle sizes, such as elemental silicon, silicon carbide, At least one of the silicon oxides is further elemental silicon particles.

The second carbon source containing the ceramic precursor can be a mixture of the ceramic precursor and the carbon source, and can also be a carbon-containing ceramic precursor. In an embodiment, when the second carbon source containing the ceramic precursor is a ceramic precursor and carbon In the case of a mixture of sources, the ceramic precursor includes at least one ceramic precursor among alumina, silicon carbide, and titanium dioxide. The second carbon source includes at least one of an organic aluminum source and an organic titanium source.

When the second carbon source containing the ceramic precursor is a carbon-containing ceramic precursor, the carbon-containing ceramic precursor includes at least one of an organic aluminum source and an organic titanium source. Wherein, the organic aluminum source includes but not only at least one of aluminum ethoxide, aluminum isopropoxide, aluminum alkoxide and the like.

The mixing treatment in step S011 can be any mixing method that can realize the coating of the second carbon source containing the ceramic precursor on the surface of the silicon-based particles, which is within the scope disclosed in this specification, such as mixing the second carbon source containing the ceramic precursor Two carbon sources and silicon-based particles are prepared into a dispersion, and the dispersion is mixed, such as by ball milling or sand milling, so that the second carbon source containing the ceramic precursor forms a coating layer on the surface of the silicon-based particles to obtain Composite silicon particle precursor.

In addition, the mixing ratio of the silicon-based particles and the second carbon source containing the ceramic precursor can control the thickness of the carbon coating layer contained in the composite silicon particles. For example, through the mixing ratio of the two, the thickness of the carbon coating layer can be controlled as above The thickness of the carbon coating layer 22 contained in the composite silicon particle 20 .

The second carbonization treatment in step S012 is to carbonize the composite silicon particle precursor prepared in step S011, so that the second carbon source is carbonized and the ceramic precursor forms ceramics, thereby forming the composite silicon particle 20 above. In the embodiment, the temperature of the second carbonization treatment is 600-900°C. In specific embodiments, the temperature of the second carbonization treatment is 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, etc. and non-limiting temperature. The temperature of the second carbonization treatment can be flexibly adjusted and controlled according to the type of the second carbon source and the ceramic precursor. In addition, the second carbonization treatment should be sufficient, at least to ensure that the second carbon source is completely carbonized, and the ceramic precursor is fully formed into a ceramic. Therefore, on the basis of the type of components in step S011, the carbonization temperature is controlled, and the generated carbon coating layer (that is, the carbon coating layer 22 contained in the composite silicon particle 20 above) is uniformly dispersed with ceramic components, giving The generated carbon coating layer has good mechanical properties and electrolyte isolation properties, so that the prepared composite silicon particles have high specific capacity, the carbon coating layer is complete, and the particle mechanical properties are good.

In step S02, the mixed material obtained after mixing the composite silicon particles with the conductive agent and the first carbon source in step S01 is the precursor of the above-mentioned silicon-carbon negative electrode material. In an embodiment, the composite silicon particles, the conductive agent and the first carbon source are mixed according to a mass ratio of 10:(5-20):(85-70). In a specific embodiment, the mass ratio of the composite silicon particles, the conductive agent, and the first carbon source is typical and non-limiting ratios such as 10:20:85, 10:15:80, 10:5:70, and the like. By controlling and optimizing the mixing ratio of the three, the mass ratio of composite silicon particles, conductive agent and carbon contained in the silicon-carbon negative electrode material can be controlled, thereby improving the charge-discharge efficiency, charge-discharge rate, and ratio of the prepared silicon-carbon negative electrode material. performance such as capacity.

Further, before the step of subjecting the mixed material to the first carbonization treatment, the mixed material is formulated into a mixture dispersion; then the mixture dispersion is spray-dried and granulated to obtain mixture particles; then the mixture particles are subjected to the first carbonization treatment . By spraying and granulating the mixed materials, on the one hand, the raw materials of each component can be mixed evenly, and the particle size of the formed precursor particles is complete and uniform.

Since the mixed material obtained in step S02 is the precursor of the silicon-carbon anode material mentioned above. Therefore, the conductive agent is the conductive agent 30 contained in the aforementioned silicon-carbon negative electrode material. In an embodiment, the first carbon source in step S02 is a precursor for forming the carbon 10 contained in the silicon-carbon negative electrode material above, which includes at least one of pitch, biochar, polyethylene glycol, PVP, citric acid, and phenolic resin. A sort of.

In step S03, after the mixed material obtained in step S02 is subjected to the first carbonization treatment, the first carbon source in the mixed material is cracked to form carbon, which is the carbon 10 contained in the silicon-carbon negative electrode material above, and the material generated after cracking It is the above silicon carbon negative electrode material. In the embodiment, the temperature of the first carbonization treatment is 600-900°C. In specific embodiments, the temperature of the first carbonization treatment is 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, etc. and non-limiting temperature. The temperature of the first carbonization treatment can be flexibly adjusted and controlled according to the type of the first carbon source. In addition, the first carbonization treatment should be sufficient, at least to ensure that the first carbon source is completely carbonized, and the temperature of the carbonization treatment is controlled to improve the electrochemical performance of the silicon-carbon negative electrode material.

According to the preparation methods of silicon-carbon negative electrode materials in the above-mentioned embodiments, the preparation methods of silicon-carbon negative electrode materials in the embodiments of the present invention can effectively ensure that the composite silicon particles, conductive agents and carbon generated by carbonization are evenly dispersed, thereby ensuring that the prepared silicon-carbon negative electrode materials contain The carbon, composite silicon particles and conductive agent play a synergistic role, endowing the prepared silicon-carbon anode material with high charge and discharge efficiency, charge and discharge rate, specific capacity and cycle performance, and at the same time, the particle structure of the material has good mechanical properties. In addition, the preparation method of the silicon-carbon negative electrode material can ensure that the prepared silicon-carbon negative electrode material has a stable structure and electrochemical performance, and has high efficiency and saves production costs.

In yet another aspect, the embodiments of the present invention also provide a negative electrode and a lithium ion battery containing the negative electrode.

The negative electrode can be a conventional negative electrode of a lithium ion battery, such as a current collector and a negative active layer combined on the surface of the current collector. Wherein, the negative electrode active layer contains the silicon-carbon negative electrode material of the above-mentioned embodiment of the invention.

The lithium ion battery of the embodiment of the present invention contains the negative electrode. Certainly, the lithium-ion battery of the embodiment of the present invention also has necessary components such as a positive electrode, a diaphragm, and an electrolyte necessary for the lithium-ion battery.

Since the lithium-ion battery of the embodiment of the present invention contains the above-mentioned silicon-carbon negative electrode material, the negative electrode cycle performance is good and the internal resistance is low, thereby endowing the lithium-ion battery of the embodiment of the present invention with excellent rate performance and cycle performance, long life, and fast charging Strong ability and stable electrochemical performance.

A number of specific examples are used to illustrate the silicon-carbon negative electrode material of the present invention and its preparation method and application.

1. Silicon carbon negative electrode material and its preparation method:

Example 1

This embodiment provides a silicon carbon negative electrode material and a preparation method thereof. The silicon carbon negative electrode material is the granular material shown in Figure 1 and Figure 2, including the mixture particles formed by sintered carbon, graphite, composite silicon particles and CNT conductive agent, and the mass ratio of sintered carbon, composite silicon particles and CNT conductive agent is given by Composite silicon particles, conductive agent and pitch are mixed according to the mass ratio of 10:10:80 and then carbonized. The content of graphite is 8% of the total weight of the silicon-carbon negative electrode material. Among them, the composite silicon particles include a D90≤100nm nano-silicon core body and a carbon coating layer containing aluminum oxide coated on the nano-silicon core body. The content of aluminum oxide and carbon in the carbon coating layer is the content formed by the carbonization of aluminum ethoxide. .

After testing, the D90 of the silicon-carbon negative electrode material is ≤ 25 μm, and the D90 of the composite silicon particles is ≤ 300 nm.

The preparation method of the silicon carbon negative electrode material in this embodiment comprises the following steps:

S1. Preparation of composite silicon particles: D90≤100μm micro-silicon is ground in anhydrous ethanol solvent by sand milling, and aluminum ethylate is added during the sand milling process to achieve nano-fine powder size on the surface of nano-silica powder with D90≤100nm Coated with a carbon coating layer containing alumina, and then carbonized at a high temperature of 500°C to obtain nanocomposite silicon particles;

S2. Preparation of silicon-carbon secondary particles: mix the prepared composite silicon particles, D90≤20 μm graphite powder and pitch, and CNT conductive agent in absolute ethanol in proportion (composite silicon particles, CNT conductive agent and pitch are mixed according to the mass ratio 10:10:80, graphite is added according to the proportion of 8% of the total weight of the silicon-carbon anode material), spray granulation is carried out at 300°C by spray drying, and after high-temperature carbonization at 500°C, D90≤ 25μm silicon carbon secondary particles with a three-dimensional conductive network, that is, silicon carbon negative electrode material.

Example 2

This embodiment provides a silicon carbon negative electrode material and a preparation method thereof. The structure of the silicon-carbon negative electrode material is the same as that of the silicon-carbon negative electrode material in Example 1. The content of graphite is 5% of the total weight of the silicon-carbon negative electrode material. Among them, the composite silicon particles include a D90≤100nm nano-silicon core body and a carbon coating layer containing aluminum oxide coated on the nano-silicon core body. The content of aluminum oxide and carbon in the carbon coating layer is formed by carbonization of aluminum isopropoxide content.

After testing, the D90 of the silicon-carbon negative electrode material is ≤ 25 μm, and the D90 of the composite silicon particles is ≤ 300 nm.

The preparation method of the silicon carbon negative electrode material in this embodiment comprises the following steps:

S1. Preparation of composite silicon particles: D90≤100μm micron silicon is ground in isopropanol solvent by sand milling, and aluminum isopropoxide is added during the sand milling process to achieve nano-silicon with a size of D90≤100nm The surface of the powder is coated with a layer of carbon and aluminum materials, and then carbonized at a high temperature of 800°C to obtain carbon-coated and alumina ceramic-coated nano-silicon particles;

S2. Preparation of silicon-carbon secondary particles: the preparation of the prepared composite silicon particles, D90≤300nm graphite powder and biochar, CNT conductive agent are mixed in absolute ethanol in proportion (composite silicon particles, CNT conductive agent and The asphalt is added according to the mass ratio of 10:15:75, and the graphite is added according to the proportion of 5% of the total weight of the silicon-carbon negative electrode material), and the spray granulation is carried out at 500°C by spray drying, and carbonized at 800°C Finally, silicon-carbon secondary particles with a D90≤25 μm and a three-dimensional conductive network are obtained.

Example 3

This embodiment provides a silicon carbon negative electrode material and a preparation method thereof. The structure of the silicon-carbon negative electrode material is the same as that of the silicon-carbon negative electrode material in Example 1. The content of graphite is 10% of the total weight of the silicon-carbon negative electrode material. Among them, the composite silicon particles include D90≤100nm nano-silicon core body and a carbon coating layer containing aluminum oxide coated on the nano-silicon core body. The content of aluminum oxide and carbon in the carbon coating layer is formed by carbonization of aluminum alkoxide content.

After testing, the D90 of the silicon-carbon negative electrode material is ≤ 25 μm, and the D90 of the composite silicon particles is ≤ 300 nm.

The preparation method of the silicon carbon negative electrode material in this embodiment comprises the following steps:

S1. Preparation of composite silicon particles: D90≤100μm micron silicon is ground in an ethanol solvent by sand milling, and aluminum alkoxide is added during the sand milling process to realize the coating of nano-fine powder on the surface of D90≤100nm nano-silica powder. A layer of carbon and aluminum-containing materials is coated, and then carbonized at a high temperature of 600°C to obtain nano-silicon particles coated with carbon and alumina ceramics.

S2. Preparation of silicon-carbon secondary particles: the preparation of the prepared composite silicon particles, D90≤20 μm graphite powder and polyethylene glycol, and CNT conductive agent are mixed in absolute ethanol in proportion (composite silicon particles, CNT conductive agent and asphalt according to the mass ratio of 10:5:85, and the graphite is added according to the proportion of 10% of the total weight of the silicon carbon negative electrode material), spray granulation is carried out at 400°C by spray drying method, and the high temperature is 600°C After carbonization, silicon-carbon secondary particles with a D90≤25 μm and a three-dimensional conductive network are obtained.

Example 4

This embodiment provides a silicon carbon negative electrode material and a preparation method thereof. The structure of the silicon-carbon negative electrode material is the same as that of the silicon-carbon negative electrode material in Example 1. Compared with Example 1, no graphite is contained.

The preparation method of the silicon-carbon negative electrode material in this example was prepared according to the method in Example 1.

2. Lithium-ion battery embodiment:

The silicon carbon negative electrode material provided by the above-mentioned embodiment 1 to embodiment 4 and the silicon carbon negative electrode material provided by the comparative example were respectively assembled into a negative electrode electrode and a lithium ion battery according to the following methods:

Negative electrode: The silicon-carbon negative electrode materials provided in the above-mentioned examples 1 to 4 and the silicon-carbon negative electrode materials provided in the comparative example were respectively used as negative electrodes, and the negative electrodes were respectively prepared according to the following methods;

Negative electrode: the silicon-based negative electrode material provided by the above examples and the silicon-based negative electrode material provided by the comparative example are used as the negative electrode active material, and 96wt% of the silicon-based negative electrode active material, 1wt% of the Super P conductive material and 1wt% of carboxymethyl Cellulose thickener and 2wt% styrene-butadiene rubber binding agent are mixed in pure water solvent, with paper cup negative electrode active material slurry and sizing material is coated on Cu foil current collector, then dry, roll Pressed and cut to make negative electrodes.

Positive electrode: 96wt% LiCoO ₂ positive electrode active material, 2wt% Super P conductive material and 2wt% PVDF binder were mixed in N-methylpyrrolidone solvent to prepare positive electrode active material slurry, and coated on the slurry cloth on Al foil current collectors, followed by drying, rolling and cutting to fabricate positive electrodes.

Using a general process, a positive electrode, a negative electrode, and a non-aqueous electrolyte are used to fabricate a rechargeable lithium battery. As the non-aqueous electrolytic solution, a mixed solvent (containing different kinds of additives) of ethylene carbonate and diethyl carbonate in which 1.1 M LiPF ₆ was dissolved was used.

Lithium-ion battery assembly: Assemble the battery in an inert atmosphere glove box according to the assembly sequence of the lithium-ion battery structure.

3. Related characteristic test

Lithium-ion battery electrochemical performance test

The negative electrode in Section 2 above was electrochemically intercalated lithium three times (the charge-discharge rate is 0.05C, and the charge-discharge cut-off voltage is 0.05-1.5V), and then assembled into a lithium-ion battery, and tested the first-time charge-discharge efficiency of each lithium-ion battery, rate, and cycle life. The measured results are shown in Table 1 below:

Table 1

First charge and discharge efficiency Maximum charge rate 0.5C cycle life Example 1 92.3% 2C 955 times Example 2 90.7% 2C 976 times Example 3 91.0% 2C 943 times

It can be seen from Table 1 that the first charge and discharge efficiency of the lithium-ion battery containing the silicon-carbon negative electrode material provided by the embodiment of the present invention is higher than 90%, the highest charge rate can reach 2C, and the 0.5C cycle life can reach more than 955 times, which has excellent First effect, rate performance and cycle performance, and has good fast charging performance. Therefore, the silicon-carbon anode material of the embodiment of the present invention has low resistance and high conductivity, stable particle structure during charging, high specific capacity, high charge-discharge efficiency and charge-discharge rate performance.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (10)

1. A silicon-carbon negative electrode material is characterized in that: the composite silicon particles comprise a silicon-based core body and a carbon coating layer coating the silicon-based core body, and the carbon coating layer is doped with ceramic.

2. The silicon-carbon anode material according to claim 1, wherein: the mass ratio of the carbon to the composite silicon particles to the conductive agent is that the composite silicon particles, the conductive agent and the first carbon source are mixed according to the mass ratio of 10: (5-20): (85-70) ratio of carbonization treatment after mixing; and/or

The carbon is a carrier, and the composite silicon particles and the conductive agent are dispersed in the carrier; and/or

The particle size of the composite silicon particles is in a nanometer range; and/or

The conductive agent comprises at least one of carbon nano tube, super p, graphene and graphite micro powder; and/or

The carbon is a cracked carbon.

3. The silicon-carbon anode material according to claim 1, wherein: the silicon core body is simple substance silicon; and/or

The ceramic comprises at least one of alumina, silicon carbide and titanium dioxide; and/or

The thickness of the carbon coating layer is 5-8nm.

4. The silicon-carbon anode material according to any one of claims 1 to 3, wherein: the silicon carbon anode material further includes a capacity extender mixed with the carbon, the composite silicon particles, and the conductive agent.

5. The silicon-carbon anode material according to claim 4, wherein: the content of the capacity replenisher in the silicon-carbon negative electrode material is 5% -10%; and/or

The capacity extender includes graphite.

6. A preparation method of a silicon-carbon negative electrode material comprises the following steps:

providing composite silicon particles; the composite silicon particles comprise a silicon-based core body and a carbon coating layer coating the silicon-based core body, and the carbon coating layer is doped with ceramic;

mixing the composite silicon particles with a conductive agent and a first carbon source to obtain a mixed material;

and carrying out first carbonization treatment on the mixed material.

7. The production method according to claim 6, wherein the composite silicon particles, the conductive agent and the first carbon source are mixed in a mass ratio of 10: (5-20): (85-70) carrying out mixing treatment;

and/or

Preparing the mixed material into a mixture dispersion liquid before the step of performing the first carbonization treatment on the mixed material; then carrying out spray drying granulation on the mixture dispersion liquid to obtain mixture particles; then subjecting the mixture particles to the first carbonization treatment;

and/or

The composite silicon particles are prepared by the method comprising the following steps:

mixing silicon-based particles with a second carbon source containing a ceramic precursor to form a coating layer on the surface of the silicon-based particles by the second carbon source containing the ceramic precursor, thereby obtaining a composite silicon particle precursor;

and carrying out second carbonization treatment on the composite silicon particle precursor to obtain the composite silicon particles.

8. The method according to claim 7, wherein the silicon-based particles comprise at least one of elemental silicon, silicon carbide, and silicon monoxide; and/or

The second carbon source comprises at least one of an organic aluminum source and an organic titanium source; and/or

The temperature of the second carbonization treatment is 600-900 ℃.

9. The production method according to any one of claims 6 to 8, wherein the first carbon source includes at least one of pitch, biomass charcoal, polyethylene glycol, PVP, citric acid, and phenol resin; and/or

The temperature of the first carbonization treatment is 600-900 ℃.

10. A lithium ion battery comprises a negative electrode, wherein the negative electrode comprises a current collector and a negative active layer combined on the surface of the current collector, and is characterized in that: the negative electrode active layer contains the silicon-carbon negative electrode material according to any one of claims 1 to 5 or the silicon-carbon negative electrode material prepared by the preparation method according to any one of claims 6 to 9.

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