阅读说明：本技术 复合硅基负极材料及其制备方法和锂离子电池 (Composite silicon-based negative electrode material, preparation method thereof and lithium ion battery ) 是由 钟泽钦 万远鑫 孔令涌 陈彩凤 任望保 于 2020-11-27 设计创作，主要内容包括：本发明公开了一种复合硅基负极材料及其制备方法和锂离子电池。所述复合硅基负极材料为核壳结构,所述核壳结构包括核体、包覆于所述核体的第一壳层和包覆于所述第一壳层的第二壳层；其中,所述核体的材料包括硅负极材料,所述第一壳层的材料包括预锂化材料,所述第二壳层的材料包括碳。本发明复合硅基负极材料首次库伦效率,内阻低,双壳层力学性能高,能有效抑制硅基负极材料体积膨胀,在充放电过程中保持结构稳定性,且循环性能优异。而且其工艺条件易控,能够保证制备的复合硅基负极材料结构和性能稳定。锂离子电池含有本发明复合硅基负极材料,其首次库伦效率高,具有优异的循环性能,寿命长,电化学性能稳定。(The invention discloses a composite silicon-based negative electrode material, a preparation method thereof and a lithium ion battery. The composite silicon-based negative electrode material is of a core-shell structure, and the core-shell structure comprises a core body, a first shell layer coated on the core body and a second shell layer coated on the first shell layer; wherein the material of the core body comprises a silicon negative electrode material, the material of the first shell layer comprises a pre-lithiated material, and the material of the second shell layer comprises carbon. The composite silicon-based negative electrode material disclosed by the invention has the advantages of low initial coulombic efficiency, low internal resistance and high mechanical property of double shells, can effectively inhibit the volume expansion of the silicon-based negative electrode material, keeps the structural stability in the charging and discharging processes, and has excellent cycle performance. And the process conditions are easy to control, and the stable structure and performance of the prepared composite silicon-based negative electrode material can be ensured. The lithium ion battery contains the composite silicon-based negative electrode material, and has the advantages of high coulombic efficiency for the first time, excellent cycle performance, long service life and stable electrochemical performance.)

1. The composite silicon-based negative electrode material is of a core-shell structure and is characterized in that: the core-shell structure comprises a core body, a first shell layer coated on the core body and a second shell layer coated on the first shell layer; wherein the material of the core body comprises a silicon negative electrode material, the material of the first shell layer comprises a pre-lithiated material, and the material of the second shell layer comprises a carbon layer.

2. The method of claim 1The composite silicon-based negative electrode material is characterized in that: the silicon cathode material comprises SiO_xWherein x is more than or equal to 0.5 and less than 1.5; and/or

The silicon negative electrode material is at least one of block, sheet and particle; and/or

The prelithiated material includes Li₂SiO₃、Li₄SiO₄、Li₂SiO₅At least one of; and/or

The carbon layer is formed by liquid phase or gas phase deposition of at least one organic carbon including pitch and/or C1-C4.

3. The composite silicon-based anode material according to claim 1 or 2, wherein: the thickness of the first shell layer is 10nm-5 mu m; and/or

The thickness of the second shell layer is 1-100 nm.

4. The composite silicon-based anode material according to claim 1 or 2, wherein: the gram capacity of the composite silicon-based negative electrode material is 1400-1700 mAh/g; and/or

The initial coulombic efficiency of the composite silicon-based negative electrode material is more than 85%, and the capacity retention rate is more than 90% after 100 times of circulation.

5. The preparation method of the composite silicon-based negative electrode material is characterized by comprising the following steps of:

forming a pre-lithiation-containing material layer coated on the surface of the silicon negative electrode material;

and forming a carbon-containing coating layer on the surface of the pre-lithiation-containing material layer.

6. The preparation method of claim 5, wherein the method for forming the pre-lithiation-containing material layer coated on the silicon negative electrode material on the surface of the silicon negative electrode material comprises the following steps:

constructing a galvanic cell by using an electrolyte and an electrode, and generating a pre-composite silicon-based negative electrode material containing a pre-lithiation material layer coated with a silicon negative electrode material by performing a reduction reaction in the electrolyte;

and/or

Carrying out electrolytic treatment on the electrolyte to enable the electrolyte to carry out reduction reaction to generate a pre-composite silicon-based negative electrode material containing a pre-lithiation material layer coated with a silicon negative electrode material;

wherein the electrolyte comprises a solvent and a lithium salt dissolved in the solvent, and SiO is arranged in the electrolyte_xA material.

7. The method of claim 6, wherein: the solvent comprises at least one of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl maleate, tetrahydrofuran and methyl carbonate; and/or

The lithium salt comprises at least one of lithium hexafluorophosphate, lithium aluminum tetrachloride, lithium trifluoroformate, lithium borate, lithium hexafluoroarsenate, lithium perchlorate, lithium nitrate, lithium sulfate, lithium hydroxide, lithium oxide, lithium fluoride, lithium oxalate, lithium acetate and lithium formate; and/or

The concentration of the electrolyte is 0.1-10 mol/L; and/or

In the electrolyte, the mass ratio of the solvent to the lithium salt is (0.1-98): (0.001-15); and/or

In the electrolytic treatment process, the electrifying voltage is 0.01-1V, and the current density is 0.1-5mAh/cm²(ii) a And/or

A stirring step is also carried out in the process of the reduction reaction, and the stirring speed is 500-2000 rpm; and/or

The SiO_xThe material is at least one of block, sheet and granule.

8. The production method according to claim 6 or 7, characterized in that: the galvanic cell comprises a container and an electrode, wherein the electrolyte is contained in the container, the inner wall of the container, which is submerged below the liquid level of the electrolyte, is at least partially conductive, the electrode is at least partially submerged in the electrolyte, and the conductive part of the inner wall is electrically connected with the electrode and forms the galvanic cell together with the electrolyte; and/or

The method for forming the carbon-containing coating layer on the surface of the pre-lithiation-containing material layer is to form the carbon coating layer on the surface of the pre-lithiation-containing material layer in situ by adopting at least one of a solid-phase method, a liquid-phase method and a gas-phase method.

9. A negative electrode comprising a current collector and a silicon-based active layer bonded to a surface of said current collector, characterized in that: the silicon-based active layer contains the composite silicon-based negative electrode material as defined in any one of claims 1 to 4 or the composite silicon-based negative electrode material prepared by the preparation method as defined in any one of claims 5 to 9.

10. A lithium ion battery comprising a negative electrode, characterized in that: the negative electrode is the negative electrode of claim 9.

Technical Field

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

Background

Along with the enhancement of awareness of environmental protection and energy crisis, the lithium ion battery is more and more popular as an environment-friendly energy storage technology. Lithium ion batteries are widely used due to their high capacity density, long cycle and high stability. With the wide application of electronic products and the vigorous development of electric automobiles, the market of lithium ion batteries is increasingly wide, but higher requirements on the safety of the lithium ion batteries are provided.

At present, a commercial lithium ion battery mainly adopts a graphite negative electrode material, but the theoretical specific capacity of the lithium ion battery is only 372mAh/g, and the requirement of the market on the high capacity density of the lithium ion battery cannot be met.

At present, the silicon-based negative electrode material has high theoretical specific capacity and a suitable lithium embedding platform, and is an ideal high-capacity negative electrode material for a lithium ion battery. However, in the process of charging and discharging, the volume change of silicon reaches more than 300%, and the internal stress generated by the violent volume change easily causes electrode pulverization and peeling, thereby influencing the cycle stability.

In order to effectively overcome the adverse effect caused by volume expansion of silicon in the charging and discharging processes, the current research directions of silicon cathode materials mainly include nano silicon-carbon composite materials, silicon protoxide materials, amorphous silicon alloys, porous silica materials and the like, and a continuous carbon film formed on the surface of a silicon core material can improve the conductivity of the silicon base material and inhibit side reactions between the material and electrolyte. However, it is well documented that the coating film is cracked due to excessive volume expansion during long cycling, so that the electrical contact is reduced, the electrical conductivity is deteriorated, and the cycling performance is still not ideal, and the first coulombic efficiency of the battery is low.

At present, attempts are also made to improve the first coulombic efficiency of a silicon-based negative electrode material, for example, an organic substance and a lithium salt are reacted at a high temperature to generate a silicon-based negative electrode material containing organic lithium, but in practical application, the organic lithium is found to be unstable, the lithium supplementing effect is not ideal, and the conductivity is low.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provides a composite silicon-based negative electrode material and a preparation method thereof, so as to solve the technical problems that the cycle performance and the first coulombic efficiency of the conventional silicon-based negative electrode material are not ideal.

The invention also aims to provide a negative electrode and a lithium ion battery containing the negative electrode, so as to solve the technical problems of cycle performance and first coulombic efficiency of the conventional silicon-based negative electrode lithium ion battery.

In order to achieve the above object, according to an aspect of the present invention, a composite silicon-based negative electrode material is provided. The composite silicon-based negative electrode material is of a core-shell structure, and the core-shell structure comprises a core body, a first shell layer coated on the core body and a second shell layer coated on the first shell layer; wherein the material of the core body comprises a silicon negative electrode material, the material of the first shell layer comprises a pre-lithiated material, and the material of the second shell layer comprises carbon.

In another aspect of the invention, a preparation method of the composite silicon-based negative electrode material is provided. The preparation method of the composite silicon-based negative electrode material comprises the following steps:

forming a pre-lithiation-containing material layer coated on the surface of the silicon negative electrode material;

and forming a carbon-containing coating layer on the surface of the pre-lithiation-containing material layer.

In yet another aspect of the present invention, a negative electrode is provided. The negative electrode comprises a current collector and a silicon-based active layer combined on the surface of the current collector, wherein the silicon-based active layer contains the composite silicon-based negative electrode material or the composite silicon-based negative electrode material prepared by the preparation method of the composite silicon-based negative electrode material.

In yet another aspect of the present invention, a lithium ion battery is provided. The lithium ion battery comprises a negative electrode, and the negative electrode is the negative electrode of the invention.

Compared with the prior art, the invention has the following technical effects:

the composite silicon-based negative electrode material takes a silicon-containing negative electrode material as a core body, so that the composite silicon-based negative electrode material is endowed with higher capacity; the composite silicon-based negative electrode material is endowed with high initial coulombic efficiency performance by adopting a first shell layer containing a pre-lithiation material to coat a core body; the carbon-containing second shell layer is adopted to coat the first shell layer, so that on one hand, the direct contact between the pre-lithiation material and the electrolyte can be effectively isolated, and the stability of the first shell layer is obviously improved so as to ensure that the composite silicon-based negative electrode material has high initial coulombic efficiency performance; on the other hand, the conductivity of the composite silicon-based negative electrode material is effectively improved, and the internal resistance of the composite silicon-based negative electrode material is reduced. In addition, the double-shell coating core body is formed by the first shell layer and the second shell layer, so that the mechanical property of the shell layers is effectively improved, the volume expansion of the silicon-based negative electrode material is effectively inhibited, the circulation is improved, and the structural stability and the circulation performance of the composite silicon-based negative electrode material in the charging and discharging process are obviously enhanced.

According to the preparation method of the composite silicon-based negative electrode material, the pre-lithiation material layer and the carbon layer coated on the silicon negative electrode material are sequentially formed on the surface of the silicon negative electrode material, so that the coating rate of the pre-lithiation material layer on the silicon negative electrode material is effectively enhanced, the prepared composite silicon-based negative electrode material has the advantages of high initial coulombic efficiency, low internal resistance and the like, the shell layer has high mechanical property, the volume expansion of the silicon-based negative electrode material is effectively inhibited, the circulation is improved, and the prepared composite silicon-based negative electrode material has the advantages of the composite silicon-based negative electrode material; on the other hand, the process conditions are easy to control, the structure and the performance stability of the composite silicon-based negative electrode material can be ensured, and the efficiency is high.

The negative electrode and the lithium ion battery containing the negative electrode have high first coulombic efficiency, good cycle performance and low internal resistance because the composite silicon-based negative electrode material is contained, so that the lithium ion battery has high first coulombic efficiency, excellent cycle performance, long service life and stable electrochemical performance.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.

Fig. 1 is a schematic structural diagram of a composite silicon-based negative electrode material according to an embodiment of the invention;

FIG. 2 is a schematic diagram of a galvanic cell architecture for producing a pre-composite silicon-based negative electrode material comprising a pre-lithiated material layer coated with a silicon negative electrode material;

FIG. 3 is a schematic diagram of an electrolytic processing system for preparing a pre-composite silicon-based anode material for forming a silicon anode material coated with a pre-lithiation material layer;

fig. 4 is a first coulombic efficiency (first effect) curve for a lithium ion battery containing the composite silicon-based anode material of example 1 and a lithium ion battery containing the carbon-coated silicon anode material of the comparative example.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects to be solved by the present application more clearly apparent, the present application is further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

In this application, the term "and/or" describes an association relationship of associated objects, meaning that there may be three relationships, e.g., a and/or B, which may mean: a is present alone, A and B are present simultaneously, and B is present alone. Wherein A and B can be singular or plural. The character "/" generally indicates that the former and latter associated objects are in an "or" relationship.

In the present application, "at least one" means one or more, "a plurality" means two or more. "at least one of the following" or similar expressions refer to any combination of these items, including any combination of the singular or plural items. For example, "at least one (a), b, or c", or "at least one (a), b, and c", may each represent: a, b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c, wherein a, b, and c may be single or plural, respectively.

It should be understood that, in various embodiments of the present application, the sequence numbers of the above-mentioned processes do not mean the execution sequence, some or all of the steps may be executed in parallel or executed sequentially, and the execution sequence of each process should be determined by its function and inherent logic, and should not constitute any limitation to the implementation process of the embodiments of the present application.

The terminology used in the embodiments of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in the examples of this application and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

The weight of the related components mentioned in the description of the embodiments of the present application may not only refer to the specific content of each component, but also represent the proportional relationship of the weight among the components, and therefore, the content of the related components is scaled up or down within the scope disclosed in the description of the embodiments of the present application as long as it is scaled up or down according to the description of the embodiments of the present application. Specifically, the mass described in the specification of the embodiments of the present application may be a mass unit known in the chemical industry field such as μ g, mg, g, kg, etc.

The terms "first" and "second" are used for descriptive purposes only and are used for distinguishing purposes such as substances from one another, and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. For example, a first XX may also be referred to as a second XX, and similarly, a second XX may also be referred to as a first XX, without departing from the scope of embodiments of the present application. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature.

In one aspect, embodiments of the present invention provide a composite silicon-based negative electrode material. The composite silicon-based negative electrode material is shown in fig. 1, and the composite silicon-based negative electrode material is a core-shell structure with double shell layers and comprises a core body 1, a first shell layer 2 coated on the core body 1 and a second shell layer 3 coated on the first shell layer 2. Thus, the first shell 2 and the second shell 3 together form a double-shell composite shell structure.

Wherein the core body 1 includes a silicon negative electrode material, such that the core body imparts higher capacity characteristics to the composite silicon-based negative electrode material. In one embodiment, the silicon cathode material comprises SiO_x. Wherein x is more than or equal to 0.5 and less than 1.5. The silicon negative electrode material has high specific capacity characteristic. In another embodiment, it may be any one of granular, block, and tablet. When SiO is present_xIn the case of a granular composite silicon-based negative electrode material, the structure of the composite silicon-based negative electrode material is shown in fig. 1(a), and the particle size of the core body 1 is 1 to 50 nm. By optimizing the particle size of the core body 1, the nano silicon core provides a faster lithium ion migration path, and the problem of volume expansion of the nano silicon core can be relieved. When SiO is present_xWhen the silicon-based composite negative electrode material is in a block shape or a sheet shape, the structure of the silicon-based composite negative electrode material is shown in figure 1(B), and SiO in the case_xAnd also the size of the nucleus 1, can be controlled and adjusted according to the needs of the specific application. Regardless of SiO_xIn the form of particles, blocks or flakes, SiO_xPreferably the surface has a porous structure.

The first shell layer 2 comprises a pre-lithiation material which is coated on the core body 1, and a coating shell layer containing lithium is formed on the surface of the core body 1, so that the composite silicon-based negative electrode material has higher capacity, and lithium supplement can be realized, so that the first coulomb efficiency of the composite silicon-based negative electrode material is improved. In an embodiment, the prelithiation material includes Li₂SiO₃、Li₄SiO₄、Li₂SiO₅At least one of (1). The prelithiation material is prepared by adding SiO in silicon core, which is unstable during lithium insertion and lithium removal during battery charging and discharging₂The components are pre-modified to additional lithium silicate, thereby reducing irreversible capacity loss and improving first coulombic efficiency. In one embodiment, the thickness of the first shell 2 is 10nm to 5 μm, preferably 50 to 100 nm. By optimizing the thickness of the first shell 2, not only can the package be effectively carried outThe core body 1 is coated, abundant lithium and silicon are provided, the capacity of the composite silicon-based negative electrode material is improved, and the lithium supplementing effect on the negative electrode is optimized.

The second shell layer 3 comprises a carbon layer which is coated on the first shell layer 2 to form an outer shell layer of the composite silicon-based negative electrode material and effectively coat the pre-lithiation material. Because the first shell layer 2 contains the pre-lithiation material, and lithium is a very active component, the lithium is very easy to oxidize, and at the moment, the second shell layer 3 covers carbon, the second shell layer 3 can effectively protect the pre-lithiation material, the pre-lithiation material is prevented from directly contacting with an electrolyte to prevent the lithium from reacting, and the structural stability of the silicon-based negative electrode material is maintained. Meanwhile, carbon contained in the second shell layer 3 has excellent conductivity, so that the internal resistance of the composite silicon-based negative electrode material can be effectively reduced, and the electrochemical performance is improved. In one embodiment, the carbon layer is produced by liquid or vapor deposition of at least one organic carbon comprising pitch and/or C1-C4, wherein the C1-C4 organic carbon comprises at least one of methane, ethane, acetylene, ethylene, and the like. The material of the carbon layer comprises at least one of amorphous carbon, graphite, carbon nanotubes, graphene, carbon black, carbon nanofibers, conductive carbon. In another embodiment, the thickness of the second shell 3 is 1-100nm, preferably 2-50 nm. By optimizing the material and thickness of the second shell layer 3, the first shell layer 2 can be effectively coated, the stability of the pre-lithiation material is improved, and the rate capability of the composite silicon-based negative electrode material is improved.

Therefore, in each of the above embodiments, the composite silicon-based negative electrode material uses the silicon-containing negative electrode material as the core body 1, and a higher capacity is given to the composite silicon-based negative electrode material. The first shell layer 2 containing the pre-lithiation material is adopted to coat the core body 1, so that the composite silicon-based negative electrode material can be oxidized, fallen and reconstructed into an SEI film through the pre-lithiation-containing material contained in the first shell layer 2 in the first charge-discharge process, the irreversible loss of lithium forming the SEI film is reduced, the first coulombic efficiency is improved, and the capacity is further improved. The first shell layer 2 is coated by the carbon-containing second shell layer 3, so that the direct contact between the pre-lithiation material and the electrolyte can be effectively isolated, and the stability of the first shell layer 2 is obviously improved; meanwhile, the conductivity of the composite silicon-based negative electrode material is effectively improved, and the internal resistance of the composite silicon-based negative electrode material is reduced. The gram capacity of the composite silicon-based negative electrode material is 1400-1700 mAh/g. The first coulombic efficiency is more than 85%, and the capacity retention rate is more than 90% after 100 times of circulation. In addition, the first shell layer 2 and the second shell layer 3 form the double-shell-layer clad core body 1, so that the mechanical property of the shell layers is effectively improved, the volume expansion of the silicon-based negative electrode material is effectively inhibited, the circulation is improved, and the structural stability and the circulation performance of the composite silicon-based negative electrode material in the charging and discharging process are obviously enhanced.

Correspondingly, the embodiment of the invention also provides a preparation method of the composite silicon-based anode material. The preparation method of the composite silicon-based negative electrode material comprises the following steps:

step S01: forming a pre-lithiation-containing material layer coated on the surface of the silicon negative electrode material;

step S02: a carbon coating layer is formed on the surface of the pre-lithiated material-containing layer in step S01.

Thus, the composite silicon-based negative electrode material preparation method sequentially forms the pre-lithiation material layer and the carbon layer coated on the silicon negative electrode material on the surface of the silicon negative electrode material, effectively enhances the coating rate of the pre-lithiation material layer on the silicon negative electrode material, endows the prepared composite silicon-based negative electrode material with the advantages of high initial coulombic efficiency, low internal resistance, high capacity and the like, endows the shell layer with high mechanical property, effectively inhibits the volume expansion of the silicon-based negative electrode material, improves the cycle, and endows the prepared composite silicon-based negative electrode material with the advantages of the composite silicon-based negative electrode material disclosed by the invention; on the other hand, the process conditions are easy to control, the structure and the performance stability of the composite silicon-based negative electrode material can be ensured, and the efficiency is high.

In step S01, the silicon negative electrode material forms the core body 1 of the composite silicon-based negative electrode material, and the pre-lithiation-containing material layer coated on the silicon negative electrode material forms the first shell layer 2 of the composite silicon-based negative electrode material.

In one embodiment, in step S01, the method for forming the pre-lithiation-containing material layer coated on the surface of the silicon negative electrode material includes the following steps:

constructing the galvanic cell with an electrolyte and electrodes such that the electrolyte occursCarrying out reduction reaction to generate a pre-composite silicon-based negative electrode material containing a pre-lithiation material layer and coating the silicon negative electrode material; wherein the electrolyte comprises a solvent and a lithium salt dissolved in the solvent, and SiO is arranged in the electrolyte_xThe material, wherein x is more than or equal to 0.5 and less than 1.5.

In one embodiment, SiO_xThe material is at least one of granular, block and cake, preferably SiO_xThe material is arranged into a block shape, a cake shape and the like, namely SiO_xThe powder is pressed into a block, and further preferably, the surface of the block is loose and porous, so that lithium can be deposited in pores on the surface and reacts with SiOx on the surface to form a pre-lithiated layer.

The method has the advantages that the original battery system is constructed to directly react, and the pre-lithiation-containing material layer is directly grown on the surface of the silicon cathode in situ to coat the silicon cathode material, so that on one hand, the energy consumption is effectively reduced, and the reaction condition is mild and controllable, thereby effectively overcoming the defects of high energy consumption and uncontrollable stability and reliability in the existing method for generating the organic pre-lithiation-containing material by adopting a lithium source and an organic matter to carry out a high-temperature (such as 160-250 ℃) thermal reaction. On the other hand by SiO provided in the electrolyte_xThe lithium ion battery can directly generate oxidation-reduction reaction with the contained lithium ion to generate a silicon negative electrode material and a coating layer containing the pre-lithiation material, so that the compactness of the coating layer containing the pre-lithiation material is effectively enhanced, and the bonding strength between the coating layer containing the pre-lithiation material and the surface of the negative electrode material can be enhanced. In addition, the reaction time can be flexibly controlled to control the grain diameter of the silicon negative electrode and the thickness of the coating layer containing the pre-lithiation material.

The implementation of the above galvanic cell system can be a galvanic cell system as shown in fig. 2, comprising a container 01 and electrodes 02 (e.g. electrodes 21 and 22), wherein the electrolyte 03 is contained in said container 01, the inner wall 11 of the container 01 submerged below the liquid level of the electrolyte 03 is at least partially conductive, the electrodes 02 are at least partially submerged in said electrolyte 03, and the conductive parts of the inner wall 11 are electrically connected to the electrodes 02 (e.g. to the electrodes 21 and 22, respectively) and together with the electrolyte 03 constitute two galvanic cells. Wherein the conductive portions of the inner wall 11 are in direct contact with the electrodes 02 (e.g., with the electrodes 21 and 22, respectively) to achieve electrical connection, as shown in fig. 2, the electrodes 21 are in direct contact with the conductive portions of the inner wall 11, and the electrodes 22 are in direct contact with the conductive portions of the inner wall 11, thereby constructing two galvanic cells in the container 01. Of course, the conductive portion of the inner wall 11 and the electrode 02 may be electrically connected by a wire, and in this case, the electrode 02 may be spaced from the inner wall 11. It will be appreciated that there is a potential difference between the electrically conductive part of the inner wall 11 and the electrode 02. As in the embodiment where the electrodes 02 are two pieces of lithium metal, the electrically conductive portion of the inner wall 11 should be at a potential difference with the lithium metal pieces, the container 01 may be a conductive metal container, and SiOx is near one end of the lithium metal pieces.

It is of course also possible to select the materials of the electrodes 21 and 22 such that a potential difference exists between the electrodes 21 and 22, so that the electrodes 21 and 22 form a galvanic cell with the electrolyte 03.

In a preferred embodiment, the reaction process of the primary battery further includes stirring treatment, so that the redox reaction can be relatively uniformly performed in the electrolyte 03, and the uniformity of the pre-composite silicon-based negative electrode material is improved. In one embodiment, the stirring rate is preferably 500-2000 rpm.

The electrolyte 03 comprises a solvent, a lithium salt dissolved in the solvent and SiO dispersed in the solvent_x. Thus, SiO in the electrolyte 03_xCan be in contact with the conductive part of the inner wall 11 for short circuit, and a galvanic cell can be formed due to the difference between the potential difference of silicon oxide (more than 0.4V) and lithium (0V), thereby leading the SiO to be in contact with the conductive part of the inner wall_xReacts with lithium ions and deposits. Specifically, the redox reaction in the above-mentioned galvanic cell system includes the following:

Li⁺+e^-+SiO_x→Li₂SiO₃、Li₄SiO₄、Li₂SiO₅

of course, when the electrode 02 is a lithium sheet, the lithium sheet may also participate in the reaction, maintaining the lithium ion balance in the electrolyte. Therefore, in the galvanic cell system, lithium ions and SiO contained in the electrolyte 03_xSiO of the surface_xThe above-mentioned redox reaction occurs, thereby forming a film on SiO_xSurface in-situ growth of Li-containing₂SiO₃、Li₄SiO₄、Li₂SiO₅Etc. and coating with SiO_xThe surface forms a core-shell structure in which unreacted SiO occurs_xThe core body is formed, specifically the core body 1 of the composite silicon-based negative electrode material, and the coating layer formed by the in-situ generated pre-lithiation material forms the first shell layer 2 of the composite silicon-based negative electrode material. Therefore, the reaction system of the primary battery system effectively reduces the energy consumption, and the reaction condition is mild and controllable, thereby effectively reducing the energy consumption. But also in SiO_xThe whole surface of the pre-lithiation coating layer is reacted simultaneously, so that the compactness of the generated pre-lithiation coating layer is effectively improved, and the efficiency is high.

In another embodiment, the method for forming a pre-lithiation-containing material layer coated on the surface of the silicon anode material in step S01 includes the following steps:

carrying out electrolytic treatment on the electrolyte to enable the electrolyte to generate a reduction reaction to generate a pre-composite silicon-based negative electrode material containing a pre-lithiation material layer coated with a silicon negative electrode material; wherein the electrolyte comprises a solvent and a lithium salt dissolved in the solvent, and SiO is arranged in the electrolyte_xThe material, wherein x is more than or equal to 0.5 and less than 1.5.

In one embodiment, SiO_xThe material is at least one of granular, block and cake, preferably SiO_xThe material is arranged into a block shape, a cake shape and the like, namely SiO_xThe powder is pressed into a block, and further preferably, the SiO is_xThe surface of the material is loose and porous, which is beneficial to the deposition of lithium on the surface pores and the reaction with SiOx on the surface to generate a pre-lithiation layer.

By directly mixing lithium ions with SiO_xThe electrolytic solution of (2) is subjected to electrolytic treatment, SiO contained in the electrolytic solution_xThe method has the advantages that the energy consumption is effectively reduced on one hand, and the reaction condition is mild and controllable as in the original battery system, so that the defects of high energy consumption and uncontrollable stability and reliability existing in the conventional method for generating the organic pre-lithiation-containing material by carrying out high-temperature (such as 160-250 ℃) thermal reaction on a lithium source and an organic substance are effectively overcome. On the other hand by SiO provided in the electrolyte_xThe lithium ion battery can directly generate oxidation-reduction reaction with the contained lithium ion to generate a silicon negative electrode material and a coating layer containing the pre-lithiation material, so that the compactness of the coating layer containing the pre-lithiation material is effectively enhanced, and the bonding strength between the coating layer containing the pre-lithiation material and the surface of the negative electrode material can be enhanced. In addition, the reaction time can be flexibly controlled to control the grain diameter of the silicon negative electrode and the thickness of the coating layer containing the pre-lithiation material.

The electrolytic treatment system may be a battery system as shown in fig. 3, and includes a container 01 'and an electrolyte 03' contained in the container 01 ', a pair of electrodes 02' (an electrode 21 'and an electrode 22') are inserted into the electrolyte 03 ', the electrode 02' is at least partially immersed in the electrolyte 03 ', the electrode 21' and the electrode 22 'are respectively connected to the positive and negative electrodes of a power source 04', the electrode 21 'is electrically connected to the positive electrode of the power source 04', and the electrode 22 'is electrically connected to the negative electrode of the power source 04'. In one embodiment, the voltage supplied by the power source 04' is 0.01-1V and the current density is 0.1-5mAh/cm during the electrolysis process of the electrolysis system². Under the voltage condition, the time of the electrolytic treatment can be, but not limited to, 15-60 min. In a particular embodiment, the electrodes 02 'may be two pieces of lithium metal and the container 01' may be a conductive metal container.

In a preferred embodiment, the electrolytic treatment process further comprises a stirring treatment, so that the electrolytic treatment can be relatively uniformly carried out in the electrolyte 03', and the uniformity of the pre-composite silicon-based negative electrode material is improved. In one embodiment, the stirring rate is preferably 500-2000 rpm.

Since the electrolyte 03' includes a solvent and a lithium salt dissolved in the solvent and SiO dispersed in the solvent_x. Therefore, the redox reaction in the above electrolytic treatment system includes the following:

Li⁺+e^-+SiO_x→Li₂SiO₃、Li₄SiO₄、Li₂SiO₅

of course, when the electrode 02 is a lithium sheet, the lithium sheet may also participate in the reaction, maintaining the lithium ion balance in the electrolyte. Therefore, in the electrolytic processing system, lithium ions and SiO contained in the electrolytic solution 03_xSiO of the surface_xThe above-mentioned redox reaction occurs, whereby SiO_xSurface in-situ growth of Li-containing₂SiO₃、Li₄SiO₄、Li₂SiO₃And pre-lithiated material coated with SiO_xThe surface of the surface forms a core-shell structure, in which the SiO is reacted_xThe core body is formed, specifically the core body 1 of the composite silicon-based negative electrode material, and the coating layer formed by the in-situ generated pre-lithiation material forms the first shell layer 2 of the composite silicon-based negative electrode material. Therefore, the reaction system of the solution treatment system effectively reduces the energy consumption, and the reaction condition is mild and controllable, thereby effectively reducing the energy consumption. But also in SiO_xThe whole surface of the pre-lithiation coating layer is reacted simultaneously, so that the compactness of the generated pre-lithiation coating layer is effectively improved, and the efficiency is high.

In one embodiment, the mass ratio of the solvent to the lithium salt in the electrolyte 03 and the electrolyte 03' is (0.1-98): (0.001-15). For example, the concentration of lithium salt in the electrolyte 03 and the electrolyte 03' is preferably 0.1 to 10 mol/L. In specific embodiments, the lithium salt comprises at least one of lithium hexafluorophosphate, lithium aluminum tetrachloride, lithium trifluoroformate, lithium borate, lithium hexafluoroarsenate, lithium perchlorate, lithium nitrate, lithium sulfate, lithium hydroxide, lithium oxide, lithium fluoride, lithium oxalate/acetate, lithium formate. The solvent contained in the electrolyte comprises at least one of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl maleate, tetrahydrofuran and methyl carbonate. Through selection of the concentration of the electrolyte 03 and the electrolyte 03', lithium salt, solvent and other component types, the redox reaction in the primary battery system or the electrolytic treatment system is optimized, the efficiency of the redox reaction is improved, and the forming rate and compactness of a coating layer formed by the pre-lithiation material and the uniformity of a core-shell structure are improved.

In step S02, after the pre-lithiation material in step S02 is prepared by using the galvanic cell and the electrolytic treatment, the method further includes a step of filtering and washing the coating structure material to obtain the target material of the coating structure material.

In the above step S02, after the carbon-containing coating layer is formed on the surface of the pre-lithiation-containing material layer, the carbon coating layer forms the second shell layer 3 included in the above composite silicon-based negative electrode material, and covers the pre-lithiation-containing material layer in the step S01, and forms the double shell layer of the above composite silicon-based negative electrode material together with the pre-lithiation-containing material layer. Thus, the second shell layer 3 can effectively isolate the pre-lithiation-containing material layer from directly contacting with the electrolyte, so that the stability of the pre-lithiation-containing material layer is remarkably improved to ensure the high first coulombic efficiency characteristic of the composite silicon-based negative electrode material; meanwhile, the conductivity of the composite silicon-based negative electrode material is effectively improved, and the internal resistance of the composite silicon-based negative electrode material is reduced. In addition, the double-shell-layer clad core body formed by the pre-lithiation material layer and the second shell layer 3 improves the mechanical property of the shell layers, effectively inhibits the volume expansion of the silicon-based negative electrode material, improves the cycle, and obviously enhances the structural stability and the cycle performance of the composite silicon-based negative electrode material in the charging and discharging processes. The method for forming the carbon-containing coating layer on the surface of the prelithiation material layer may be any method capable of forming a carbon coating layer, and as described in the first paragraph, the carbon coating layer is formed by in-situ precipitation of the carbon coating layer on the surface of the prelithiation material layer by at least one of a liquid phase method and a gas phase method. Preferably, an organic carbon source is introduced at a certain temperature by adopting a gas phase method, and a carbon coating layer is formed on the surface of the material layer containing the pre-lithiation in situ. In addition, the preferable thickness of the second shell 3 after the carbon-containing coating layer is formed as above, for example, 1 to 100nm, preferably 2 to 50nm, by controlling and optimizing the process conditions for forming the carbon-containing coating layer.

Therefore, the composite silicon-based negative electrode material with the complete double-shell coating structure can be formed by the preparation method of the composite silicon-based negative electrode material, the prepared composite silicon-based negative electrode material has the advantages of high first coulombic efficiency, low internal resistance, higher capacity, stable structure and the like, the process conditions are easy to control, the structure and the performance stability of the composite silicon-based negative electrode material can be ensured, and the efficiency is high.

On the other hand, the embodiment of the invention also provides a negative electrode and a lithium ion battery containing the negative electrode.

The negative electrode is a silicon-based negative electrode, and for example, the negative electrode comprises a current collector and a silicon-based active layer combined on the surface of the current collector, wherein the silicon-based active layer contains the composite silicon-based negative electrode material of the embodiment of the invention. Therefore, the negative electrode has high capacity and multiplying power, high first coulombic efficiency, stable cycle performance and difficult occurrence of undesirable phenomena such as powder falling and peeling.

The lithium ion battery includes a positive electrode, a negative electrode, and a separator stacked between the positive electrode and the negative electrode, and certainly includes other components necessary for the lithium ion battery, such as an electrolyte solution. Wherein, the negative electrode is the negative electrode of the embodiment of the invention. Therefore, the lithium ion battery has high energy and first coulombic efficiency, excellent cycle performance, long service life and stable electrochemical performance.

The composite silicon-based negative electrode material, the preparation method and the application thereof according to the embodiment of the invention are illustrated by a plurality of specific examples.

Example 1

The embodiment provides a composite silicon-based negative electrode material and a preparation method thereof. The structure of the composite silicon-based negative electrode material is shown in figure 1, the composite silicon-based negative electrode material is a double-shell core-shell structure, and the material of a core body 1 is SiO_xSlicing; the material of the first shell layer 2 is lithium silicate, and the average thickness is 1 mu m; the second shell 3 is a vapor-deposited conductive carbon layer with an average thickness of 50 nm.

The preparation method of the composite silicon-based negative electrode material comprises the following specific steps:

s1: constructing a primary battery system shown in figure 2, carrying out redox reaction to generate a pre-composite silicon-based negative electrode material containing a pre-lithiation material layer coated silicon negative electrode material, wherein the container 01 is a conductive metal container, the electrode 21 and the electrode 22 are both made of lithium metal, the electrode 21 and the electrode 22 are respectively attached to the inner wall of the container 01 and are immersed in an electrolyte 03, and the electrolyte 03 comprises a vinyl carbonate solvent and lithium hexafluorophosphate with the mass ratio of 98: 2; SiO is not put into the electrolyte 03_xChip, SiO_xThe sheet is close to one end of the lithium metal;

s2: and (3) forming a carbon coating layer on the surface of the pre-composite silicon-based negative electrode material prepared in the step S1 by vapor deposition by adopting the following vapor phase method: and (3) placing the product obtained in the step into a tubular furnace, introducing a gaseous organic carbon source for 0.5-5h at 700-900 ℃, and cooling to room temperature.

Example 2

The embodiment provides a composite silicon-based negative electrode material and a preparation method thereof. The structure of the composite silicon-based negative electrode material is shown in figure 1, the composite silicon-based negative electrode material is a double-shell core-shell structure, and the material of a core body 1 is SiO_xA block; the material of the first shell layer 2 is lithium silicate, and the average thickness is 5 mu m; the second shell 3 is a conductive carbon layer with an average thickness of 10 nm.

The preparation method of the composite silicon-based negative electrode material comprises the following specific steps:

s1: constructing an electrolytic system shown in figure 3, carrying out redox reaction to generate a pre-composite silicon-based anode material containing a pre-lithiation material layer coated silicon anode material, wherein the container 01 'is a conductive metal container, the electrode 21' and the electrode 22 'are both made of lithium metal, the electrode 21' and the electrode 22 'are respectively connected to the positive electrode end and the negative electrode end of a power supply 04' and are immersed in an electrolyte 03 ', and the electrolyte 03' comprises a tetrahydrofuran solvent and lithium borate in a mass ratio of 85: 15; SiO is not introduced into the electrolyte 03_xBulk, SiO_xThe block is close to one end of the lithium metal;

s2: forming a carbon coating layer on the surface of the pre-composite silicon-based negative electrode material prepared in the step S1 by adopting the following solid phase method: and (3) uniformly mixing the material obtained in the step (1) with a carbon source liquid phase to form a conductive carbon coating layer.

Example 3

The embodiment provides a composite silicon-based negative electrode material and a preparation method thereof. The structure of the composite silicon-based negative electrode material is shown in figure 1, the composite silicon-based negative electrode material is a double-shell core-shell structure, and the material of a core body 1 is SiO_xSlicing; the material of the first shell layer 2 is lithium silicate, and the average thickness is 20 nm; the second shell 3 is a conductive carbon layer formed by vapor deposition and has an average thickness of 90 nm.

The preparation method of the composite silicon-based negative electrode material comprises the following specific steps:

s1: constructing an electrolytic system shown in figure 3 and carrying out redox reaction to generate a pre-composite silicon-based anode material containing a pre-lithiation material layer coated with a silicon anode material, wherein a container 01' isThe electrode 21 ' and the electrode 22 ' are both made of lithium metal, the electrode 21 ' and the electrode 22 ' are respectively connected to the positive electrode end and the negative electrode end of a power supply 04 ' and are immersed in an electrolyte 03 ', and the electrolyte 03 ' comprises mixed lithium of dimethyl maleate, lithium oxide and lithium formate in a mass ratio of 90: 10; SiO is not introduced into the electrolyte 03_xChip, SiO_xThe sheet is close to one end of the lithium metal;

s2: and (3) forming a carbon coating layer on the surface of the pre-composite silicon-based negative electrode material prepared in the step S1 by adopting a solid phase method through vapor deposition: and (3) forming a conductive carbon coating layer on the surface of the material obtained in the step (1) according to the generation method of the carbon nano tube.

Comparative example 1

The comparative example is a carbon-coated silicon negative electrode material, and compared with the composite silicon-based negative electrode material provided in example 1, the difference is that the comparative example does not contain the first shell layer of lithium silicate, but directly coats the second shell layer 3 coated with a conductive carbon layer with SiO_xAnd (3) slicing.

Lithium ion Battery embodiment

The composite silicon-based negative electrode materials provided in the above examples 1 to 3 and the composite silicon-based negative electrode material provided in the comparative example were assembled into a negative electrode and a lithium ion battery, respectively, as follows:

a negative electrode: the composite silicon-based anode materials prepared in examples 1 to 3 were directly used as an anode. According to the following steps; the granular negative electrode material of carbon-coated silicon in comparative example 1 was prepared as follows: graphite: LA133 80: 10: 10, adding a hydrosolvent, stirring to obtain slurry with the solid content of 40%, uniformly coating the slurry on the surface of a copper foil, rolling, and carrying out vacuum drying at 110 ℃ overnight to prepare a negative pole piece:

the cathode, the anode of a conventional lithium ion battery and electrolyte are respectively assembled into the lithium ion battery.

Correlation characteristic test

Electrochemical performance of the lithium ion battery:

the lithium ion battery containing the composite silicon-based negative electrode material in examples 1 to 2 and the lithium ion battery containing the carbon-coated silicon negative electrode material in comparative example 1 were subjected to the first coulombic efficiency test:

placing the assembled lithium ion battery at room temperature for 12h, performing charge-discharge test, discharging at constant current of 0.1C to 0.01V, changing to constant current of 0.01C to 0.01V, and recording the first discharge capacity as Q_PutThen charged to a constant voltage of 1.5V at 0.1C, and the corresponding reversible charge capacity is recorded as Q_{Charging device}. First coulombic efficiency E ═ Q_{Charging device}/Q_PutX 100%. And cycling for 100 times to obtain the discharge capacity, and obtaining the ratio of the discharge capacity to the first capacity, namely the capacity retention rate. The first coulombic efficiency (first effect) curves of the lithium ion battery containing the composite silicon-based negative electrode material in example 1 and the lithium ion battery containing the carbon-coated silicon negative electrode material in the comparative example are shown in fig. 4. In addition, the first-effect test results of the lithium ion batteries containing the composite silicon-based negative electrode materials in the examples 2 and 3 are similar to those in fig. 4. Therefore, the first-time coulombic efficiency of the composite silicon-based negative electrode material is high according to the first-time test result, and further determination shows that the composite silicon-based negative electrode material disclosed by the embodiment of the invention has excellent structural stability and cycle performance in the charging and discharging processes.

According to the first coulombic efficiency test result, the lithium ion battery containing the composite silicon-based negative electrode material provided by the embodiment of the invention has the advantages of high first coulombic efficiency, good cycle performance, long service life and stable electrochemical performance.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.