JP2017069165A - Negative electrode material for lithium secondary battery and manufacturing method thereof, composition for negative electrode active material layer formation, negative electrode for lithium secondary battery, lithium secondary battery, and resin composite silicon particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode material for a lithium secondary battery, which can impart a superior charge/discharge capacity, a superior coulomb efficiency and a superior cycle characteristic to lithium secondary battery; and a method for manufacturing such a negative electrode material.SOLUTION: A negative electrode material for a lithium secondary battery comprises complex particles A. The complex particles A are each formed by coating the surface of a silicon particle 1 with a carbide layer 2; and pores 3 are formed in the carbide layer 2. A method for manufacturing the negative electrode material comprises the steps of: preparing resin composite silicon particles each arranged by coating the surface of a silicon particle with a resin layer; and performing a heat treatment on the resin composite silicon particles. The resin layer is formed to have at least a first layer coating the surface of each silicon particle, and a second layer further coating the first layer. The first layer is lower than the second layer in burn-out starting temperature. In the step of performing a heat treatment, the heat treatment is performed at least at the burn-out starting temperature of the first layer or higher.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a negative electrode material for a lithium secondary battery and a production method thereof, a composition for forming a negative electrode active material layer, a negative electrode for a lithium secondary battery, a lithium secondary battery, and a negative electrode material for a lithium secondary battery. The present invention relates to resin composite silicon particles.

  In recent years, downsizing and weight reduction of portable electronic devices typified by mobile phones and portable information devices (for example, electronic notebooks, notebook computers, tablet computers) and the like have been making remarkable progress. Therefore, today, it is desired to reduce the size and weight of the secondary battery for driving portable electronic devices. Under such circumstances, a lithium secondary battery (for example, a lithium ion secondary battery) that can be configured in a small size and that has a high energy density has attracted attention, and its development is actively performed. In addition to the above-described portable electronic devices, the needs for lithium secondary batteries are expanding to electric vehicles and power storage for renewable energy. In order to meet these needs, there is a need for technological development capable of further increasing the energy density of the electrode material constituting the lithium secondary battery.

  In general, many lithium secondary batteries composed of carbon materials capable of entering and leaving lithium ions, that is, insertion and removal, rather than lithium that easily generates dendrites, have been proposed and gradually being put into practical use. is there. Such a carbon material is attracting attention as a negative electrode material capable of realizing a lithium secondary battery excellent in cycle characteristics and safety. Negative electrode materials for lithium secondary batteries made of carbon materials are mainly classified into two types: carbon-based negative electrode materials fired at about 1000 ° C. and graphite-based negative electrode materials fired at a temperature exceeding 2000 ° C. Can do. However, the carbon-based negative electrode material has a drawback that the potential change accompanying the release of lithium ions is large and it is difficult to form a stable lithium secondary battery. On the other hand, a graphite-based negative electrode material is known to be advantageous over a carbon-based negative electrode material because such a potential change is small and a stable lithium secondary battery can be formed. Therefore, graphite-based negative electrode materials are becoming mainstream as negative electrode materials for lithium secondary batteries.

  The above-mentioned graphite-based negative electrode material has a theoretical capacity of 372 mAh / g, while silicon has a theoretical capacity of 4200 mAh / g, and has a theoretical capacity about 10 times that of the graphite-based negative electrode material. It is expected (see, for example, Non-Patent Documents 1 and 2). However, since the volume change due to charging / discharging is extremely large in silicon, the negative electrode material is cracked or peeled off from the electrode (see, for example, Non-Patent Document 3), and the actual capacity is reduced. There exists a problem that it cannot become a negative electrode material which has sufficient charging / discharging capacity | capacitance and cycling characteristics. Therefore, recently, in order to obtain a negative electrode material having sufficient charge / discharge capacity and cycle characteristics, it has been studied to combine silicon with a carbon material (see, for example, Non-Patent Documents 4 and 5).

Robert A. Huggins, Journal of Power Sources, 81-82 (1999) 13-19 B. A. Boukamp, G. C. Lesh, and R. A. Huggins, Journal of The Electrochemical Society, volume 128 (1981) 725-729 H. Li, X. J. Huang, L. Q. Chen, Z. G. Wu, and Y. Liang, Electrochemical. And Solid-State Letters, 2 (11) (1999) 547-549 T. Morita and N. Takami, Journal of Electrochemical Society, 153 (2) (2006) A425-A430 Xin Zhao, Cary M. Hayner, Mayfair C. Kung, Harold H. Kung, Advanced Energy Materials, 1 (2011) 1079-1084

  Although the charge / discharge capacity and the cycle characteristics are improved as compared with the conventional technique, the actual condition is that the performance required for practical use has not been achieved. From such a viewpoint, a negative electrode material for a lithium secondary battery capable of further improving charge / discharge capacity and cycle characteristics is required.

  The present invention has been made in view of the above, and a negative electrode material for a lithium secondary battery capable of imparting excellent charge / discharge capacity, coulomb efficiency and cycle characteristics to a lithium secondary battery, and a method for producing the same The purpose is to provide. Furthermore, it aims at providing the resin composite silicon particle for manufacturing the negative electrode material for lithium secondary batteries.

  As a result of intensive studies to achieve the above-mentioned object, the present inventor is excellent in using composite particles having a specific structure formed of silicon particles and a carbide layer as a negative electrode material for a lithium secondary battery. The present inventors have found that the negative electrode material for a lithium secondary battery having charge / discharge capacity, coulomb efficiency, and cycle characteristics is obtained, and completed the present invention.

That is, the present invention includes the subject matters of the following items.
Item 1. A negative electrode material for a lithium secondary battery containing composite particles,
The composite particle is a negative electrode material for a lithium secondary battery, wherein a surface of a silicon particle is coated with a carbide layer, and voids are formed inside the carbide layer.
Item 2. Item 2. The negative electrode material for a lithium secondary battery according to Item 1, wherein the silicon particles are primary particles and / or aggregates.
Item 3. Item 3. The negative electrode material for a lithium secondary battery according to Item 1 or 2, wherein the carbide layer is in partial contact with the surface of the silicon particles.
Item 4. Item 3. The negative electrode material for a lithium secondary battery according to Item 1 or 2, wherein the carbide layer has a thickness of 0.001 μm to 1 μm.
Item 5. Item 5. The negative electrode material for a lithium secondary battery according to any one of Items 2 to 4, wherein the average particle size of the primary particles is 0.01 to 100 µm.
Item 6. Item 5. The negative electrode material for a lithium secondary battery according to any one of Items 2 to 4, wherein the aggregate has an average particle size of 0.05 to 100 µm.
Item 7. Item 7. The negative electrode material for a lithium secondary battery according to any one of Items 1 to 6, wherein the total volume of voids of the composite particles is 50 to 500% of the volume of the silicon particles.
Item 8. Item 8. The negative electrode material for a lithium secondary battery according to any one of Items 1 to 7, further comprising graphite.
Item 9. The composition for negative electrode active material layer formation for lithium secondary batteries containing the negative electrode material for lithium secondary batteries of any one of said claim | item 1 -8.
Item 10. The negative electrode for lithium secondary batteries provided with the negative electrode active material layer formed with the composition for negative electrode active material layer formation of said claim | item 9 on a collector.
Item 11. A lithium secondary battery comprising the negative electrode for a lithium secondary battery according to Item 10.
Item 12. A method for producing a negative electrode material for a lithium secondary battery, comprising:
A step of preparing resin composite silicon particles obtained by coating the surface of silicon particles with a resin layer;
A step of heat-treating the resin composite silicon particles,
The resin layer is formed to have at least a first layer that covers the surface of the silicon particles and a second layer that further covers the first layer, and the burning start temperature of the first layer is Lower than the burning start temperature of the second layer,
The method for producing a negative electrode material for a lithium secondary battery, wherein, in the heat treatment step, the heat treatment is performed at least at a burning start temperature of the first layer.
Item 13. Item 13. The method according to Item 12, wherein the silicon particles are primary particles and / or aggregates.
Item 14. Item 14. The method according to Item 13, wherein the primary particles have an average particle size of 0.01 to 100 µm.
Item 15. Item 14. The method according to Item 13, wherein the aggregate has an average particle size of 0.05 to 100 µm.
Item 16. Resin composite silicon particles for producing a negative electrode material for a lithium secondary battery,
The resin composite silicon particles, the surface of the silicon particles are coated with a resin layer,
The resin layer has at least a first layer that covers the surface of the silicon particles and a second layer that further covers the first layer;
Resin composite silicon particles, wherein the burning start temperature of the first layer is lower than the burning start temperature of the second layer.
Item 17. Item 17. The resin composite silicon particles according to Item 16, wherein the resin composite silicon particles are primary particles and / or aggregates.
Item 18. Item 18. The resin composite silicon particles according to Item 17, wherein the average particle diameter of the primary particles is 0.01 to 100 µm.
Item 19. Item 18. The resin composite silicon particles according to Item 17, wherein the aggregate has an average particle size of 0.05 to 100 µm.
Item 20. Item 16 wherein the silicon particles have a negative zeta potential in water, the resin constituting the first layer has a positive zeta potential in water, and the resin constituting the second layer has a negative zeta potential in water. The resin composite silicon particles according to any one of ˜19.
Item 21. Item 21. The resin composite silicon particles according to any one of Items 16 to 20, wherein the resin layer further includes a third layer interposed between the first layer and the second layer.
Item 22. Item 22. The resin composite silicon particles according to any one of Items 16 to 21, wherein the first layer is a urea resin and the second layer is a melamine resin.

  According to the negative electrode material for a lithium secondary battery according to the present invention, excellent charge / discharge capacity, coulomb efficiency and cycle characteristics can be imparted to the lithium secondary battery.

  Since the composition for forming a negative electrode active material layer for a lithium secondary battery according to the present invention contains the above-described negative electrode material for a secondary battery, it is suitable as a material for forming a negative electrode active material layer for a lithium secondary battery.

  According to the method for producing a negative electrode material for a lithium secondary battery according to the present invention, a negative electrode material for a lithium secondary battery that can impart excellent charge / discharge capacity, coulomb efficiency, and cycle characteristics to the lithium secondary battery can be easily obtained. Can be obtained.

  The resin composite silicon particles according to the present invention are a precursor for producing a negative electrode material for a lithium secondary battery, and the negative electrode material for a lithium secondary battery can be obtained by heat treatment. Therefore, it is suitable as a material for producing the negative electrode material for lithium secondary batteries, and is a material that can impart excellent charge / discharge capacity, coulomb efficiency, and cycle characteristics to the lithium secondary battery.

An example of embodiment of the negative electrode material for lithium secondary batteries of this invention is shown, (a) shows typically an example of the cross section of a composite particle, (b) has shown the other example typically. It is a schematic diagram which shows an example of other embodiment of the negative electrode material for lithium secondary batteries of this invention. It is an example of embodiment of the resin composite silicon particle used in order to manufacture the negative electrode material for lithium secondary batteries, and is the schematic diagram of the cross section. 2 is an electron microscope (SEM) image of silicon particles used in Example 1. FIG. 3 is an electron microscope (SEM) image of silicon particles having a first layer formed on the surface prepared in Example 1. FIG. 2 is an electron microscope (SEM) image of silicon particles (resin composite silicon particles) in which a first layer and a second layer are formed in this order on the surface prepared in Example 1. FIG. It is an electron microscope (SEM) image after baking (450 degreeC) of the resin composite silicon particle prepared in Example 1. FIG. It is an electron microscope (SEM) image after baking (900 degreeC) of the resin composite silicon particle prepared in Example 2. FIG. (A)-(c) shows the measurement result of TG-DTA, the sample of (a) is a particle in which a layer of urea resin is formed on silicon particles, the sample of (b) is a melamine resin on silicon particles (C) is a particle in which a urea resin layer and a melamine resin layer are formed in this order on silicon particles.

  Hereinafter, embodiments of the present invention will be described in detail.

1. Negative Electrode Material for Lithium Secondary Battery FIGS. 1A and 1B are diagrams schematically showing a cross section of the composite particle A included in the negative electrode material for a lithium secondary battery.

  Specifically, the composite particle A of the present embodiment is formed by covering the surface of the silicon particle 1 with the carbide layer 2, and the void 3 is formed inside the carbide layer 2. Providing excellent charge / discharge capacity, coulombic efficiency, and cycle characteristics to a lithium secondary battery by producing a negative electrode for a lithium secondary battery using a negative electrode material for a lithium secondary battery containing such composite particles A Can do.

  The material which comprises the silicon particle 1 is not specifically limited, For example, the material which can produce | generate baking products, such as a silicon compound, is mentioned. Such a silicon compound is particularly preferably a material capable of increasing the charge / discharge capacity of a lithium secondary battery.

Examples of the silicon particles 1 include particles composed of silicon alone (Si) or particles composed of a compound containing Si, and may be a mixture thereof. If silicon particles 1 is composed of a compound containing Si is, SiO, silicon oxide such as SiO _2, silicon nitride, silicon _{boride, TiSi 2, ZrSi 2, VSi} 2, CrSi 2, MoSi 2, WSi 2, CoSi Such a silicide may be exemplified, and any one of these may be used alone, or a mixture of two or more may be used. Preferred silicon particles 1 are exemplified by silicon alone and silicon oxide, and particularly preferred silicon particles 1 are silicon alone.

  The silicon particles 1 may have a single crystal or polycrystalline crystal structure, or an amorphous structure.

  The silicon particles 1 may be prepared by a chemical synthesis method, for example, or may be a commercially available product. The silicon particles 1 may be prepared from silicon waste material.

  The form of the silicon particles 1 is not particularly limited, and may be primary particles and / or aggregates. The aggregate here refers to a state in which a plurality of primary silicon particles are aggregated, and can also be referred to as secondary particles.

  The silicon particles 1 may be composed only of primary particles or may be composed only of aggregates. Further, the silicon particles 1 may include both primary particles and aggregates.

  The average particle diameter of the primary particles is not particularly limited and is, for example, 0.01 to 100 μm. The average particle diameter of the primary particles is preferably 0.05 to 50 μm.

  Moreover, the average particle diameter of an aggregate is not restrict | limited in particular, For example, the average particle diameter of the aggregate which is 0.05-100 micrometers is preferably 0.1-50 micrometers.

  You may adjust the average particle diameter of the silicon particle 1 by grind | pulverizing the coarse silicon particle about 10-100 micrometers, for example. As a means for performing the pulverization, for example, a pulverizer such as a ball mill or a hammer mill can be used.

  In addition, the average particle diameter as used in the present specification can be measured by a dynamic light scattering method, and can be measured by Microtrac MT3300EXII manufactured by Nikkiso Co., Ltd.

  The shape of the silicon particles 1 is not particularly limited, and may be any shape such as a true sphere, an oval sphere, or an indefinite shape.

  The carbide layer 2 is a layer formed of carbide. Such a carbide layer 2 is a layer that can be formed, for example, by heat treating and carbonizing a resin composed of a carbonizable material. Specifically, as described later, this is a layer that can be formed by heat-treating the silicon particles 1 coated with the resin and carbonizing the resin. Further, the carbide layer 2 is not limited to a layer that can be formed by carbonizing a resin, and may be a layer formed of a carbon material. Such a carbon material is, for example, graphite or fired graphite.

  The thickness of the carbide layer 2 is not particularly limited, but may be, for example, 0.001 μm to 1 μm. The thickness of the carbide layer 2 here refers to the distance from the surface of the silicon particle 1 to the outermost surface of the carbide layer 2. The thickness of the carbide layer 2 is, for example, that the composite particle A is cut, the cross section is observed with an electron microscope, and the thickness of the carbide layer 2 is determined from the cross-sectional images of a plurality of arbitrarily selected composite particles A. It can be obtained by measuring the average value.

  As shown in FIGS. 1A and 1B, the carbide layer 2 is preferably formed in partial contact with the surface of the silicon particles 1. In this case, since the silicon particles 1 are conducted through the carbide layer 2, when the composite particles A are applied to a negative electrode material for a lithium secondary battery, it is easy to suppress a decrease in electric capacity and cycle characteristics of the negative electrode. The carbide layer 2 may be in contact with the entire surface of the silicon particles 1 to cover the silicon particles 1.

  A plurality of voids 3 are formed inside the carbide layer 2. The location and the size of the void 3 in the carbide layer 2 are not particularly limited. For example, the void 3 may be formed uniformly throughout the carbide layer 2. Moreover, the space | gap 3 may be formed more or larger inside the carbide | carbonized_material layer 2 than the outside, or vice versa. Further, the void 3 is formed only inside the carbide layer 2 and may not be formed outside. Hereinafter, a specific example will be described.

  In the composite particle A of FIG. 1A, the void 3 is formed over the entire carbide layer 2, and in particular, the size of the void 3 formed inside the carbide layer 2 is that of the carbide layer 2. It is larger than the size of the gap 3 formed on the outside. Specifically, in the composite particle A in FIG. 1A, a plurality of branch-like carbide layers 2 are formed on the surface of the silicon particles 1, and the outside of these branch-like carbide layers 2 is formed in a shell shape. The carbide layer 2 is covered, and a plurality of voids 3 are formed in the shell-like carbide layer 2. As described above, the carbide layer of the composite particles is more than the first carbide layer having voids and the voids that cover the first carbide layer and are formed in the first carbide layer. It can be formed with a second carbide layer having small voids. Alternatively, the carbide layer of the composite particle A includes a first carbide layer having voids and the number of voids that cover the first carbide layer and are formed in the first carbide layer. And a second carbide layer having few voids.

  On the other hand, in the composite particle A in FIG. 1B, a plurality of branch-like carbide layers 2 are formed on the surface of the silicon particles 1, and the outside of these branch-like carbide layers 2 is formed in a shell-like shape. The carbonized layer 2 covers the same as in the form of FIG. 1A, but no void 3 is formed in the shell-like carbonized layer 2. Thus, the carbide layer of the composite particles includes a first carbide layer having voids, and a second carbide layer that covers the first carbide layer and has no voids formed therein. Can be formed.

  The total volume of the voids 3 is preferably 50 to 500% of the volume of the silicon particles 1. In this case, the negative electrode material for a lithium secondary battery can impart superior charge / discharge capacity, coulomb efficiency, and cycle characteristics to the lithium secondary battery.

  As described above, the composite particle A of the present embodiment has a structure in which the surface of the silicon particle 1 is covered with the carbide layer 2 and the void 3 is formed inside the carbide layer 2. With such a so-called capsule structure, the expansion of the silicon particles 1 can be absorbed by the voids 3 in the capsule. Therefore, if a negative electrode is comprised with the negative electrode material for lithium secondary batteries containing the composite particle A, the crack of the negative electrode material resulting from the volume expansion of the silicon particle 1 and peeling from an electrode will be suppressed. As a result, the negative electrode material for a lithium secondary battery including the composite particles A can impart excellent charge / discharge capacity, coulomb efficiency, and cycle characteristics to the lithium secondary battery. In particular, when the negative electrode material for a lithium secondary battery includes the composite particles A, for example, the capacity of the lithium secondary battery is improved as compared with a case where only the graphite is included.

  The negative electrode material for a lithium secondary battery may contain other additives as long as the performance of the composite particles A is not hindered. Or the negative electrode material for lithium secondary batteries may be comprised only with the said composite particle A. FIG.

  Examples of other additives include graphite. In this case, it is possible to further improve the cycle characteristics of the lithium secondary battery.

  Examples of graphite include artificial graphite, natural graphite, and the like including graphitized mesophase spherules, and any one of these may be used, or two or more may be combined. The crystal structure of graphite is not particularly limited, and examples thereof include a structure that can exchange lithium ions. Specifically, a crystal structure having an interplanar spacing d (002) of 0.3354 to 0.34 nm, preferably about 0.3354 to 0.337 nm is exemplified. The length Lc in the c-axis direction can be 30 to 200 nm, preferably about 50 to 150 nm, and the length La in the a-axis direction can be about 50 to 300 nm, preferably about 70 to 200 nm.

  The shape of the graphite is not particularly limited, and examples thereof include an indefinite shape, a flat plate shape (or flat shape), a flake shape, and a granular shape. The average particle diameter of the graphite particles is not particularly limited, and can be selected from a wide range of, for example, about 0.1 to 100 μm, and is usually about 0.1 to 40 μm, preferably about 0.1 to 20 μm, more preferably about 0.1. 1 to 10 μm, specifically about 0.5 to 10 μm.

The specific surface area of graphite can be, for example, 0.5 to 30 m ² / g, preferably 0.8 to 10 m ² / g, and more preferably 0.8 to ⁵ m ² / g. The bulk density of graphite is, for example, about 0.1 to 1.5 g / ml, preferably 0.8 to 1.5 g / ml, and more preferably about 1 to 1.5 g / ml.

  When the negative electrode material for a lithium secondary battery contains the above graphite in addition to the composite particles A, the presence state of graphite is not particularly limited. For example, as shown in FIG. 2, the composite contained in the negative electrode material for a lithium secondary battery It can be attached to the surface of particle A.

  FIG. 2 schematically shows a secondary battery negative electrode material containing composite particles A and graphite 4. As shown in this figure, the graphite 4 can exist in a state of adhering to the surface of the composite particle A. Thus, if the graphite 4 exists in the state adhering to the surface of the composite particle A, it is possible to further improve the cycle characteristics of the lithium secondary battery. Of course, the graphite 4 may exist without adhering to the surface of the composite particle A.

2. Method for producing negative electrode material for lithium secondary battery The negative electrode material for lithium secondary battery is a step of preparing resin composite silicon particles obtained by coating the surface of silicon particles with a resin layer (hereinafter abbreviated as "preparation step"). Can be manufactured through a step of heat-treating the resin composite silicon particles (hereinafter sometimes abbreviated as “heating step”).

  The resin composite silicon particles are formed such that the resin layer has at least a first layer that covers the surface of the silicon particles and a second layer that further covers the first layer. The burning start temperature is lower than the burning start temperature of the second layer.

  In the heat treatment step, the heat treatment is performed at least above the burning start temperature of the first layer. Through such a heating step, a negative electrode material for a lithium secondary battery is obtained. The negative electrode material for a lithium secondary battery obtained by the above production method can impart excellent charge / discharge capacity, coulomb efficiency, and cycle characteristics to the lithium secondary battery.

  Hereinafter, the resin composite silicon particles, the preparation process, and the heating process will be described in detail.

(Resin composite silicon particles)
FIG. 3 schematically shows a cross section of the resin composite silicon particle B described above. As shown in this figure, the resin composite silicon particles B have silicon particles 1 and a resin layer 20, and the resin layer 20 covers the surface of the silicon particles 1.

  The configuration of the silicon particles 1 is the same as that of the silicon particles 1 described in the section “1. Negative electrode material for lithium secondary battery”.

  The resin layer 20 is formed in a multilayer structure in which at least two layers are laminated. In the embodiment of FIG. 3, the resin layer 20 includes a first layer 21 and a second layer 22 that further covers the first layer 21. The first layer 21 is a layer closer to the silicon particle 1, that is, the inner layer of the resin layer 20, and the second layer 22 is an outer layer.

  The first layer 21 is made of a material whose burning start temperature is lower than the burning start temperature of the second layer 22. In the TG / DTA measurement, weight loss occurs when the material is heated in a nitrogen atmosphere in the TG / DTA measurement. However, in this measurement, it is clearly different from the removal of solvation components such as moisture (rapidly). N) The temperature at which weight loss begins.

  The type of resin constituting the first layer 21 and the second layer 22 is not particularly limited as long as the above conditions are satisfied. As a specific combination of materials constituting the first layer 21 and the second layer 22, the first layer 21 is urea resin, and the second layer 22 is melamine resin. As another example of the combination of materials constituting the first layer 21 and the second layer 22, the first layer 21 is a hydrophobic polymer that decomposes at 250 ° C. or lower, and the second layer 22 is a melamine resin or a urea resin. It is. Examples of the hydrophobic polymer that decomposes at 250 ° C. or lower include water-insoluble cellulose derivatives such as ethyl cellulose and cellulose acetate, and binders used for ceramic green sheets such as polyoxymethylene and poly (meth) acrylate. Other combinations of the first layer 21 and the second layer 22 include polyamic acid in which the first layer 21 is melamine resin or urea resin, and the second layer 22 is polyimideized by thermosetting.

  The resin layer 20 may further include a third layer interposed between the first layer 21 and the second layer 22. The third layer serves as a so-called buffer layer, and can improve the adhesion between the first layer 21 and the second layer 22.

  There is no restriction | limiting in particular in the material which comprises a 3rd layer, Polyethyleneimine, cationic polyvinyl alcohol, another water-soluble cationic polymer, etc. are illustrated.

  When the resin layer 20 has a third layer, for example, the first layer 21 is a hydrophobic polymer that decomposes at 250 ° C. or lower, the second layer 22 is a melamine resin or a urea resin, and the third layer is anhydrous. Examples include maleic acid-modified polystyrene, polyethyleneimine, cationic polyvinyl alcohol, and other water-soluble cationic polymers.

(Preparation process)
The method for preparing the resin composite silicon particle B is not particularly limited. For example, the resin composite silicon particle B is prepared by coating the surface of the silicon particle 1 with the first layer 21 and then coating the surface with the second layer 22. Can do. Specifically, the silicon particles 1 are dispersed in water, and a solution in which a material for forming the first layer 21 is dissolved is added to the dispersion liquid. A layer 21 of At this time, the temperature and pH of the solution can be performed under appropriate conditions. In addition, after coating in this way, you may refine | purify by filtration etc. as needed. After preparing the silicon particles 1 coated with the first layer 21 as described above, a solution in which a material for forming the second layer 22 is dissolved is added to the dispersion liquid of the particles, The surface of the first layer 21 is covered with the second layer 22. At this time, the temperature and pH of the solution can be performed under appropriate conditions. Through such a procedure, the resin composite silicon particles B can be obtained. Hereinafter, the above procedure may be referred to as a “solution method”.

  In addition, for example, when forming the 1st layer 21 with the above-mentioned hydrophobic polymer which decomposes | disassembles below 250 degreeC, it can form by the phase-separation method in an organic solvent.

  When the resin composite silicon particles B are prepared by the solution method as described above, the silicon particles 1 have a negative zeta potential in water, the resin constituting the first layer 21 has a positive zeta potential in water, and the second It is preferable that the resin constituting the layer 22 has a negative zeta potential in water. In this case, the first layer 21 and the second layer 22 are easily uniformly coated on the surface of the silicon particles 1, and the dispersibility of the resin composite silicon particles B is improved.

  It is known that the zeta potential of the silicon particles 1 in water can be made negative by adjusting the conditions during the preparation of the silicon particles 1. Examples of the resin having a positive zeta potential in water include urea resins, and examples of the resin having a negative zeta potential in water include melamine resins. The urea resin having a positive zeta potential can be produced by adding formaldehyde to a mixed solution of urea and resorcin under acidic conditions. Moreover, as a melamine resin which has a negative zeta potential, it can be produced | generated by using as a raw material the prepolymer obtained by alkali-treating melamine and formaldehyde.

  On the other hand, when the resin layer 20 includes the above-described third layer, for example, if the resin composite silicon particles B are prepared by the solution method as described above, the resin constituting the third layer is anionic. It is preferable to show. In this case, the coating layer by the second layer 22 is more easily formed, and the adhesion with the first layer 21 is further increased.

  In the preparation process, graphite may be further added. For example, graphite can be added after the second layer 22 of the resin composite silicon particles B is formed. In adding graphite, either wet or dry methods may be used.

  When graphite is added, the negative electrode material for a lithium secondary battery manufactured by the heating process described later includes graphite. For example, the negative electrode material for a lithium secondary battery as shown in FIG. 2 described above is manufactured. Is done. The graphite added here is the same as the above-described graphite.

  The content of graphite added to the resin composite silicon particles B is not particularly limited. For example, from the viewpoint of increasing the charge / discharge capacity of the lithium secondary battery and ensuring safe charge / discharge, the content of the resin composite silicon particles B is 3 with respect to the total of the resin composite silicon particles B and graphite. -80% by weight, preferably 5-60% by weight, more preferably 10-50% by weight.

(Heating process)
In the heating step, the heat treatment of the resin composite silicon particles B is performed at an atmosphere temperature at least equal to or higher than the burning start temperature of the first layer 21. Therefore, although the heating temperature (atmosphere temperature) differs depending on the material constituting the first layer 21, the productivity is hardly lowered when the temperature is usually 300 ° C. or higher, and a desired negative electrode material for a lithium secondary battery is obtained. Can be manufactured. In addition, if the heating temperature is 900 ° C. or lower, it is easy to prevent the resin layer 20 from being burned out, so that it is easy to manufacture a desired negative electrode material for a lithium secondary battery. In particular, the heating temperature is preferably less than 600 ° C. In this case, the negative electrode material for a lithium secondary battery having the above-described composite particle A form is easily produced. From the above viewpoint, the heating temperature in the heating step is preferably 300 ° C. or higher and 600 ° C. or lower, and particularly preferably 350 ° C. or higher and 550 ° C. or lower. On the other hand, when adding graphite as mentioned above, the temperature of heat processing may be 900 degreeC or more. In this case, even if the resin layer 20 is almost burned out, the aggregate of silicon particles is formed so as to be surrounded by graphite by the gas generated at the time of burning, and as a result, as shown in FIG. The negative electrode material for lithium secondary batteries is obtained.

  Note that the heating method in the heating step is not limited, and a heating furnace or the like generally used for heat treatment may be used.

  For example, when the first layer 21 is formed of urea resin and the second layer 22 is formed of melamine resin, for example, if the heating temperature in the heating process is 350 ° C. or higher and 550 ° C. or lower, the second Most of the layer 22 is burned out, but most of the first layer 21 is burned out. As a result, for example, the composite particles A in the form shown in any of FIGS. 1A and 1B, that is, the surfaces of the silicon particles 1 are formed by being covered with the carbide layer 2. Can obtain a negative electrode material for a lithium secondary battery containing composite particles A in which voids 3 are formed. For example, if the heating temperature in the heating process is 420 ° C. or more and 520 ° C. or less, the form shown in FIG. 1A, if the heating temperature in the heating process is 260 ° C. or more and less than 420 ° C. (preferably 400 ° C. or less). 1 (b).

  Taking the form of FIGS. 1A and 1B as an example, the inner branch-like carbide layer 2 is a portion where the first layer 21 in the resin composite silicon particle B is fired, and the outer shell-like shape is formed. The carbonized layer 2 is a portion where the second layer 22 in the resin composite silicon particle B is fired.

  The heating time in the heating step is not particularly limited. For example, if it is 10 minutes or longer, a desired negative electrode material for a lithium secondary battery can be produced, and preferably 20 minutes or longer. If the heating time in the heating step is, for example, 5 hours or less, it is possible to prevent the first layer 21 from being completely burned out, and it becomes easy to produce a desired negative electrode material for a lithium secondary battery.

  Although the heating atmosphere in a heating process is not specifically limited, For example, heat processing can be performed in nitrogen atmosphere.

  As mentioned above, the negative electrode material for lithium secondary batteries is obtained by baking the resin composite silicon particle B by a heating process. The negative electrode material for a lithium secondary battery thus obtained can be, for example, a composite particle A as shown in FIG. 1, and thus the resin composite silicon particle B can be said to be a precursor of the composite particle A. The fired product of the resin composite silicon particles B may be used as it is as a negative electrode material for a lithium secondary battery, and is usually used as a granular material (for example, a granular carbon material) by pulverization, pulverization or the like. The average particle size of the powder is usually 1 to 40 μm, preferably 1 to 20 μm, more preferably about 5 to 15 μm.

  The negative electrode material for a lithium secondary battery obtained by the above production method can impart excellent charge / discharge capacity, coulomb efficiency, and cycle characteristics to the lithium secondary battery. The negative electrode material for a lithium secondary battery obtained by the above production method is formed by coating the surface of the silicon particles 1 with the carbide layer 2 and forming the voids 3 inside the carbide layer 2. Can be. However, the form of the obtained negative electrode material for a lithium secondary battery differs depending on the heating conditions in the heating step, and may be in a form other than the composite particle A described above. Moreover, when the resin composite silicon particle B further contains graphite, for example, as shown in FIG. 2, particles in which the graphite 4 adheres to the surface of the composite particle A can be manufactured.

3. The composition for forming an active material layer can be prepared using the negative electrode active material layer-forming composition of the lithium secondary battery negative electrode material. Moreover, the composition for negative electrode active material layer forming can be prepared using the negative electrode material for lithium secondary batteries obtained with the manufacturing method of said negative electrode material for lithium secondary batteries. Such a composition for forming a negative electrode active material layer can impart excellent charge / discharge capacity, coulomb efficiency, and cycle characteristics to a lithium secondary battery, and is suitable as a material for forming a negative electrode active material layer.

  The composition for forming a negative electrode active material layer can contain, for example, a binder resin, a solvent, and the like as long as the performance of the negative electrode material for a lithium secondary battery is not impaired.

  Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene, styrene butadiene rubber (SBR resin), carboxymethyl cellulose, and the like. Any one of these may be used alone, or two or more may be mixed. Can be used. The amount of binder used (in the case of dispersion, the amount used in terms of solid content) is not particularly limited, and the lower limit is usually 3 parts by weight with respect to 100 parts by weight of the negative electrode material for lithium secondary batteries. About the above, preferably about 5 parts by weight or more. The upper limit of the amount of the binder used is usually 20 parts by weight or less (for example, 15 parts by weight or less), preferably about 10 parts by weight or less with respect to 100 parts by weight of the negative electrode material.

  As the solvent, a solvent that can dissolve or decompose the binder is usually used, and examples thereof include organic solvents such as water, N-methylpyrrolidone, and N, N-dimethylformamide. The amount of the solvent used may be, for example, that the negative electrode active material layer forming composition is in a paste form. For example, it is usually about 60 to 150 parts by weight with respect to 100 parts by weight of the negative electrode material for a lithium secondary battery, preferably Is about 60 to 100 parts by weight.

  The method for preparing the negative electrode active material layer forming composition is not particularly limited, and examples thereof include a method of mixing a mixed liquid or dispersion of a binder and a solvent and a negative electrode material for a lithium secondary battery. . A mixing method is not limited, For example, a well-known means is employable.

4). The negative electrode for a lithium secondary battery and the composition for forming a negative electrode active material layer for a lithium secondary battery can be used as a constituent material of a negative electrode for a lithium secondary battery, and can form a negative electrode for a lithium secondary battery by a conventional method. . For example, the negative electrode for a lithium secondary battery can be formed by a method of forming a composition for forming a negative electrode active material layer. Specifically, a negative electrode for a lithium secondary battery having an arbitrary shape can be formed by applying a paste of a composition for forming a negative electrode active material layer to a negative electrode current collector by a coating means such as a doctor blade. In forming the negative electrode for a lithium secondary battery, it may be combined with a terminal as necessary.

  The type of the negative electrode current collector is not particularly limited, and examples thereof include a known current collector, for example, a conductor such as copper.

  In forming a negative electrode for a lithium secondary battery, a conductive material for forming a negative electrode for a lithium secondary battery (including a carbonaceous material and a conductive carbon material) may be used in combination. The ratio of the conductive material used is not particularly limited, but can be about 1 to 10% by weight, preferably about 1 to 5% by weight, based on the total amount of the negative electrode material for the lithium secondary battery and the conductive material. By using a conductive material in combination, the conductivity as an electrode can be improved, and the discharge capacity and cycle characteristics of the lithium secondary battery can also be improved.

Examples of the conductive material include carbon black such as acetylene black, thermal black, and furnace black, and one of these may be used, or two or more may be used in combination. For example, the conductive material may be mixed in a paste containing a negative electrode material for a lithium secondary battery and a solvent. The amount of the paste applied to the negative electrode current collector is not particularly limited, but is usually 5 to 15 mg / cm ^2, and preferably 7 to 13 mg / cm ² .

  A lithium secondary battery can be produced using the above-described negative electrode for a lithium secondary battery (hereinafter, sometimes simply referred to as “negative electrode”).

  The lithium secondary battery includes at least a negative electrode, a positive electrode, and a nonaqueous electrolyte. More specifically, a lithium secondary battery can be produced by a conventional method using a negative electrode, a positive electrode, an electrolytic solution, a separator, and the like.

The positive electrode is preferably a material capable of inserting and extracting lithium. A known positive electrode can be used as long as it is such a positive electrode. For example, a material composed of a positive electrode current collector, a positive electrode active material, a conductive agent, and the like can be used. Examples of the positive electrode current collector include aluminum. Examples of the positive electrode active material include lithium composite oxides such as LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ . Examples of the conductive agent include conductive carbon black such as acetylene black.

The electrolytic solution is not particularly limited, and a known material can be used. For example, if a solution in which an electrolyte is dissolved in an organic solvent is used as the electrolytic solution, a non-aqueous lithium secondary battery can be manufactured. As the electrolyte, for _{example, LiPF 6, LiClO 4, LiBF} 4, LiClF 4, LiAsF 6, LiSbF 6, LiAlO 4, LiAlCl 4, LiCl, be mentioned lithium salt that produces a hard anion solvated such LiI it can. Examples of the organic solvent include carbonates such as propylene carbonate, ethylene carbonate and diethyl carbonate; lactones such as γ-butyrolactone; chain ethers such as 1,2-dimethoxyethane, dimethyl ether and diethyl ether; tetrahydrofuran; Cyclic ethers such as methyltetrahydrofuran, dioxolane, 4-methyldioxolane, sulfolanes such as sulfolane, sulfoxides such as dimethylsulfoxide, nitriles such as acetonitrile, propionitrile, benzonitrile, N, N-dimethylformamide, N, Examples of the aprotic solvent include amides such as N-dimethylacetamide and polyoxyalkylene glycols such as diethylene glycol. An organic solvent may be used individually by 1 type, and may be used as a 2 or more types of mixed solvent.

  The separator is not particularly limited, and examples thereof include known separators such as polyolefin porous membranes such as porous polypropylene nonwoven fabrics and porous polyethylene nonwoven fabrics.

  The lithium secondary battery may further include, for example, a gasket, a sealing plate, a case, and the like that are usually used in this field, in addition to the negative electrode including the negative electrode material of the present invention, the positive electrode, and the electrolytic solution.

  Although there is no restriction | limiting in particular in the shape of a lithium secondary battery, It can be set as arbitrary forms, such as a cylindrical shape, a square shape, and a button type.

  Since the above-described lithium secondary battery is manufactured using a composition for forming a negative electrode active material layer containing at least a negative electrode material for a lithium secondary battery, it has excellent charge / discharge capacity, coulomb efficiency, and cycle characteristics. Accordingly, the lithium secondary battery as described above can be used as a power source or auxiliary power source for electronic devices, electric devices, automobiles, power storage, etc., as a distributed and portable battery.

  EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited to the aspect of these Examples.

Example 1
Production of Resin Composite Silicon Particles 2 g of silicon particles (“Silgrain e-Si400” manufactured by Elkem) having an average particle diameter of 2 μm shown in FIG. 4 were added to 70 mL of distilled water and dispersed using an ultrasonic cleaner. In this dispersion, 2.5 g of urea (manufactured by Nacalai Tesque) and 0.25 g of resorcin (manufactured by Nacalai Tesque) were dissolved. Next, after adjusting the dispersion to pH 4 using acetic acid, 7 g of 37% aqueous formaldehyde solution was further added, and stirring was continued at 80 ° C. for 2 hours. Thereafter, the dispersion was filtered and washed with water to obtain particles, which were dried at 60 ° C. for 8 hours. Hereinafter, the particles are sometimes referred to as “single capsule particles” (coated with urea resin) and abbreviated as “UC # 1”.

  FIG. 5 shows the results of observation of the obtained single capsule particles (UC # 1) with FE-SEM (JEOL JSM-6700F). In FIG. 5, (a) is an image of 3000 times and (b) is an image of 10,000 times. Compared to the silicon particles in FIG. 4, the shapes themselves are similar, but the surface states are clearly different. This shows that the 1st layer (urea resin) is formed in the silicon particle surface.

  Next, 5.5 g of poly (styrene-maleic anhydride) resin (“SMA Resin 1000SP” manufactured by Kawa Crude Chemical Co., Ltd.) is dissolved in 10 mL of methanol, and 1.08 g of NaOH / 5 mL of water is added to this solution at room temperature. Stir. After the liquid became transparent, 45 mL of distilled water was added and methanol was removed with an evaporator to obtain a poly (styrene-maleic anhydride) resin solution (SMAaq.). On the other hand, 2.5 g of melamine (manufactured by Nacalai Tesque) and 37% formaldehyde water (manufactured by Nacalai Tesque) are added to 30 mL of distilled water, and 0.2 ml of 5N NaOH aqueous solution is further added, followed by stirring at 70 ° C. for 2 hours, colorless and transparent A melamine prepolymer aqueous solution was obtained.

  Next, 1 g of UC # 1 was dispersed in 50 mL of distilled water using an ultrasonic cleaner, and the SMAaq. After mixing 7 ml and stirring at room temperature for 1 hour, the particles were filtered and washed with distilled water. After washing, the resultant was re-dispersed in 70 mL of distilled water, adjusted to pH 4 by adding 17 mL of the melamine prepolymer aqueous solution and acetic acid, and then stirred at 80 ° C. for 2 hours. Then, it filtered and washed with water, solid content was obtained, and this was dried at 60 degreeC for 8 hours, and the powder of particle | grains was obtained. Hereinafter, the particles are sometimes referred to as “double capsule particles” (urea resin and melamine resin are coated in this order) and abbreviated as “MC-UC # 1”.

  FIG. 6 shows the result of observing the obtained double capsule particles (MC-UC # 1) with FE-SEM (JEOL JSM-6700F). In FIG. 6, (a) is 1000 times, (b) is 3000 times, and (c) is 10,000 times. FIG. 6 shows that the double capsule particles MC-UC # 1 are formed as aggregates of about 10 to 100 μm.

Manufacture of negative electrode material for lithium secondary battery MC-UC # 1 obtained as described above was fired at 450 ° C. in a nitrogen atmosphere for 1 hour to obtain a fired product.

  FIG. 7 shows the result of observing the fired product with FE-SEM (JEOL JSM-6700F). In FIG. 7, (a) is 1000 times, (b) is 3000 times, and (c) is 10,000 times. In FIG. 7, particles in which the negative electrode material for a lithium secondary battery obtained by firing is partially collapsed appear. When the collapsed particles are seen, a plurality of voids are observed. From this, it can be said that a negative electrode material for a lithium secondary battery in which voids are formed is formed by firing (particularly, see the arrow portion in FIG. 7B). . After firing, as shown in FIG. 7, although the surface is slightly shrunk and the surface becomes wrinkled, it is formed as an aggregate of 10 to 100 μm as before firing.

Production of Negative Electrode for Lithium Secondary Battery Next, the fired product is passed through a mesh having an opening of 53 μm so that the solid equivalent concentration is 98 wt% of the fired product, 1 wt% of SBR resin, and 1 wt% of CMC (carboxymethyl cellulose). , SBR resin and CMC resin were mixed to prepare an aqueous dispersion paste (a composition for forming a negative electrode active material layer). The obtained aqueous dispersion paste was applied to a copper foil and dried, and then press-molded to prepare a negative electrode for a lithium secondary battery having an electrode density of 1.47 g / cm ³ and an electrode thickness of 59 μm as an evaluation sample.

With respect to the obtained negative electrode, a cell was assembled using metal lithium as a counter, and a charge / discharge test was performed. The test conditions were as follows.
Charging conditions: 0.3 C-CC (constant current), 0.01 Vvs. Li / Li ⁺ CV (constant voltage), total charging time 5 h.
Discharge conditions: 0.3 C-CC (constant current), 2 V cut electrolyte solution: EC (ethylene carbonate): EMC (ethyl methyl carbonate) (1: 2 v / v%) + VC (vinylene carbonate) 2 wt%
Further, this charge / discharge cycle was repeated three times, and the ratio of the discharge capacity at the third cycle to the charge / discharge capacity was calculated as efficiency (Coulomb efficiency) (%).

(Example 2)
Production of negative electrode material for lithium secondary battery MC-UC # 1 produced in Example 1 was prepared by using 12 g of “OMAC-R” manufactured by Osaka Gas Chemical, 0.36 g of acetylene black manufactured by Denki Kagaku Kogyo, and 0.12 g of carbon nanotubes manufactured by Arkema. Were mixed to obtain a mixture. 7.4 g of this mixture was fired at 900 ° C. in a nitrogen atmosphere for 1 hour to obtain 6.7 g of a fired product (corresponding to composite particle A coated with graphite).

  FIG. 8 shows the result of observing the fired product with FE-SEM (JEOL JSM-6700F). In FIG. 8, (a) is 1000 times, (b) is 3000 times, and (c) is 10,000 times. In FIG. 8, it can be seen that the negative electrode material for a lithium secondary battery is fused in units of several tens of μm, and that the surroundings are surrounded by graphite. In this negative electrode material for a lithium secondary battery, by firing MC-UC # 1 coated with graphite, most of the resin layer covering silicon particles is burned out and surrounded by graphite by the gas generated at the time of burning. It is considered that an aggregate of silicon particles formed is formed. In FIG. 8, no collapsed particles were observed, so the internal voids were not visible, but it is presumed that the internal voids were formed as in Example 1.

Manufacture of negative electrode for lithium secondary battery The above fired product was prepared by using the negative electrode for lithium secondary battery as an evaluation sample in the same procedure as in Example 1, a cell was assembled using metallic lithium as a counter, and a charge / discharge test was conducted. I did it. The test conditions were the same as in Example 1.

(Example 3)
Production of negative electrode material for lithium secondary battery 1.8 g of MC-UC # 1 produced in Example 1 was prepared, and 9 g of “OMAC-R” manufactured by Osaka Gas Chemical Co., Ltd. 27 g and 0.09 g of Arkema carbon nanotubes were mixed to obtain a mixture. 7 g of this mixture was fired at 450 ° C. in a nitrogen atmosphere for 1 hour to obtain 6 g of a fired product (corresponding to composite particle A coated with graphite).

Manufacture of negative electrode for lithium secondary battery The above-mentioned calcined product is passed through a mesh having a mesh size of 53 μm, and the solid conversion concentration is 98 wt% of calcined product, 1 wt% of SBR resin, 1 wt% of CMC (carboxymethylcellulose). Then, it was mixed with CMC resin to prepare an aqueous dispersion paste (a composition for forming a negative electrode active material layer). The obtained aqueous dispersion paste was applied to a copper foil and dried, and then press-molded to prepare a negative electrode for a lithium secondary battery having an electrode density of 1.52 g / cm ³ and an electrode thickness of 62 μm as an evaluation sample.

  With respect to the obtained negative electrode, a cell was assembled using metal lithium as a counter, and a charge / discharge test was performed. The test conditions were the same as in Example 1.

(Comparative Example 1)
The negative electrode for lithium secondary batteries was created using the silicon particle in which the resin layer is not formed on the surface.

  Specifically, 2.8 g of silicon particles having an average particle diameter of 2 μm used in Example 1 were replaced with 40 g of “OMAC-R” manufactured by Osaka Gas Chemical, 1.2 g of acetylene black manufactured by Denki Kagaku Kogyo Co., Ltd. 4 g was mixed to obtain a mixture. By burning 23 g of this mixture at 900 ° C. in a nitrogen atmosphere for 1 hour, 22.6 g of a fired product was obtained.

The above baked product is passed through a mesh having an opening of 53 μm, mixed with SBR resin and CMC resin so that the solid equivalent concentration is 98 wt% of baked product, 1 wt% of SBR resin, and 1 wt% of CMC (carboxymethylcellulose). A dispersion paste was prepared. The obtained aqueous dispersion paste was applied to a copper foil and dried, and then press-molded to prepare a negative electrode for a lithium secondary battery having an electrode density of 1.52 g / cm ³ and an electrode thickness of 63 μm as an evaluation sample.

  With respect to the obtained negative electrode, a cell was assembled using metal lithium as a counter, and a charge / discharge test was performed. The test conditions were the same as in Example 1.

(Comparative Example 2)
A negative electrode for a lithium secondary battery was prepared using silicon particles in which the first layer was not formed on the surface and only the second layer was formed.

  Specifically, 2.5 g of melamine (manufactured by Nacalai Tesque) and 37% formaldehyde water (manufactured by Nacalai Tesque) are added to 30 mL of distilled water, and 0.2 ml of 5N NaOH aqueous solution is further added, followed by stirring at 70 ° C. for 2 hours. A colorless and transparent melamine prepolymer aqueous solution was obtained. Next, 2 g of silicon particles having an average particle diameter of 2 μm used in Example 1 were added to 70 mL of distilled water and dispersed using an ultrasonic cleaner, and 17 mL of the melamine prepolymer aqueous solution and acetic acid were added thereto to adjust the pH to 4 The mixture was stirred at 80 ° C. for 3 hours. Then, it filtered and washed with water, the particle | grains were obtained, and this particle | grain was dried at 60 degreeC for 8 hours. Hereinafter, this particle may be abbreviated as “MC # 1”.

  1.6 g of the above MC # 1 was prepared, and 9 g of “OMAC-R” manufactured by Osaka Gas Chemical Co., Ltd., 0.27 g of acetylene black manufactured by Denki Kagaku Kogyo Co., Ltd. and 0.09 g of carbon nanotubes manufactured by Arkema were mixed to obtain a mixture. . This mixture was baked for 1 hour at 450 ° C. in a nitrogen atmosphere to obtain 9.9 g of a baked product.

The above baked product is passed through a mesh having an opening of 53 μm, mixed with SBR resin and CMC resin so that the solid equivalent concentration is 98 wt% of baked product, 1 wt% of SBR resin, and 1 wt% of CMC (carboxymethylcellulose). A dispersion paste was prepared. The obtained aqueous dispersion paste was applied to a copper foil and dried, and then press-molded to prepare a negative electrode for a lithium secondary battery having an electrode density of 1.35 g / cm ³ and an electrode thickness of 68 μm as an evaluation sample.

  With respect to the obtained negative electrode, a cell was assembled using metal lithium as a counter, and a charge / discharge test was performed. The test conditions were the same as in Example 1.

(TG-DTA measurement result)
FIG. 9 shows a TG-DTA measurement result. FIG. 9A shows a TG-DTA measurement result of particles in which only the urea resin layer (first layer) is formed on the surface of the silicon particles. These particles are “UC # 1” purified in the production process of the resin composite silicon particles of Example 1 above. FIG. 9B shows a TG-DTA measurement result of the particle “MC # 1” in which only the melamine resin layer (second layer) is formed on the silicon particle. This is “MC # 1” prepared in Comparative Example 2. FIG. 9C shows a TG-DTA measurement result of the MC-UC # 1.

  In UC # 1 in FIG. 9 (a), a rapid weight loss is observed at about 300 ° C., and in MC # 1 in FIG. 9 (b), a rapid weight loss is observed at about 400 ° C. That is, it can be seen that the weight of UC # 1 is greatly reduced at a temperature lower than that of MC # 1. These results show that the urea resin layer (first layer) has a lower sintering start temperature than the melamine resin layer (second layer). On the other hand, in FIG. 9 (c), the thermal behavior is different from that in FIGS. 9 (a) and 9 (b), and the weight loss occurs more slowly than in FIGS. 9 (a) and 9 (b). I understand that. That is, in MC-UC # 1 of FIG.9 (c), it turns out that the carbonization and burning of a resin layer progress gradually with heating, and the weight reduction has arisen.

  From the comparison between this result and the results shown in FIGS. 9 (a) and 9 (b), when MC-UC # 1 is heated to increase the temperature, first, the carbonization and burning of the urea resin layer occurs. It is believed that carbonization and burnout of the melamine resin layer has occurred as it starts and then increases in temperature. This is because MC-UC # 1 prepared in Example 1 is formed by having a urea resin layer (first layer) and a melamine resin layer (second layer) on the surface of silicon particles. It shows that. Furthermore, it can be said that the composite particles A shown in FIG. 1A are obtained by firing (heating step) MC-UC # 1.

  In Example 3 in which MC-UC # 1 was fired at 450 ° C., considering the results of FIGS. 9A and 9B, carbonization and burning of the urea resin layer proceeded mainly. It is thought that carbonization and burning of the melamine resin layer hardly proceeded. Therefore, it can be seen that the fired product obtained by firing (heating process) of MC-UC # 1 of Example 3 is in the form of composite particles A shown in FIG.

Charge / Discharge Measurement Results Table 1 shows the charge / discharge measurement results (charge capacity [mAh / g], discharge capacity [mAh / g] and efficiency [%]).

  As shown in Table 1, it can be seen that all of the negative electrodes prepared in Examples 2 and 3 are lithium secondary batteries having excellent charge / discharge capacity, efficiency, and cycle characteristics. From this, the negative electrode produced using the composite particles in which the surface of the silicon particles is coated with a carbide layer and voids are formed inside the carbide layer is excellent in charge and discharge capacity, efficiency and lithium secondary battery. It can be seen that cycle characteristics are imparted. Moreover, if the negative electrode material for lithium secondary batteries obtained by the method for producing a negative electrode material for lithium secondary batteries of the present invention is used, the lithium secondary battery is provided with excellent charge / discharge capacity, coulomb efficiency and cycle characteristics. And is suitable as a material for forming the negative electrode active material layer. In particular, it can be seen that the negative electrode material for a lithium secondary battery obtained in Example 3 shows better cycle characteristics than Example 2. In Comparative Example 1, since the silicon particles were not covered with the carbonized layer having voids, the cycle characteristics were inferior to those of Examples 2 and 3. In Comparative Example 2, although silicon particles were covered with a carbonized layer, no voids were formed in the carbonized layer, so that the cycle characteristics were inferior to those of Examples 2 and 3.

A composite particle B resin composite silicon particle 1 silicon particle 2 carbide layer 20 resin layer 21 first layer 22 second layer 3 void 4 graphite

Claims (22)

A negative electrode material for a lithium secondary battery containing composite particles,
The composite particle is a negative electrode material for a lithium secondary battery, wherein a surface of a silicon particle is coated with a carbide layer, and voids are formed inside the carbide layer.   The negative electrode material for a lithium secondary battery according to claim 1, wherein the silicon particles are primary particles and / or aggregates.   The negative electrode material for a lithium secondary battery according to claim 1, wherein the carbide layer is in partial contact with the surface of the silicon particles.   The negative electrode material for a lithium secondary battery according to claim 1, wherein the carbide layer has a thickness of 0.001 μm to 1 μm.   The negative electrode material for a lithium secondary battery according to any one of claims 2 to 4, wherein an average particle size of the primary particles is 0.01 to 100 µm.   The negative electrode material for a lithium secondary battery according to any one of claims 2 to 4, wherein the aggregate has an average particle size of 0.05 to 100 µm.   The negative electrode material for a lithium secondary battery according to any one of claims 1 to 6, wherein a total volume of voids of the composite particles is 50 to 500% of a volume of the silicon particles.   The negative electrode material for a lithium secondary battery according to any one of claims 1 to 7, further comprising graphite.   The composition for negative electrode active material layer formation for lithium secondary batteries containing the negative electrode material for lithium secondary batteries of any one of Claims 1-8.   The negative electrode for lithium secondary batteries provided with the negative electrode active material layer formed with the composition for negative electrode active material layer forming of Claim 9 on a collector.   A lithium secondary battery comprising the negative electrode for a lithium secondary battery according to claim 10. A method for producing a negative electrode material for a lithium secondary battery, comprising:
A step of preparing resin composite silicon particles obtained by coating the surface of silicon particles with a resin layer;
A step of heat-treating the resin composite silicon particles,
The resin layer is formed to have at least a first layer that covers the surface of the silicon particles and a second layer that further covers the first layer, and the burning start temperature of the first layer is Lower than the burning start temperature of the second layer,
The method for producing a negative electrode material for a lithium secondary battery, wherein, in the heat treatment step, the heat treatment is performed at least at a burning start temperature of the first layer.   The manufacturing method according to claim 12, wherein the silicon particles are primary particles and / or aggregates.   The manufacturing method of Claim 13 whose average particle diameter of the said primary particle is 0.01-100 micrometers.   The manufacturing method of Claim 13 whose average particle diameters of the said aggregate are 0.05-100 micrometers. Resin composite silicon particles for producing a negative electrode material for a lithium secondary battery,
The resin composite silicon particles, the surface of the silicon particles are coated with a resin layer,
The resin layer has at least a first layer that covers the surface of the silicon particles and a second layer that further covers the first layer;
Resin composite silicon particles, wherein the burning start temperature of the first layer is lower than the burning start temperature of the second layer.   The resin composite silicon particles according to claim 16, wherein the resin composite silicon particles are primary particles and / or aggregates.   The resin composite silicon particles according to claim 17, wherein the primary particles have an average particle diameter of 0.01 to 100 μm.   The resin composite silicon particles according to claim 17, wherein the aggregate has an average particle size of 0.05 to 100 μm.   The silicon particles have a negative zeta potential in water, the resin constituting the first layer has a positive zeta potential in water, and the resin constituting the second layer has a negative zeta potential in water. The resin composite silicon particles according to any one of ˜19.   The resin composite silicon particles according to any one of claims 16 to 20, wherein the resin layer further includes a third layer interposed between the first layer and the second layer.   The resin composite silicon particles according to any one of claims 16 to 21, wherein the first layer is a urea resin, and the second layer is a melamine resin.