JP2015072849A - Negative electrode material for secondary battery, method for producing negative electrode material for secondary battery, and negative electrode for secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode material for a secondary battery, capable of improving cycle characteristics thereof furthermore by improving adhesion between a Si particle and a covering material.SOLUTION: A negative electrode material 1 (a negative electrode material for a secondary battery) constitutes an active material layer 11 formed on a collector layer 10 of a negative electrode 100. The negative electrode material 1 includes: a Si particle 2; a Ni-P plating layer 3 containing Ni formed on a surface 2a of the Si particle 2; and a Ni-Si reaction layer 4 formed on an interface 1a between the Si particle 2 and the Ni-P plating layer 3 and containing at least Ni and Si.

Description

  The present invention relates to a negative electrode material for a secondary battery, a method for producing a negative electrode material for a secondary battery, and a negative electrode for a secondary battery, and in particular, a negative electrode material for a secondary battery including Si particles, and the production of the negative electrode material for the secondary battery. The present invention relates to a method and a negative electrode for a secondary battery including the negative electrode material for the secondary battery.

  In recent years, Si having a large charge / discharge capacity has been promising as an active material for a negative electrode material for a secondary battery (a negative electrode material for a secondary battery) in order to increase the capacity of the lithium ion secondary battery. However, when Si is repeatedly charged and discharged with respect to the lithium ion secondary battery, the charge / discharge cycle life is shortened due to the fact that the discharge capacity of the secondary battery negative electrode is greatly reduced from the initial value. It is known that the cycle characteristics are low. The reason why the cycle characteristics are low in Si is that stress generated in the secondary battery negative electrode material due to the large difference between the volume of the negative electrode for secondary battery after charging and the volume of the negative electrode for secondary battery after discharge. This is considered to be because the Si particles collapse (miniaturize) due to the above, and a part of the negative electrode for secondary battery does not function.

  Therefore, as one means for suppressing the deterioration of cycle characteristics, it has been proposed to use an active material in which Ni plating is formed on the surface of Si particles as an active material of a negative electrode material for a lithium ion secondary battery. (For example, refer to Patent Document 1).

  Patent Document 1 discloses active material particles constituting an active material layer of a negative electrode for a secondary battery, and a metal thin film (coating material) made of Si particles and Ni plating formed so as to cover the surface of the Si particles. ) Active material particles (secondary battery negative electrode material). In this way, Ni plating formed so as to cover the surface of the Si particles can withstand the stress generated in the negative electrode material for the secondary battery and suppress collapse to some extent, so that the cycle characteristics are lowered. Can be suppressed.

JP 2005-63767 A

  However, with the active material particles made of Ni-plated Si particles described in Patent Document 1 described above, it is possible to withstand a certain amount of stress generated in the negative electrode material for a secondary battery and suppress collapse to some extent by Ni plating. When the Si particles and the Ni plating are not sufficiently adhered, it is considered that the Ni plating peels from the Si particles, and as a result, the collapse of the Si particles cannot be sufficiently suppressed. For this reason, it is considered that the active material particles described in Patent Document 1 may not be able to sufficiently improve the cycle characteristics.

  The present invention has been made to solve the above problems, and one object of the present invention is to further improve cycle characteristics by improving the adhesion between the Si particles and the coating material. A secondary battery negative electrode material, a method for producing the secondary battery negative electrode material, and a secondary battery negative electrode comprising the secondary battery negative electrode material.

  A negative electrode material for a secondary battery according to a first aspect of the present invention is a negative electrode material for a secondary battery that constitutes an active material layer formed on a current collector layer of a negative electrode for a secondary battery, and includes Si particles and And a coating material containing at least Ni formed on the surface of the Si particles, and a bonding layer formed at the interface between the Si particles and the coating material and containing at least Ni and Si.

  In the negative electrode material for a secondary battery according to the first aspect of the present invention, as described above, the bonding layer is formed by forming a bonding layer containing at least Ni and Si at the interface between the Si particles and the coating material. By including both Si contained in the Ni and Ni contained in the coating material, the adhesion between the Si particles and the bonding layer can be improved, and the adhesion between the coating material and the bonding layer can be improved. Can do. Thereby, since the adhesiveness of Si particle | grains and coating | covering material through a joining layer can be improved, the cycling characteristics of the negative electrode for secondary batteries using the negative electrode material for secondary batteries can be improved.

  In the negative electrode material for a secondary battery according to the first aspect, preferably, the bonding layer includes a Ni—Si alloy. If comprised in this way, while it can make the adhesiveness of Si particle | grains and a joining layer more favorable by the joining layer containing a Ni-Si alloy, it makes the adhesiveness of a coating | covering material and a joining layer more favorable. Therefore, the adhesion between the Si particles and the covering material via the bonding layer can be further improved.

  In the negative electrode material for a secondary battery according to the first aspect, preferably, the thickness of the bonding layer is 0.1 μm or more. If comprised in this way, it can suppress that the adhesiveness of Si particle | grains and a joining layer and the adhesiveness of a coating | covering material and a joining layer fall due to the thickness of a joining layer being small. .

In the negative electrode material for a secondary battery according to the first aspect, preferably, the Si particles and the covering material are bonded to each other via a bonding layer without using a natural oxide film. According to this structure, mainly ceramics (oxide (SiO ₂₎₎ without going through the natural oxide film of the Si particles consisting, by joining together the the Si particle coating material via a bonding layer, Si The particle Si (metalloid element) and the coating material Ni (metal element) can be brought into direct contact. Thereby, compared with the case where Si particle | grains and a coating | covering material are mutually joined through the natural oxide film which consists of ceramics, the adhesiveness of Si particle | grains and a coating | coated material can further be improved.

  In the negative electrode material for a secondary battery according to the first aspect, preferably, the surface of the Si particles is formed in an uneven shape. If comprised in this way, since the contact area of Si particle | grains which has an uneven | corrugated surface, and a coating | covering material can be increased, the adhesiveness of Si particle | grains and a coating | covering material can be improved effectively.

  In the negative electrode material for a secondary battery according to the first aspect, preferably, the coating material contains Ni and P, and P of the coating material diffuses into the Si particles. If comprised in this way, the electrical conductivity of Si particle | grains can be improved because P diffused in Si particle | grains becomes a dopant. Thereby, since the electrical conductivity of the negative electrode for secondary batteries in which the negative electrode material for secondary batteries is used can be improved, the output characteristics of the negative electrode for secondary batteries can be improved.

  A method for producing a negative electrode material for a secondary battery according to a second aspect of the present invention includes a step of forming a coating material containing at least Ni on the surface of Si particles, and heat-treating the Si particles on which the coating material is formed. Forming a bonding layer containing at least Ni and Si at the interface between the Si particles and the covering material.

  In the method for producing a negative electrode material for a secondary battery according to the second aspect of the present invention, as described above, a bonding layer containing at least Ni and Si is formed at the interface between the Si particles and the coating material, thereby forming the bonding layer. By including both Si contained in the Si particles and Ni contained in the coating material, the adhesion between the Si particles and the bonding layer can be improved, and the adhesion between the coating material and the bonding layer can be improved. Can be. Thereby, since the adhesiveness of Si particle | grains and coating | covering material through a joining layer can be improved, the cycling characteristics of the negative electrode for secondary batteries using the negative electrode material for secondary batteries can be improved. Further, by heat-treating the Si particles on which the coating material is formed, Si of the Si particles can be diffused into the coating material, so that a bonding layer can be easily formed at the interface between the Si particles and the coating material. .

  In the method for producing a negative electrode material for a secondary battery according to the second aspect, preferably, the step of forming the bonding layer heat-treats the Si particles on which the covering material is formed under a temperature condition of 700 ° C. or higher and 900 ° C. or lower. This includes a step of forming a bonding layer at the interface between the Si particles and the covering material. If comprised in this way, since Si of Si particle | grains can be reliably diffused in a coating | covering material by heat-processing under the temperature conditions of 700 degreeC or more and 900 degrees C or less, in the interface of Si particle | grains and a coating | covering material. The bonding layer can be reliably formed.

  In the method for manufacturing a negative electrode material for a secondary battery according to the second aspect, preferably, the step of forming the covering material includes a step of forming a covering material containing Ni and P on the surface of the Si particles, and bonding In the step of forming the layer, the Si particles on which the covering material is formed are heat-treated to form a bonding layer containing a Ni—Si alloy at the interface between the Si particles and the covering material, and the covering material P is changed to the Si particles. Diffusing in. If comprised in this way, the electrical conductivity of Si particle | grains can be improved because P diffused in Si particle | grains becomes a dopant. Thereby, since the electrical conductivity of the negative electrode for secondary batteries in which the negative electrode material for secondary batteries is used can be improved, the output characteristics of the negative electrode for secondary batteries can be improved. In addition, the heat treatment not only diffuses Si of the Si particles into the coating material, but also diffuses P of the coating material into the Si particles, so a bonding layer can be easily formed at the interface between the Si particles and the coating material. However, the electrical conductivity of the Si particles can be improved.

In this case, preferably, the step of forming the covering material containing Ni and P forms a covering material composed of P and Ni whose content in the covering material is 0.5 mass% or more and 15 mass% or less. Process. According to this structure, the dressing by including P of 0.5 mass% or more, including the Ni 3 _P having a withstand easy crystal structure the stresses generated in the Si particles of the negative electrode for a secondary battery dressing Therefore, the close contact state between the Si particles and the covering material can be maintained for a long time. Further, when the content of P in the coating material is set to 15% by mass or less, sufficient Ni can be secured in the coating material. Therefore, the heat treatment reacts with Si in which Ni in the coating material diffuses to form a bonding layer. Even when is formed, it is possible to sufficiently ensure the electrical conductivity in the covering material containing Ni and P.

In the method for manufacturing a negative electrode material for a secondary battery according to the second aspect, preferably, the step of forming the covering material includes a step of removing a natural oxide film formed on the surface of the Si particles by etching, Forming a covering material on the surface of the Si particles so that the Si particles and the covering material are in contact with each other without an oxide film, and the step of forming the bonding layer is performed without using a natural oxide film. Forming a bonding layer at the interface between the Si particles and the coating material such that the particles and the coating material are bonded to each other via the bonding layer. According to this structure, mainly ceramics (oxide (SiO ₂₎₎ by removing the natural oxide film of the Si particles consisting of Si particles of Si (metalloid element) and the coating material Ni (metal element) Can be brought into direct contact with each other. Thereby, compared with the case where it joins not only through a joining layer but through the natural oxide film which consists of ceramics, the adhesiveness of Si particle | grains and coating | covering material through a joining layer can be improved further. In addition, the natural oxide film formed on the surface of the Si particles can be easily removed by etching as compared with polishing or the like.

  In this case, preferably, the step of removing the natural oxide film by etching includes a step of removing the natural oxide film by etching and forming the surface of the Si particles in an uneven shape. If comprised in this way, since the contact area of Si particle | grains which has an uneven | corrugated surface, and coating | covering material can be increased, the adhesiveness of Si particle | grains and coating | covering material through a joining layer is improved effectively. be able to. In addition, since the surface of the Si particles can be made uneven while removing the natural oxide film by etching, a process for forming the surface of the Si particles in an uneven shape is not required. As a result, the negative electrode for a secondary battery The manufacturing process of the material can be simplified.

  A negative electrode for a secondary battery according to a third aspect of the present invention is a negative electrode for a secondary battery comprising a current collector layer and an active material layer formed on the surface of the current collector layer, wherein the active material layer Is a secondary battery having Si particles, a coating material containing at least Ni formed on the surface of the Si particles, and a bonding layer formed at an interface between the Si particles and the coating material and containing at least Ni and Si. A negative electrode material is included.

  In the negative electrode for a secondary battery according to the third aspect of the present invention, as described above, a bonding layer containing at least Ni and Si at the interface between the Si particles and the coating material is formed on the active material layer, thereby forming the bonding layer. By including both Si contained in the Si particles and Ni contained in the coating material, the adhesion between the Si particles and the bonding layer can be improved, and the adhesion between the coating material and the bonding layer can be improved. Can be. Thereby, since the adhesiveness of Si particle | grains and coating | covering material through a joining layer can be improved, the cycling characteristics of the negative electrode for secondary batteries can be improved.

  According to the present invention, as described above, the cycle characteristics can be further improved by improving the adhesion between the Si particles and the coating material.

It is sectional drawing which showed the structure of the negative electrode by 1st Embodiment of this invention. It is sectional drawing which showed the structure of the negative electrode material by 1st Embodiment of this invention. It is the expanded sectional view which showed the surface vicinity of the Si particle along the 300-300 line of FIG. It is an expanded sectional view for demonstrating the pickling in the manufacturing process of the negative electrode material by 1st Embodiment of this invention. It is an expanded sectional view for demonstrating the heat processing in the manufacturing process of the negative electrode material by 1st Embodiment of this invention. It is the expanded sectional view which showed the structure of the negative electrode material by 2nd Embodiment of this invention. It is the table | surface which showed the data of the confirmation experiment performed in order to confirm the effect of this invention. It is the figure which showed the result of the X-ray diffraction performed in order to confirm the effect of this invention. It is the schematic diagram which showed the cross-sectional shape of the test material corresponding to the reference example 3 performed in order to confirm the effect of this invention. It is the schematic diagram which showed the distribution state of P in the test material corresponding to the reference example 3 performed in order to confirm the effect of this invention. It is the schematic diagram which showed the cross-sectional shape of the test material corresponding to the reference example 4 performed in order to confirm the effect of this invention. It is the schematic diagram which showed the distribution state of P in the test material corresponding to the reference example 4 performed in order to confirm the effect of this invention. It is the figure which showed the change of the discharge capacity with respect to the cycle number among the cycle characteristic measurement (discharge charge rate fixed) performed in order to confirm the effect of this invention. It is the figure which showed the change of the Coulomb efficiency with respect to the number of cycles among the cycle characteristic measurements (charge / discharge rate fixation) performed in order to confirm the effect of this invention. In the cycle characteristic measurement performed in order to confirm the effect of this invention, it is the figure which showed the change of the discharge capacity with respect to the cycle number at the time of changing a discharge rate.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
First, with reference to FIGS. 1-3, the structure of the negative electrode 100 by 1st Embodiment of this invention is demonstrated. The negative electrode 100 is an example of the “negative electrode for secondary battery” in the present invention.

  The negative electrode 100 according to the first embodiment of the present invention is a negative electrode used for a so-called lithium ion secondary battery (not shown), and as shown in FIG. 1, a current collector layer 10 and a current collector layer 10. And an active material layer 11 formed on one surface. The active material layer 11 may be formed not only on one surface of the current collector layer 10 but also on both surfaces. The current collector layer 10 is made of Cu foil (copper foil) or SUS foil (stainless steel foil). Here, when Cu foil is used as the current collector layer 10, while the electrical conductivity of the current collector layer 10 is improved, the mechanical strength of the Cu foil is low. As a result, the active material layer 11 is easily peeled off from the current collector layer 10. On the other hand, when the SUS foil is used as the current collector layer 10, the mechanical strength of the SUS foil is high, so that it resists the expansion and contraction of the Si particles 2 and hardly undergoes plastic deformation, but the electrical conductivity of the current collector layer 10. Decreases.

  The active material layer 11 is formed by spraying a plurality of negative electrode materials 1 (see FIG. 2) on the surface 10 a of the current collector layer 10. The negative electrode material 1 is an example of the “negative electrode material for secondary battery” in the present invention.

  Here, in the first embodiment, as shown in FIGS. 2 and 3, the negative electrode material 1 includes Si particles 2, a Ni—P plating layer 3 formed on the surface 2 a of the Si particles 2, and Si particles. 2 and a Ni—Si reaction layer 4 (see FIG. 3) formed at the interface 1 a between the Ni—P plating layer 3. The Ni—P plating layer 3 is an example of the “coating material” in the present invention, and the Ni—Si reaction layer 4 is an example of the “bonding layer” in the present invention.

The Si particles 2 are made of Si (silicon) and have a particle size of about 15 μm or less. Further, the surface 2a of the Si particle 2 is formed in a concavo-convex shape while the natural oxide film 5 (see FIG. 4) made of Si oxide (SiO ₂ ) as a ceramic is removed. As a result, the oxidation amount on the surface 2a of the Si particles 2 is reduced. In addition, part of P in the Ni—P plating layer 3 is diffused in the Si particles 2.

  The Ni-P plating layer 3 is mainly made of Ni (nickel) and contains P (phosphorus). The Ni—P plating layer 3 is formed on the surface 2a of the Si particle 2 so as to be distributed in an island shape, a dot shape, or a net shape.

  Further, in the first embodiment, the Ni—Si reaction layer 4 is mainly made of a Ni—Si alloy and contains a little P of the Ni—P plating layer 3. The Ni—Si reaction layer 4 is formed by diffusing a part of Si of the Si particles 2 toward the Ni—P plating layer 3 during heat treatment. Although Ni in the Ni—P plating layer 3 is also considered to slightly diffuse to the Si particle 2 side, the Ni diffusion rate is faster than the Ni diffusion rate, so that the Ni—Si reaction layer 4 includes the Si particles 2. The Ni-P plating layer 3 side of the interface 1a between the Ni-P plating layer 3 and the Ni-P plating layer 3 is substantially formed.

  The Ni—Si reaction layer 4 has a function of improving the adhesion between the Si particles 2 and the Ni—P plating layer 3. The thickness t1 of the Ni—Si reaction layer 4 is about 0.1 μm or more. The thickness t1 of the Ni—Si reaction layer 4 is an average of the thicknesses of the Ni—Si reaction layer 4 at a plurality of points that can be measured when the cross sections of the plurality of negative electrode materials 1 are observed.

  In addition, the Si particles 2 and the Ni—P plating layer 3 are joined to each other via the Ni—Si reaction layer 4 without the natural oxide film 5 interposed therebetween.

  In the first embodiment, the following effects can be obtained.

  In the first embodiment, as described above, the Ni—Si reaction layer 4 is included in the Si particles 2 by forming the Ni—Si reaction layer 4 at the interface 1 a between the Si particles 2 and the Ni—P plating layer 3. By including both Si and Ni contained in the Ni—P plating layer 3, the adhesion between the Si particles 2 and the Ni—Si reaction layer 4 can be improved, and the Ni—P plating layer 3 Adhesiveness with the Ni—Si reaction layer 4 can be improved. Thereby, since the adhesiveness of the Si particle 2 and the Ni-P plating layer 3 through the Ni-Si reaction layer 4 can be improved, the cycle characteristics of the negative electrode 100 using the negative electrode material 1 can be improved. it can.

  Moreover, in 1st Embodiment, while the Ni-Si reaction layer 4 mainly consists of Ni-Si alloys, while being able to make the adhesiveness of the Si particle 2 and the Ni-Si reaction layer 4 more favorable, Since the adhesion between the Ni—P plating layer 3 and the Ni—Si reaction layer 4 can be made better, the adhesion between the Si particles 2 and the Ni—P plating layer 3 through the Ni—Si reaction layer 4. Can be further improved.

  In the first embodiment, when the thickness t1 of the Ni—Si reaction layer 4 is set to about 0.1 μm or more, the Ni-Si reaction layer 4 has a small thickness, so that the Si particles 2 and the Ni— It can suppress that the adhesiveness with Si reaction layer 4, and the adhesiveness of Ni-P plating layer 3 and Ni-Si reaction layer 4 fall.

In the first embodiment, the Si particles 2 and the Ni—P plating layer 3 are combined with the Ni—Si reaction layer 4 without using the natural oxide film 5 of the Si particles 2 made of ceramics (oxide (SiO ₂ )). By bonding to each other via the Si, the Si (metalloid element) of the Si particles 2 and the Ni (metal element) of the Ni-P plating layer 3 can be brought into direct contact with each other. Thereby, compared with the case where it joins not only via the Ni-Si reaction layer 4 but the natural oxide film 5 which consists of ceramics, the Si particle 2 and the Ni-P plating layer 3 via the Ni-Si reaction layer 4 Adhesion can be further improved.

  In the first embodiment, the contact area between the Si particles 2 having the concavo-convex surface 2a and the Ni-P plating layer 3 can be increased by forming the surface 2a of the Si particle 2 in the concavo-convex shape. Therefore, the adhesion between the Si particles 2 and the Ni—P plating layer 3 can be effectively improved.

  Moreover, in 1st Embodiment, by diffusing a part of P of the Ni-P plating layer 3 in the Si particle 2, P diffused in the Si particle 2 becomes a dopant, so that the Si particle 2 Electrical conductivity can be improved. Thereby, since the electrical conductivity of the negative electrode 100 in which the negative electrode material 1 is used can be improved, the output characteristic of the negative electrode 100 can be improved.

  Next, with reference to FIGS. 2-5, the manufacturing process of the negative electrode material 1 and the negative electrode 100 by 1st Embodiment of this invention is demonstrated.

  First, Si particles (not shown) having various particle diameters are created by pulverizing a predetermined lump of Si. Then, Si particles 2 having a particle diameter of about 15 μm or less as shown in FIG. 2 are prepared by selecting Si particles 2 using a sieve having an opening of about 15 μm. At this time, it is possible to easily select the Si particles 2 as compared with the case where the Si particles 2 are limited to only fine particles having a particle diameter of about 1 μm or less. Thereafter, as shown in FIG. 4, the surface 2a of the Si particles 2 is pickled by chemical etching using hydrofluoric acid. Thereby, the natural oxide film 5 on the surface 2a of the Si particle 2 is removed, and a part of the surface 2a of the Si particle 2 is removed, so that the surface 2a of the Si particle 2 is formed in an uneven shape.

And the Ni-P plating layer 3 is formed in the surface 2a of the Si particle 2 using the electroless deposition (ELD) method which is a kind of plating process. Specifically, in a H ₂ SO ₄ aqueous solution in which NiSO ₄ .6H ₂ O is dissolved, a plurality of Si particles 2 from which the natural oxide film 5 has been removed, NaBH ₄ , NaH ₂ PO ₂ .H ₂ O, and , the addition of the _{Na 3 C 6 H 5 O 7} · 2H 2 O. Under the present circumstances, it adjusts so that the mass (content) of P in the Ni-P plating layer 3 may be about 2.0 mass%. And the electroless-plating process is performed by stirring the created solution under predetermined temperature. As a result, the Ni—P plating layer 3 containing about 2.0 mass% of P and Ni is formed on the surface 2 a of the Si particle 2 without the natural oxide film 5 interposed therebetween. Thereby, as shown in FIG. 2, the Ni-P plating layer 3 in which the surface 2a of the Si particle 2 is distributed in an island shape, a dot shape, or a net shape is formed. At this time, the Ni-P plating layer 3 is formed so that the mass (content) of the Ni-P plating layer 3 in the total mass of the Si particles 2 and the Ni-P plating layer 3 is about 5.0% by mass. To do.

  Here, in the manufacturing process of the first embodiment, as shown in FIG. 5, the Si particles 2 on which the Ni—P plating layer 3 is formed are in an inert gas (Ar) atmosphere and are generally 600 ° C. or higher. Heat treatment is performed for a predetermined time under a predetermined temperature condition of 1000 ° C. or lower. In addition, when performing heat processing on the temperature conditions of 1000 degreeC vicinity, in order to suppress the fall of the cycling characteristics resulting from excessive diffusion of Si of the Si particle 2, it is necessary to make heat processing time short ( For example, 10 minutes). Further, the temperature condition of the heat treatment is generally preferably 700 ° C. or higher and 900 ° C. or lower, and more preferably 750 ° C. or higher and 850 ° C. or lower, based on the measurement results of cycle characteristics in Examples described later. In particular, a temperature of about 800 ° C. is most preferable.

  By this heat treatment, Si in the Si particles 2 diffuses into the Ni—P plating layer 3 and P in the Ni—P plating layer 3 diffuses into the Si particles 2. As a result, Si and Ni react mainly on the Ni-P plating layer 3 side in the interface 1a between the Si particles 2 and the Ni-P plating layer 3, so that Ni--mainly composed of a Ni-Si alloy. Si reaction layer 4 is formed. As a result, the Si particles 2 and the Ni—P plating layer 3 are bonded to each other through the Ni—Si reaction layer 4 without the natural oxide film 5 by the heat treatment. In the Ni—Si reaction layer 4, P of the Ni—P plating layer 3 is also included. In this way, the negative electrode material 1 shown in FIGS. 2 and 3 is formed.

  Thereafter, a plurality of negative electrode materials 1 are sprayed onto the surface 10a of the current collector layer 10 at a predetermined gas pressure using an aerosol deposition method. Thereby, the active material layer 11 is formed on the surface 10a of the current collector layer 10, and the negative electrode 100 shown in FIG. 1 is formed.

  In the manufacturing process of the first embodiment, the following effects can be obtained.

  In the manufacturing process of the first embodiment, as described above, Si of the Si particles 2 can be diffused into the Ni-P plating layer 3 by the heat treatment. Therefore, Si and Ni are easily reacted to form the Si particles 2. The Ni—Si reaction layer 4 can be easily formed at the interface 1 a between the Ni—P plating layer 3 and the Ni—P plating layer 3.

  Further, in the manufacturing process of the first embodiment, Si of the Si particles 2 can be reliably diffused into the Ni-P plating layer 3 by performing heat treatment under a predetermined temperature condition of approximately 700 ° C. or more and 900 ° C. or less. Therefore, the Ni—Si reaction layer 4 can be reliably formed at the interface 1 a between the Si particles 2 and the Ni—P plating layer 3.

  In the manufacturing process of the first embodiment, not only Si of the Si particles 2 is diffused into the Ni—P plating layer 3 but also P of the Ni—P plating layer 3 is diffused into the Si particles 2 by heat treatment. Therefore, the electrical conductivity of the Si particles 2 can be easily improved while forming the Ni—Si reaction layer 4 at the interface 1a between the Si particles 2 and the Ni—P plating layer 3.

Further, in the manufacturing process of the first embodiment, the Ni—P plating layer 3 containing Ni having a content of about 2.0 mass% in the Ni—P plating layer 3 and Ni— Since the P plating layer 3 can contain Ni ₃ P having a crystal structure that can easily withstand the stress generated in the Si particles 2 of the negative electrode 100, the adhesion state between the Si particles 2 and the Ni—P plating layer 3 can be maintained for a long time. can do. In addition, since sufficient Ni can be secured in the Ni-P plating layer 3, the Ni-Si reaction layer 4 is formed by the reaction with Ni diffused in the Ni-P plating layer 3 by heat treatment. Even so, the electrical conductivity in the Ni-P plating layer 3 can be sufficiently ensured.

  In the manufacturing process of the first embodiment, the surface 2a of the Si particles 2 is pickled by chemical etching using hydrofluoric acid, thereby removing the natural oxide film 5 on the surface 2a of the Si particles 2. Then, a part of the Si particles 2 is removed, and the surface 2a of the Si particles 2 is formed in an uneven shape. Thereby, the natural oxide film 5 formed on the surface 2a of the Si particle 2 can be easily removed by etching as compared with polishing or the like. Further, since the surface 2a of the Si particles 2 can be formed into an uneven shape while removing the natural oxide film 5 by etching, a process for forming the surface 2a of the Si particles 2 into an uneven shape is not required. The manufacturing process of the negative electrode material 1 can be simplified.

(Second Embodiment)
Next, with reference to FIG. 6, the negative electrode material 201 by 2nd Embodiment of this invention is demonstrated. In the second embodiment, unlike the negative electrode material 1 of the first embodiment, a negative electrode material 201 from which the natural oxide film 5 is not removed will be described. The negative electrode material 201 is an example of the “negative electrode material for secondary battery” in the present invention.

As shown in FIG. 6, the negative electrode material 201 according to the second embodiment of the present invention is different from the negative electrode material 1 (see FIG. 3) of the first embodiment, and is a natural oxide made of Si oxide (SiO ₂ ). The Ni—P plating layer 3 is formed on the surface 202 a of the Si particle 202 on which the natural oxide film 5 is formed without removing the film 5. Further, a Ni—Si reaction layer 204 is formed mainly on the Ni—P plating layer 3 side in the interface 201 a between the Si particles 202 and the Ni—P plating layer 3. In the Ni—Si reaction layer 204, in the heat treatment, a part of Si of the Si particles 202 passes through a gap (not covering the Si particles 202) (not shown) of the natural oxide film 5 to form a Ni—P plating layer. It is formed by diffusing to 3. In addition, the other structure of 2nd Embodiment is the same as that of the said 1st Embodiment.

  Next, with reference to FIG. 6, the manufacturing process of the negative electrode material 201 by 2nd Embodiment of this invention is demonstrated.

  First, similarly to the first embodiment, Si particles 202 as shown in FIG. 2 are prepared. Thereafter, in the second embodiment, unlike the first embodiment, chemical etching using hydrofluoric acid is not performed. That is, the surface 202a of the Si particle 202 is not formed in an uneven shape. Then, the Ni—P plating layer 3 is formed on the surface 202a of the Si particles 202 by using an electroless deposition method. Then, heat treatment is performed on the Si particles 202 on which the Ni—P plating layer 3 has been formed in the same manner as in the first embodiment. Thereby, the Ni-Si reaction layer 204 is formed mainly on the Ni-P plating layer 3 side in the interface 201a between the Si particles 202 and the Ni-P plating layer 3. The other manufacturing processes of the second embodiment are the same as those of the first embodiment.

  In the second embodiment, the following effects can be obtained.

  In the second embodiment, as described above, the Ni—Si reaction layer 204 is formed at the interface 201 a between the Si particles 202 and the Ni—P plating layer 3, so that the Ni—Si reaction is the same as in the first embodiment. Since the adhesion between the Si particles 202 and the Ni—P plating layer 3 through the reaction layer 204 can be improved, the cycle characteristics of the negative electrode using the negative electrode material 201 can be improved.

  In the manufacturing process of the second embodiment, it is necessary to etch the Si particles 202 by forming the Ni-P plating layer 3 on the surface 202a of the Si particles 202 on which the natural oxide film 5 is formed. Therefore, the manufacturing process of the negative electrode material 201 can be simplified. The remaining effects of the second embodiment are similar to those of the aforementioned first embodiment.

[Example]
Next, with reference to FIGS. 7 to 15, a confirmation experiment performed for confirming the effect of the negative electrode material of the present invention will be described.

  In this confirmation experiment, as shown in FIG. 7, negative electrode materials of Examples 1 to 4, Reference Example 1, and Comparative Examples 1 and 2 were prepared. Here, as Example 1, a negative electrode material 201 from which the natural oxide film 5 corresponding to the second embodiment was not removed was prepared. Specifically, Si particles 202 having a size of 15 μm or less were prepared by sorting the Si particles 202 using a sieve having a mesh size of 15 μm. And without performing chemical etching (pickling) with respect to the Si particle 202, the Ni-P plating layer 3 was formed as it was using the electroless deposition (ELD) method. At this time, the Ni-P plating layer 3 was formed so that the mass (content) of the Ni-P plating layer 3 in the total mass of the Si particles 202 and the Ni-P plating layer 3 was 5.0% by mass. . Thereafter, the Si particles 202 on which the Ni—P plating layer 3 was formed were heat-treated for 1 hour under an inert gas (Ar) atmosphere and at a temperature of 600 ° C. As a result, the Ni—Si reaction layer 204 was formed at the interface 201 a between the Si particles 202 and the Ni—P plating layer 3. Thus, the negative electrode material 201 of Example 1 corresponding to the second embodiment was produced.

  In Example 2, a negative electrode material 201 of Example 2 corresponding to the second embodiment was produced in the same manner as in Example 1 except that the heat treatment was performed at 700 ° C. for 1 hour.

  In Example 3, a negative electrode material 201 of Example 3 corresponding to the second embodiment was produced in the same manner as in Example 1 except that the heat treatment was performed at 800 ° C. for 1 hour.

  In Example 4, before forming the Ni-P plating layer 3, the Si particles 2 were subjected to chemical etching (pickling) using hydrofluoric acid, and were subjected to heat treatment at 900 ° C. for 1 hour. A negative electrode material 1 of Example 4 corresponding to the first embodiment was produced in the same manner as Example 1 except for the above.

  In Reference Example 1, a negative electrode material 1 of Reference Example 1 corresponding to the first embodiment was produced in the same manner as in Example 4 except that the heat treatment was performed at 1000 ° C. for 1 hour.

  On the other hand, in Comparative Example 1, a negative electrode material of Comparative Example 1 was produced in the same manner as in Example 1 except that no heat treatment was performed. In Comparative Example 2, a negative electrode material of Comparative Example 2 was produced in the same manner as in Example 1 except that pickling and heat treatment were not performed.

(Composition measurement (ICP emission spectroscopy))
First, the compositions of the negative electrode materials of Examples 1 to 4, Reference Example 1, and Comparative Examples 1 and 2 were measured by ICP emission spectroscopy. Specifically, the negative electrode materials of Examples 1 to 4, Reference Example 1, and Comparative Examples 1 and 2 were each dissolved in a dilute acid aqueous solution to form a solution. Then, the atomized solution was introduced into Ar plasma. The composition of the negative electrode material was measured by dispersing the light generated at this time. Note that the Ni—Si alloy did not substantially melt in the dilute acid aqueous solution. That is, Ni and Si based on the Ni—Si alloy were not measured by the current ICP emission spectroscopic analysis.

  FIG. 7 shows the measurement results of ICP emission spectroscopy. In any of Examples 1 to 4 and Reference Example 1 in which heat treatment was performed, the mass% of Ni was smaller than in Comparative Examples 1 and 2 in which heat treatment was not performed. This is presumably because Ni and Si react to form Ni—Si alloy by heat treatment, thereby reducing detectable Ni. In Examples 1 to 4 and Reference Example 1 in which heat treatment was performed, the mass% of Ni became smaller as the heat treatment temperature was higher. That is, by raising the temperature of the heat treatment, it is considered that Ni and Si react to generate a Ni—Si alloy.

(Composition measurement (EDX, oxygen concentration measurement))
Next, the oxygen concentration on the surface of the Si particles before and after pickling in Comparative Example 2 was measured by EDX. Specifically, at any six points, the oxygen concentration on the surface of the Si particles before and after pickling was measured by EDX. And the oxygen concentration before pickling and after pickling was obtained by calculating the average of the obtained data.

  As an EDX measurement result, the average oxygen concentration before pickling was 1.6 mass%, and the average oxygen concentration after pickling was 0.3 mass%. Thereby, it can be confirmed that the oxygen concentration is reduced by 1.3% by mass before and after the pickling, and as a result, it can be estimated that the natural oxide film is sufficiently removed by the pickling.

(Composition measurement (X-ray diffraction))
Next, the surface states of the negative electrode materials of Examples 1 to 3, Reference Example 1 and Comparative Example 1 were observed by X-ray diffraction. Specifically, the presence or absence of Si, Ni and Ni ₃ P on the surface of the negative electrode material was measured. In X-ray diffraction, X is measured at angles (2θ) corresponding to the lattice planes (220) and (311) of Si, the lattice planes (111) and (200) of Ni, and the lattice plane (321) of Ni ₃ P, respectively. When the diffracted light of the line is detected, it is determined that Si, Ni or Ni ₃ P corresponding to the corresponding angle (2θ) has been detected.

  FIG. 8 shows the results of X-ray diffraction. Regarding Si, in all of Examples 1 to 3, Reference Example 1 and Comparative Example 1, a clear peak of diffracted light was detected. That is, it was confirmed that in any of Examples 1 to 3, Reference Example 1 and Comparative Example 1, Si particles were exposed on the surface of the negative electrode material. Thereby, it is considered that the Ni-P plating layer covers only a part of the surface of the Si particles.

On the other hand, with respect to Ni, the detected amount of Ni was lower in Example 3 where heat treatment was performed at 800 ° C. and Reference Example 1 where heat treatment was performed at 1000 ° C. than in Comparative Example 1, Examples 1 and 2. Further, in Example 2 where the heat treatment was performed at 700 ° C., the detected amount of Ni was slightly reduced compared to Example 1 where the heat treatment was performed at 600 ° C. Further, with respect to Ni ₃ P, in Example 3 and Reference Example 1, the detected amount of Ni ₃ P than Examples 1 and 2 were reduced. This is presumably because the amount of P in the Ni—P plating layer diffusing into the Si particles was increased by the heat treatment at 700 ° C. or higher. As a result, it is considered that the electrical conductivity in the Si particles can be improved by heat treatment at 700 ° C. or higher. Moreover, it is considered that the Ni—Si alloy was sufficiently formed in the Ni—P plating layer by the heat treatment at 800 ° C. or higher. On the other hand, it is considered that in the heat treatment at 600 ° C., Si did not sufficiently diffuse and a Ni—Si alloy was not formed so much in the Ni—P plating layer.

(Composition measurement (SEM-EDX, image observation))
Next, the cross-sectional shapes of Reference Examples 2 to 4 were observed by SEM-EDX. In this SEM-EDX measurement, it is difficult to actually measure the cross-section of the fine negative electrode material. Therefore, test materials of Reference Examples 2 to 4 corresponding to the negative electrode material of the first embodiment were prepared. Specifically, a Si wafer having a predetermined size was prepared. And after pickling, similarly to the said Example, the Ni-P plating layer was created on the surface of Si wafer so that it might become thickness of 8 micrometers using the electroless deposition method. And the test material of Reference Examples 2-4 was heat-processed for 1 hour on the temperature conditions of 600 degreeC, 700 degreeC, and 800 degreeC, respectively. Then, each test material was cut | disconnected and the cut | disconnected cross section was observed. At that time, the cross section was observed using SEM, and the distribution state of P in the cross section was observed using SEM-EDX. Here, in cross-sectional observation, the thickness of several Ni-Si reaction layers was measured, and the average of these was taken as the thickness of the Ni-Si reaction layer. Each point (dot) shown in FIGS. 10 and 12 indicates the distribution of P.

  As an observation result, in the test material of Reference Example 2, the Ni—P plating layer was peeled before the cross-sectional observation. Accordingly, it is considered that the Ni—Si reaction layer was not sufficiently formed at the interface between the Si wafer and the Ni—P plating layer in the test material of Reference Example 1 that was heat-treated at a temperature of 600 ° C. In the test material of Reference Example 2, since the Ni—P plating layer was peeled before the cross-section observation, the cross-section observation and the P distribution state were not observed.

  Moreover, in the cross-sectional observation of Reference Example 3 shown in FIG. 9, it was confirmed that a Ni—Si reaction layer was formed between the Si wafer and the Ni—P plating layer. The thickness of this Ni—Si reaction layer was about 0.5 μm on average. Further, in the distribution state of P in Reference Example 3 shown in FIG. 10 (the dots (dots in FIG. 10 indicate the distribution of P)), although P was mainly present in the Ni-P plating layer, It was confirmed that some diffused into the Si wafer and the Ni—Si reaction layer.

  Moreover, in the cross-sectional observation of Reference Example 4 shown in FIG. 11, it was confirmed that the Ni—Si reaction layer was clearly formed between the Si wafer and the Ni—P plating layer. The thickness of this Ni—Si reaction layer was about 2.0 μm on average. As a result, it was confirmed that the Ni—Si reaction layer was clearly formed with a sufficient thickness in Reference Example 4 as compared with Reference Example 3. Thus, it has been found that the Ni—Si reaction layer can be clearly formed with a sufficient thickness by increasing the temperature of the heat treatment. Further, in the distribution state of P in Reference Example 4 shown in FIG. 12 (the dots (dots in FIG. 12 indicate the distribution of P)), P was present substantially uniformly throughout. Thus, it has been found that by increasing the temperature of the heat treatment, P in the Ni—P plating layer can be diffused so as to be distributed over substantially the entire negative electrode material containing Si particles. In addition, it is thought that the result similar to the test material of the reference examples 2-4 which pickled each is obtained also in the negative electrode material of Examples 1-3 which is not pickled. That is, even when pickling is not performed, the Ni—Si reaction layer can be clearly formed with a sufficient thickness by increasing the temperature of the heat treatment, and P of the Ni—P plating layer is changed to Si particles. It is thought that it can be diffused so as to be distributed over substantially the whole of the negative electrode material containing.

(Cycle characteristics (fixed discharge rate))
Next, the cycle characteristics of the negative electrodes using the negative electrode materials of Examples 1 to 3, Reference Example 1 and Comparative Example 1 were measured. Specifically, the negative electrode materials of Examples 1 to 3, Reference Example 1 and Comparative Example 1 are each sprayed onto the surface of the current collector layer made of Cu foil at a predetermined gas pressure using the aerosol deposition method. Thus, negative electrodes of Examples 1 to 3, Reference Example 1 and Comparative Example 1 were prepared. Then, Examples 1 to 3, together with use of the negative electrode of Example 1 and Comparative Example 1, a lithium metal as a counter electrode (reference electrode), _LiN of 1M as an electrolytic solution _{(CF 3 SO 2) 2 (} LiTFSA) A secondary battery model (tripolar beaker cell) was prepared using propylene carbonate (PC). The cycle characteristics were measured by repeatedly charging and discharging the secondary battery model. Under the present circumstances, the discharge rate (current value of discharge charge) was fixed to 0.4C (1.44Ag < ^-1 >). As the cycle characteristics, changes in discharge capacity with respect to the number of cycles and changes in coulomb efficiency (discharge capacity / charge capacity) with respect to the number of cycles were measured.

  7 and 13 show measurement results of changes in discharge capacity with respect to the number of cycles, and FIG. 14 shows measurement results of changes in coulomb efficiency with respect to the number of cycles. In Examples 1 to 3 in which the negative electrode material was heat-treated, the discharge capacity increased in the number of cycles 50 times or more, as compared with Comparative Example 1 in which the negative electrode material was not heat-treated. In particular, in Examples 2 and 3, compared with Comparative Example 1, the discharge capacity increased regardless of the number of cycles. Further, in Examples 1 and 3, the Coulomb efficiency is increased regardless of the number of cycles as compared with Comparative Example 1, and in Example 2, compared with Comparative Example 1, in the initial cycle (up to about 50 times), Coulomb efficiency has increased.

  Thereby, in Examples 1-3, it has confirmed that the fall of the discharge capacity was suppressed. That is, it was found that the cycle characteristics can be improved by a heat treatment at 600 ° C. or higher and 800 ° C. or lower. In particular, it was found that in Example 3 where the heat treatment was performed at 800 ° C., the cycle characteristics were remarkably improved. As a result, it is more preferable to perform the heat treatment at 750 ° C. or more and 850 ° C. or less, and it is more preferable to perform the heat treatment at a temperature around 800 ° C. In addition, as a reason which cycling characteristics improved in Examples 1-3, even if it is a case where the expansion / contraction of Si particle | grains is repeated by repeating discharge and discharge, by the Ni-Si reaction layer formed by heat processing, This is probably because the adhesion between the Si particles and the Ni—P plating layer was improved, and the peeling of the Ni—P plating layer was suppressed. It was also confirmed that the Ni—P plating layer having high electrical conductivity fulfills the electrical conduction function (function as a conduction path) in the active material layer for a long period of time. Furthermore, the formed Ni—Si reaction layer is considered to have a function of facilitating insertion of Li ions into the Si particles.

On the other hand, in Reference Example 1 in which the negative electrode material was heat-treated at 1000 ° C., compared with Comparative Example 1, the discharge capacity and the Coulomb efficiency were reduced overall, and the cycle characteristics deteriorated. This is because the heat treatment at 1000 ° C. was performed for a long time, and the Ni—P plating layer of the negative electrode material was melted by the diffusion of Si, so that the Si concentration in the Ni—P plating layer became too high. This is thought to be because it became brittle. This can also be inferred from the result of X-ray diffraction shown in FIG. 8 (result that Ni and Ni ₃ P were not detected in Reference Example 1).

(Cycle characteristics (change charge / discharge rate))
Next, the cycle characteristics of the negative electrode using the negative electrode materials of Examples 1 to 3 and Comparative Example 1 when the discharge rate (discharge current value) was changed every 10 cycles were measured. At this time, the charge / discharge rate was repeatedly changed in the order of 0.4C, 1C, 2C, 5C and 10C every 10 cycles. And the change of the discharge capacity with respect to the number of cycles was measured.

  FIG. 15 shows the measurement result of the change in discharge capacity with respect to the number of cycles. Even in the case where the discharge rate is changed, in the first to third examples in which the negative electrode material is heat-treated as in the case where the discharge charge rate is fixed, as compared with Comparative Example 1 in which the negative electrode material is not heat-treated, as a whole As a result, the discharge capacity increased. In particular, in Examples 2 and 3, compared to Comparative Example 1, the discharge capacity increased regardless of the number of cycles and the discharge / charge rate.

  Thus, the cycle characteristics can be improved by heat treatment at 600 ° C. or higher and 800 ° C. or lower regardless of the charge / discharge rate, and the cycle characteristics can be further improved by heat treatment at 700 ° C. or higher and 800 ° C. or lower. found. As a result, not only for EVs that require a large output (current) but also a large output (current), a large discharge (charge) capacity is required, and also for HEV lithium secondary batteries that require a large output (current). A negative electrode using the negative electrode material of the invention is considered suitable.

  Further, it was found that even when the discharge rate was changed, the cycle characteristics were remarkably improved in Example 3 where the heat treatment was performed at 800 ° C. Also by this, it is more preferable to perform the heat treatment at 750 ° C. or more and 850 ° C. or less, and it is more preferable to perform the heat treatment at a temperature around 800 ° C.

  The embodiments and examples disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments and examples but by the scope of claims for patent, and includes all modifications within the meaning and scope equivalent to the scope of claims for patent.

  For example, in the first and second embodiments, the Ni—P plating layer has been shown to be distributed in the form of islands, dots, or nets on the surface of the Si particles. Not limited to. In the present invention, the Ni-P plating layer may be formed so as to cover the entire surface of the Si particles, or the surface of the Si particles may be exposed in some places while substantially covering the entire surface of the Si particles. It may be formed. In addition, since it is more difficult for the Ni-P plating layer to peel off due to the expansion and contraction of the Si particles, the Ni-P plating layer is distributed on the surface of the Si particles so as to be distributed in the form of islands, dots, or nets. preferable.

  Moreover, although the example which formed the Ni-P plating layer as a coating | covering material on the surface of Si particle was shown in the said 1st and 2nd embodiment, this invention is not limited to this. In the present invention, the covering material only needs to contain at least Ni.

  Moreover, in the said 1st and 2nd embodiment, although the example adjusted so that the mass of P in the Ni-P plating layer 3 might be about 2.0 mass% was shown, this invention is not limited to this. In the present invention, the mass of P in the Ni—P plating layer may be other than about 2.0 mass%. At this time, the mass of P in the Ni—P plating layer is preferably about 0.5 mass% or more and about 15 mass% or less.

  In the first embodiment, the surface 2a of the Si particle 2 is pickled by etching, thereby removing the natural oxide film 5 on the surface 2a of the Si particle 2 and removing a part of the Si particle 2. Although an example in which the surface 2a of the Si particle 2 is formed in an uneven shape has been shown, the present invention is not limited to this. In the present invention, by adjusting the etching conditions, the natural oxide film on the surface of the Si particles is removed, while the surface of the Si particles need not be formed in an uneven shape. In addition, by adjusting the etching conditions, the surface of the Si particles may be formed in an uneven shape without removing the natural oxide film on the surface of the Si particles.

  In the first and second embodiments, the example in which the mass of the Ni-P plating layer in the total mass of the Si particles and the Ni-P plating layer is about 5.0% by mass is shown. Is not limited to this. In the present invention, the mass of the Ni—P plating layer in the total mass is not limited to about 5.0 mass%. In addition, it is preferable that the mass of a Ni-P plating layer is about 0.1 mass% or more and about 20.0 mass% or less.

  In the manufacturing processes of the first and second embodiments, the active material layer is formed on the surface of the current collector layer by spraying a plurality of negative electrode materials on the surface of the current collector layer with a predetermined gas pressure. However, the present invention is not limited to this. In the present invention, for example, after a plurality of negative electrode materials are dispersed in a slurry, the slurry is applied to the surface of the current collector layer and dried, whereby the active material layer containing the negative electrode material on the surface of the current collector layer May be formed.

  In the manufacturing processes of the first and second embodiments, an example in which an active material layer is formed on the surface of the current collector layer by spraying a negative electrode material onto the surface of the current collector layer after performing heat treatment is shown. However, the present invention is not limited to this. In the present invention, before performing the heat treatment, after spraying a plurality of negative electrode materials on the surface of the current collector layer, or dispersing and dispersing a plurality of negative electrode materials in a slurry as described above The active material layer may be formed on the surface of the current collector layer by performing a heat treatment. Also by this manufacturing process, it is considered that a Ni—Si reaction layer is formed at the interface between the Si particles and the Ni—P plating layer, and the adhesion between the Si particles and the Ni—P plating layer is improved.

1,201 Negative electrode material (negative electrode material for secondary battery)
1a, 201a Interface 2 Si particle 2a (Si particle) surface 3 Ni-P plating layer (coating material)
4 Ni-Si reaction layer (bonding layer)
5 Natural oxide film 10 Current collector layer 11 Active material layer 100 Negative electrode (negative electrode for secondary battery)

Claims (13)

A secondary battery negative electrode material constituting an active material layer formed on a current collector layer of a secondary battery negative electrode,
Si particles,
A coating material containing at least Ni formed on the surface of the Si particles;
A negative electrode material for a secondary battery, comprising a bonding layer formed at an interface between the Si particles and the covering material and including at least Ni and Si.   The negative electrode material for a secondary battery according to claim 1, wherein the bonding layer includes a Ni—Si alloy.   The negative electrode material for a secondary battery according to claim 1, wherein the bonding layer has a thickness of 0.1 μm or more.   The negative electrode material for a secondary battery according to any one of claims 1 to 3, wherein the Si particles and the covering material are bonded to each other via the bonding layer without using a natural oxide film.   The negative electrode material for a secondary battery according to claim 1, wherein the surface of the Si particles is formed in an uneven shape. The covering material includes Ni and P,
The negative electrode material for a secondary battery according to claim 1, wherein P of the covering material is diffused in the Si particles. Forming a coating material containing at least Ni on the surface of the Si particles;
And a step of forming a bonding layer containing at least Ni and Si at an interface between the Si particles and the covering material by heat-treating the Si particles on which the covering material is formed. Manufacturing method.   In the step of forming the bonding layer, the bonding layer is formed at the interface between the Si particles and the coating material by heat-treating the Si particles on which the coating material is formed under a temperature condition of 700 ° C. or more and 900 ° C. or less. The manufacturing method of the negative electrode material for secondary batteries of Claim 7 including the process of forming. The step of forming the covering material includes the step of forming the covering material containing Ni and P on the surface of the Si particles,
The step of forming the bonding layer includes heat-treating the Si particles on which the coating material is formed, thereby forming the bonding layer containing a Ni-Si alloy at the interface between the Si particles and the coating material, The manufacturing method of the negative electrode material for secondary batteries of Claim 7 or 8 including the process of diffusing P of the said covering material in the said Si particle.   The step of forming the coating material containing Ni and P includes the step of forming the coating material made of Ni and P whose content in the coating material is 5% by mass or more and 15% by mass or less. Item 10. A method for producing a negative electrode material for a secondary battery according to Item 9. The step of forming the covering material includes a step of removing a natural oxide film formed on the surface of the Si particles by etching, and a contact between the Si particles and the covering material without passing through the natural oxide film. Forming the covering material on the surface of the Si particles so as to
The step of forming the bonding layer includes the bonding at the interface between the Si particles and the coating material such that the Si particles and the coating material are bonded to each other via the bonding layer without the natural oxide film. The manufacturing method of the negative electrode material for secondary batteries of any one of Claims 7-10 including the process of forming a layer.   The secondary battery according to claim 11, wherein the step of removing the natural oxide film by the etching includes a step of removing the natural oxide film by the etching and forming a surface of the Si particles in an uneven shape. Manufacturing method for negative electrode material. A current collector layer;
A negative electrode for a secondary battery comprising an active material layer formed on a surface of the current collector layer,
The active material layer is
Si particles,
A coating material containing at least Ni formed on the surface of the Si particles;
A secondary battery negative electrode comprising a secondary battery negative electrode material formed at an interface between the Si particles and the covering material and having a bonding layer containing at least Ni and Si.

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