Systems, methods and compositions to produce fine powders are described. These include forming a hypereutectic melt including a target material, a sacrificial-matrix material, and an impurity, rapidly cooling the hypereutectic melt to form a hypereutectic alloy having a first phase and a second phase, annealing the hypereutectic alloy to alter a morphology of the target material to thereby produce target particles, and removing the sacrificial matrix to thereby produce a fine powder of the target particles. The first phase is defined by the target material and the second phase is defined by the sacrificial-matrix material. The sacrificial-matrix material forms a sacrificial matrix having the target material dispersed therethrough.

Disclosed are a silicon-aluminum alloy and its preparation method. The method comprises: adding aluminum metal or molten aluminum into a container, wherein the temperature of the molten aluminum is between 700° C. and 800° C.; adding a semi-metallic silicon raw material to the molten aluminum, closing a furnace cover, carrying out vacuumization, and introducing argon, to ensure that the interior of a magnetic induction furnace is in a positive-pressure state, and stirring the aluminum metal or molten aluminum with a graphite stirring head; powering on and heating so that the aluminum metal or molten aluminum is heated to 1000° C. or above and molten, and holding the temperature between 1000° C. and 1500° C.; and after alloying is completed, cooling the molten aluminum to 1000° C. or below, opening the furnace cover, pouring the silicon-aluminum alloy into a corresponding mold, and cooling for molding.

Disclosed are a silicon-aluminum alloy and its preparation method. The method comprises: adding aluminum metal or molten aluminum into a container, wherein the temperature of the molten aluminum is between 700° C. and 800° C.; adding a semi-metallic silicon raw material to the molten aluminum, closing a furnace cover, carrying out vacuumization, and introducing argon, to ensure that the interior of a magnetic induction furnace is in a positive-pressure state, and stirring the aluminum metal or molten aluminum with a graphite stirring head; powering on and heating so that the aluminum metal or molten aluminum is heated to 1000° C. or above and molten, and holding the temperature between 1000° C. and 1500° C.; and after alloying is completed, cooling the molten aluminum to 1000° C. or below, opening the furnace cover, pouring the silicon-aluminum alloy into a corresponding mold, and cooling for molding.

Methods for producing nanostructures from copper-based catalysts on porous substrates, particularly silicon nanowires on carbon-based substrates for use as battery active materials, are provided. Related compositions are also described. In addition, novel methods for production of copper-based catalyst particles are provided. Methods for producing nanostructures from catalyst particles that comprise a gold shell and a core that does not include gold are also provided.

Methods for producing nanostructures from copper-based catalysts on porous substrates, particularly silicon nanowires on carbon-based substrates for use as battery active materials, are provided. Related compositions are also described. In addition, novel methods for production of copper-based catalyst particles are provided. Methods for producing nanostructures from catalyst particles that comprise a gold shell and a core that does not include gold are also provided.

Disclosed is a process for producing graphene-semiconductor nanowire hybrid material, comprising: (A) preparing a catalyst metal-coated mixture mass, which includes mixing graphene sheets with micron or sub-micron scaled semiconductor particles to form a mixture and depositing a nano-scaled catalytic metal onto surfaces of the graphene sheets and/or semiconductor particles; and (B) exposing the catalyst metal-coated mixture mass to a high temperature environment (preferably from 100° C. to 2,500° C.) for a period of time sufficient to enable a catalytic metal-catalyzed growth of multiple semiconductor nanowires using the semiconductor particles as a feed material to form the graphene-semiconductor nanowire hybrid material composition. An optional etching or separating procedure may be conducted to remove catalytic metal or graphene from the semiconductor nanowires.

Disclosed is a process for producing graphene-semiconductor nanowire hybrid material, comprising: (A) preparing a catalyst metal-coated mixture mass, which includes mixing graphene sheets with micron or sub-micron scaled semiconductor particles to form a mixture and depositing a nano-scaled catalytic metal onto surfaces of the graphene sheets and/or semiconductor particles; and (B) exposing the catalyst metal-coated mixture mass to a high temperature environment (preferably from 100° C. to 2,500° C.) for a period of time sufficient to enable a catalytic metal-catalyzed growth of multiple semiconductor nanowires using the semiconductor particles as a feed material to form the graphene-semiconductor nanowire hybrid material composition. An optional etching or separating procedure may be conducted to remove catalytic metal or graphene from the semiconductor nanowires.

A method for manufacturing a negative electrode active material includes: an alloying step of causing an Na source and an Si source to react to produce an Na—Si alloy containing Na and Si; and a silicon clathrate production step of heating the Na—Si alloy and reducing an amount of Na in the Na—Si alloy to produce a type-II silicon clathrate. Porous Si with a BET specific surface area of 20 m.sup.2/g or more is used as the Si source.

A method for manufacturing a negative electrode active material includes: an alloying step of causing an Na source and an Si source to react to produce an Na—Si alloy containing Na and Si; and a silicon clathrate production step of heating the Na—Si alloy and reducing an amount of Na in the Na—Si alloy to produce a type-II silicon clathrate. Porous Si with a BET specific surface area of 20 m.sup.2/g or more is used as the Si source.

A main object of the present disclosure is to provide an active material wherein a volume variation due to charge/discharge is small. The present disclosure achieves the object by providing an active material comprising a silicon clathrate II type crystal phase, including a void inside a primary particle, and a void amount A of the void with a fine pore diameter of 100 nm or less is more than 0.15 cc/g and 0.40 cc/g or less.