Energy storage material and method of producing the same
The instant invention includes a spherical porous secondary silicon-based particle and methods for producing the same. The spherical porous secondary silicon-based particle is comprised of agglomerated primary silicon-based nanoparticles. The secondary particle comprises a carbon coating that reduces the effective exposed surface area of the primary particles to the electrolyte, thus improving first cycle efficiency. The secondary particle further comprises porous regions that enable the silicon nanoparticles to expand during lithiation. Advantages include ease of castability with micron-sized spherical particles, ease of mixing spherical particles, ease of flow for spherical particles in various processing steps, and ease with obtaining higher loading, which translates to higher areal capacity and overall energy density of the cell. A readily scalable process for producing the particles using low-cost materials and low-cost processing methods is disclosed.
1. A method for making a spherical particle of primary silicon nanoparticles, an internal void space, and an external carbon coating, comprising the steps of:
a. dispersing SiO (2-x) nano-particles, wherein X=0 to 2, and a pore former, in a liquid to form a liquid mixture;
b. spraying the liquid mixture to form spherical droplets;
c. freeze-drying the mixture to form spherical agglomerates of the SiO (2-x) nanoparticles;
d. forming void spaces within the agglomerated nanoparticles;
e. lowering the pressure and sublimating the liquid;
f. coating the agglomerates with carbon; and
g. chemically reducing the carbon-coated SiO (2-x) nanoparticles to SiO (2-y) , where y is greater than x;
wherein the pore former comprises a water soluble salt.
2. The method according to claim 1 , wherein the agglomerated spherical nanoparticles have a diameter of less than 100 microns.
3. The method according to claim 1 , wherein the void space comprises 30% to 70% by volume of the nanoparticles.
4. The method according to claim 1 , wherein a carbon content of the agglomerated spherical nanoparticles is between 10% and 50% by mass.