Active materials comprising secondary active-material structures for high rate battery applications and methods of fabricating such active materials
Described herein are active materials for use in negative electrodes of lithium-ion electrochemical cells as well methods of forming such active materials. In some examples, an active material comprises secondary active-material structures, each formed by physical or chemical attachment of multiple primary active-material structures. These primary active-material structures can comprise one of silicon, silicon oxide, tin, tin oxides, germanium, metal, and silicide, and each structure can have a size of between 5 nanometers and 30 micrometers. The small size of the primary active-material structures helps to maintain the mechanical stability of these structures as well as of the secondary active-material structures during battery cycling. Furthermore, these specific arrangements of the primary active-material structures support high charge-discharge rates. Some of the secondary active-material structures can be joined with other such structures, e.g., forming a network of the structures. An active material can be a powder and incorporated into slurries.
1 . An active material for use in negative electrodes of lithium-ion electrochemical cells, the active material comprising:
secondary active-material structures, each formed by physical or chemical attachment of multiple primary active-material structures using attachment entities, wherein:
each of the primary active-material structures has an average size of between 5 nanometers and 30 micrometers,
each of the primary active-material structures has a core-shell structure formed by a core, comprising graphite, and a shell, comprising silicon,
the secondary active-material structures are at least 10 times larger than the primary active-material structures,
at least some of the secondary active-material structures are disjoined from each other,
the attachment entities comprise a metal forming a metal silicide at interfaces with the primary active-material structures, and
each of the secondary active-material structures has a porosity greater than 1%.
2 . The active material of claim 1 , wherein a surface area of each of the secondary active-material structures is less than a combined surface area of individual ones of the multiple primary active-material structures, forming each of the secondary active-material structures, by at least 5%.
3 . The active material of claim 1 , further comprising interconnecting structures, wherein each of the interconnecting structures is connected to two or more of the secondary active-material structures forming an interconnected network.
4 . The active material of claim 3 , wherein the interconnecting structures comprises one or more of carbon, silicide, metal, and a metal alloy.
5 . The active material of claim 3 , wherein the interconnecting structures have a shape of a 3-D network.
6 . The active material of claim 3 , wherein the interconnecting structures have a shape of a 2-D film wrapping around the secondary active-material structures.
7 . The active material of claim 3 , wherein the interconnecting structures are physically or chemically attached to an exterior of at least some of the secondary active-material structures.
8 . The active material of claim 5 , wherein the interconnecting structures extend inside at least some of the secondary active-material structures.
9 . The active material of claim 5 , wherein:
the interconnecting structures are attached to the secondary active-material structures using adhesive entities, bound to both the interconnecting structures and the secondary active-material structures,
each of the adhesive entities comprises both hydrophilic functional groups and hydrophobic functional groups.
10 . The active material of claim 9 , wherein the adhesive entities comprises one or more of sodium dodecyl sulfate, sodium stearate, octaethylene glycol monododecyl ether, abietic acid, benzalkonium chloride, cetrimonium bromide, cetrimonium chloride, cetrimonium hexafluorophosphate, aluminum isopropoxide, decyltrimethoxysilane, Perfluorooctanesulfonic acid, lignosulfonates, titanium triisostearoylisopropoxide, Isopropoxyaluminum distearate, octylphenoxypolyethoxyethanol, or 2-(4-(2,4,4-trimethylpentan-2-yl)phenoxy) ethanol.
11 . The active material of claim 1 , wherein the active material is a powder form or a slurry form.
12 . The active material of claim 1 , wherein each of the secondary active-material structures has an average size greater than 5 micrometers.
13 . The active material of claim 1 , wherein each of the secondary active-material structures has a porosity greater than 10%.
14 . The active material of claim 1 , wherein each of the secondary active-material structures has a porosity greater than 20%.
15 . The active material of claim 1 , wherein each of the secondary active-material structures has a porosity greater than 30%.
16 . The active material of claim 1 , wherein a portion of a total surface of the secondary active-material structures formed by silicon is at least about 10%.
17 . The active material of claim 1 , wherein a portion of a total surface of the secondary active-material structures formed by silicon is at least about 50%.