Method of Fabricating Fibres Composed of Silicon or a Silicon-Based Material and Their Use in Lithium Rechargeable Batteries

Abstract

A method of fabricating fibres of silicon or silicon-based material comprises the steps of etching pillars on a substrate and detaching them. A battery anode can then be created by using the fibres as the active material in a composite anode electrode.

1 . A method of fabricating a porous structure comprising a felt of fibers of silicon material, the method comprising:
 providing a slurry of the fibers and a binder in a solvent;   depositing the slurry on a substrate; and   allowing the solvent to evaporate.   
     
     
         2 . A method as claimed in  claim 1 , wherein the fibers have transverse dimensions in the range 0.08 to 0.5 microns and lengths in the range 20 to 300 microns. 
     
     
         3 . A method as claimed in  claim 2  in which the silicon material is undoped silicon or doped silicon. 
     
     
         4 . A method as claimed in  claim 3 , wherein the fibers are single crystal fibers. 
     
     
         5 . A method as claimed in  claim 2 , wherein the fibers have aspect ratios of greater than 40:1. 
     
     
         6 . A method as claimed in  claim 1 , wherein the fibers are made by a method comprising etching a substrate comprising the silicon material to form a plurality of pillars; and detaching the pillars from the substrate to form the fibers. 
     
     
         7 . An anode for a lithium-ion battery comprising:
 a current collector;   a porous structure comprising a felt of fibers of silicon material disposed on and in electrical contact with the current collector, the felt comprising a disorded non-woven mat of the fibers of silicon material, the fibers of silicon material having transverse dimensions in the range 0.08 to 0.5 microns and lengths in the range 20 to 300 microns.   
     
     
         8 . An anode as claimed in  claim 7 , wherein the silicon material is undoped silicon or doped silicon. 
     
     
         9 . An anode as claimed in  claim 8 , wherein the fibers are single crystal fibers. 
     
     
         10 . An anode as claimed in  claim 7 , wherein the fibers are fabricated by a method according to  claim 2 . 
     
     
         11 . An anode as claimed in  claim 7 , wherein the porous felt has a percentage pore volume of about 10-30 percent. 
     
     
         12 . An anode as claimed in  claim 7 , wherein the disordered non-woven mat comprises a plurality of welds, each at an intersection between fibers. 
     
     
         13 . An anode as claimed in  claim 7 , wherein the porous structure further comprises a binder, an electronic additive, or both. 
     
     
         14 . An anode as claimed in  claim 13 , wherein the mass of the fibers in the porous structure is between 70 percent and 95 percent of the mass of the porous structure. 
     
     
         15 . A method for making an anode as claimed in  claim 13 , the method comprising depositing a slurry containing the fibers and the binder, the electronic additive or both in a solvent on a current collector, and allowing the solvent to evaporate. 
     
     
         16 . An electrochemical cell comprising:
 an anode comprising a porous structure comprising a felt of fibers of silicon material disposed on and in electrical contact with the current collector, the felt comprising a disorded non-woven mat of the fibers of silicon material, the fibers of silicon material having transverse dimensions in the range 0.08 to 0.5 microns and lengths in the range 20 to 300 microns;   a cathode comprising a lithium-containing compound capable of releasing and reabsorbing lithium ions as its active material;   an electrolyte disposed between and in contact with the anode and the cathode, and in the pores of the porous structure of the anode.   
     
     
         17 . An electrochemical cell as claimed in  claim 16 , wherein the cathode comprises lithium-based metal oxide or phosphate as its active material. 
     
     
         18 . An electrochemical cell as claimed in  claim 16 , wherein the porous structure further comprises a binder, an electronic additive, or both.