Composite structures containing high capacity porous active materials constrained in shells
Provided are novel electrode material composite structures containing high capacity active materials formed into porous base structures. The structures also include shells that encapsulate these porous base structures. During lithiation of the active material, the shell mechanically constrains the porous base structure. The shell allows lithium ions to pass through but prevents electrolyte solvents from interacting with the encapsulated active material. In certain embodiments, the shell contains carbon, while the porous base structure contains silicon. Although silicon tends to swell during lithiation, the porosity of the base structure and/or void spaces inside the shell helps to accommodate this additional volume within the shell without breaking it or substantially increasing the overall size of the composite structure. This allows integration of the composite structures into various types of battery electrodes and cycling high capacity active materials without damaging the electrodes' internal structures and deteriorating cycling characteristics of batteries.
1. A method of fabricating an electrode for use in a lithium ion cell, the method comprising:
providing porous base structures comprising a high capacity active material; and
forming one or more shells over the porous base structures to encapsulate the high capacity active material of the porous base structures, the one or more shells mechanically constrain the porous base structure and allow passage of lithium ions through the one or more shells during lithiation and delithiation of the high capacity active material while substantially preventing one or more electrolyte solvents from interacting with the high capacity active material encapsulated within the one or more shells,
wherein a porosity of the porous base structure decreases during lithiation of the high capacity active material and increases during delithiation of the high capacity active material; and
wherein the porous base structures and the shell form composite structures that have forms selected from the group consisting of rods, tubes, and wires with high aspect ratios greater than about 4, and particles.
2. The method of claim 1 , further comprising:
mixing the porous base structures encapsulated in the one or more shells in a binder to form a slurry; and
coating the slurry onto a conductive substrate.
3. The method of claim 1 , wherein forming the one or more shells comprises attaching the porous base structures to a conductive substrate.
4. The method of claim 1 , wherein the porous base structures are provided on a conductive substrate.
5. The method of claim 4 , wherein a portion of the one or more shells forms a layer over the conductive substrate.
6. The method of claim 1 , further comprising, prior to providing the porous base structures, forming the porous base structures by reducing fumed silica at a temperature of less than about 700° C.
7. The method of fabricating the electrode of claim 1 , further comprising, prior to providing the porous base structures, forming the porous base structures by etching silicon structures.
8. The method of fabricating the electrode of claim 1 , further comprising, prior to providing the porous base structures, forming the porous base structures from metallurgical grade silicon.
9. The method of fabricating the electrode of claim 1 , wherein forming the one or more shells comprises chemical vapor deposition of a carbon-containing material on the porous base structures.
10. The method of fabricating the electrode of claim 1 , wherein forming the one or more shells comprises carbonizing a polymer precursor.