Interconnected hollow nanostructures containing high capacity active materials for use in rechargeable batteries
Provided are electrode layers for use in rechargeable batteries, such as lithium ion batteries, and related fabrication techniques. These electrode layers have interconnected hollow nanostructures that contain high capacity electrochemically active materials, such as silicon, tin, and germanium. In certain embodiments, a fabrication technique involves forming a nanoscale coating around multiple template structures and at least partially removing and/or shrinking these structures to form hollow cavities. These cavities provide space for the active materials of the nanostructures to swell into during battery cycling. This design helps to reduce the risk of pulverization and to maintain electrical contacts among the nanostructures. It also provides a very high surface area available ionic communication with the electrolyte. The nanostructures have nanoscale shells but may be substantially larger in other dimensions. Nanostructures can be interconnected during forming the nanoscale coating, when the coating formed around two nearby template structures overlap.
1. A method for preparing an electrode layer of interconnected hollow nanostructures containing a high capacity electrochemically active material, the method comprising:
receiving a template comprising template structures; forming a nanoscale coating of the high capacity material around the template structures; and
at least partially removing and/or shrinking the template to form the electrode layer of the interconnected hollow nanostructures comprising the high capacity active material, wherein forming the nanoscale coating of the high capacity materials around the template comprises:
an initial deposition stage performed at initial process conditions, wherein no substantial shape distortions of the template occur during the initial deposition stage; and
a bulk deposition stage performed at bulk process conditions that are different from the initial process conditions and configured to provide a higher deposition rate of the nanoscale coating during the bulk deposition stage.
2. The method of claim 1 , wherein receiving the template comprises electrospinning a polymeric material to form template nanofibers having a length of at least about 5 micrometers.
3. The method of claim 1 , wherein the template comprises one or more polymeric materials selected from the group consisting of poly-acrylic nitrides (PAN), nylons, polyethylenes, polyethylene oxides, polyethylene terephthalates, polystyrenes, and polyvinyls.
4. The method of claim 1 , wherein the template is formed as a layer having a thickness of between about 10 micrometer and 150 micrometers and a porosity of between about 20% and 80%.
5. The method of claim 1 , further comprising pre-treating the template by compressing the template, thermally stabilizing the template, and/or carbonizing the template.
6. The method of claim 1 , further comprising:
heating the template in an argon atmosphere to between about 150° C. and 250° C. for at least about 2 hours.
7. The method of claim 1 , further comprising forming a nanoscale substrate coating of the high capacity materials over a conductive substrate surface adjacent to the template, wherein the nanoscale template coating and the nanoscale substrate coating partially overlap to interconnect the conductive substrate and the interconnected hollow nanostructures.
8. The method of claim 1 , wherein at least some removal or shrinking of the template occurs during forming the nanoscale coating of the high capacity material around the template structures.
9. The method of claim 1 , wherein partially removing or shrinking the template comprises one or more operations selected from the group consisting of burning the template at a temperature of at least about 300° C. in presence of an oxidant, chemical etching the template, and annealing the template.
10. The method of claim 1 , further comprising forming a second coating over the interconnected hollow nanostructures, the second coating is configured to increase an electronic conductivity of the electrode layer, improve solid electrolyte interphase (SEI) characteristics of the electrode layer, and/or to limit structural changes of the interconnected hollow nanostructures.
11. The method of claim 1 , wherein the template is at least partially removed.