| 摘要 |
The gravimetric and volumetric efficiency of lithium ion batteries may be increased if higher capacity materials like tin and silicon are substituted for carbon as the lithium-accepting host in the negative electrode of the battery. But both tin and silicon, when fully charged with lithium, undergo expansions of up to 300% and generate appreciable internal stresses. These internal stresses, which will develop on each discharge-charge cycle, may lead to a progressive reduction in battery capacity, also known as battery fade. The effects of the internal stresses may be significantly reduced by partially embedding tin or silicon nanowires in the current collector. Additional benefit may be obtained if a 5 to 50% portion of the nanowire length at its embedded end are coated or masked with a composition which impedes lithium diffusion. Methods for embedding and masking the nanowires are described. |
| 主权项 |
1. A method of fabricating a negative electrode for a lithium-ion battery, the electrode comprising a plurality of upstanding nanowires of a lithium-accepting composition, each embedded, at a lower end portion, in a metal current collector, the embedding of the end portions of the nanowires in the metal current collector structure of the electrode serving to reduce the stresses resulting from the expansion of the nanowires during diffusion of lithium into the lithium-accepting composition during charging of the battery, the method comprising the steps of:
preparing a surface of the metal current collector to accommodate the embedded end portions of a preselected density of nanowires of the lithium-accepting composition by masking the surface of the current collector with a removable mask adapted to bar access to the metal collector surface except at a plurality of generally circular openings in the mask, the density of the mask openings being equal to, or greater than, the preselected nanowire density; then etching the surface of the current collector with a suitable etchant for a predetermined time through the openings in the removable mask, the etchant and mask cooperating to create, at each mask opening, a cavity of suitable depth for the end portions of the nanowire, each cavity extending part-way through the current collector to produce, on the surface of the current collector, a plurality of such cavities; depositing a metal catalyst within the cavities by chemical or physical vapor deposition, the catalyst being a particle or a nanometer cluster, the catalyst being selected and adapted to promote growth of the nanowires of the lithium-accepting composition; removing the mask and growing nanowires of the lithium-accepting negative electrode composition from the catalyst particles by physical or vapor deposition, an end portion of the nanowires being anchored in the cavity and embedded in the current collector; and continuing to grow the nanowires until they extend above the surface of the current collector and achieve a predetermined length above the surface of the current collector. |
