Several modifications of the basic design of carbon lithium-intercalating anodes with copper current collectors in rechargeable lithium-ion electrochemical cells have been proposed. These modifications are intended to prevent or at least retard the internal short-circuiting and consequent premature failure that can be caused by lithium dendrite and copper dendrite.
A rechargeable lithium-ion electrochemical cell that contains a carbon anode with a copper current collector is susceptible to internal short-circuiting by either or both of two mechanisms: (1) During overcharge, lithium dendrites can grow to form conductive anode-to-cathode bridges. (2) During overdischarge, the copper current collector becomes dissolved and copper becomes redeposited elsewhere, forming a conductive anode-to-cathode bridge. In experimental cells that have become short-circuited, lithium dendrites have been found to grow on the anode tabs (which are parts of the copper current collectors), and copper deposits have been found to grow in the separators adjacent to the anode tabs.
One of the proposed modifications is to cover each anode tab, which directly faces the cathode active material, with active carbon anode material (see figure). The carbon covering would prevent direct exposure of the copper tab material to the active cathode material. The carbon covering would reduce the lithium activity at the surface of the tab sufficiently to prevent the deposition of lithium there. Another proposed modification is to orient the cathode separator pores perpendicular to the anode separator pores.
This work was done by Chen-Kuo Huang of Caltech for NASA's Jet Propulsion Laboratory.
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Refer to NPO-19966