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Thin Film Lithium-Ion Batteries

New inorganic anode materials recently discovered at ORNL have enabled the development of thin film lithium ion batteries that can survive temperatures up to at least 250°C. This allows thin film batteries to be incorporated into integrated circuits by the solder reflow process.

The nitride and oxynitride anode films 0.01 to 1 µm thick are deposited by magnetron sputtering. During battery charge, the lithium provided by the cathode (typically LiCoO₂) reacts with the anode material producing conductive nanocrystalline Li-Sn alloy particles embedded in an amorphous matrix. A fraction of the Li from the cathode is irreversibly comsumed in the formation of the amorphous matrix phase. This irreversible loss is minimized by reducing the anode film thickness and the N content of the film.

Li-ion anode materials:

• "SiTON," a silicon-tin oxynitride (SiSn_0.9ON_1.9) is deposited by rf magnetron sputtering of SnO₂-SiO₂ in N₂.
• SnN_x (0 £ x £ 1.33) is deposited by reactive sputtering of Sn in an Ar + N₂ gas mixture. Composition by RBS.
• InN_x (0 £ x £ 1) is deposited by reactive sputtering of In in an Ar + N₂ gas mixture.

SiTON Li-ion batteries

Discharge of a SiTON-LiCoO₂ battery before and after heating at 250°C in air for 10 min. The 1 cm² battery has a 500Å thick SiTON anode and a 6000Å thick LiCoO₂ cathode.

Discharge of a SiTON-LiCoO₂ battery at different current densities following a 250°C heat treatment. The specific capacity of the SiTON film exceeds 1000 mAh/g at 1 mA/cm². The cathode (6000Å) and anode (500Å) films are balanced to maximize the cell potential.

Discharge capacity vs. cycle number for a SiTON-LiCoO₂ cell. Blue points: 3.9 V - 2.7 V; red points: 4.1 V - 2.7 V. The anode is 100Å x 1cm²; the cathode is 2000Å x 1cm². Specific capacity based on the mass of the anode.

SnN_x Lithium-ion batteries

Discharge profiles of batteries with a LiCoO₂ cathode 1 cm² x 1 µm thick. The capacity loss for the Li-ion anode films is minimized by using a subnitride composition and supersaturating the anode with Li. For the SnN_0.5 anode, 10 µAh of the capacity is due to reversible plating of metallic Li at the anode. Batteries with a SnN_x anode can be discharged at high current densities (dashed curve).

Cycle stability of selected SnN_x-LiCoO₂ batteries. All were discharged 4.2 to 2.7V at 1 mA/cm², except for the SnN_0.9 battery which was discharged to 2.0V at 10 mA/cm². The capacities are normalized to a 1 µm thick cathode.

Properties or Battery Home

Date revised - 3/21/00 (njd)

http://www.ssd.ornl.gov/BatteryWeb/Lithium-ion.html