New lithium battery design charges up

From Boston, at the fall meeting of the Materials Research Society.

Millions of laptops and cell phones get their power from rechargeable lithium-ion batteries.

With all that power in a small, lightweight package, such batteries might also run the cars of the future. Yet current batteries require expensive control circuitry to prevent their highly reactive components from causing fires or explosions. Since larger batteries would contain more of this reactive material, they’d pose even greater risk.

Many research groups are trying to improve the safety and power of lithium-ion batteries by changing the batteries’ internal conductive fluids, or electrolytes, and electrodes (SN: 2/12/00, p. 103: Stopping batteries from starting fires). Now, one team has come up with a new family of materials for the battery’s negative electrode.

Conventional anodes are made of graphite, or sheets of carbon. Lithium ions pass in and out between them as a battery charges and discharges. When fully charged, the system requires an electronic safety switch to ensure stability.

Scientists have tried to replace the lithium-loaded carbon electrode with a less dangerous, less reactive material, such as aluminum, tin, or silicon, reports Michael M. Thackeray of Argonne (Ill.) National Laboratory. Yet the crystal structure of each material expands and contracts significantly during charging and discharging, thereby damaging the electrode’s structure and making it difficult for the lithium ions to make efficient round trips.

Thackeray and his colleagues have developed lithium-based anodes that contain two other elements, for example, copper and tin, he says. The anodes assume crystal structures that don’t change much during charge-discharge cycles, and they contain spaces in their crystal lattice that accommodate the flow of lithium ions. These materials could remove the need for expensive safety swithes in lithium-ion batteries, says Thackeray.