In APL-Materials Paper, Researchers Show how to Keep Cathode Material ‘In Line’ to Enhance Performance
From the Journal: APL Materials
WASHINGTON D.C. Nov. 19, 2013 — The ever-increasing market for portable electronic devices such as laptops, cell phones and MP3 players has resulted in an equally heavy demand for secondary batteries — more commonly known as rechargeable batteries — Lithium-ion (Li-ion) being among the most popular.
Scientists and engineers worldwide are seeking ways to improve the power density, durability and overall performance of Lithium-ion batteries, and in a recent paper in the AIP Publishing journal APL Materials, Japanese researchers from a public-private team report an advance in Li-ion battery technology that they describe as a major breakthrough. They fabricated a cathode (positive electrode) of lithium cobalt oxide (LiCoO2) in which the compound’s individual grains are aligned in a specific orientation. The researchers claim that this yields a significantly higher-performing battery than one with a randomly-oriented LiCoO2 cathode.
Primary, or non-rechargeable, batteries and secondary batteries both produce current through an electrochemical reaction involving a cathode, an anode, and an electrolyte (an ion-conducting material). However, apply an outside current to a secondary battery and the negative-to-positive electron flow that occurs during discharge is reversed. This allows the battery to restore lost charge.
“In a lithium-ion battery, lithium ions move from the anode to the cathode during discharge and back when charging,” said Tohru Suzuki, a co-author on the APL Materials paper. “The material in the cathode has a layered structure to facilitate intercalation [insertion] of the lithium ions; if the structure is oriented in a specific fashion, the lithium ions have better access to the lattice and, in turn, charge-discharge performance is improved.”
Using a rotating magnetic field, the researchers were able to fabricate the ideal textured microstructure of the individual LiCoO2 grains making up the cathode: a perpendicular alignment of the c-plane (the vertical side) and a random orientation of the c-axis. Unlike cathodes where the microstructures in both the c-plane and c-axis are randomly oriented, the specialized grains allow easy access for lithium ions while relaxing the stress associated with intercalation.
“This yields a highly efficient flow of electrons in both directions,” Suzuki said.
Hideto Yamada, Tohru S. Suzuki, Tetsuo Uchikoshi, Masato Hozumi, Toshiya Saito and Yoshio Sakka
The National Institute for Materials Science (Tsukuba, Japan), the NIMS-Toyota Materials Center of Excellence for Sustainable Mobility (Tsukuba, Japan) and Toyota Motor Corporation’s Higashifuji Technical Center (Susono, Japan)