Composite Electrodes for Rechargeable Lithium-Ion Batteries

Electrode compositions of this type are receiving worldwide attention. Such electrodes offer superior cost and safety features over state-of-the-art LiCoO₂ electrodes that power conventional lithium-ion batteries. Moreover, they demonstrate outstanding cycling stability and can be charged and discharged at high rates, making them excellent candidates to replace LiCoO₂ for consumer electronic applications and hybrid electric vehicles.

In Argonne's patented technology, the electrodes are defined as having composite xLi₂M'O₃·(1-x)LiMO₂ structures in which an electrochemically inactive Li₂M'O₃ component is integrated with an electrochemically active LiMO₂ component to provide improved structural and electrochemical stability. The preferred M' ions are manganese, titanium and zirconium, whereas the preferred M ions are manganese and nickel, which can be used in combination with other metals such as cobalt. For example, the composite electrode 0.10Li₂MnO₃·0.90LiMn_0.26Ni_0.37Co_0.37O₂, which can also be represented in conventional layered notation as Li[Li_0.0475Mn_0.3175Ni_0.3175Co_0.3175]O₂, shows outstanding electrochemical properties. The structural compatibility between the two components, both of which have layered configurations (Fig. 1), allows integration to occur at the atomic level.

Fig. 1. Structural illustrations of the components of xLi2MO3·(1-x)LiMO2 electrodes

During charge and discharge of a lithium-ion cell, Li⁺ ions are electrochemically removed from and reinserted into the LiMO₂ component, respectively, as shown schematically in a compositional phase diagram of a Li₂M'O₃ - LiMO₂ - MO₂ - Li₂MO₂ electrode system (Fig. 2). An additional advantage of using electrode structures with manganese and nickel ions in the LiMO₂ component is that these structures can accommodate additional lithium; they form layered Li₂MO₂ structures without compromising the reversibility of the reaction, thereby providing additional capacity to the electrode. The Li₂M'O₃ component not only provides structural stability but also ensures, with its high lithium content, that the lithium layers in the composite electrodes are not contaminated by small amounts of transition metal ions, such as Ni²⁺ ions.

Fig. 2. The compositional phase diagram of a Li2MO3 - LiMO2 - MO2 - Li2MO2 electrode system

Patents

Argonne National Laboratory has been granted two U.S. patents (U.S. Pat. 6,677,082 and U.S. Pat. 6,680,143) on new "composite-structure" electrode materials for rechargeable lithium-ion batteries. Additional patents are pending on this technology

For More Information

For technical information, contact Michael Thackeray, Chemical Engineering Division, Argonne National Laboratory (630-252-9184, thackeray@cmt.anl.gov).

For information on licensing agreements and working with Argonne, contact Steve Lake, Office of Technology Transfer, Argonne National Laboratory (630-252-5685, slake@anl.gov).

Printer friendly (pdf)

More on the Chemical Engineering Division's battery research.