A Lithium ion manganese oxide battery is a lithium ion cell that uses manganese dioxide, MnO
2, as the primary cathode material. They function through the same intercalation/de-intercalation mechanism as other commercialized secondary battery technologies, such as LiCoO
2. They are a promising technology as their manganese-oxide components are earth-abundant, inexpensive, non-toxic, and provide better thermal stability.
Contents
Spinel LiMn 2O 4
One of the more prominent compounds is LiMn
2O
4, a lithium-manganese-oxide based material with a spinel structure (space group Fd3m). In addition to being a cheap and non-toxic alternative material, the spinel structure of LiMn
2O
4 provides a three-dimensional framework for the insertion and de-insertion of Li+
ions during discharge and charge of the battery. In particular, the Li+
ions occupy the interstitial spaces defined by the Mn
2O
4 polyhedral frameworks. Thus, batteries with LiMn
2O
4 cathodes should be able to provide a higher rate-capability compared to materials with two-dimensional frameworks for Li+
diffusion.
One main disadvantage of LiMn
2O
4 based batteries is that they suffer from lower overall capacities as a result of their spinel structure. Furthermore, at higher temperatures, the LiMn
2O
4 spinel structure is inherently unstable in the Li-based electrolytes used in Li-ion batteries. This results in dissolution of Mn ions and further capacity loss.
Layered Li 2MnO 3
Li
2MnO
3 is layered rocksalt structure that is made of alternating layers of lithium ions and lithium and manganese ions in a 1:2 ratio, similar to the layered structure of LiCoO
2. Although Li
2MnO
3 is electrochemically inactive, it can be charged to a high potential (4.5 V v.s Li0) in order to undergo lithiation/de-lithiation. However, extracting lithium from Li
2MnO
3 at such a high potential results in loss of oxygen from the electrode surface which leads to poor capacity and cycling stability.
Research
One of the main research efforts in the field of lithium-manganese oxide electrodes for lithium-ion batteries involves developing composite electrodes using structurally integrated layered Li
2MnO
3 and spinel LiMn
2O
4, with a chemical formula of xLi
2MnO
3 • (1-x)Li
1+yMn
2-yO
4. The combination of both structures provides increased structural stability during electrochemical cycling while achieving higher capacity and rate-capability. A rechargeable capacity in excess of 250 mAh/g was reported in 2005 using this material, which has nearly twice the capacity of current commercialized rechargeable batteries of the same dimensions.