lithium ion manganese oxide battery

A lithium ion manganese oxide battery (LMO) is a lithium-ion cell that uses manganese dioxide, , as the cathode material. They function through the same intercalation/de-intercalation mechanism as other commercialized secondary battery technologies, such as . Cathodes based on manganese-oxide components are earth-abundant, inexpensive, non-toxic, and provide better thermal stability.

Compounds

Spinel

One of the more studied manganese oxide-based cathodes is , a cation ordered member of the spinel structural family (space group Fd3m). In addition to containing inexpensive materials, the three-dimensional structure of lends itself to high rate capability by providing a well connected framework for the insertion and de-insertion of ions during discharge and charge of the battery. In particular, the ions occupy the tetrahedral sites within the polyhedral frameworks adjacent to empty octahedral sites. As a consequence of this structural arrangement, batteries based on cathodes have demonstrated a higher rate-capability compared to materials with two-dimensional frameworks for diffusion.

A significant disadvantage of cathodes based on is the surface degradation observed when the average oxidation state of the manganese drops below Mn^+3.5. At this concentration, the formally Mn(III) at the surface can disproportionate to form Mn(IV) and Mn(II) by the Hunter mechanism. The Mn(II) formed is soluble in most electrolytes and its dissolution degrades the cathode. With this in mind many manganese cathodes are substituted or doped to keep the average manganese oxidation state above +3.5 during battery use or they will suffer from lower overall capacities as a function of cycle life and temperature.

Layered

is a lithium rich 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 . In the nomenclature of layered compounds it can be written Li(Li_0.33Mn_0.67)O₂. Although is electrochemically inactive, it can be charged to a high potential (4.5 V v.s Li⁰) in order to undergo lithiation/de-lithiation or delithiated using an acid leaching process followed by mild heat treatment. However, extracting lithium from at such a high potential can also be charge compensated by loss of oxygen from the electrode surface which leads to poor cycling stability. New allotropes of have been discovered which have better structural stability against oxygen release (longer cycle-life).

Layered

The layered manganese oxide is constructed from corrugated layers of manganese/oxide octahedra and is electrochemically unstable. The distortions and deviation from truly planar metal oxide layers are a manifestation of the electronic configuration of the Mn(III) Jahn-Teller ion. A layered variant, isostructural with LiCoO₂, was prepared in 1996 by ion exchange from the layered compound NaMnO₂, however long term cycling and the defect nature of the charged compound led to structural degradation and cation equilibration to other phases.

Layered

The layered manganese oxide is structurally related to and LiCoO₂ with similar transition metal oxide layers separated by a layer containing two lithium cations occupying the available two tetrahedral sites in the lattice rather the one octahedral site. The material is typically made by low voltage lithiation of the parent compound, direct lithiation using liquid ammonia, or via use of an organic lithiating reagent. Stability on cycling has been demonstrated in symmetric cells although due to Mn(II) formation and dissolution cycling degradation is expected. Stabilization of the structure using dopants and substitutions to decrease the amount of reduced manganese cations has been a successful route to extending the cycle life of these lithium rich reduced phases. These layered manganese oxide layers are so rich in lithium.

''x'' • ''y'' • ''z'' LiMnO₂ composites

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 , layered LiMnO₂, and spinel , with a chemical formula of ''x'' • ''y'' • ''z'' LiMnO₂, where x+y+z=1. The combination of these 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. C. S. Johnson, J. T. Vaughey, M. M. Thackeray, T. E. Bofinger, and S. A. Hackney "Layered Lithium-Manganese Oxide Electrodes Derived from Rock-Salt LixMnyOz (x+y=z) Precursors" 194th Meeting of the Electrochemical Society, Boston, MA, Nov. 1–6, (1998)

See also

* List of battery types
* List of battery sizes
* Comparison of battery types

References

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Lithium-ion batteries