LiMn₂O₄ (LMO): spinel structure, voltage and capacity fade

LiMn₂O₄ crystallizes in the cubic spinel structure, space group Fd-3m: oxygen ions occupy the 32e sites, manganese the octahedral 16d sites and lithium the tetrahedral 8a sites (Bakierska et al. 2016). The MnO₆ octahedra form the framework, and the lithium sites are connected into a three-dimensional diffusion network (Liu et al. 2026). In the closely related spinel LiNi₀.₅Mn₁.₅O₄, lithium moves from a tetrahedral 8a site through an empty octahedral 16c site, the 8a–16c path (Zhang et al. 2025).

This 3D network is the main structural difference from olivine LiFePO₄, where lithium can move only along one direction. It is why spinel LMO has good rate capability and suits power-oriented applications (Liu et al. 2026).

On charge, lithium leaves the 8a sites and manganese is oxidized from Mn³⁺ to Mn⁴⁺. The charge–discharge curve shows two plateaus near 4.1 V vs Li/Li⁺, both from the Mn³⁺/Mn⁴⁺ couple, and cyclic voltammetry shows them as a doublet of peaks around 4.1 V (Bakierska et al. 2016). The theoretical capacity is about 148 mAh g⁻¹ (Bakierska et al. 2016), which matches one lithium per LiMn₂O₄ (148.2 mAh g⁻¹, calculated from the molar mass of 180.81 g mol⁻¹), a little lower than the 170 mAh g⁻¹ of LiFePO₄ but delivered at a higher voltage.

Stoichiometric LiMn₂O₄ suffers from severe capacity fading during cycling (Bakierska et al. 2016), above all at elevated temperature, high rate or over long cycling (Liu et al. 2026). Two causes dominate:

• Jahn–Teller distortion. High-spin Mn³⁺ in an octahedron has a single electron in the doubly degenerate eg orbitals, so the MnO₆ octahedron distorts and the lattice turns tetragonal (Zhang et al. 2025). In LMO this drives a cubic-to-orthorhombic phase transition near room temperature (Bakierska et al. 2016).
• Manganese dissolution. The surface of the highly delithiated cathode reacts with the electrolyte and manganese dissolves (Bakierska et al. 2016). Mn³⁺ disproportionation generates soluble manganese that migrates through the electrolyte and can deposit on the anode, consuming active manganese and damaging the spinel framework (Liu et al. 2026); divalent manganese has been detected in the electrolyte (Zhang et al. 2025).

The remedies attack both causes: cation substitution (for example Ni for Mn) to reduce the Jahn–Teller distortion, and surface coatings to limit contact with the electrolyte (Liu et al. 2026). Spinel co-doped with Ni and S no longer showed the room-temperature phase transition and kept 80.6% of its capacity after 650 cycles at 5C (Bakierska et al. 2016).

Replacing a quarter of the manganese with nickel gives LiNi₀.₅Mn₁.₅O₄ (LNMO), a cobalt-free spinel that works at about 4.7 V vs Li/Li⁺ with a theoretical energy density of about 650 Wh kg⁻¹ (Zhang et al. 2025) and a theoretical capacity of 147 mAh g⁻¹ (Madinabeitia et al. 2022). The capacity now comes from nickel: plateaus near 4.6 and 4.8 V from the Ni²⁺/Ni³⁺ and Ni³⁺/Ni⁴⁺ couples. In the disordered (Fd-3m) form a small plateau near 4.0 V from residual Mn³⁺ remains; the Ni/Mn-ordered form lacks it (Zhang et al. 2025). Uncoated LNMO can crystallize in the ordered space group P4₃32 (Chong et al. 2014).

The high voltage is also its problem. Conventional ethylene-carbonate-based electrolytes are stable only to about 4.3 V and decompose on the LNMO surface (Zhang et al. 2025), and manganese dissolution still causes capacity fading (Cho et al. 2015). Coatings such as Al₂O₃, TiO₂ and Li₃PO₄ are used to protect the surface (Cho et al. 2015; Chong et al. 2014).

LMO is unlikely to compete with Ni-rich layered oxides in energy density; its place is in cost-sensitive, safety-sensitive and high-power applications (Liu et al. 2026). It is one of the cathodes compared on our battery materials page, alongside olivine LiFePO₄ and layered oxides.

For a paper, slide or poster, draw the cubic spinel cell with MnO₆ octahedra as polyhedra and lithium as isolated spheres in the tetrahedral sites between them, or a slab of edge-sharing octahedra with the lithium sites above; arrows between the tetrahedral 8a sites through the empty 16c octahedra show the 3D diffusion path. To show capacity fade, add a distorted, elongated Mn³⁺O₆ octahedron and Mn ions leaving the surface into the electrolyte. The LabCanvas figure editor Library has a battery crystal object for spinel LMO that you can drop into a figure, recolour and resize, and export as a high-resolution image.