Abstract:
he market for lithium-ion batteries (LIBs) is rapidly expanding owing to the increasing demand for portable electronics, electric vehicles, and large-scale energy storage systems. As LIBs move toward transportation and grid-level applications, cathode materials must satisfy higher requirements in energy density, safety, cost, lifetime, and sustainability. Although Ni-rich layered cathodes have been widely investigated because of their high specific capacity, their practical use remains challenged by cation mixing, gas evolution, interfacial instability, and safety concerns. In this context, Co-free high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) has attracted growing attention as a promising cathode candidate. LNMO operates at around 4.7 V versus Li/Li+ through the Ni2+/Ni4+ redox couple and offers advantages such as high power capability, three-dimensional Li-ion diffusion pathways, relatively low cost, and improved thermal stability.
Despite these advantages, the commercialization of LNMO is still limited by several interconnected challenges. First, LNMO can exist as a disordered spinel phase with the Fd3̅m space group or an ordered spinel phase with the P4₃32 space group. In practical synthesis, LNMO usually contains a mixture of ordered and disordered domains because the phase ordering is highly sensitive to the Ni/Mn ratio, calcination temperature, holding time, cooling rate, and atmosphere. Second, the high operating voltage of LNMO accelerates electrolyte oxidation, cathode–electrolyte interphase formation, HF generation, Mn dissolution, and impedance growth. Third, conventional polycrystalline LNMO particles may suffer from intergranular cracking during cycling, exposing fresh reactive surfaces and further accelerating degradation.
In this presentation, we discuss recent progress in addressing these issues through electrolyte additive design and flux-cation-assisted single-crystal engineering. Benzimidazole-salt-based additives were investigated for both ordered and disordered LNMO cathodes to improve electrolyte oxidation durability and stabilize the high-voltage cathode interface. Electrochemical and structural analyses reveal that these additives can postpone the formation of intermediate phase transitions at different states of charge, indicating a regulated reaction pathway during cycling. In addition, 1H NMR analysis shows that the N–Li functional group in the imidazole ring suppresses HF formation, thereby mitigating Mn dissolution and improving interfacial stability [1-3].
Beyond electrolyte design, we further demonstrate the transformation of polycrystalline LNMO into well-defined single-crystal particles with highly exposed {111} facets through flux engineering. By systematically comparing Li2MoO4 and Na2MoO4 fluxes, the results show that flux-cation compatibility is critical for driving single-crystal formation, while the MoO42− anion selectively lowers the surface energies of the {111} and {110} facets. This synergistic flux-cation effect provides a rational route to control LNMO morphology and surface structure [4].
Synchrotron-based characterization at NSRRC plays a key role in revealing the structure–interface relationships of LNMO, including phase evolution, redox behavior, and high-voltage interfacial reactions. Overall, this work highlights an integrated strategy for developing safer, Co-free, and high-energy LNMO cathodes. From a broader perspective, LNMO offers a promising pathway to reduce cobalt dependence, lower battery cost, strengthen supply-chain sustainability, and support future electric vehicles and renewable-energy storage systems.
References
[1] Fu-Ming Wang et al. Chem. Eng. J. 494 (2024) 152988
[2] Fu-Ming Wang et al, ACS Sus. Chem. Eng. 11 (2023) 4374
[3] Fu-Ming Wang et al, J. Energy Storage 97 (2024) 112883
[4] Fu-Ming Wang et al, (2026) submitted
Keywords – High voltage, Spinel, Synchrotron, LNMO, electrolyte, ordered, disordered