Unlocking the Potential of Lithium-Excess Spinel Cathodes for Next-Generation Li-Ion Battery Applications
Authors: Shi Boyu , Gim Jihyeon , Vu Anh D. , Li Tianyi , Sultanov Maksim A. , Wen Jianguo , Balasubramanian Mahalingam , Croy Jason R. , Thackeray Michael M. , Lee Eungje 
Published: December 2024

The growing electric vehicle (EV) market necessitates the pursuit of cathode materials with enhanced energy density and economic viability. Currently, widely utilized cathode materials include LiMnxNiyCo1-x-yO2 (NMC), LiNixCoyAl1-x-yO2, and LiFePO4 (LFP). Despite nickel’s recognition as an abundant element, concerns have arisen regarding its demand and supply chain stability, potentially posing challenges to the cost-effectiveness of high-nickel cathodes.1 Conversely, while LiFePO4 exhibits cost-effective manufacturing, its limited energy density remains a bottleneck for enhancing EV range.2 Thus, there persists a substantial demand for the development of high energy density cathodes utilizing abundant elements.

Mn stands out as an earth-abundant elements with significantly lower costs compared to Ni and Co. The history of Mn-based cathode development is notably extensive, including noteworthy examples like the spinel-structured LiMn2O4 and the layered lithium manganese rich cathode (LMR-NMC). These achievements collectively make Mn-based cathodes immensely appealing. Nevertheless, the traditional spinel-structured LiMn2O4 suffers from low operatable capacity due to the Jahn-Teller distortion caused by reduced Mn ions which hinders its further application. Although the LMR-NMC cathode exhibit impressively high capacity, it also suffers from voltage hysteresis and fading which inhibits the energy density and making it hard to control by the energy management system (EMS). Thus, there is still an imperative demand for development of next generation high energy density Mn rich cathode material.3

In 2021, our group have reported a novel Co-free lithium-excess spinel (LxS) structure cathode material denoted as LxS-Li2MnNiO4. The unique LxS-structured Li2MnNiO4 surpasses conventional spinels such as LiMn2O4 and LiMn1.5Ni0.5O4 by doubling the Li concentration in its pristine state, while maintaining its cubic symmetry. The Li/LxS-L2MnNiO4 cell exhibits remarkable performance, delivering ~225 mAh/g capacity from 2.5 – 5.0 V, with nearly 96% retention after 50 cycles. The exceptional electrochemical performance of LxS-Li2MnNiO4 is attributed to the stable spinel framework and the inherent 3D Li-ion diffusion pathways, facilitating rapid Li-ion diffusion.4 Recently, we synthesized a new series of Mn-rich LxS cathodes. These newly developed Mn-rich compounds exhibit an even better electrochemical performance, showcasing exceptional structural stability. The successful synthesis of high-performance Mn-rich LxS-LMNO not only broadens the compositional space of LxS materials but also positions them as promising, high-energy density, and cost-effective next generation cathode materials.

(1) Wang, L.; Wang, J.; Wang, L.; Zhang, M.; Wang, R.; Zhan, C. A critical review on nickel-based cathodes in rechargeable batteries. International Journal of Minerals, Metallurgy and Materials
2022, 29 (5), 925-941.

(2) Wang, Y.; He, P.; Zhou, H. Olivine LiFePO4: development and future. Energy & Environmental Science
2011, 4 (3), 805-817, 10.1039/C0EE00176G. DOI: 10.1039/C0EE00176G.

(3) Gutierrez, A.; Tewari, D.; Chen, J.; Srinivasan, V.; Balasubramanian, M.; Croy, J. R. Earth-Abundant, Mn-Rich Cathodes for Vehicle Applications and Beyond: Overview of Critical Barriers. Journal of The Electrochemical Society
2023.

(4) Shi, B.; Gim, J.; Li, L.; Wang, C.; Vu, A.; Croy, J. R.; Thackeray, M. M.; Lee, E. LT-LiMn 0.5 Ni 0.5 O 2: a unique co-free cathode for high energy Li-ion cells. Chemical Communications
2021, 57 (84), 11009-11012.