Mesoporous Spinel Metal Oxides As High Performance Cathode in Aqueous Rechargeable Lithium Ion Battery
Authors: Schuppert Nicholas David , Mukherjee Santanu , Bates Alex , Choi Moon Jong , Park Taehee , Park Sam 
Published: February 2020

1. Introduction – Secondary Li ion batteries, regarded as the current benchmark for new battery technologies, are under extensive development throughout the world [1]. However, their requirement that organic electrolytes be used limits the rate capacity and specific power the cell can achieve and present several safety hazards and cost limitations that prevent their application in medium to large-scale storage systems [1, 2]. Here, aqueous rechargeable lithium ion batteries (ARLBs) utilizing mesoporous spinel metal oxide cathodes are investigated, due to their high capacity, cycling stability and high rate capability [3, 4].
2. Fabrication procedures – LiMn2O4 (LMO) anode is fabricated by solid state reaction of 5 mmol Li2CO3 and 10 mmol Mn2O3 at 750 °C for 24 hrs. Activated carbon (AC, Kureha BAC) is utilized as received. Electrochemical testing was performed on Teflon sealed CR2032 coin cells utilizing type 304 S.S. mesh as electrode substrates. 6 M LiNO3 in D.I. water is used as the electrolyte, with addition of 0.01 M HNO3 and LiOH to create acidic and basic electrolytes, respectively.
3. Experimental setup and results – Average mass loadings of 5 mg cm-2 are utilized. Charge and discharge is done at a rate of 2 mA cm-2 between potentials of 0 and 2 V. HiRes TEM images, EDX spectrum and discharge capacity results of three LMO based cells are shown in Figure 1(a-d). Evidence of the pH dependence of the development of a porous nanoscale layer of Fe2O3 is shown in Figure 1(a-c), and is reflected in the superior performance of the basic cell, as shown in Figure 1(d). Capacity fading characteristic of the development of mixed material phases and Jahn-Teller distortion is observed in the two cells that do not show the development of this porous Fe2O3 layer (acidic and neutral), while the introduction of the new coating creates a capacity increase of ~ 50 % with high stability up to 500 cycles.
4. Conclusions – Influence of the creation of a porous nanoscale Fe2O3 layer on the LMO cathode is directly responsible for observed increases in cell discharge capacity and the stabilization of material capacity fade, greatly increasing the performance of both functional indicators. Future work aims to develop an inexpensive and efficient way to create mesoporous and nanoporous microstructures of Fe2O3 and other spinel metal oxides with high porosity and active surface area, thereby increasing material capacity and rate capability of ARLBs required by medium and large scale energy storage.
5. References –
[1] G.X. Wang, S. Zhong, D.H. Bradhurst, S.X. Dou, H.K. Liu, Journal of Power Sources, 74 (1998) 198-201.
[2] X. Zeng, Q. Liu, M. Chen, L. Leng, T. Shu, L. Du, H. Song, S. Liao, Electrochimica Acta, 177 (2015) 277-282.
[3] W. Tang, S. Tian, L.L. Liu, L. Li, H.P. Zhang, Y.B. Yue, Y. Bai, Y.P. Wu, K. Zhu, Electrochemistry Communications, 13 (2011) 205-208.
[4] J. Zhang, T. Huang, Z. Liu, A. Yu, Electrochemistry Communications, 29 (2013) 17-20.

Figure 1