Study of Aqueous Lithium Ion Batteries Utilizing Spinel Compound Anodes
Authors: Schuppert Nicholas David , Mukherjee Santanu , Son ByungRak , Kim Joo Gon , Choi Jae Sung , Lee Dong-Ha , Choi Moon Jong , 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 limit their application in large-scale storage systems [1, 2]. Here, aqueous Li ion cells utilizing LiMn2O4 spinel compound anodes is investigated, due to its ample capacity, cycling stability and high rate capability [3].
2. Fabrication procedures – LiMn2O4 (LMO) anode is fabricated by solid state reaction of 5 mmol Li2CO3 and 10 mmol Mn2O3 at 750 °C for 20 hrs. Li2Mn4O9 cathode is fabricated by solid state reaction of 10 mmol LiOH·H2O and 20 mmol MnCO3 at 380 °C for 24 hrs. LiMn2O4 solid microspheres were prepared by calcination of LiOH·H2O and MnCO3 microspheres at 650 °C for 3 hrs in air. MnCO3 solid microspheres were prepared as follows: 1 mmol MnSO4·H2O and 1 mmol NaHCO3 were dissolved separately in 70 ml of distilled water. 7 ml of ethanol was added to the MnSO4 solution under stirring. Direct mixing of the NaHCO3 and MnSO4 solutions is done, and precipitate is allowed to form overnight. MnCO3 microspheres were obtained from multiple centrifugation and washing cycles. Obtained product was allowed to dry overnight at 100 °C in air. Activated carbon (AC, Kureha BAC) is utilized as received.
3. Experimental setup and results – XRD spectra of the solid state LiMn2O4 anode (LMO¬_SS) and LiMn2O4 solid microspheres (LMO_Sμ) are shown in Figure 1(a). SEM image of the LMO solid microspheres is shown in Figure 1(b). Cycling performance of LMO_SS vs. Li2Mn4O9 in 6M LiCl (pH 12, 0.01 M LiOH) is shown in Figure 2. 1st discharge capacities and charge voltage plateaus of cells utilizing LMO_SS vs. AC in 6M LiCl with varying pH is shown in Figure 3. Charge currents of 1.5 mA cm-2 and discharge currents of 0.25 mA cm-2 are used for all cell tests.
4. Conclusions – An initial decrease in discharge capacity of the LiMn2O4 and Li2Mn4O9 cell is observed from the 1st to 20th discharge cycle. The discharge capacity of the cell is observed to asymptotically approach 60 mAh/g by the 100th cycle. Discharge voltage and capacity of the LMO and AC cell is observed to be greatly dependent on electrolyte pH. A voltage plateau during is observed during charging that did not contribute to cell discharge capacity. Future work aims to investigate the processes occurring at the anode during the observed charge voltage plateau as well as the change in charge transfer kinetics and cell capacity when employing both solid and hollow LiMn2O4 microspheres as the active anode. Due to the dissolution tendencies of Mn in aqueous electrolyte, methods of increasing cell cycling stability are also of interest.
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.

Figure 1