Probing the Na⁺/Li⁺-ions Insertion Mechanism in an Aqueous Mixed-Ion Rechargeable Batteries with NASICON- NaTi₂(PO₄)₃ Anode and Olivine- LiFePO₄ Cathode

A Venkatesha and D Seth and RM Varma and S Das and M Agarwal and MA Haider and AJ Bhattacharyya, CHEMELECTROCHEM, 10 (2023).

DOI: 10.1002/celc.202201013

Aqueous rechargeable mixed-ion batteries (ARMBs), where two types of ions shuttle between the cathode and anode, are an important alternative to conventional non-aqueous electrolyte-based rechargeable batteries. Herein, we present fundamental insights into the function of an ARMB comprising of NASICON-based sodium titanium phosphate (NaTi2(PO4)(3)/NTP) and olivine-based lithium iron phosphate (LiFePO4/LFP) employed as the anode and cathode respectively in combination with mixed-ion electrolytes, x-M Li2SO4: y-M Na2SO4 (x+y=1). Electrochemical and ex situ structural studies interestingly reveal a preferential Na+-ion insertion into NTP, despite the presence of two different cations in the electrolyte. This is strongly supported by molecular dynamics simulations, which show a 1-2 orders higher diffusion coefficient for Na+-ion than Li+-ion in NTP. In contrast, co-insertion of Li+ and Na+-ions into LFP takes place when cycled in mixed-ion electrolytes. We also show that batteries with mixed-ion electrolytes perform better than electrolytes with individual cations.

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