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Issue 37, 2016
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Experimental and first-principles DFT study on the electrochemical reactivity of garnet-type solid electrolytes with carbon

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Abstract

The operating stability of the solid electrolyte component is one of paramount importance in the design of all-solid-state Li ion batteries. In this work, we investigated the origin of capacity fading during the charge process of an air-isolated Li ion battery with a garnet Li6.625La3Zr1.625Ta0.375O12 (LLZrTaO) solid electrolyte, a Li metal anode, and a LiFePO4 + carbon (LFP + C) active cathode material. Cyclic voltammetry measurements of the fabricated Li/LLZrTaO/(LLZrTaO + C) and Li/LLZrTaO/Al cells revealed a rise and an absence, respectively, of oxidation current which points to the garnet oxide electrolyte being decomposed via a reaction with carbon. XRD patterns of the solid electrolyte at post-charging showed no detectable impurity phases, suggesting that the decomposition product(s) is (are) likely made up of light elements. Based on first-principles calculations, the decomposition route may involve the formation of defective garnet by Li removal, oxygen release, and formation of products such as Li2CO3 and possibly of CO2; formation of the latter product is facilitated at elevated operating temperatures. Among the evaluated base garnet compounds (Li5+xLa3M2O12, with M: Nb Ta for x = 0 and M: Zr, Ti, Hf for x = 2), Li7La3Hf2O12 is predicted to be the most stable against Li2CO3 formation. A strong correlation has been determined between stability at charging and the electronegativity of the M cation, that is, the smaller the M electronegativity, the more stable is the garnet compound against carbon reactions.

Graphical abstract: Experimental and first-principles DFT study on the electrochemical reactivity of garnet-type solid electrolytes with carbon

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Publication details

The article was received on 23 May 2016, accepted on 19 Aug 2016 and first published on 19 Aug 2016


Article type: Paper
DOI: 10.1039/C6TA04280E
Citation: J. Mater. Chem. A, 2016,4, 14371-14379
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    Experimental and first-principles DFT study on the electrochemical reactivity of garnet-type solid electrolytes with carbon

    R. Jalem, Y. Morishita, T. Okajima, H. Takeda, Y. Kondo, M. Nakayama and T. Kasuga, J. Mater. Chem. A, 2016, 4, 14371
    DOI: 10.1039/C6TA04280E

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