Response to Comment on “Cycling Li-O ₂ batteries via LiOH formation and decomposition”

Abstract

We described a lithium-oxygen (Li-O 2 ) battery comprising a graphene electrode, a dimethoxyethane-based electrolyte, and H 2 O and lithium iodide (LiI) additives, lithium hydroxide (LiOH) being the predominant discharge product. We demonstrate, in contrast to the work of Shen et al., that the chemical reactivity between LiOH and the triiodide ion (I 3 -) to form IO 3 -indicates that LiOH can be removed on charging; the electrodes do not clog, even after multiple cycles, confirming that solid products are reversibly removed. We reported on a lithium-oxygen battery that formed LiOH as the predominant discharge product, formed from a reduced graphene oxide (rGO) electrode, a dimethoxyethane (DME)-based electrolyte, and H 2 O and LiI additives (1). On the basis of observed oxygen release, we suggested the following charge reaction.We also clearly stated, "We stress, however, that the equilibria that occur in the presence of oxygen, water, and iodine are complex, often involving a series of polyanions (including IO -and its protonated form); further mechanistic studies are required to understand the role of these complex equilibria in the redox processes" (1). Some of these equilibria are as follows (2) 3IShen et al. First, removal of LiOH in lithium-oxygen batteries below 3.2 V has previously been observed-e.g., with ruthenium-based catalysts and tetraglyme (4)/dimethyl sulfoxide (5)-based electrolytes and added water. Because the catalyst does not alter the equilibrium voltage, the equilibrium itself must be altered. In another Technical Response (6), we argued that the free-energy change of reaction 1 on moving from an aqueous to nonaqueous electrolyte system cannot be ignored and will change the equilibrium potential. Of note, we have observed that LiOH can be quantitatively removed via reactions 2 to 5, I 3 -reacting to form IO 3 -and I -and suggesting an alternative mechanism [see figure 1 in (6) for details], the rate depending strongly on the amount of water and LiTFSI concentrations present in the system (Fig. 1). Reaction 1 is a four-electron process and will be strongly affected by the nature of the electrode; further studies are required to determine the relative rates of reaction 1 versus reactions 3 to 5 and the potential role that catalysts may play in determining this.2) Shen et al. (3) observed in a transparent cell that the electrolyte color darkens on cycling due to I 3 -accumulation. They concluded that the first discharge involves the formation of LiOH via O 2 reduction at~2.6 V [figure 1B in (3)] but that the subsequent charge process involves the direct oxidation of I -to I 3 -, rather than the removal of LiOH, subsequent discharge processes, also observed at~2.6 V, being a combination of further LiOH formation and I 3 -reduction. Because our ultraviolet (UV)-visible experiments show that the kinetics for reactions 2 to 5 are highly dependent on the water content [figure 1 in (6)], we suggest that the conditions used in Shen et al.´s experiment, 5 A/g for a charge/discharge capacity of 1 Ah/g-...

A Long‐Life Lithium–Air Battery in Ambient Air with a Polymer Electrolyte Containing a Redox Mediator

“…Recently, Liu et al. have shown that the reaction between LiOH and I 3 − can result in the formation of LiIO or LiIO 3 …”

Solvent-Dependent Oxidizing Power of LiI Redox Couples for Li-O2 Batteries

“…18,47,48 Similarly, Zhu et al 48 to form iodine (I 2 ), 53 where the potentials of the I À /I 3 À and I 3 À /I 2 redox transitions can be significantly influenced by solvent. [52][53][54] While it has been previously suggested that changes in these redox potentials may be important for the performance of LiI as a redox mediator in Li-O 2 batteries, 26,52 this effect has not been studied systematically.…”

Proton enhanced dynamic battery chemistry for aprotic lithium–oxygen batteries

“…For instance, water and protons were found in one study to significantly influence the crystal growth of Li 2 O 2 (refs 20 , 21 ). In other studies, lithium hydroxide (LiOH) was however identified as the main discharge product in the presence of moisture 15 16 , whereas disputes persist on the oxidation of LiOH by triiodide (I 3 − ) during charging process 22 23 24 25 26 27 . Moreover, water was believed to catalyse the ORR reaction in aprotic Li-O 2 battery resulting in the formation of LiOH 28 , and good cycling performance was achieved in humid O 2 (ref.…”