Raman Evidence for Late Stage Disproportionation in a Li–O<sub>2</sub> Battery

Zhai, Dengyun; Wang, Hsien Hau; Lau, Kah Chun; Gao, Jing; Redfern, Paul C.; Kang, Feiyu; Li, Baohua; Indacochea, Ernesto; Das, Ujjal; Sun, Ho Hyun; Amine, Khalil; Curtiss, Larry A.

doi:10.1021/jz501323n

Cited by 152 publications

(198 citation statements)

References 23 publications

Supporting

Mentioning

172

Contrasting

Order By: Relevance

“…The AIMD simulations give free energies of solvation of −29. 4 and −40.3 kcal/mol for LiO 2 and Li 2 O 2 , respectively. Solvation energies calculated using the monomer cycles with 4 DME solvent molecules and continuum models PCM and CPCM were found to be comparable with the AIMD results.…”

Section: Discussionmentioning

confidence: 98%

Computational Studies of Solubilities of LiO₂and Li₂O₂in Aprotic Solvents

Cheng¹,

Redfern²,

Lau³

et al. 2017

J. Electrochem. Soc.

Self Cite

View full text Add to dashboard Cite

Knowledge of the solubilities of Li 2 O 2 and LiO 2 in aprotic solvents is important for insight into the discharge and charge processes of Li-O 2 batteries, but these quantities are not well known. In this contribution, the solvation free energies of molecular LiO 2 and Li 2 O 2 in various organic solvents were calculated using various explicit and implicit solvent models, as well as ab initio molecular dynamics (AIMD) methods. The solvation energies from these calculations along with calculated lattice energies of Li 2 O 2 and LiO 2 were used to determine the solubility of bulk LiO 2 and Li 2 O 2 . The computed solubility of LiO 2 (1.8 × 10 −2 M) is about 15 orders higher than that of Li 2 O 2 (2.0 × 10 −17 M) due to a much less negative lattice energy of bulk LiO 2 compared to that of Li 2 O 2 . The difference in solubilities between LiO 2 and Li 2 O 2 likely will affect the nucleation and growth mechanisms and resulting morphologies of the products formed during battery discharge, influencing the performance of the battery cell. Lithium-O 2 battery technology has received much research interest due to its high theoretical gravimetric energy density compared to conventional Li-ion batteries.1 The system uses oxidation of lithium at the anode and reduction of oxygen at the cathode to induce a current flow. Depending on the reaction kinetics of different discharge mechanisms, the discharge products are generally composed of Li 2 O 2 with a low solubility and in some cases different ratios of LiO 2 and Li 2 O 2 .2-6 Much of research focus has been on the cathode. One of the challenges of Li-O 2 batteries is the incomplete utilization of the active materials due to the insulating nature of the discharge products and the clogging the porous carbon cathode. The formation of these products may involve a nucleation and growth mechanism from the solution phase.2,7-13 Nazar reported a Li 2 O 2 formation mechanism by disproportionation reaction of a limited amount of LiO 2 in solution.2 A through-solution mechanism was also proposed involving heterogeneous nucleation from a supersaturated solution of LiO 2 . 10There is other evidence that LiO 2 is soluble in the electrolyte prior to deposition on the surface based on a quartz microbalance study.14 Results from several research groups suggest that the composition and morphology of the discharge products have a significant effect on charging overpotential and rechargeability of the Li-O 2 battery. 10,15,16 Therefore, understanding the chemistry and growth mechanism of discharge products in the cell is crucial for improving Li-O 2 battery. The study and modeling of nucleation and crystal growth requires knowledge of bulk solubility. 17,18 However, there are limited experimental solubility measurements reported in the literature on discharge products LiO 2 and Li 2 O 2 . Solubility also highly depends on the size and morphologies of the solid as well as impurities so the values will depend on the experimental conditions. 24 The reason for the wide range of values for the s...

show abstract

Section: Discussionmentioning

confidence: 98%

Computational Studies of Solubilities of LiO₂and Li₂O₂in Aprotic Solvents

Cheng¹,

Redfern²,

Lau³

et al. 2017

J. Electrochem. Soc.

Self Cite

View full text Add to dashboard Cite

show abstract

“…The data in Figure 8 show that in LiTFSI and NaPF 6 anion was found to have little effect on the 13 C shift. Since all of the ions studied have the same single positive charge, the radius (and, hence, ionic volume) is roughly inversely proportional to the charge density and polarizability, which are the measures of Lewis acidity.…”

Section: Solvation and Lewis Acidity Of Cations Of Conducting Salts Imentioning

confidence: 96%

“…The different life-times of LiO 2 in the various organic electrolytes have led to one school of thought (primarily from quantitative determination of the O 2 generated during OER following an ORR step in DME-based electrolytes 13 ) that the initial ORR in the Li-O 2 cell is a two-electron process to form Li 2 O 2 . Eventually, this line of thought has given way to the ORR processes described by the reactions in equations 1-4, supported by extensive electrochemistry results coupled with product analysis.…”

Section: Anodic (Oer) Reactionsmentioning

confidence: 99%

“…Li-ion solvation by ethers 24 and organic carbonates 25 had been previously established by nuclear magnetic resonance (NMR) studies. We has been suggested that the 13 C NMR chemical shift and spin lattice relaxation times (T 1 ) of the C=O functional group in propylene carbonate (PC) due to its interaction (or formation of the acid-base complex) with each of the cations studied would provide information of the relative acidity of the cations. Although the Li + to PC molar ratio in a 1M Li salt solution was much less than four, only one 13 C signal was seen in the Li salt solution because of the rapid exchange with Li + of the solvated and unsolvated PC molecules at room temperature in the NMR time scale.…”

Section: Solvation and Lewis Acidity Of Cations Of Conducting Salts Imentioning

confidence: 99%

“…24 Our results are presented in Figure 8. The Li + with relatively high positive charge density or strong Lewis acidity formed a stronger complex with C=O as depicted in Structure I, and hence exhibited a larger 13 C=O chemical shift relative to PC. The very large IL and TBA cations with their low charge densities exhibited the least Lewis acidity and, therefore, the least chemical shift change.…”

Section: Solvation and Lewis Acidity Of Cations Of Conducting Salts Imentioning

confidence: 99%

See 2 more Smart Citations

Electrolyte-Directed Reactions of the Oxygen Electrode in Lithium-Air Batteries

Abraham

2014

J. Electrochem. Soc.

130

133

View full text Add to dashboard Cite

Non-aqueous electrolytes play a prominent role in the redox reactions of the oxygen electrode in the non-aqueous Li-air battery. In all electrolytes the initial O 2 reduction reaction (ORR) product is superoxide, O 2 − , whose stability is determined by the Lewis acidity of the ion-pairing cations present in the medium as governed by the Hard Soft Acid Base (HSAB) theory. Our results suggest that depending on the basicity of the solvent as measured by its Donor Number (DN), the superoxide will be stabilized to varying lengths of time before transforming to O 2 2− via a chemical or an electrochemical reaction. Organic solvents decrease the Lewis acidity of Li + through the formation of solvates, Li + (solvent) n . As a result, high DN solvents such as dimethyl sulfoxide (DMSO), which decrease Li + acidity more than low DN solvents, provide longer life-time for the soft base O 2 − by forming the ion pair, Li + (DMSO) n -O 2 − . In low DN solvents such as 1, 2-dimethoxy ethane (DME) and tetraethyleneglycol dimethyl ether (TEGDME), the LiO 2 rapidly decomposes to the peroxide, Li 2 O 2 . As the ionic bond strength between the O 2 reduction product and the conducting salt cation becomes stronger, its rechargeability becomes poorer. Solvent electron donor property affects ORR catalysis also. There is intense world-wide research and development of a rechargeable lithium battery based on the Li/O 2 chemical couple, popularly known as the Li-air battery, encouraged by its very high theoretical specific energy (5200 Wh/kg) and low cost of the materials from which it can be fabricated.1,2 The theoretical specific energy of the Li-air battery is surpassed only by a battery based on the Li/F 2 couple.3 However, F 2, because of its high reactivity, is an impractical electrode material to construct batteries for powering consumer products such as cellphones, laptop computers, tablets, digital cameras, and electric vehicles. This leaves Li-air as the candidate of choice for an ultra-high energy density, low cost (air is free) rechargeable lithium battery. The Li-air battery is environmentally friendly as nontoxic electrolytes and other materials, besides Li and O 2, needed for fabricating it can be formulated. It is a safe battery despite having a Li metal anode because the cathode active material is not stored inside the battery cell.The Li-air battery is one of many metal-air batteries that could conceivably be fabricated (Table I).Among the various metal-O 2 couples, the Li-air is the most attractive battery since the cell discharge reaction involving metallic Li and oxygen to yield Li 2 O, according to the reaction 4Li + O 2 → 2Li 2 O, has an open circuit voltage of 2.91 V and a theoretical specific energy of 5200 Wh/kg (Table I). In practice, oxygen does not have to be stored in the battery which makes the theoretical specific energy excluding oxygen to be 11140 Wh/kg when the battery is initially fabricated. The battery weight will increase and its specific energy will decrease as it is discharged due to the accumulation ...

show abstract