Enhancing the Reaction Kinetics and Reversibility of Li–O₂ Batteries by Multifunctional Polymer Additive

Abstract

As a potential candidate for next‐generation energy storage systems, Li–O2 batteries (LOBs) with their attractive theoretical energy density have triggered great interest. However, tough issues of sluggish oxygen reduction reaction/oxygen evolution reaction (ORR/OER) kinetics, poor rechargeability, superoxide‐derived side reactions, and Li‐metal corrosion in LOBs limit their practical applications. Herein, a poly(2,2,2‐trifluoroethyl methacrylate) (PTFEMA) additive is introduced into the typical electrolyte, giving superior cycling performance to LOBs. Enabling strong solvation of Li+, PTFEMA regulates a uniform Li+ flow at the cathode and anode sides of LOBs. Induced by homogeneous Li+ flux and favorable adsorption with superoxide species, PTFEMA promotes superoxide transformation in the ORR and inhibits superoxide‐induced parasitic reactions. Uniform Li+ flux gives evenly‐distributed Li2O2 that can be completely decomposed during OER. In addition, PTFEMA protects Li‐metal against corrosion from O2, superoxide, and byproducts shuttle. Hence, accelerated ORR/OER kinetics, facilitated rechargeability, suppressed superoxide‐derived side reactions, and well‐protected Li‐metal can be simultaneously realized with PTFEMA, resulting in significantly enhanced electrochemical performance of LOBs. This electrolyte engineering involving facile multifunctional polymer additives provides a practical alternative to complex componential optimization toward commercial LOBs and gives insight to the understanding of uniform Li+ flux on reaction kinetics and reversibility.

Protecting Li-metal in O2 atmosphere by a sacrificial polymer additive in Li–O2 batteries

“…The peaks at around 3.7-3.4 ppm are assigned to the -CH 3 groups (d) in PAMMA. 13,16 Thus, the 1 H NMR measurement further verified the different hydrogen environments of the functional groups, especially -CONH 2 in PAMMA. Gel permeation chromatography (GPC) measurement gave a weight-average molecular weight (M w ) and number-average molecular weight (M n ) of ∼2.2 × 10 5 and ∼2.5 × 10 4 g mol −1 , respectively, revealing the successful synthesis of the PAMMA polymer, as shown in Fig.…”

“…Red color usually stands for electron-rich functional groups, while blue color exhibits electron-deficient species. 13 As shown in Fig. 1d, only –NH 2 in the –CONH 2 functional group represents an apparent electron-deficient state, resulting in much easier bond breaking and decomposition than the other groups in PAMMA.…”

“…Unlike the popular organic/inorganic materials with a low molecule weight, polymers, which are characterized by tunable functional groups and excellent flexibility, have been rarely reported as effective additives for the modification of the SEI in LOBs to date. 13,14 Herein, a polyacrylamide-co-polymethyl acrylate (PAMMA) copolymer with the amide group of -CONH 2 was successfully synthesized and solvated in the ether-based electrolyte (1.0 M LiTFSI in TEGDME) of an Li-O 2 cell. Due to the localized charge distribution, PAMMA with an electron-deficient -CONH 2 group could preferentially decompose more readily than the common electrolyte species (solvent and Li salt) to form an Li 3 N-rich SEI layer at the Li-metal/electrolyte interface, which significantly protected the Li-metal anode from corrosion by O 2 , superoxide species, protons and soluble side products.…”

“…Unlike the popular organic/inorganic materials with a low molecule weight, polymers, which are characterized by tunable functional groups and excellent flexibility, have been rarely reported as effective additives for the modification of the SEI in LOBs to date. 13,14…”

Quantifying the Influence of Li Plating on a Graphite Anode by Mass Spectrometry

“…In this study, we employed an online electrochemical mass spectrometry (OEMS) method − to clearly and accurately detect the onset of microscale Li plating in real time based on H 2 evolution capture from the reaction of plated Li with the polymer binder. Moreover, the titration mass spectrometry (TMS) method , was used to analyze quantitatively the influence of Li plating on the SEI components, dead Li, and other irreversible capacity assignments.…”