Interfaces; In situ methods; Synthesis; Characterization; Non-aqueous electrolytes; Electrochemical energy storage; Lithium-ion batteries; energy storage devices; batteries; carbon electrodes; interface electrochemistry; infrared spectroscopy
Verma Pallavi, Novák Petr (2012), Formation of Artificial Solid Electrolyte Interphase by Grafting for Improving Li-Ion Intercalation and Preventing Exfoliation of Graphite, in Carbon
, 50(7), 2599-2614.
Simmen Franziska, Foelske-Schmitz Annette, Verma Pallavi, Horisberger Michael, Lippert Thomas, Novák Petr, Schneider Christof Walter, Wokaun Alexander (2011), Surface Layer Formation on Li1+xMn2O4-δ Thin Film Electrodes during Electrochemical Cycling, in Electrochim. Acta
, (56), 8539-8544.
Verma Pallavi, Maire Pascal, Novák Petr (2010), A Review of the Features and Analyses of the Solid Electrolyte Interphase in Li-Ion Batteries, in Electrochim. Acta
, 55(22), 6332-6341.
Verma Pallavi, Maire Pascal, Novák Petr (2010), Concatenation of Electrochemical Grafting with Chemical or Electrochemical Modification for Preparing Electrodes with Specific Surface Functionality, in Electrochim. Acta
, 56(10), 3555-3561.
Verma Pallavi, Sasaki Tsuyoshi, Novák Petr, Chemical Surface Treatments for Decreasing Irreversible Charge Loss and Preventing Exfoliation of Graphite in Li-Ion Batteries, in Electrochim. Acta
SummaryThe great scientific challenge of this project is the characterization of surface films formed on carbon negative electrodes of lithium-ion batteries and especially the preparation of such films by chemical synthesis. In more detail, all the electrolytes used today in lithium-ion batteries are thermodynamically unstable at the very negative potential of lithiated graphite electrodes. Reductive decomposition of the electrolyte at the electrode surface leads to formation of a surface film - the Solid Electrolyte Interphase (SEI) - which prevents further degradation of the electrolyte. The SEI is of key importance for the function of lithium-ion batteries, and its formation and composition have been the objects of many scientific studies in the past. Despite these efforts, many scientific questions about the SEI composition remain unresolved. Herein we propose to address these open scientific questions by chemical synthesis of SEI components and subsequent deposition of SEI-like layers on carbon materials. Electrochemical properties and analytical data of electrodes covered with synthetic layers shall be compared with data obtained from real electrodes. Thereby the goal is to prove or disprove the different models for the structure of the SEI proposed in the past.The project is divided into two tasks, namely the synthesis of products mimicking the surface layers on negative electrode materials, and the development of novel analytical tools for the characterization thereof. The two interrelated tasks will be tackled in parallel, in order to benefit from mutual synergy effects and to verify continuously whether the spectroscopic and electrochemical properties of the synthesized materials are identical to those of the “natural” SEI.The SEI layers are made up of two main compound classes - inorganic lithium salts and polymeric products stemming from the reductive degradation of carbonate solvents. While the former are mostly commercially available, the synthesis of the polymeric products will be done in our laboratory using modern synthesis tools like transition metal catalyzed reactions and radical reactions. A special focus will be on polymers resembling the products originating from film forming additives like vinylene carbonate. The polymers will be deposited from solutions onto carbon materials either in pure form or as (stratified) layers together with other SEI components. At a later stage polymers will be covalently grafted to the surface of graphite powders and other carbon materials. Selected polymers will be further modified, e.g. by crosslinking or co-polymerization with other monomers in order to prepare hybrid materials acting as SEI and binder. Composite electrodes will be prepared using these polymers. Due to the particular properties of the SEI - a very thin film consisting of a variety of highly air sensitive inorganic, organic, and polymeric molecules - special analytical methods are needed for its characterization. In situ methods for the spectroscopic and electrochemical characterization of battery materials are already established in our laboratory and will be used to study the newly synthesized materials. An advanced in situ cell for infrared spectroscopy with the possibility to exchange the electrolyte will be tested and used to investigate the influence of electrolyte additives. To avoid the common drawback of in situ cells for infrared spectroscopy, i.e. the strong absorption of infrared light by the electrolyte, a completely new setup based on optically transparent carbon electrodes will be tested. An ATR-crystal coated with a nanolayer of graphitized carbon will serve as model electrode. Surface films formed electrochemically on top of this electrode can then be monitored from the backside, with less interference of the electrolyte solvents. Supporting synchrotron based methods like infrared microscopy shall be used to investigate the homogeneity of SEI layers on graphite powders. Pre-coating of graphite electrodes with synthetic SEI layers will ultimately lead to a reduced irreversible charge capacity in the first charging cycles of lithium-ion batteries and therefore to higher energy densities. Once the identity and function of the different SEI components is clarified, tailor-made layers for specific applications can be prepared. Layers with better high temperature stability could improve the safety and lifetime of lithium-ion batteries, and layers with reduced resistance could lead to batteries with higher power capability.