K.-C. Möller

Acrylic acid nitrile, a film-forming electrolyte component for lithium-ion batteries, which belongs to the family of additives containing vinyl groups

We present results on the electrolyte additive acrylic acid nitrile (AAN), which allows the use of propylene carbonate (PC)-based electrolytes together with graphitic anodes. This report will focus on the basic electrochemical properties and on XPS results of the films formed in the presence of AAN. Further data on in situ investigations of AAN is presented in another paper of this proceedings. The combination of both reports gives strong evidence, that the initiative step for solid electrolyte interphase (SEI) formation is a cathodic, i.e. by reduction induced electro-polymerisation of the vinyl-group. It is concluded that this electro-polymerisation may also be a main reduction mechanism of other vinyl compounds such as vinylene carbonate (VC), vinylene acetate and others.

Fluorinated organic solvents in electrolytes for lithium ion cells

A novel partly fluorinated solvent for lithium ion batteries, N,N-dimethyl trifluoracetamide (DTA), is presented. The physical properties and the electrochemical behaviour of this compound are investigated. With its low viscosity and high boiling point and flash point it could replace low viscosity solvents (thinners) such as dimethyl carbonate or diethyl carbonate currently used in lithium ion battery electrolytes to achieve the demand for safer lithium ion batteries. The outstanding filming properties allow to use the DTA even in mixtures with PC in amounts of 10%. With both solvents having a freezing point below −40°C, the mixture is promising as low temperature electrolyte.

In situ characterization of the SEI formation on graphite in the presence of a vinylene group containing film-forming electrolyte additives

Abstract Acrylic acid nitrile (AAN) is introduced as a novel example out of the large class of vinylene groups containing film-forming additives for lithium-ion batteries. The electrochemical behaviour, especially the electrolyte additive reduction and the associated film formation in the presence of this compound is investigated with the in situ methods of Fourier transform infrared (FT-IR) spectroscopy and electrochemical quartz crystal micro balance (EQCMB). The results clearly point at a solid electrolyte interphase (SEI) formation mechanism, which proceeds via the cathodically induced polymerization of AAN. We suggest that the electro-polymerisation of vinylene groups is a main electrolyte reduction mechanism for a vinylene group containing electrolyte additives. The outstanding filming properties of vinylene compounds such as AAN allow the use of graphitic carbon anodes in PC-based electrolytes even when only 1% of the additive is present in the electrolyte.

Studies on the Anode/Electrolyte Interface in Lithium Ion Batteries

Rechargeable lithium ion cells operate at voltages of 3.5–4.5 V, which is far beyond the thermodynamic stability window of the battery electrolyte. Strong electrolyte reduction and anode corrosion has to be anticipated, leading to irreversible loss of electroactive material and electrolyte and thus strongly deteriorating cell performance. To minimize these reactions, anode and electrolyte components have to be combined that induce the electrolyte reduction products to form an effectively protecting film at the anode/electrolyte interface, which hinders further electrolyte decomposition reactions, but acts as membrane for the lithium cations, i.e. behaving as a solid electrolyte interphase (SEI). This paper focuses on important aspects of the SEI. By using key examples, the effects of film forming electrolyte additives and the change of the active anode material from carbons to lithium storage alloys are highlighted.