Electrochemical Interfaces in Batteries
Within the framework of the Rudolf Diesel Industry Fellowship program, Peter Lamp and his team will collaborate with Moniek Tromp’s group (Inorganic Chemistry – Catalyst Characterisation, TUM) in catalyst characterization (CCH) and with his TUM host Hubert Gasteiger’s group (Technical Electrochemistry, TUM) in technical electrochemistry (TEC) in the chemistry department of TUM on a research project focused on aging mechanisms in high-voltage cathode materials.
Project’s background The possibility of a large scale commercialization of electric and hybrid vehicles relies on the ability to improve battery characteristics such as energy, power density, safety, lifetime, and cost.
Capacity fade and impedance increase are the main phenomena that impair the long time functioning of battery cells. Both phenomena originate from a large number of simultaneous chemical processes that occur under both storage and cycling conditions. Structural and chemical changes within the bulk electrode materials generally produce capacity fade. On the other hand, phenomena involving the electrolyte-electrode interface, including transition metal dissolution from the cathode, not only contribute to capacity fade but also contribute to the rise of cell impedance. The mechanism and kinetic of the ageing reactions depend not only on a large number of physical and operating variables including temperature, voltage, charge state, C-rate, etc., but also on the specific cell chemistry and design.
Project targets This project aims at a detailed fundamental understanding of the dissolution of transition metals for a large number of novel, high-voltage, cathode materials. At high cathode potentials, substantial capacity fading is observed. It is predominantly caused by transition metal dissolution which can lead to: i) loss of cathode active material; ii) passivation film formation on the cathode active material, causing increased cathode charge-transfer and film diffusion resistance; iii) transition metal deposition on the anode, causing increased anode charge-transfer resistance. Impurities like water and HF (produced by the decomposition of LiPF6 salt with water) may also accelerate transition metal dissolution, while electrolyte additives (e.g., TMB, FEC) may suppress it.
The project’s goals will be pursued by investigating the effect of water contamination, additive concentration, positive potential, and temperature using a combined electrochemical, chemical, and spectroscopic approach taking advantage of both ex-situ and in-situ techniques.
Roland Jung, Technical Electrochemistry