Intercalation electrochemistry for thermoelectric energy harvesting from temperature fluctuations.

The effective use of energy from sustainable sources is considered a crucial step on the way to a CO2-neutral economy. Low-grade waste heat (<100 °C) is widely and ubiquitously available, but difficult to convert into electrical energy with current technologies. Here, we demonstrate an electrochemical cell capable of directly converting ambient temperature fluctuations into electricity. Based on intercalation reactions with different entropies, any temperature change leads to a cell voltage and electrical energy can be extracted. The new cell concept features the advantages of thermo-electrochemical cells and pyroelectric-like energy harvesting, which opens a wide range of possibilities for effective and sustainable use of low-grade waste heat.

Determining the Diffusion Coefficient of Lithium Insertion Cathodes from GITT measurements: Theoretical Analysis for low Temperatures*.

Accurate knowledge of transport properties of Li-insertion materials in application-relevant temperature ranges is of crucial importance for the targeted optimization of Li-ion batteries (LIBs). Galvanostatic intermittent titration technique (GITT) is a widely applied method to determine Li-ion diffusion coefficients of electrode materials. The well-known calculation formulas based on Weppner's and Huggins' approach, imply a square-root time dependence of the potential during a GITT pulse. Charging the electrochemical double layer capacitance at the beginning of a GITT pulse usually takes less than one second. However, at lower temperatures down to -40 °C, the double layer charging time strongly increases due to an increase of the charge transfer resistance. The charging time can become comparable with the pulse duration, impeding the conventional GITT diffusion analysis. We propose a model to describe the potential change during a galvanostatic current pulse, which includes an initial, relatively long-lasting double layer charging, and analyze the accuracy of the lithium diffusion coefficient, derived by using the Weppner-Huggins method within a suitably chosen time interval of the pulse. Effects leading to an inaccurate determination of the diffusion coefficient are discussed and suggestions to improve GITT analyses at low temperature are derived.

Scalable Fabrication of Nanostructured Tin Oxide Anodes for High-Energy Lithium-Ion Batteries.

Although tin and tin oxides have been considered very promising anode materials for future high-energy lithium-ion batteries due to high theoretical capacity and low cost, the development of commercial anodes falls short of expectations. This is due to several challenging issues related to a massive volume expansion during operation. Nanostructured electrodes can accommodate the volume expansion but typically suffer from cumbersome synthesis routes and associated problems regarding scalability and cost efficiency, preventing their commercialization. Herein, a facile, easily scalable, and highly cost-efficient fabrication route is proposed based on electroplating and subsequent electrolytic oxidation of tin, resulting in additive-free tin oxide anodes for lithium-ion batteries. The electrodes prepared accordingly exhibit excellent performance in terms of gravimetric and volumetric capacity as well as promising cycle life and rate capability, making them suitable for future high-energy lithium-ion batteries.