C. Heubner

Reversible heat generation rates of blended insertion electrodes

The blending of lithium ion insertion compounds is a novel and promising approach to design advanced electrodes for future secondary batteries. Recently, considerable improvements regarding power density and safety issues have been achieved by combining several insertion compounds. However, the understanding of basic interactions between the constituents of the blend is still ongoing. In the present theoretical study, we derive a mathematical model of the reversible heat generation rate of a blended insertion electrode based on the thermodynamic properties of its constituents. The reversible heat is found to be a function of the entropy of the lithium insertion reaction, the mass fraction, and the differential capacity of each constituent in the blend. The impact and the significance of these parameters on the reversible heat generation rate and its state of charge dependence are analyzed. The derived relations can be used to determine the reversible heat profile of a blended insertion electrode for all possible compositions if the properties of the pure constituents are known. The results suggest the opportunity of designing specific reversible heat profiles by a targeted compilation of the blend.

Investigations on the reversible heat generation rates of blended Li-insertion electrodes

Recently, considerable improvements regarding the electrochemical performance of cathodes for lithium-ion batteries have been achieved by combining multiple lithium insertion compounds with complementary advantageous properties in one electrode. Herein, reversible heat generation rates of blended insertion electrodes are systematically investigated by temperature-dependent measurements of the equilibrium potential. The results are compared to theoretical predictions showing excellent agreement. Both the reversible heat profile and the corresponding dissipated heat significantly depend on the type and mass ratio of the constituents of the blend. The results indicate that reversible heat profiles of blended electrodes can be tailored to a certain extent by the targeted compilation of the active material mixture.

Heat generation rates of NaFePO 4 electrodes for sodium-ion batteries and LiFePO 4 electrodes for lithium-ion batteries: a comparative study

AbstractThe heat generation connected to charging and discharging NaFePO4 (NFP) electrodes in sodium-ion batteries and LiFePO4 (LFP) electrodes in lithium-ion batteries is investigated. NFP-based electrodes are prepared with an electrochemical displacement method using LFP electrodes as the starting material. This approach guarantees identical particle size distribution, active material loading, binder, conductive additives, etc., of the electrodes. Consequently, differences in the heat generation rates are exclusively determined by the substitution of the alkali metal cation. Irreversible heat generation rates are computed from galvanostatic intermittent titration technique measurements at different C-rates. Reversible heat generation rates are determined by the temperature dependence of the equilibrium potential. For both, NFP and LFP electrodes, the total heat generation increases with increasing C-rate. The reversible heat is found to be significant at low C-rate, whereas the irreversible heat dominates at high C-rate. For both NFP and LFP electrodes, differences in the total heat generation rates during charging and discharging are mainly attributed to the reversible heat. The comparison between NFP and LFP reveals substantially larger heat generation rates for NFP electrodes, which are mainly caused by larger limitations of charge transfer reaction and the solid-state diffusion. Graphical abstractᅟ

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.