Effect of Carbon Content on Electrochemical Properties of LiFePO4/C Composite Cathode

Olivine-type LiFePO4/C composite cathode materials were synthesized by a solid-state reaction method in an inert atmosphere. The glucose was added as conductive precursors before the formation of the crystalline phase. The effects of glucose content on the properties of as-synthesized cathode materials were investigated. The crystal structure and the electrochemical performance were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, laser particle-size distribution measurement and electrochemical performance testing. The material has a single crystal olivine structure with grain-sizes ca. 100-200 nm. SEM micrographs and the corresponding energy dispersive spectrometer （EDS） data confirm that the carbon particulates produced by glucose pyrogenation are uniformly dispersed among the LiFePO4 grains, ensuring a good electronic contact. Impedance spectroscopy was used to investigate the ohmic and kinetic contributions to the cell performance. It is found that increasing the carbon content leads to a reduction of the cell impedance due to the reduction of the charge transfer resistance. The galvanostatically charge and discharge tests show that the material obtained by adding 10% C （by mass） gives a maximum discharge capacity of 140.8mA·h·g^-1 at the same rate （C/10）. The material also displays a more stable cycle-life than the others.

The scaling of charging rate and cycle number of commercial batteries

Health management for commercial batteries is crowded with a variety of great issues,among which reliable cycle-life prediction tops.By identifying the cycle life of commercial batteries with different charging histories in fast-charging mode,we reveal that the average charging rate c and the resulted cycle life N of batteries obey c=c_(0)N^(b),where c_(0) is a limiting charging rate and b is an electrode-dependent constant.This c-N law,resembling the classic stress versus cycle number relationship(the S-N curve or Wohler curve)of solids subject to cyclic loading,could be applicable to most batteries.Such a scaling law,in combination with a physics-augmented machine-learning algorithm,could foster the predictability of battery life with high fidelity.The scaling of charging rate and cycle number may pave the way for cycle-life prediction and the directions of optimization of advanced batteries.

Supercapacitors as redox mediators for decoupled water splitting

With the help of the redox mediator, decoupled water-splitting allows O_(2)and H_(2)to be produced at different times, at different rates, and even in different cells, which promotes both the operation safety and the utilization of renewable power sources. However, the current densities and stabilities of these redox mediators are commonly low, which require further improvements for practical applications. Here, we propose to use supercapacitors as solid state redox mediators for decoupled water splitting. For demonstration, Na_(0.5)MnO_(2)(pseudocapacitor) and active carbon(double layer capacitor), are both used as the redox mediator. These supercapacitors show superior current density(1 A/cm^(2)) and ultralong cycle-life(8000 cycles) compared with commonly investigated battery-based mediators(NiOOH/Ni(OH)_(2)). Our research proves supercapacitors can be used as redox relay with high current density and stability, which may bring new insights in the design of decoupled water splitting systems.