Oxygen-containing functional groups were found to effectively boost the K+ storage performance of carbonaceous materials, however, the mechanism behind the performance enhancement remains unclear. Herein, we report higher rate capability and better long-term cycle performance employing oxygen-doped graphite oxide (GO) as the anode material for potassium ion batteries (PIBs), compared to the raw graphite. The in situ Raman spectroscopy elucidates the adsorption-intercalation hybrid K+ storage mechanism, assigning the capacity enhancement to be mainly correlated with reversible K+ adsorption/desorption at the newly introduced oxygen sites. It is unraveled that the C=O and COOH rather than C-O-C and OH groups contribute to the capacity enhancement. Based on in situ Fourier transform infrared (FT-IR) spectra and in situ electrochemical impedance spectroscopy (EIS), it is found that the oxygen-containing functional groups regulate the components of solid electrolyte interphase (SEI), leading to the formation of highly conductive, intact and robust SEI. Through the systematic investigations, we hereby uncover the K+ storage mechanism of GO-based PIB, and establish a clear relationship between the types/contents of oxygen functional groups and the regulated composition of SEI.
Potassium ion hybrid capacitors (PIHCs) are of particular interest benefiting from high energy/power densities. However, challenges lie in the kinetic mismatch between battery‐type anode and capacitive‐type cathode, as well as the difficulty in achieving optimized charge/mass balance. These significantly sacrifice the electrochemical performance of PIHCs. Here, strategies including charge/mass balance pursuance, electrolyte optimization, and tailored electrode design, are employed, together, to address these challenges. The key parameters determining the energy storage properties of PIHCs are identified. Specifically, i) the good kinetic match between anode and cathode translates into the very small variation of cathode/anode mass ratio at various rates. This sets general rules for the pursuance of charge balance, and to maximize the electrochemical performance of hybrid devices. ii) A potassium bis(fluoroslufonyl)imide (KFSI)‐based electrolyte promotes better electrode kinetics and allows for the formation of more stable and intact solid electrolyte interphase layer, with respect to potassium hexafluorophosphate (KPF6)‐based electrolyte. And iii) hierarchically porous N/O codoped carbon nanosheets (NOCSs) with enlarged interlayer spacing, disordered structure, and abundant pyridinic‐N functional groups are advantageous in terms of high electronic/ionic transport dynamics and structural stability. All these together, contribute to the high energy/power density of the activated carbon//NOCSs PIHCs (113.4 Wh kg−1, at 17,000 W Kg−1).
An in-depth understanding of battery degradation and aging in-Operando not only plays a vital role in the design of battery managing systems but also helps to ensure safe use and manufacturing optimization of lithium-ion batteries (LIBs) in large-scale applications. Electrochemical impedance spectroscopy (EIS) is a nondestructive method which unravels electrode kinetic processes inside the batteries in different time domains, including charge-transfer reactions, interfacial evolutions, and mass diffusions. It has become a powerful diagnosis and pre/prognosis tool in battery aging research, as it provides important insight into the changes of internal electrochemical processes by correlating the impedance evolution to degradation mechanisms. This review gives a critical overview on rapidly developing impedance techniques for degradation and aging investigation of Li-ion batteries. The EIS variations of LIBs at different aging conditions of calendar aging and accelerated aging are systematically summarized. In addition, the working principles, data validation, and modeling methods, including equivalent circuit model (ECM), distribution of relaxation times (DRT), and transmission line model (TLM), of classical EIS and dynamic EIS are elaborately concluded. Finally, the challenges and perspectives of further application of EIS in the aging research of LIBs are presented.
Designing low-cost preparation of high-activity electrocatalysts with excellent stability is the route one must take to fully realize large-scale application implementation of zinc–air batteries. 3D nitrogen-doped nanocarbons with transition metals or their derivatives encapsulated in show promising potential in the field of non-precious metal oxygen electrocatalysis. Herein, we report a simple, economical, and large-scale production method to construct worm-like porous nitrogen-doped carbon with in situ-grown carbon nanotubes and uniformly embedded Fe/Fe3C nanoparticles. It not only has high conductivity owing to the nitrogen-doped nature but also has ample active sites and electrolyte diffusion channels benefitting from the uniformly distributed heterostructural Fe/Fe3C nanoparticles and discrete hierarchically porous structures. When used as catalyst materials for a zinc–air battery, an energy density of 719.1 Wh kg–1 and a peak power density of 101.3 mW cm–2 at a 50 mA cm–2 discharge current density is achieved. Additionally, throughout charging and discharging for 200 cycles at a current density of 20 mA cm–2, the charge/discharge voltage gap is nearly constant.
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