What Do Laser-Induced Transient Techniques Reveal for Batteries? Na- and K‑Intercalation from Aqueous Electrolytes as an Example

Technological advancement has been revolutionized by rechargeable batteries, without which the use of various modern devices would not be possible. Aqueous Na ion batteries have lately garnered much attention, being recognized as a promising alternative to the commonly used Li ion batteries for the large-scale energy storage systems. However, further improvement and optimization of such systems require a more detailed understanding of intercalation mechanisms. In this work, we for the first time demonstrate the implementation of the laser-induced current transient (LICT) technique for in situ characterization of battery systems and investigate the interface between Na₂Ni­[Fe­(CN)₆] model battery electrodes and aqueous electrolytes in contact with aqueous electrolytes. Quite counterintuitively, the LICT method revealed that at the quasi-steady-state the electrode surface stays positively charged within the potential range where the intercalation/deintercalation of sodium as well as of potassium is possible, evidencing that the intercalation mechanism of the alkali-metal cations should be rather complex. Furthermore, the specific shape of the observed current transients indicates that the interfacial processes of intercalation/deintercalation have at least three different relaxation time constants. The relaxation behavior is highly influenced by the nature of the alkali-metal cationsmost likely through their different solvation energy. In addition, we outline how the laser-based experiments can intensify detailed in situ investigations of battery systems

Multistage Mechanism of Lithium Intercalation into Graphite Anodes in the Presence of the Solid Electrolyte Interface

A so-called solid electrolyte interface (SEI) in a lithium-ion battery largely determines the performance of the whole system. However, it is one of the least understood objects in these types of batteries. SEIs are formed during the initial charge–discharge cycles, prevent the organic electrolytes from further decomposition, and at the same time govern lithium intercalation into the graphite anodes. In this work, we use electrochemical impedance spectroscopy and atomic force microscopy to investigate the properties of a SEI film and an electrified “graphite/SEI/electrolyte interface”. We reveal a multistage mechanism of lithium intercalation and de-intercalation in the case of graphite anodes covered by SEI. On the basis of this mechanism, we propose a relatively simple model, which perfectly explains the impedance response of the “graphite/SEI/electrolyte” interface at different temperatures and states of charge. From the whole data obtained in this work, it is suggested that not only Li⁺ but also negatively charged species, such as anions from the electrolyte or functional groups of the SEI, likely interact with the surface of the graphite anode

Electrochemically Formed Na_<i>x</i>Mn[Mn(CN)₆] Thin Film Anodes Demonstrate Sodium Intercalation and Deintercalation at Extremely Negative Electrode Potentials in Aqueous Media

The development of electrode materials for Na-ion batteries has been substantially accelerated recently with respect to application in grid energy storage systems. Specifically, development of Na-ion batteries operating in aqueous media is considered more promising for this application due to safety issues. Many different types of cathode materials for aqueous Na-ion batteries have been proposed; however, the number and performance of contemporary anode materials are still insufficient for practical deployment. In this work, we demonstrate that electrochemically deposited Na_<i>x</i>Mn­[Mn­(CN)₆] thin films are very promising anode materials for aqueous Na-ion batteries. Na_<i>x</i>Mn­[Mn­(CN)₆] films exhibit (i) very low half-charge potential ca. −0.73 V vs SHE (ca. −0.93 V vs SSC) being one of the lowest among those reported in the literature for the electrode materials, which also inhibit hydrogen evolution reaction; (ii) a specific capacity of ca. 85 mA h g^–1; and (iii) only ∼3% loss of capacity and high round-trip efficiency (99.6%) after 3,000 cycles. Surprisingly, the choice of the electrolyte composition has a very strong influence not only on the intercalation process but also on the long-term performance of battery anodes and their electrode surface morphology

Synergistically Enhanced Electrochemical Performance of Hierarchical MoS₂/TiNb₂O₇ Hetero-nanostructures as Anode Materials for Li-Ion Batteries

As potential high-performance anodes for Li-ion batteries (LIBs), hierarchical heteronanostructures consisting of TiNb₂O₇ nanofibers and ultrathin MoS2 nanosheets (TNO@MS HRs) were synthesized by simple electrospinning/hydrothermal processes. With their growth mechanism revealed, the TNO@MS HRs exhibited an entangled structure both for their ionic and electronic conducting pathways, which enabled the synergetic combination of one- and two-dimensional structures to be realized. In the potential range of 0.001–3 V <i>vs</i> Li/Li⁺, the TNO@MS HR-based LIBs exhibited high capacities of 872 and 740 mAh g^–1 after 42 and 200 cycles at a current density of 1 A g^–1, respectively, and excellent rate performance of 611 mAh g^–1 at 4 A g^–1. We believe that the fabrication route of TNO@MS HRs will find visibility for the use of anode electrodes for high capacity LIBs at low cost