Solid-state Ion Transport Research Articles

Photothermally enhanced ion-transport in solid-state, non-Faradic energy storage devices for sub-freezing operability

The universal direct dependence of ionic mobility on temperature severely restricts the low-temperature operation of energy storage devices. We overcome this limitation by synergizing photothermal conversion with electrochemical energy storage, using non-graphitizable nanocarbon florets (NCF) as multi-functional electrodes. NCF-based supercapacitors leverage the photothermal energy, directing it to the High Internal Phase Emulsion polymer (poly-HIPE) infused ionic conductor [BMIm]-[TFSI], resulting in 15% increase in specific capacitance (Csp) at 30 °C and a 45% at −30 °C. This is the first solid-state energy storage device usable at sub-freezing conditions (< − 4 °C) without compromising its performance. Importantly, the device exhibits identical characteristics at 10 °C (with sunlight) and 30 °C (in the dark), thereby offsetting a temperature difference of 20 °C. Experimental evidences points to the reduction in electrolyte resistance by 86% and 34% in relaxation time constant as the origin of such improved functioning. Furthermore, the advantage of processability is translated to configurational form-factor to efficiently heat the ionic conductor and thereby realise a 15% increase in Csp.

Introducing a Novel Light Scattering Technique for Visualising Operando State-of-Charge Changes Within Individual Active Particles and Across the Electrode

In our presentation we will demonstrate the application of a recently developed operando optical microscopy technique to mechanistic studies of lithium-ion battery electrodes and active material characterisation. Our technique probes state-of-charge (SoC) changes in the active particles within the electrode during battery operation, based on the intensity variation of scattered light across each active particle. This enables detailed spatially resolved data on an individual particle level to be utilised for furthering mechanistic understanding of battery capability and degradation, and it also allows global statistics to be established for the optimisation and screening of new electrode materials. The technique is agnostic to the underlying battery chemistry, so in principle can be applied to study any battery electrode.In this talk, we will demonstrate how our technique can be used in the study of two key dynamic processes, solid-state ion transport and mechanical degradation. The ability to quantify ion transport during battery operation helps to provide insights into how lithium-ion dynamics affect the (de)lithiation mechanisms and degradation mechanisms of battery electrodes, which is crucial to improving their electrochemical performance. Using lithium cobalt oxide (LCO) as a case study, we will show how ion-transport mechanisms can be deduced by observing moving phase boundaries within particles during cycling.We will then demonstrate how local SoC changes within Ni-rich nickel manganese cobalt oxide (NMC) active particles can be visualised during operation, and how the intra-particle ion gradients identified can be used to determine the mechanistic origins of first-cycle capacity losses. Building on this, we will highlight how variation in the rates of (dis)charge between a population of active particles could be used to characterise the performance of new electrode compositions.In addition, we will highlight how lithium-ion concentration gradients can also be identified in high-rate niobium tungsten oxide (NWO) anode materials during initial lithiation and under initial rapid delithiation conditions and demonstrate how this can lead to particle cracking. Expanding on this, we illustrate how the proportion of cracked particles within an electrode can be quantified and then monitored over successive cycles as a potential metric for screening the stability of new electrode materials.

Science and Technological Understanding of Nano-ionic Resistive Memories (RRAM)

Ion transport in the solid state has been regarded as imperative with regards to high energy density electrochemical storage devices (for instance, batteries) for efficient electric mobility. Of late, there is another niche application involving ion transport in solid state which manifested itself as nonvolatile memory namely memristor. Such memories are classified under the emerging category of novel solid state Resistive Random Access Memories (RRAM). In 2008, HP labs unveiled the first practical memristor device employing TiO2 and non-stoichiometric titania as bilayer stack structure and on both sides of two titania layers platinum (pt) are used as blocking electrode for ions. It is understood that switching fundamentals are correlated to the filamentary conduction in metal oxide memristors owing to the formation and rupture of the filament-like nano-dendrites, one of the key mechanisms widely accepted in the arena of memristor analysis. This paper critically reviews the fundamental materials being employed in novel memristor memories. It is believed that solid electrolytes (fast ion conductors) are the fundamental building blocks of these memories. We have chosen a few archetypes, solid electrolytes are considered and their impact on the state-of-art research in this domain is discussed in detail. An indepth analysis of the fundamentals of resistive switching mechanism involved in various classes of memristive devices viz., Electrochemical Metallization Memories (ECM) and Valence Change Memories (VCM) is elucidated. A few important applications of memristors such as neuristor and artificial synapse in neuromorphic computing are reviewed as well.

Liquid crystalline polymeric wires for selective proton transport, part 2: Ion transport in solid-state

A study of ion transport in a new generation of hybrid biomimetic membranes, which are based on the formation of polymeric ionic wires via exo-recognition and subsequent orientation by thermal treatment, is presented. The specific conductivity of the hybrid membranes, obtained by electrochemical impedance spectroscopy, is not strongly affected by relative humidity and temperature; the values are found around 10−5 S/cm for all studied materials. However, in the case of ion transport observed by linear sweep voltammetry, the hybrid materials containing homeotropically oriented columns exhibited lower resistance than unoriented samples. The preferential selectivity, expressed as conductance ratio compared to proton cation, show remarkably better results for biomimetic membranes when compared to Nafion® 117. Low values of methanol crossover are also found. Taking into account these findings, these materials hold great promise for practical application requiring selective ion transport.

Solid state ion transport and phase behaviour in composites of N,N-methyl propylpyrrolidinium tetrafluoroborate and amorphous polyethylene oxide

The binary and ternary addition of 2 wt.% LiBF4 and 2 wt.% amorphous polyethylene oxide (aPEO) respectively to the plastic crystal forming salt P13BF4 (where P13+ = methylpropyl pyrrolidinium cation) was investigated with specific focus on the phase behaviour and evaluation of transport characteristics. Differential scanning calorimetry (DSC), optical thermomicroscopy, solid state nuclear magnetic resonance (NMR), and AC impedance spectroscopy were used to develop an understanding of the conduction process in the pure and mixed systems. The morphology of the ternary compound appeared as hexagonal spherulites upon solidification. Multinuclear NMR Pulsed Field Gradient measurements (1H,19F,7Li) to probe both cation and anion diffusion coefficients are reported. The anion is shown to be the most diffusive (at 320 K:19F = 2.5 × 10−11 m2 s−1; 1H: 1.8 × 10−11 m2 s−1; 7Li: 1.1 × 10−11 m2 s−1) in the ternary compound, with enhanced conductivity (2.7 × 10−5 S cm−1 at 310 K) just below the melt.