Direct correlation between void formation and lithium dendrite growth in solid-state electrolytes with interlayers.

Solid-state Li-ion batteries with lithium anodes offer higher energy densities and are safer than conventional liquid electrolyte-based Li-ion batteries. However, the growth of lithium dendrites across the solid-state electrolyte layer leads to the premature shorting of cells and limits their practical viability. Here, using solid-state Li half-cells with metallic interlayers between a garnet-based lithium-ion conductor and lithium, we show that interfacial void growth precedes dendrite nucleation and growth. Specifically, void growth was observed at a current density of around two-thirds of the critical current density for dendrite growth. Computational calculations reveal that interlayer materials with higher critical current densities for dendrite growth also have the largest thermodynamic and kinetic barriers for lithium vacancy accumulation at their interfaces with lithium. Our results suggest that interfacial modification with suitable metallic interlayers decreases the tendency for void growth and improves dendrite growth tolerance in solid-state electrolytes, even in the absence of high stack pressures.

Enhancement of the electrochemical performance of zinc-silver batteries with a gold nano-scaffold.

Primary zinc-silver batteries are widely employed in military, aerospace, and marine applications. However, the development of secondary zinc-silver batteries is still a subject of on-going research. For example, these batteries suffer from rapid capacity loss during cycling due to instabilities of the zinc anode and the silver cathode. While there is a large body of work on the Zn anode, there is limited work toward stabilizing the Ag electrode and thereby achieving a long cycle life. In this work, we propose a gold-silver nanostructure where gold acts as a scaffolding material and improves the retention of structural integrity during cell cycling. We show that this nanostructure improves battery capacity as well as capacity retention after 35 cycles. Our work emphasizes the role of nanostructuring in enabling a newer secondary battery chemistry based on existing primary ones.

Modulation-doping a correlated electron insulator.

Correlated electron materials (CEMs) host a rich variety of condensed matter phases. Vanadium dioxide (VO2) is a prototypical CEM with a temperature-dependent metal-to-insulator (MIT) transition with a concomitant crystal symmetry change. External control of MIT in VO2-especially without inducing structural changes-has been a long-standing challenge. In this work, we design and synthesize modulation-doped VO2-based thin film heterostructures that closely emulate a textbook example of filling control in a correlated electron insulator. Using a combination of charge transport, hard X-ray photoelectron spectroscopy, and structural characterization, we show that the insulating state can be doped to achieve carrier densities greater than 5 × 1021 cm-3 without inducing any measurable structural changes. We find that the MIT temperature (TMIT) continuously decreases with increasing carrier concentration. Remarkably, the insulating state is robust even at doping concentrations as high as ~0.2 e-/vanadium. Finally, our work reveals modulation-doping as a viable method for electronic control of phase transitions in correlated electron oxides with the potential for use in future devices based on electric-field controlled phase transitions.

Charge polarity-dependent ion-insertion asymmetry during electrochemical doping of an ambipolar π-conjugated polymer.

Electrochemical doping is central to a host of important applications such as bio-sensing, neuromorphic computing and charge storage. However, the mechanisms that enable electrochemical dopability and the various parameters that control doping efficiencies are poorly understood. Here, employing complementary electrochemical and spectroelectrochemical measurements, we report a charge-polarity dependent ion insertion asymmetry in a diketopyrrolopyrrole-based ambipolar π-conjugated polymer. We argue that electrostatic interactions are insufficient to fully account for the observed charge-specific ion insertion into the polymer matrix. Using polymer side-chain dependent electrochemical doping studies, we show that electron density donating and accepting tendencies of polymer side-chains sufficiently describe the observed charge-polarity dependent electrochemical doping. Our observations are akin to the solvation of dopant ions by polymer side-chains. We propose that Gutmann donor/acceptor number framework qualifies the 'solvent-like' properties of polymer side-chains and provides a rational basis for designing π-conjugated polymers with favorable mixed ionic electronic transport properties.