Lithium metal is known to possess a very high theoretical capacity of 3,842 mAh g À 1 in lithium batteries. However, the use of metallic lithium leads to extensive dendritic growth that poses serious safety hazards. Hence, lithium metal has long been replaced by layered lithium metal oxide and phospho-olivine cathodes that offer safer performance over extended cycling, although significantly compromising on the achievable capacities. Here we report the defect-induced plating of metallic lithium within the interior of a porous graphene network. The network acts as a caged entrapment for lithium metal that prevents dendritic growth, facilitating extended cycling of the electrode. The plating of lithium metal within the interior of the porous graphene structure results in very high specific capacities in excess of 850 mAh g À 1 . Extended testing for over 1,000 charge/discharge cycles indicates excellent reversibility and coulombic efficiencies above 99%.

Conventional graphitic anodes in lithium-ion batteries cannot provide high-power densities due to slow diffusivity of lithium ions in the bulk electrode material. Here we report photoflash and laser-reduced free-standing graphene paper as high-rate capable anodes for lithium-ion batteries. Photothermal reduction of graphene oxide yields an expanded structure with micrometer-scale pores, cracks, and intersheet voids. This open-pore structure enables access to the underlying sheets of graphene for lithium ions and facilitates efficient intercalation kinetics even at ultrafast charge/discharge rates of >100 C. Importantly, photothermally reduced graphene anodes are structurally robust and display outstanding stability and cycling ability. At charge/discharge rates of ~40 C, photoreduced graphene anodes delivered a steady capacity of ~156 mAh/g(anode) continuously over 1000 charge/discharge cycles, providing a stable power density of ~10 kW/kg(anode). Such electrodes are envisioned to be mass scalable with relatively simple and low-cost fabrication procedures, thereby providing a clear pathway toward commercialization.

No abstract

No abstract

In this study, we report a novel route via microwave irradiation to synthesize a bio-inspired hierarchical graphene--nanotube--iron three-dimensional nanostructure as an anode material in lithium-ion batteries. The nanostructure comprises vertically aligned carbon nanotubes grown directly on graphene sheets along with shorter branches of carbon nanotubes stemming out from both the graphene sheets and the vertically aligned carbon nanotubes. This bio-inspired hierarchical structure provides a three-dimensional conductive network for efficient charge-transfer and prevents the agglomeration and restacking of the graphene sheets enabling Li-ions to have greater access to the electrode material. In addition, functional iron-oxide nanoparticles decorated within the three-dimensional hierarchical structure provides outstanding lithium storage characteristics, resulting in very high specific capacities. The anode material delivers a reversible capacity of ~1024 mA · h · g(-1) even after prolonged cycling along with a Coulombic efficiency in excess of 99%, which reflects the ability of the hierarchical network to prevent agglomeration of the iron-oxide nanoparticles.

Silicon (Si) shows promise as an anode material in lithium-ion batteries due to its very high specific capacity. However, Si is highly brittle, and in an effort to prevent Si from fracturing, the research community has migrated from the use of Si films to Si nanoparticle based electrodes. However, such a strategy significantly reduces volumetric energy density due to the porosity of Si nanoparticle electrodes. Here we show that contrary to conventional wisdom, Si films can be stabilized by two strategies: (a) anchoring the Si films to a carbon nanotube macrofilm (CNM) current collector and (b) draping the films with a graphene monolayer. After electrochemical cycling, the graphene-coated Si films on CNM resembled a tough mud-cracked surface in which the graphene capping layer suppresses delamination and stabilizes the solid electrolyte interface. The graphene-draped Si films on CNM exhibit long cycle life (>1000 charge/discharge steps) with an average specific capacity of ∼806 mAh g. The volumetric capacity averaged over 1000 cycles of charge/discharge is ∼2821 mAh cm, which is 2 to 5 times higher than what is reported in the literature for Si nanoparticle based electrodes. The graphene-draped Si anode could also be successfully cycled against commercial cathodes in a full-cell configuration.

No abstract

In recent years, Reliance Jio’s offer of 4G services, guaranteeing free voice calls and ‘unlimited’ data streaming, lead to disruption in the Indian telecom market with other cellular operators losing their revenue and customer base. To comprehensively analyze this churn in the Indian telecom industry and its impact on mobile phone customers, the article argues for observing the entanglement of infrastructural and platform-related discourses at three levels of operation: Jio’s strategies to capture the Indian telecom market and the responses by the leading incumbent service provider (Airtel), ordinary citizens’ phone use practices and infrastructural encounters, and the government’s vision for India’s digital future. Connecting pipes to platforms, Jio made infrastructural investments (in spectrum, cell towers, and fiber optics networks) to promote its suite of apps (JioTV, JioChat, and JioMoney). Ordinary citizens relate their access/proximity to telecom infrastructure (cell antennas) to their ability to effectively use apps on their phones. ‘Digital India’ vision purportedly facilitated infrastructural growth to create platforms that would support demonetization and facilitate transparent governance. Through such a three-pronged analysis, I conceptualize ‘infrastructural imaginaries’ that are coproduced by states and citizens, and lie at the intersection of structured state policy/corporate initiatives and lived experiences/affective encounters of ordinary citizens.