Reversible Capacity of Conductive Carbon Additives at Low Potentials: Caveats for Testing Alternative Anode Materials for Li-Ion Batteries

The electrochemical performance of alternative anode materials for Li-ion batteries is often measured using composite electrodes consisting of active material and conductive carbon additives. Cycling of these composite electrodes at low voltages demonstrates charge storage at the operating potentials of viable anodes, however, the conductive carbon additive is also able to store charge in the low potential regime. The contribution of the conductive carbon additives to the observed capacity is often neglected when interpreting the electrochemical performance of electrodes. To provide a reference for the contribution of the carbons to the observed capacity, we report the charge storage behavior of two common conductive carbon additives Super P and Ketjenblack as a function of voltage, rate, and electrolyte composition. Both carbons exhibit substantial capacities after 100 cycles, up to 150 mAh g^(−1), when cycled to 10 mV. The capacity is dependent on the discharge cutoff voltage and cycling rate with some dependence on electrolyte composition. The first few cycles are dominated by the formation of the SEI followed by a fade to a steady, reversible capacity thereafter. Neglecting the capacity of the carbon additive can lead to significant errors in the estimation of charge storage capabilities of the active material

Reversible Capacity of Conductive Carbon Additives at Low Potentials: Caveats for Testing Alternative Anode Materials for Li-Ion Batteries

The electrochemical performance of alternative anode materials for Li-ion batteries is often measured using composite electrodes consisting of active material and conductive carbon additives. Cycling of these composite electrodes at low voltages demonstrates charge storage at the operating potentials of viable anodes, however, the conductive carbon additive is also able to store charge in the low potential regime. The contribution of the conductive carbon additives to the observed capacity is often neglected when interpreting the electrochemical performance of electrodes. To provide a reference for the contribution of the carbons to the observed capacity, we report the charge storage behavior of two common conductive carbon additives Super P and Ketjenblack as a function of voltage, rate, and electrolyte composition. Both carbons exhibit substantial capacities after 100 cycles, up to 150 mAh g^(−1), when cycled to 10 mV. The capacity is dependent on the discharge cutoff voltage and cycling rate with some dependence on electrolyte composition. The first few cycles are dominated by the formation of the SEI followed by a fade to a steady, reversible capacity thereafter. Neglecting the capacity of the carbon additive can lead to significant errors in the estimation of charge storage capabilities of the active material

Ab initio structure search and in situ 7Li NMR studies of discharge products in the Li-S battery system.

The high theoretical gravimetric capacity of the Li-S battery system makes it an attractive candidate for numerous energy storage applications. In practice, cell performance is plagued by low practical capacity and poor cycling. In an effort to explore the mechanism of the discharge with the goal of better understanding performance, we examine the Li-S phase diagram using computational techniques and complement this with an in situ (7)Li NMR study of the cell during discharge. Both the computational and experimental studies are consistent with the suggestion that the only solid product formed in the cell is Li2S, formed soon after cell discharge is initiated. In situ NMR spectroscopy also allows the direct observation of soluble Li(+)-species during cell discharge; species that are known to be highly detrimental to capacity retention. We suggest that during the first discharge plateau, S is reduced to soluble polysulfide species concurrently with the formation of a solid component (Li2S) which forms near the beginning of the first plateau, in the cell configuration studied here. The NMR data suggest that the second plateau is defined by the reduction of the residual soluble species to solid product (Li2S). A ternary diagram is presented to rationalize the phases observed with NMR during the discharge pathway and provide thermodynamic underpinnings for the shape of the discharge profile as a function of cell composition.Fellowship support to KAS from the ConvEne IGERT Program of the National Science Foundation (DGE 0801627) is gratefully acknowledged. AJM acknowledges the support from the Winton Programme for the Physics of Sus-tainability. PDM and DSW thank the UK-EPSRC for financial support. This research made use of the shared experimental facilities of the Materials Research Laboratory (MRL), sup-ported by the MRSEC Program of the NSF under Award No. DMR 1121053. The MRL is a member of the NSF-funded Mate-rials Research Facilities Network (www.mrfn.org). CPG and ML thank the U.S. DOE Office of Vehicle Technologies (Con-tract No. DE-AC02-05CH11231) and the EU ERC (via an Ad-vanced Fellowship to CPG) for funding.This is the final published version. It first appeared at http://pubs.acs.org/doi/abs/10.1021/ja508982p

A High Capacity Calcium Primary Cell Based on the Ca–S System

Conversion reaction cells afford the ability to explore new energy storage paradigms that transcend the dogma of small, low‐charge cations essential to intercalative processes. Here we report the use of earth‐abundant and green calcium and sulfur in unprecedented conversion reaction Ca–S primary cells. Using S‐infiltrated mesoporous carbon (abbreviated S@meso‐C) cathodes, we achieve discharge capacities as high as 600 mAh g^(−1) (S basis) within the geometry Ca|Ca(ClO_4)_2/CH_3CN|S@meso‐C, at a discharge rate of C/3.5. The electrolyte system in the Ca–S battery is of paramount importance as the solid electrolyte interface (SEI) formed on the Ca anode limits the capacity and stability of the cell. We determine that 0.5 M Ca(ClO_4)_2 in CH_3CN forms an SEI that advantageously breaks down under anodic bias to allow oxidation of the anode. This same SEI, however, exhibits high impedance which increases over time at open circuit limiting the shelf life of the cell

A High Capacity Calcium Primary Cell Based on the Ca–S System

Conversion reaction cells afford the ability to explore new energy storage paradigms that transcend the dogma of small, low‐charge cations essential to intercalative processes. Here we report the use of earth‐abundant and green calcium and sulfur in unprecedented conversion reaction Ca–S primary cells. Using S‐infiltrated mesoporous carbon (abbreviated S@meso‐C) cathodes, we achieve discharge capacities as high as 600 mAh g^(−1) (S basis) within the geometry Ca|Ca(ClO_4)_2/CH_3CN|S@meso‐C, at a discharge rate of C/3.5. The electrolyte system in the Ca–S battery is of paramount importance as the solid electrolyte interface (SEI) formed on the Ca anode limits the capacity and stability of the cell. We determine that 0.5 M Ca(ClO_4)_2 in CH_3CN forms an SEI that advantageously breaks down under anodic bias to allow oxidation of the anode. This same SEI, however, exhibits high impedance which increases over time at open circuit limiting the shelf life of the cell

Understanding the role of crystallographic shear on the electrochemical behavior of niobium oxyfluorides

The effects of shear planes in perovskite materials have been studied in order to identify their role in the electrochemical behavior of Li⁺ intercalation hosts. These planes modulate the structural stability and ionic transport pathways and therefore play an intimate role in the characteristics and performance of shear compounds. Herein, two Nb-based compounds, NbO₂F and Nb₃O₇F, were chosen as representative perovskite and shear derivatives respectively to investigate the role of crystallographic shear. A series of operando measurements, including X-ray diffraction and X-ray absorption spectroscopy, in conjunction with structural analysis, Raman spectroscopy, and detailed electrochemical studies identified the effect of shear planes. It was found that shear planes led to increased structural stability during Li⁺ (de)intercalation with shear layers being maintained, while perovskite layers were seen to degrade rapidly. However, disordering in the shear plane stacking introduced during delithiation ultimately led to poor capacity retention despite structural maintenance as Li⁺ diffusion channels are disrupted

Bimodal Mesoporous Titanium Nitride/Carbon Microfibers as Efficient and Stable Electrocatalysts for Li–O_2 Batteries

The rechargeable Li–O_2 battery has been considered as a sustainable chemical power source for electric vehicles and grid energy storage systems due to the high theoretical specific energy (∼3500 Wh/kg). The practical performance of Li–O_2 batteries is, however, still far below expectations. This is mainly attributed to the (1) intrinsic sluggish reaction kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), (2) passivation of the electrodes by electrical isolation and pore blocking, and (3) chemical instability of the organic cell components, i.e., electrolyte, polymer binder, and carbon electrode, in the presence of O_2•– and Li_2O_2. It is crucial to develop highly porous, three-dimensional, conducting cathode catalyst/gas diffusion layer (GDL) architectures possessing superior catalytic activity and stability with respect to the ORR and the OER in order to address these issues. All of these requirements prompted us to examine the catalytic performance of porous framework metal nitride electrodes for Li–O_2 batteries

Accelerating Progress towards Universal Water Sanitation and Hygiene (WASH): Governance, Technology and Data for Urban Settings

Access to safe water, sanitation and hygiene (WASH) continues to be a universal challenge that affects human health and well-being. The latest global reports from the Joint Monitoring Programme (JMP) for Water Supply, Sanitation and Hygiene led by the World Health Organization (WHO) and the United Nations Children’s Fund (UNICEF) have highlighted the global scale of WASH issues, particularly in the least developed countries (LDCs). In 2020, it was estimated that there were 2 billion people that did not have access to safe drinking water, 2.3 billion people who lacked access to basic hygiene services, and 3.6 billion people who did not have safe sanitation in their households (WHO/UNICEF JMP, 2021). In addition, more than 500 million children still lack basic WASH services in their schools (WHO/UNICEF JMP, 2022). This is also common in health care facilities, which are fundamental for the prevention and control of diseases such as diarrhoea, and more recently COVID-19 (WHO/UNICEF JMP, 2020). Moreover, those living in slums and informal settlements, which are characterised by the lack of durable housing, insufficient living space, lack of access to clean drinking water, inadequate sanitation and insecure tenure (UN HABITAT, 2010), have a disproportionately higher disease burden due to the lack of access to safe WASH. Slums and informal settlements also reinforce gender inequalities and gender-based violence, due to the higher vulnerabilities of women and adolescent girls, in part because of their menstruation and sanitation requirements (Goddard and Sommer, 2020)

Sulfur-Functionalized Mesoporous Carbons as Sulfur Hosts in Li–S Batteries: Increasing the Affinity of Polysulfide Intermediates to Enhance Performance

The Li–S system offers a tantalizing battery for electric vehicles and renewable energy storage due to its high theoretical capacity of 1675 mAh g^(–1) and its employment of abundant and available materials. One major challenge in this system stems from the formation of soluble polysulfides during the reduction of S_8, the active cathode material, during discharge. The ability to deploy this system hinges on the ability to control the behavior of these polysulfides by containing them in the cathode and allowing for further redox. Here, we exploit the high surface areas and good electrical conductivity of mesoporous carbons (MC) to achieve high sulfur utilization while functionalizing the MC with sulfur (S–MC) in order to modify the surface chemistry and attract polysulfides to the carbon material. S–MC materials show enhanced capacity and cyclability trending as a function of sulfur functionality, specifically a 50% enhancement in discharge capacity is observed at high cycles (60–100 cycles). Impedance spectroscopy suggests that the S-MC materials exhibit a lower charge-transfer resistance compared with MC materials which allows for more efficient electrochemistry with species in solution at the cathode. Isothermal titration calorimetry shows that the change in surface chemistry from unfunctionalized to S-functionalized carbons results in an increased affinity of the polysulfide intermediates for the S–MC materials, which is the likely cause for enhanced cyclability