Researchers must find a sustainable way of providing the power our modern lifestyles demand.

Building better batteries

The increasing interest in energy storage for the grid can be attributed to multiple factors, including the capital costs of managing peak demands, the investments needed for grid reliability, and the integration of renewable energy sources. Although existing energy storage is dominated by pumped hydroelectric, there is the recognition that battery systems can offer a number of high-value opportunities, provided that lower costs can be obtained. The battery systems reviewed here include sodium-sulfur batteries that are commercially available for grid applications, redox-flow batteries that offer low cost, and lithium-ion batteries whose development for commercial electronics and electric vehicles is being applied to grid storage.

Electrical Energy Storage for the Grid: A Battery of Choices

Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

Li-ion batteries have transformed portable electronics and will play a key role in the electrification of transport. However, the highest energy storage possible for Li-ion batteries is insufficient for the long-term needs of society, for example, extended-range electric vehicles. To go beyond the horizon of Li-ion batteries is a formidable challenge; there are few options. Here we consider two: Li-air (O(2)) and Li-S. The energy that can be stored in Li-air (based on aqueous or non-aqueous electrolytes) and Li-S cells is compared with Li-ion; the operation of the cells is discussed, as are the significant hurdles that will have to be overcome if such batteries are to succeed. Fundamental scientific advances in understanding the reactions occurring in the cells as well as new materials are key to overcoming these obstacles. The potential benefits of Li-air and Li-S justify the continued research effort that will be needed.

Li-O2 and Li-S batteries with high energy storage.

There is great interest in developing rechargeable lithium batteries with higher energy capacity and longer cycle life for applications in portable electronic devices, electric vehicles and implantable medical devices. Silicon is an attractive anode material for lithium batteries because it has a low discharge potential and the highest known theoretical charge capacity (4,200 mAh g(-1); ref. 2). Although this is more than ten times higher than existing graphite anodes and much larger than various nitride and oxide materials, silicon anodes have limited applications because silicon's volume changes by 400% upon insertion and extraction of lithium which results in pulverization and capacity fading. Here, we show that silicon nanowire battery electrodes circumvent these issues as they can accommodate large strain without pulverization, provide good electronic contact and conduction, and display short lithium insertion distances. We achieved the theoretical charge capacity for silicon anodes and maintained a discharge capacity close to 75% of this maximum, with little fading during cycling.

/pdf/high-performance-lithium-battery-anodes-using-silicon-58e1j6kr4f.pdf

High-performance lithium battery anodes using silicon nanowires

Rechargeable lithium batteries represent one of the most important developments in energy storage for 100 years, with the potential to address the key problem of global warming. However, their ability to store energy is limited by the quantity of lithium that may be removed from and reinserted into the positive intercalation electrode, LixCoO2, 0.5 <x <1 (corresponding to 140 mA·h g-1 of charge storage). Abandoning the intercalation electrode and allowing Li to react directly with O2 from the air at a porous electrode increases the theoretical charge storage by a remarkable 5−10 times! Here we demonstrate two essential prerequisites for the successful operation of a rechargeable Li/O2 battery; that the Li2O2 formed on discharging such an O2 electrode is decomposed to Li and O2 on charging (shown here by in situ mass spectrometry), with or without a catalyst, and that charge/discharge cycling is sustainable for many cycles.

Rechargeable LI2O2 electrode for lithium batteries.

Charge storage in rechargeable lithium batteries is limited by the positive electrode, usually the lithium intercalation compound LiCoO2, which can store 130 mAhg . Intense efforts are underway worldwide to discover new lithium intercalation compounds for use as positive electrodes which, it is hoped, may deliver specific capacities of about 300 mAhg . However, increasing the capacity significantly beyond this limit is a major challenge requiring a more radical approach, such as replacement of the intercalation electrode by an O2 electrode, in which Li + from the electrolyte and e from the external circuit combine reversibly with O2 from the air within a porous matrix containing a catalyst. Although it provides higher capacities than intercalation electrodes, much fundamental work is required to understand and optimize the performance of the O2 electrode for lithium batteries before it can be considered further for technological application. The nature of the catalyst plays a key role. It is important to identify good catalysts for the electrode reaction before focusing on other tasks, such as reducing the catalyst loading and optimizing porosity, binder, and electrolyte. Herein we show that a-MnO2 nanowires give the highest charge storage capacity yet reported for such an electrode, reaching 3000 mAh per gram of carbon, or 505 mAhg 1 if normalized by the total electrode mass. Furthermore, by avoiding deep discharge, excellent capacity retention has been demonstrated. Finally, the capacities delivered by an O2 electrode and a conventional intercalation compound are compared. The reversible oxygen electrode is shown schematically in Figure 1. On discharge, the Li ions (electrolyte) and e (external circuit) combine with O2 (air) to form Li2O2 within the pores of the porous carbon electrode. Previously, we demonstrated that rechargeability of the Li/O2 cell involves decomposition of Li2O2 back to Li and O2. [8] Our earlier studies on the rechargeable Li/O2 cell focused on electrolytic manganese dioxide (EMD) as catalyst in the oxygen electrode. Recently, we examined a number of other potential catalyst materials including Co3O4, Fe2O3, CuO, and CoFe2O4. [9] Such investigations served to demonstrate that the nature of the catalyst is a key factor controlling the performance of the oxygen electrode, especially the capacity, which is the primary reason for interest in the O2 electrode. Herein we report on the high capacities that an a-MnO2 nanowire catalyst can deliver. We also compare the performance of a-MnO2 with other manganese oxide compounds. Note that the specific capacities are normalized with respect to the mass of carbon in the electrode, as is usual for porous electrodes; this point is discussed at the end of the paper. Synthesis and characterization of the various MnOx catalysts and their incorporation into lithium cells with porous electrodes is described in the Experimental Section. Powder X-ray diffraction data were collected for all catalysts (see the Supporting Information) and confirmed their identities (a-MnO2 in bulk and nanowire form, b-MnO2 in bulk and nanowire form, g-MnO2, l-MnO2, Mn2O3, and Mn3O4). The variation of capacity with cycle number for a porous electrode containing a-MnO2 nanowires as catalyst is presented in Figure 2a, from which the superior behavior of the a-MnO2 catalyst is evident. The initial discharge capacity is 3000 mAhg , it then drops slightly, rises again to 3100 mAhg 1 on cycle 4, before declining steadily thereafter. This may be contrasted with previous reports for EMD, the capacity of which falls below 1000 mAhg 1 after one cycle (Figure 2a). The variation of potential with state of charge for several cycles of a-MnO2 is shown in Figure 2b. As observed previously for all other catalysts, the discharge voltage is around 2.6 V versus Li/Li. 9] Previous results have demonstrated that the charging potential varies according to the catalyst type. Values ranging from 4 to 4.7 V versus Li/Li have been observed, and a-MnO2 exhibits a charging potential at the lower end of this spectrum, at around 4.0 V. This is another advantage of the a-MnO2 nanowires, since it is important to minimize the charging potential. Note that a-MnO2, and many of the other MnOx compounds described herein, support some Li intercalation. However, Figure 1. Schematic representation of a rechargeable Li/O2 battery.

α‐MnO2 Nanowires: A Catalyst for the O2 Electrode in Rechargeable Lithium Batteries

An O2 cathode for rechargeable lithium batteries: The effect of a catalyst

The electrochemical reactivity of tailor-made CuO powders prepared according to a new low-temperature synthesis method was studied by a combination of transmission electron microscopy (TEM) and electrochemical techniques. All the processes involved during cycling were successfully identified. We show that the reduction mechanism of CuO by lithium involves the formation of a solid solution of Cu II 1x Cu I x O 1 1/2 :, 0 ≤ x ≤ 0.4, a phase transition into Cu 2 O, then the formation of Cu nanograins dispersed into a lithia matrix ( Li 2 O) followed by the growth of an organic-type coating. This one is responsible for the extra capacity observed on the voltage vs. composition curve. During the subsequent charge, the organic layer vanishes first, and then the Cu grains are partially or fully oxidized with a concomitant decomposition of Li 2 O. The formation of Li 2 O and Cu nanograins and then the one of Cu. CuO, and Cu 2 O nanograins on the first discharge and subsequent charge, respectively, were identified by high-resolution TEM studies. These results enabled a better understanding of the processes governing the reactivity of 3d metal oxides vs. lithium down to 0.02 V.

https://iopscience.iop.org/article/10.1149/1.1409971/pdf

A Transmission Electron Microscopy Study of the Reactivity Mechanism of Tailor-Made CuO Particles toward Lithium

The conversion reactions associated with mesoporous and nanowire Co3O4 when used as negative electrodes in rechargeable lithium batteries have been investigated. Initially, Li is intercalated into Co3O4 up to x
				∼ 1.5 Li in LixCo3O4. Thereafter, both materials form a nanocomposite of Co particles imbedded in Li2O, which on subsequent charge forms CoO. The capacities on cycling increase on initial cycles to values exceeding the theoretical value for Co3O4 + 8 Li+ + 8e−
				→ 4 Li2O + 3 Co, 890 mAhg−1, and this is interpreted as due to charge storage in a polymer layer that forms on the high surface area of nanowire and mesoporous Co3O4. After 15 cycles, the capacity decreases drastically for the nanowires due to formation of grains that are separated one from another by a thick polymer layer, leading to electrical isolation. In contrast, the mesoporous Co3O4 losses its mesoporosity and forms a morphology similar to bulk Co3O4 (Co particles imbedded in Li2O matrix) with which it exhibits a similar capacity on cycling. In contrast to mesoporous lithium intercalation compounds, which show superior capacity at high rates compared to bulk materials, mesoporosity does not seem to improve the capacity of conversion reactions on extended cycling. If, however, mesoporosity could be retained during the conversion reaction, then higher capacities could be obtained in such systems.

Aurelie Debart

Papers

Rechargeable LI2O2 electrode for lithium batteries.

α‐MnO2 Nanowires: A Catalyst for the O2 Electrode in Rechargeable Lithium Batteries

An O2 cathode for rechargeable lithium batteries: The effect of a catalyst

A Transmission Electron Microscopy Study of the Reactivity Mechanism of Tailor-Made CuO Particles toward Lithium

Mesoporous and nanowire Co3O4 as negative electrodes for rechargeable lithium batteries