Thierry Brousse

Amorphous silicon as a possible anode material for Li-ion batteries

Silicon thin films have been deposited on porous nickel substrates by low pressure chemical vapor deposition using silane as the precursor gas. At 650°C, the substrates were covered by a 1.2 μm thick amorphous silicon layer. The films were electrochemically cycled vs. a lithium electrode. Despite high capacity up to 1000 mA h/g measured during the first three cycles, the films have shown poor cycling ability over 20 cycles. This fade of the specific capacity is assigned to mechanical disintegration of the electrode during cycling.

A Hybrid Activated Carbon-Manganese Dioxide Capacitor using a Mild Aqueous Electrolyte

A hybrid electrochemical capacitor using MnO 2 and activated carbon (AC) as positive and negative electrodes, respectively, has been designed. The electrodes were individually tested in a mild aqueous electrolyte (0.65 M K 2 SO 4 ) in order to define the adequate balance of active material in the capacitor as well as the working voltage. The hybrid electrochemical capacitor was cycled between 0 and 2.2 V for over 10,000 constant current charge/discharge cycles. A real energy density of 10 Wh/kg was reproducibly measured with a real power density reaching 3600 W/kg. The hydrogen and oxygen evolution reactions on AC and MnO 2 electrodes, respectively, were investigated in 0.65 M K 2 SO 4 . Despite the good electrochemical performance of the 2.2 V capacitor, gas evolution could be a hindrance for practical use. Subsequently, a 1.5 V capacitor was tested for more than 23,000 cycles and yielded interesting electrochemical performance with negligible gas evolution.

Thin‐Film Crystalline SnO2‐Lithium Electrodes

Crystalline SnO{sub 2} thin films have been investigated as possible negative electrodes for lithium-ion batteries. The films have been cycled electrochemically vs. lithium and shown reversible capacity as high as 500 mAh/g over more than 100 cycles. The substantial irreversibility during the first cycle can be explained by the formation of metallic tin and amorphous lithium oxide. This last phase probably plays an important role in allowing the thin-film electrode to contract and expand during the cycling process.

A Hybrid Fe3 O 4 ­ MnO2 Capacitor in Mild Aqueous Electrolyte

A hybrid electrochemical capacitor using MnO 2 and Fe 3 O 4 as active material for the positive and the negative electrode, respectively, has been designed. The electrodes have been individually tested in a mild aqueous electrolyte (0.1 M K 2 SO 4 ) to define the adequate balance of active material in the capacitor as well as the working voltage of a capacitor based on these two electrodes. The specific capacitances of MnO 2 and Fe 3 O 4 were 150 ′ 10 and 75 ′ 8 F/g, respectively whereas the specific capacitance of the Fe 3 O 4 /MnO 2 capacitor was equal to about 20 F/g of active material. The hybrid electrochemical capacitor has been cycled between 0 and 1.8 V for over 5000 constant current charge/discharge cycles. A real energy density of 7 Wh/kg was reproducibly measured with a real power density up to 820 W/kg.

Microsupercapacitors as miniaturized energy-storage components for on-chip electronics

The push towards miniaturized electronics calls for the development of miniaturized energy-storage components that can enable sustained, autonomous operation of electronic devices for applications such as wearable gadgets and wireless sensor networks. Microsupercapacitors have been targeted as a viable route for this purpose, because, though storing less energy than microbatteries, they can be charged and discharged much more rapidly and have an almost unlimited lifetime. In this Review, we discuss the progress and the prospects of integrated miniaturized supercapacitors. In particular, we discuss their power performances and emphasize the need of a three-dimensional design to boost their energy-storage capacity. This is obtainable, for example, through self-supported nanostructured electrodes. We also critically evaluate the performance metrics currently used in the literature to characterize microsupercapacitors and offer general guidelines to benchmark performances towards prospective applications.

High-resolution electron microscopy investigation of capacity fade in SnO2 electrodes for lithium-ion batteries

Nanocrystalline SnO 2 thin films have been cycled electrochemically vs. a lithium electrode. They have shown a reversible capacity of about 400-500 mAh/g over more than 100 cycles. However, a capacity fade usually occurs after a few hundred cycles. A high-resolution electron microscopy (HREM) investigation has shown the decomposition of SnO 2 crystallites into 10 to 50 nm wide tin grains during the first cycle as previously reported. An amorphous phase containing carbon and oxygen has also been detected in the cycled samples. Furthermore, the tin particles are surrounded by an amorphous 5 to 10 nm wide ring made of Sn and O. The size of the tin crystallites formed during the first cycle increases from 40 nm to an average value of 110 nm after 500 cycles. In addition, the structure of the amorphous compound made of Sn and O surrounding the tin particles changes after 500 cycles, suggesting that a beginning of crystallization has occurred. We assume that either particle expansion or the formation of this semicrystalline layer is responsible for the capacity fade observed in SnO 2 negative electrodes.

Carbon-Based Composite Materials for Supercapacitor Electrodes: A Review

Electrochemical capacitors, so-called supercapacitors, play an important role in energy storage and conversion systems. In the last decade, with the increasing volume of scientific activity and publications in this field, researchers have developed better tools to improve electrode materials. Although carbonaceous materials seem the most suitable for supercapacitor applications, a large diversity of materials has been proposed and studied. Yet, in order to accomplish performance beyond the limitations of each material, mainly in terms of energy density and durability, composite materials have been implemented, most of them being the combinations of carbon-based materials and other components. In this review, we present the recent advances in the field of composite materials that include at least one carbon-based component for supercapacitor electrodes. We focus on cases in which a single material by itself suffers from a drawback that can be overcome by combining it with other components, enabling the fabrication of a composite material with enhanced performance. We present several important compositions as well as the major routes of synthesis, characterization and performance of composite materials in this field.

TiO2(B) nanoribbons as negative electrode material for lithium ion batteries with high rate performance.

Nanosized TiO(2)(B) has been investigated as a possible candidate to replace Li(4)Ti(5)O(12) or graphite as the negative electrode for a Li-ion battery. Nanoribbon precursors, classically synthesized in autogenous conditions at temperatures higher than 170 °C in alkaline medium, have been obtained, under reflux (T ∼ 120 °C, P = 1 bar). After ionic exchange, these nanoribbons exhibit a surface area of 140 m(2) g(-1), larger than those obtained under autogenous conditions or by solid state chemistry. These nanoparticles transform after annealing to isomorphic titanium dioxide. They mainly crystallize as the TiO(2)(B) variety with only 5% of anatase. This quantification of the anatase/TiO(2)(B) ratio was deduced from Raman spectroscopy measurement. TEM analysis highlights the excellent crystallinity of the nanosized TiO(2)(B), crystallizing as 6 nm thin nanoribbons. These characteristics are essential in lithium batteries for a fast lithium ion solid state diffusion into the active material. In lithium batteries, the TiO(2)(B) nanoribbons exhibit a good capacity and an excellent rate capability (reversible capacity of 200 mA h g(-1) at C/3 rate (111 mA g(-1)), 100 mA h g(-1) at 15C rate (5030 mA g(-1)) for a 50% carbon black loaded electrode). The electrode formulation study highlights the importance of the electronic and ionic connection around the active particles. The cycleability of the nano-TiO(2)(B) is another interesting point with a capacity loss of 5% only, over 500 cycles at 3C.

All oxide solid-state lithium-ion cells

Solid-state lithium-ion cells have been prepared using thin film Li4Ti5O12 as the anode, thin film LiCoO2 as the cathode and Li0.33La0.56TiO3 as the electrolyte. The electrolyte was prepared as a relatively thick ceramic with a thickness close to 1 mm. This type of cell develops a voltage of slightly greater than 2 V and is stable to cycling. Perhaps the most interesting aspect of this cell, is that even with a relatively thick, poor quality ceramic electrolyte, this cell has been able to develop current densities as great as 40 μA/cm2.

Composite negative electrodes for lithium ion cells

Abstract In this study, the possible uses of SnO 2 and SnS 2 as anodes in lithium-ion batteries have been investigated. Powders of both materials have been synthesized. Structural as well as electrochemical characterizations have been performed. Both systems seem to follow similar mechanisms leading to the formation of metallic tin and Li 2 O or Li 2 S after the first cycle. SnO 2 and SnS 2 powders exhibit similar irreversible capacities on the first cycle in accordance with the expected theoretical values. However, the reversible capacity is much higher in the case of SnO 2 . Synthesis methods as well as differences in the inactive component of the electrode can explain the poor electrochemical performances observed for SnS 2 powder. Despite the drawbacks of the sulfide system, this study indicates that not only Li 2 O can be used as an inactive matrix in composite electrodes.