D.M. Schleich

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.

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.

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.

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.

Characterization of sprayed and sputter deposited LiCoO2 thin films for rechargeable microbatteries

Thin films of LiCoO2 have been prepared by both spray pyrolysis and r.f. sputtering. Structural properties of the films have been investigated by X-ray powder diffraction and scanning electron microscopy. The LiCoO2 hexagonal high-temperature phase was obtained on the samples after post-deposition annealing treatments at 600 °C in air. Films as thin as 75 nm have been deposited on large aluminium and aluminium/gold substrates. Sputter deposition improved the density and homogeneity of thin films compared with the spray pyrolysis method. Cells wtih sprayed and sputtered LiCoO2 compounds versus lithium using LiClO4 in propylene carbonate as the liquid electrolyte have been tested, the importance of annealing the thin films before cycling discussed, and the importance of the substrate in the cycling behaviour is evidenced. The cyclic voltammograms demonstrate that the LiCoO2 cathodes prepared by both methods are electrochemically active, showing promising cycling behaviour.

Sprayed and thermally evaporated SnO2 thin films for ethanol sensors

Abstract Tin dioxide thin films have been prepared by both spray pyrolysis and thermal evaporation on alumina substrates. The main purpose was to determine suitable microstructural and electrical properties for ethanol sensors. Chlorine content in precursor solutions used in the spray pyrolysis technique affects both the structural and the electrical properties of the films. Chlorine-free precursors were prepared to achieve porous SnO 2 films. Ethanol sensing properties were determined and compared to thermally evaporated films.

Search for suitable matrix for the use of tin-based anodes in lithium ion batteries

Abstract Graphite is proposed as matrix for tin which is able to react inside the graphite sheets with lithium. If this matrix should be able to support the cell changes associated to the formation of lithium–tin alloys, an improvement of the performance of the lithium ion battery anode would be expected. Two techniques, (vapor phase and molten salt techniques, respectively) have been considered to obtain graphite intercalation compounds (GIC) with tin chlorides. The subsequent reduction of these systems with hydrogene at 400°C must lead to tin GICs. Due to the little extent of the intercalation reaction, the obtained compounds possess a maximal composition of Sn 0.044 C 6 . Despite the small amount of intercalated tin, potentiostatic tests reveal that both tin and graphite are electrochemically active versus lithium. Galvanostatic tests indicate that the contribution of tin to the system total capacity increases for the molten salt samples and remains almost constant for the vapor phase samples. This behavior seems to indicate that the activity of tin intercalated atoms is very stable compared to pure graphite. The upper capacity found, 400 mAh/g, corresponds to the Sn 0.044 C 6 system, obtained by the molten salt technique. Its good electrochemical properties agree with our idea that graphite is an adequate matrix for the tin atoms or clusters presents therein.

Metal oxide anodes for Li-ion batteries

Recently metal oxides, especially tin oxides, have been investigated as negative electrodes in Li-ion batteries. Different compounds such as amorphous SnO2, SnO and SnSiO3 have been electrochemically cycled versus a metallic lithium electrode. In this study, the reversible capacities as well as the cycling behavior of crystalline SnO2 thin films and powders have been investigated. SnO2 powder exhibits a reversible capacity as high as 600 mAh/g over more than 50 cycles versus a metallic lithium electrode. Based on these results, we give clues for the future investigations of metal oxides as anodes in lithium ion batteries and discuss what can be the expected capacities of such negative electrodes.

Advanced oxide and metal powders for negative electrodes in lithium-ion batteries

Abstract In this study, tin dioxide, tin and bismuth have been envisioned as possible candidate to replace graphite negative electrodes in Li-ion batteries. Tin dioxide thin films and nanoscaled tin and bismuth powders have been synthesized by different techniques. Their electrochemical behaviors have been compared to electrodes made with standard commercially available powders. In all cases, nanoscaled materials have shown enhanced electrochemical properties compared to standard powders. SnO 2 thin films exhibit a longer cycle life than tin dioxide powder. The capacities measured on both bismuth and tin nanoscaled materials were more important than for the same electrodes prepared by commercially available powders. Moreover, the values are close to those expected from the theoretical reactions. However, the cycling life of tin or bismuth electrodes is still the weak point of these systems. Subsequently, an optimized matrix is required in order to prevent capacity loss upon cycling.