Composite Negative Electrode Research Articles

Isotropic Volume Expansion of Particles of Amorphous Metallic Alloys in Composite Negative Electrodes for Li-Ion Batteries

Direct observation of the particles of active material as they react in situ is necessary to build an understanding of the growth characteristics in large-volume-change active materials. A comparison between in situ optical and atomic force microscopy observations shows that particles of amorphous large-volume-change active material expand isotropically upon lithium insertion. Using the isotropic expansion upon lithium insertion characteristic of amorphous alloys, the volume change of other amorphous active materials upon lithium insertion can be measured with an optical microscope by observing only the change in particle area.

A novel composite negative electrode consist of multiphase Sn compounds and mesophase graphite powders for lithium ion batteries

A modified electroless plating technique was adopted to prepare the Sn compounds/mesophase graphite powders (MGP) composite electrode. Characterization of the composite material showed that multiphase Sn compounds were uniformly deposited on MGP. The multiphase composition which contained metallic Sn, SnP 3 and SnP 2O 7 were expected to provide a higher spectator to Sn ratio for improved cycleability. During cycling between 0.001 and 1.5 V, the charge capacity was greatly enhanced without appreciable fading. From the voltage profiles and cyclic voltammetry (CV) curves, it was revealed that the capacity fading was caused by either the formation of insulated LiP in the early stage or by aggregation of metallic Sn after prolonged cycling. For improving the cycleability, the cut-off voltage was lowered from 1.5 to 0.9 V. Adjusting the voltage range was manifested to be an effective way for obtaining superior cycling performance in the Sn–P–O/MGP composite negative electrode. The capacity retention was as high as 96% of the highest capacity after charge/discharge between 0.001 and 0.9 V for 45 cycles.

Failure Modes of Silicon Powder Negative Electrode in Lithium Secondary Batteries

Si composite negative electrodes for lithium secondary batteries degrade in the dealloying period with an abrupt increase in internal resistance that is caused by a breakdown of conductive network made between Si and carbon particles. This results from a volume contraction of Si particles after expansion in the previous alloying process. Due to the large internal resistance, the dealloying reaction is not completed while Si remains as a lithiated state. The anodic performance is greatly improved either by applying a pressure on the cells or loading a larger amount of conductive carbon in the composite electrodes.

High energy density batteries derived from conductive polymers

Allied-Signal has developed batteries which derive their superior performance from the unique combination of properties offered by conductive polymers: electroactivity, mechanical resiliency, and combined ionic and electronic conductivity. Composite electrodes fabricated from conductive polymers and alkali-metal alloys operate with high efficiency and high cycle life. Composite negative electrodes have been combined with cation inserting positive electrodes such as Li xV 6O 13 and Na xCoO 2 to produce high energy density cells having excellent cycle life and a high average voltage, 1.9 V and 2.5 V, respectively. Early Prototype AF-size cells in welded steel cans have demonstrated up to 65 mWh/g (160 mWh/cm 3) and 70 mWh/g (170 mWh/cm 3) for sodium and lithium cells, respectively. Energy densities as high as 100 mWh/g (260 mWh/cm 3) are projected for efficiently packaged sodium cells charged to a higher average voltage (2.8V).

A Rechargeable Cell Based on a Conductive Polymer/Metal Alloy Composite Electrode

A composite electrode composed of a conductive polymer and an alkali‐metal alloy has been investigated as the negative electrode for a nonaqueous rechargeable cell. A sodium‐alloy based composite electrode composed of , poly(p‐phenylene), and binder achieved a capacity of 234 mAh/g or 450 mAh/cm3. This electrode also exhibited excellent cycle life and rate capability without dendrite formation. The composite electrode exhibited kinetic behavior similar to that of pure sodium metal. A balanced cell was constructed by combining the above sodium‐ion‐inserting composite negative electrode with a sodium‐ion‐inserting positive electrode, , of approximately equal capacity. The cell exhibited excellent cycle life (>250 cycles). The semiempirical energy density of the electrode system is comparable to alternative lithium metal based cell such as assuming that excess Li is needed in the latter case.