|A 140-cell pack of Toshiba’s 3.0 Ah SCiB cells meet the FreedomCAR HEV power assist goals. Click to enlarge.|
Toshiba, which last December announced the general commercial launch of a 4.2 Ah cell version of its fast-charging SCiB—Super Charge ion Battery—lithium-ion battery (earlier post), is developing a 3.0 Ah high-power version of the cell specifically for hybrid electric vehicle (HEV) applications.
Shinichiro Kosugi, Chief Specialist for Toshiba’s Super Charge Battery Division, described the characteristics of the HEV cell during a presentation at the Advanced Automotive Battery Conference (AABC) last week.
Toshiba uses a lithium titanate (LTO) material in its anode for improved safety and support for fast recharge. An LTO anode supports high rate capabilities and fast charge even at low temperatures.
|Toshiba SCiB LTO Cells|
|SCiB 3.0||SCiB 4.2|
|Nominal voltage||2.4 V||2.4 V|
|Operating voltage @ >0°C||2.8-1.7 V
(2.8-1.5 V <0°C)
|10s discharge power @BOL, 50% SOC, 25°C||500 W
|10s charge power
@BOL, 50% SOC, 25°C
|Discharge capacity (1C)||3 Ah
|AC impedance (1kHz)||1.7 mΩ||2.6 mΩ|
|10s DC resistance
@BOL, 50% SOC, 25°C
|2.5 mΩ||6.5 mΩ|
|Weight||140 g||155 g|
|Size (mm)||62 x 90 x 13||62 x 95 x 13|
However, cell voltage is only 2.4 V (the anode is 1.4 V versus lithium) and it has a low capacity density of about half that of graphite.
It is, however, inherently more thermally stable than conventional carbon anodes.
Toshiba designed the 3.0 Ah cell specifically for automotive applications. The can material is lightweight aluminum, with high cooling efficiency (although more difficult to weld). Toshiba uses a laser weld for tightness and reliability rather than a crimp or hermetic seal. Terminal sealing uses resin caulk.
The terminal-busbar connection is welded for low resistive loss and high reliability, and the terminals are on one side of the cell for simplified connection and aggregated leak risk.
|The SCiB HEV battery compensates for lower voltage and capacity by having a larger SOC window. Click to enlarge.|
Although the cells have a lower voltage and capacity than other lithium-ion battery technologies, the LTO chemistry compensates for that by offering a larger functional state of charge range. (This is an argument similar to that proposed by EnerDel, which also uses an LTO anode chemistry. Earlier post.)
Although a pack comprising Toshiba 3.0 Ah SCiB cells would require 140 cells to meet the FreedomCAR power assist targets—150% more than conventional lithium-ion battery (LIB) technology—the pack would require 20% less material, according to Toshiba.
Dr. Menahem Anderman, president of Advanced Automotive Batteries, suggests that batteries with lithium titanate anode materials may be of interest in high-power, ultra-long-life, low-energy applications—e.g., micro and mild hybrids—in competition with ultracapacitors.