South Korea-based SK Energy has now developed six lithium-ion cells: two targeted at hybrid electric vehicle (HEV) applications and four targeted at plug-in hybrid electric vehicle (PHEV) applications. Jeon Oh, SK Energy’s Leader, Corporate R&D Center/HEV Battery Project, provided an update on the company’s Li-ion automotive battery activities at the Advanced Automotive Battery Conference 2009 this week in Long Beach.
SK Energy is Asia’s fourth largest energy provider, and was Korea’s first oil refining company, now with a domestic market share of 38%. The company was the first Korean company, and the third in the world, to independently develop a lithium-ion battery separator, which features proprietary technology for low shrinkage and heat resistance.
The company began commercial Li-ion battery production in 2005, targeting mobile devices, and is expanding to provide solutions for hybrid electric (HEV), plug-in hybrid electric (PHEV) and electric (EV) vehicles. The integrated energy and petrochemical company earlier invested 159 billion won (US$127 million) to expand its lithium-ion battery production. (Earlier post.)
SK Energy uses a lithium manganese oxide cathode material, mixing in NMC material for stabilization; a surface-modified graphite on the anode; a gel polymer electrolyte; and a ceramic-coated proprietary SK separator featuring low shrinkage and high heat resistance. SK cells have an energy density of up to 140 Wh/kg, Oh said.
|SK Cells for HEV, PHEV and EV applications|
|Cell voltage, V||3.85||3.85||3.90||3.90||3.90||3.90|
|Energy density, Wh/kg||100||115||138||131||138||140|
|Vol. energy density, Wh/L||208||222||273||260||270||279|
|Dis. power density, W/kg||4,500||3,800||3,200||4,000||4,000||4,000|
|Chg. power density, W/kg||3,300||2,800||2,100||2,500||2,500||2,500|
The cells use a pouch design, with stacked plates and wide tabs to increase power capability.
HEV Cells. Capacity and power fade are less than 10% after more than 500,000 km equivalent driving, Oh said. Cell-to-cell voltage variation after the testing was less than 120 mV; Oh suggested it might be possible to remove the cell-balancing function. After storage at 50% SOC at 45 °C (113 °F) for 400 days, the cells maintained 80% of capacity and power.
PHEV Cells. Using the USABC test pattern, the P135 PHEV cells had capacity and power retention of more than 70% after 9,000 cycles. At 5,000 cycles (the USABC target), capacity was more than 85% and power was more than 95%, according to data Oh showed.
Abuse testing on the P155 cells showed no smoke, fire or rupture under all abuse tests: penetration; high-temperature external short circuit; internal short circuit; thermal stability; and overcharge.
The P200 cells retained around 90% of both storage and capacity after storage at an 80% SOC for more than 100 days. Power retention is more than 95% after 3,000 cycles.
Battery Management System. SK is developing an application-specific integrated circuit (ASIC)-based battery management system. Use of the ASIC enables a smaller protection circuit module (PCB), higher balancing and sensing speed.
SOC estimation error are less than 5% under various driving conditions, Oh said. Errors are not accumulated even under continuous driving mode.
Modules and packs. The pouch design allows tab-to-tab connection, with reduced connection impedance (0.50mΩ), resulting in less heat generation and higher energy efficiency. SK uses a Lego-style plastic enclosure to enhance impact resistance, vibration durability and assembling efficiency.
|SK PHEV Packs|
|Energy density, Wh/kg||95||74||86|
SK has assembled three sample PHEV packs and is currently designing a compact 360V, 7.9 kWh pack, targeted at a 20-mile all-electric range PHEV. The PHEV20 pack uses 96 cells and is 65 liters (0.065 cubic meters or 2.3 cubic feet) in volume.
Oh said that SK has built a dedicated battery plant for automotive applications.
In August 2008, South Korea’s Yonhap news agency reported that Hyundai Motor was forming an alliance with LG Chem, SK Energy and SB LiMotive to develop battery packs for plug-in hybrid electric vehicles (PHEVs). (Earlier post.)