|Charge-discharge and power characteristics of a prototype 18 Ah Li-ion cell in a new elliptical format using the Mn-based cathode and new anode materials. Click to enlarge.|
The Nikkei reported that Hitachi plans to commercialize automotive lithium-ion batteries featuring its next-generation materials for use in hybrid cars within the next three to four years.
As described in a set of presentations at the recent Advanced Automotive Batteries Conference (AABC), Hitachi is developing manganese-based cathode materials and a new surface-modified graphite anode material (SMG) using a combination of amorphous carbon and Hitachi’s patented MAG artificial graphite.
In 2004, Hitachi, Shin-Kobe Electric Machinery Co. Ltd. and Hitachi Maxwell Ltd. formed a joint venture—Hitachi Vehicle Energy Ltd. (HVE) — to develop, manufacture and market rechargeable lithium-ion batteries for hybrid electric vehicles and other applications. HVE will supply the Li-ion storage for the next-generation of GM’s Hybrid System (the Belt Alternator Starter system, not the two-mode). (Earlier post.)
In January, the HVE partners injected ¥6 billion (US$58 million) to the JV company to strengthen its production and development capabilities.
LiMn2O4 (LMO) cathode materials offer high power and a lower cost per kg, but not per Wh. Life at elevated temperatures can be problematic. However, according to Dr. Menahem Anderman, president of Advanced Automotive Batteries, the manganese-based materials (LMO and NMC, LiNiCoMnO2) are becoming the most popular cathode materials today and offer good synergy between the components.
A number of other companies have LMO or NMC cathode materials in place or under development, including Panasonic, AESC, Sanyo, GS Yuasa, LG Chem, Samsung, SK Corp, Toshiba, EnerDel, and AltairNano.
Hitachi is focusing on the anode to further improve energy densities as well as power densities. Hitachi’s current Li-ion artificial graphite anode material, MAG, offers a particular particle shape and pore size than enables the high speed insertion and diffusion of lithium ions.
However, noted Tatsuya Nishida, who is responsible for anode material R&D at Hitachi Chemical Company, MAG can exhibit poor cycle and power down capabilities. The conversion to amorphous carbon on the surface of MAG is designed as a countermeasure.
Expected effects from the SMG material include:
Less SEI (solid electrolyte interface) formation, which improves power output and input;
Improved stability for the electrolyte solvent, which improves life (cycle and storage); and
Less lithium metal deposition, which improves safety.
Hitachi Vehicle Energy has developed an 18 Ah prototype elliptical cell and a 4-cell module designed for application in a fuel cell hybrid vehicle using current versions of the new materials. The module, with an operating voltage of 14.4V, has a specific energy density of 80 Wh/kg and volumetric energy density of 125 Wh/L.
Specific power output @ 50% SOC is 2,400 W/kg and specific power input @ 50% SOC is 2,120 W/kg, said Tatsuo Horiba, Chief Engineer for HVE. A mock-up of a 3 kWh pack based on the new modules yielded a calculated specific energy of 75 Wh/kg, and specific power output @ 50% SOC of 2,250 W/kg.