Idemitsu Kosan Co. Ltd., is developing a phosphorous sulfide solid electrolyte (Li2S-P2S5) for solid-state lithium-ion batteries. The company expects to commercialize solid-state lithium-ion cells using the new electrolyte around 2012.
Idemitsu is a petroleum and petrochemical company, and identified the potential of lithium sulfide as an electrolyte material for rechargeable Li-ion batteries (secondary batteries) when evaluating the uses of high-purity lithium sulfide produced for the PPS resin process. In 2006, the company announced that it was accelerating development of the solid electrolyte based on its belief that the material would be “highly suitable” for hybrid and electric vehicles, and said that the electrolyte under development possessed a lithium-ion conductivity of 4×10-3S/cm at room temperature—equivalent to the liquid organic electrolyte currently used in lithium-ion secondary batteries.
| MRS 2010 Spring Meeting |
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| At the upcoming MRS 2010 Spring Meeting in San Francisco (5-9 April 2010), Yoshikatsu Seino from Idemitsu Kosan is presenting an invited paper on the high rate capability of all-solid state batteries using the phosphorous sulfide solid electrolyte. |
Unlike liquid organic electrolytes, however, the solid electrolyte possesses excellent stability thanks to its resistance to degradation or vaporization even at high voltages and temperatures. A solid electrolyte avoids safety hazards such as solvent leakage and flammability, and also offers the advantage of a wide variety of construction techniques. A battery using the solid electrolyte under development by Idemitsu also operated at low temperatures of less than 0 °C.
The phosphorous sulfide electrolyte can be used with a variety of electrode materials. At the 214th meeting of the Electrochemical Society (ECS) in October 2008, for example, researchers from Idemitsu presented a paper showing the use of the lithium sulfide electrolyte with lithium anodes.
Idemitsu also suggests that the use of the lithium sulfide electrolyte would enable the use of a sulfur material—which electrochemically has a high capacity—in the cathode.
[In February, a team led by Dr. Yi Cui at Stanford University reported the demonstration of a new proof-of-concept lithium metal-free battery with high specific energy consisting of a lithium sulfide (Li2S)/mesoporous carbon composite cathode and a silicon (Si) nanowire anode. (Earlier post.) At the upcoming 217th meeting of the ECS, a research group from the University of Colorado, Boulder, will present a paper on the use of nanosilicon as an anode material in all solid-state batteries with a Li2S-P2S5-based solid electrolyte.]
At the 1st International Rechargeable Battery Expo in Tokyo last week, Idemitsu exhibited an A6-size (105 mm × 148 mm) laminated solid-state lithium-ion (Li-ion) battery using its lithium sulfide electrolyte.
With cells connected in series, the A6-size battery has an output voltage of 14-16V and a solid electrolyte membrane with a thickness of about 100 µm. Idemitsu did not disclose its power and energy densities.
Idemitsu Kosan said it will further the thickness of the electrolyte membrane to 10-20 µm to lower the resistance and search for an optimal electrode material.
Resources
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T. Utaka, Y. Seino, Y. Saito (2008) All-solid-state lithium batteries with sulfide-based solid electrolytes and lithium negative electrodes. (ECS 214)
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James Trevey, Conrad Stoldt, and Se-Hee Lee (2010) All-Solid-State Rechargeable Lithium-Ion Batteries with Li2S-P2S5 Based Electrolytes (ECS 217)