Ulvac Enables Flexible Li-Ion Battery
Ulvac Inc. said it has developed a process flow for very thin lithium-ion cells, which may be combined with solar cells to create and store electricity in wearable electronics.
Kenji Tsuda, Asia Contributing Editor -- Semiconductor International, 12/22/2008
Ulvac Inc. (Kanagawa, Japan) has developed a manufacturing process flow for very thin (50 μm) lithium-ion rechargeable batteries, using semiconductor process technologies and equipment. The paper-like flexible battery may be applied as the power supply of a wearable computer, or as a medically-implantable battery. And the thin lithium-ion cells may be combined with solar cells to create and store electricity, said Takehito Jimbo, an Ulvac manager.
Ulvac makes chemical and physical vapor deposition tools, etchers, implanters, and ashing systems. The lithium-ion battery technology was developed jointly with Ulvac Materials, which develops sputtering targets.
The flexible battery features a solid-state electrolyte, which the company claims is safer than the conventional liquid electrolyte that can present a fire hazard. The basic structure is similar to that of a planar semiconductor diode; with a bottom substrate, a patterned cathode current collector of MgO/Ti/Pt, a patterned cathode of LiCoO2, a patterned solid-state electrolyte of LiPON, a patterned anode current collector of nickel or copper, and an anode made of lithium. The cathode and anode electrodes react with the electrolyte. In a battery cell, the current collector plays a role similar to the metal electrodes in a semiconductor device.
Ulvac produces manufacturing equipment that can be used for the sputtering and evaporation steps required for the thin-film materials in the battery. Ulvac said its single-wafer sputtering system can be used to form the cathode of LiCoO2, the solid-state electrolyte of LiPON, and the current collector layers. The tool uses DC and RF magnetron sources, and can be configured with five chambers including RTA annealing for the cathode crystallization.
Ulvac Materials developed sputtering targets up to 440 mm in diameter, including a LiCoO3 disk for the cathode, and a Li3PO4 disk for the solid-state electrolyte. The films are chemically reduced with a N2 gas, and the anode Li metal is formed with an evaporator tool called ei-5.
Finally, the flexible cell must be encapsulated with plastic layers, much like a wafer-level package. The encapsulation film consists of the triple layers; an organic layer, a barrier layer and an organic layer formed with a single-wafer evaporator, the Ulvac PME-200. The barrier layer has the role of preventing water vapor from entering the battery.
Thin-film battery manufacturer Nuricell (Seoul, South Korea) produced a prototype lithium-ion cell using the Ulvac turnkey systems. The total thickness is 50 μm, and the cell active area is 20x20 mm. The electrical characteristics include an operating voltage of 3.0-4.1 V, a current capacity of 0.5-1.0 mAh, and a maximum operating current of 15 mA at -20-120 º C.
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| Ulvac Inc. adapted its semiconductor-processing equipment and sputtering targets to a turnkey process flow for ultra-thin batteries. |
Ulvac hopes to sell three turnkey systems in 2009 to produce paper-like batteries, covering sputtering, evaporation and encapsulation.
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