| The properties of the metal hydride electrode prepared with PTFE as a binder have been investigated. The LMNi_(4.5)Co_(0.1)Mn_(0.2)Al_(0.2) hydrogen storage alloy powders were coated by 25wt.% electroless copper plating in an acid bath, mixed with 3 to 10wt% PTFE, and then compacted at 6 ton/㎠ at room temperature. The electrode characteristics were examined through electrochemical measurements in a half cell. The electrochemical measurement showed that the addition of PTFE decreased slightly activation time at a low current. At a high current, however, the activation rate decreased with increasing the amount of PTFE. The electrode property at low temperatures was improved by adding PTFE, whereas it became worse at hgh temperatures. When the charged electrode was stored in the electrolyte for more than 1 day, the discharge capacity decreased dramatically due to a self deactivation of the alloy surfaces, but not due to a self discharge. The charge retention was scarcely changed by the addition of PTFE. The cycle life was not influenced by either one of the addition of PTFE and graphite, and sintering. On the other hand, the sintering under argon gas of low purity has oxidied the alloy powder resulting in reduction of discharge capacity. The degadration of the electrode was strongly dependent on the exposure time to electrolyte and the number of cycles. |
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