NiMH No.7 battery

Low-cost electrode material for NiMH No.7 battery - wood sulfonate

A common byproduct of the paper industry: wood sulfonate, has been proven by scientists at the Institute of Technology in Rensselaer. The research team has created a prototype of a lithium-sulfur battery for a watch, and the next step will be to try to scale up the prototype.

NiMH No.7 battery have an energy density at least twice that of lithium-ion batteries, so although rechargeable lithium-ion batteries are the hottest in the market, scientists are still very interested in the development of NiMH No.7 battery.

Rechargeable batteries mainly consist of two electrodes, a liquid electrolyte between the electrodes, and a separator. The cathode of a lithium-sulfur battery is composed of a sulfur-carbon matrix, and the anode uses lithium metal oxide. In elemental form, sulfur is non-conductive, but when sulfur is combined with carbon at high temperatures, it becomes highly conductive, so it is promising for use in new battery technologies.

However, a major challenge of NiMH No.7 battery is that sulfur easily dissolves into the battery electrolyte, causing the electrodes on both sides to deteriorate after just a few cycles. Although scientists have tried to use different forms of carbon such as nanotubes and complex carbon foams to stabilize the sulfur in place, the results are limited.

A team of researchers at the Institute of Technology in Israel has now found a simple way to create an optimal sulfur-based cathode from a single raw material. They dried lignosulfonate, a major byproduct of the paper industry, and then heated it to 700°C in a quartz tube furnace. The high heat drove off most of the sulfur gas, but left some polysulfides (chains of sulfur atoms) that can be deeply embedded in the activated carbon matrix.

The researchers repeated the heating process to get the right amount of sulfur embedded in the carbon matrix. The material was then ground and mixed with an inert polymer binder to form a cathode coating on aluminum foil, proving that this cheap and abundant paper-derived material can be used to build NiMH No.7 battery.

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