A small amount of mercury is added to conventional alkaline button batteries to control hydrogen buildup by the anode. Simply adding no mercury at all for environmental reasons would pose a risk of battery swelling and leakage. For this reason, successfully removing mercury to create a mercury-free series of alkaline button batteries called for two gas-blocking systems. Gas-suppressing technology in the anode, already used in non-mercury silver oxide batteries, is combined with original Sony gas-absorbing technology in the cathode.

• Regular alkaline button batteries contain a mercury coating to suppress the gas that forms when a zinc anode is in contact with an alkaline electrolyte.
• Without mercury, zinc would gradually dissolve from a corrosive reaction with the alkaline electrolyte, producing hydrogen. This would cause battery swelling and loss of performance.
• To suppress gas, the anode incorporates an anti-corrosion material and high-performance powdered zinc alloy, and a special finish is applied to the anode collector.
• Cathodes of alkaline button batteries do not absorb gas as readily as cathodes of silver oxide batteries. To overcome this, original Sony technology was developed to add gas-absorbing material, enabling non-mercury alkaline button batteries.

Our first breakthrough in non-mercury button batteries came in 2004 with silver oxide batteries. Within the industry at the time, it was viewed as technically challenging to create non-mercury button batteries, which were one of the few products exempt from general restrictions on mercury. What made non-mercury silver oxide batteries possible were the same gas-suppression technologies later used in alkaline button batteries, described above. This breakthrough earned the grand prize in an inaugural manufacturing award program of the Japanese government in 2005, in the product technology and development category.