D. N. Galushkin at all: Atomic metallic hydrogen (AMH) is formed inside of sintered oxide-nickel electrodes of nickel-cadmium battery over a long period of electrochemical hydrogenation (more than five years). It was established that density AMH is 12 times higher, than the density of liquid molecular hydrogen, the specific energy of hydrogen recombination is 20 times higher than of liquid hydrogen-oxygen fuel. At the room temperature AMH is a good conductor, but not a superconductor.

The long-used nickel–cadmium batteries occasionally undergo thermal runaway, during which all electrolyte evaporates and the plastic body of the battery melts down in 2-4 minutes. It was demonstrated, that as a result of the thermal runaway of battery, large amounts of hydrogen are released (KSX-25 battery with the service period of over five years releases approximately 800 liters of hydrogen in this way). This result corresponds 13.4 wt% of hydrogen in nickel which exceeds the content of hydrogen in nickel hydride by 10 times, and for any reversible metal hydrides, including magnesium hydride or complex hydrides by 2 times. Experimental and theoretical works indicate, that combination with tetravalent atoms, as in the group-14 hydrides, may significantly lower the metalization pressure of hydrogen. Hydrogen in these materials is “chemically precompressed” by the presence of the group-14 atoms within crystal lattice.

Compare also The Reasons of Thermal Runaway in Nickel-Cadmium Batteries In a case of the thermal runaway initiation, a battery heats up till high temperature values; an electrolyte evaporates instantly; a battery plastic case melts and sometimes it catches fire or explodes depending on the battery case construction and material.On the basis of all the available experimental data in the paper, there was proved, that the thermal runaway is associated with a powerful exothermic reaction going within the battery (1, 2) In the study Possibility of obtaining atomic metallic hydrogen by electrochemical method russian authors reportedly demonstrated, that the atomic metallic hydrogen (AMH) is formed inside of metal-ceramic oxide-nickel electrodes of nickel-cadmium battery over a long period of electrochemical hydrogenation (more than five years). The AMH was separated from nickel metal by electrochemical dissolution of metalceramic matrix in 22.6% sulfuric acid, and its properties were studied. It was established that density of AMH is 0.85 g cm-3, released specific energy of hydrogen recombination is 216 MJ kg-1 (?), resistivity is 1.5 ohm / cm, and AMH is not a superconductor at room temperature. The obtained parameters of AMH coincide with the theoretical values forecasted earlier.

NiCd KSX-25 battery for aircraft The KSX-25 battery operates in the mode of floating charge. Hence, it overcharges during most of the time. Considerable amount of AMH powder can be isolated only after three years of battery operation; and its maximal amount is achieved after five years of service life.