Researchers at Stanford University have developed rechargeable batteries that can store up to six times the charge.
The new development will help accelerate the adoption of rechargeable batteries and bring researchers closer to high-performance batteries for phones and electric vehicles.
The authors of the new work made a battery with chlorine from alkali metals: it is based on the reverse chemical conversion of sodium chloride (Na/Cl2) or lithium chloride (Li/Cl2) into chlorine. Electrons move from one side of a rechargeable battery to the other, and when recharged, they return to their original state.
The reason no one has yet created a high-performance, rechargeable sodium-chloride or lithium-chlorine battery is because chlorine is too reactive and difficult to convert back to chloride with high efficiency. When this was done, the battery performance was poor.
The researchers in the new work did not intend to create rechargeable sodium and lithium chloride batteries, but simply improved existing technologies using thionyl chloride – one of the main elements of lithium thionyl chloride batteries.
They then formed an electrode using a carbon material that has a nanosphere structure filled with many ultra-fine pores. In practice, these hollow spheres act like a sponge, absorbing chlorine molecules and storing them for further conversion to salt within the micropores.
The resulting cell showed a fairly high discharge capacity – 2,800 milliampere-hours per gram of cathode. After that, the authors unexpectedly discovered that the battery can be recharged and then discharged again.
The capacity of such a cycle turned out to be lower than the capacity of the first discharge – 1,200 milliamperes per hour per gram of cathode at a current of 100 milliamperes – however, the capacity did not decrease further. The battery has survived 200 charge and discharge cycles, maintaining its Coulomb efficiency (the ratio of the charge that the battery gives off during discharge to that which is required to charge) of about 99%.