Dual carbon battery
A dual carbon battery is one that uses carbon for both the cathode and the anode.
History
Dual-carbon (also called dual-graphite) batteries were first introduced in a 1989 patent. They were later studied by various other research groups.[1]
In 2014 start-up Power Japan Plus announced plans to commercialize its version, named the Ryden. Colead Kaname Takeya is known for his work on the Toyota Prius and Tesla Model S.[2] The company claimed that its cell offers energy density comparable to a lithium-ion battery, more rapid charge rate, a longer functional lifetime (3k cycles), improved safety and cradle-to-cradle sustainability. The cell used a lithium phosphorus fluoride salt (LIPF
6). The company claimed that its battery charges 20 times faster than conventional lithium ion batteries, is rated for more than 3,000 cycles and can slot directly into existing manufacturing processes, without changes to existing manufacturing lines.[1]
Precipitation and dissolution of a lithium salt takes place at any location where an aprotic electrolyte is present. However, increased precipitation on electrode surfaces decreases power density because the salt in a solid state is an insulator. One element of the company's patent introduces a method to prevent such precipitation. This also improves gravimetric energy density.[1]
The battery can fully discharge without the risk of short-circuiting and damaging the battery. The battery operates without heating at room temperature, avoiding the extensive cooling systems that appear in current electric cars and the corresponding risk of thermal runaway. It operates at over four volts. The battery is fully recyclable. The electrodes are made from cotton, to better control the crystal size.[3]
A separate research project used the same salt and a high voltage aprotic electrolyte based on a fluorinated solvent and additive, which was capable of supporting the chemistry at 5.2 V with high efficiency. Enough electrolyte salt is needed in the cell to guarantee conductivity, and enough solvent must be available to enable the salt to dissolve at any level of charge/discharge.[1]
Mode of operation
Lithium ions dispersed in the electrolyte are inserted/deposited into/on the anode during charge, as in other lithium ion batteries. Unusually, ions (anions) from the electrolyte are intercalated into the cathode at the same time. During discharge, both anions and lithium ions return to the electrolyte. The electrolyte in such a system thus acts as both charge carrier and active material.[1]
Capacity is determined by the storage capacity and amount of ion release of the electrodes and the amount of anions and cations in the aprotic electrolyte.[1]
Reactions
Positive electrode: PF6− + nC ⇄ Cn(PF6)+e− jbi Negative electrode: Li+ + nC+e− ⇄ LiCn
→ charging reaction; ← discharge reaction
Patents
- Patent A US 3844837 A
