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 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]

As an electrolyte, the cell uses one or more lithium salts in an aprotic organic solvent. These remain unspecified, but as an example in a patent, the group uses a system consisting of lithium hexafluorophosphate (LiPF
6) as the salt, and ethylene carbonate (EC) and dimethyl carbonate (DMC), mixed in a 1:2 volume ratio, as solvent.

Both electrodes are based on graphitic carbon. Graphite with the right grain size is obtained by pyrolyzing cotton.

Precipitation and dissolution of a lithium salt takes place at any location where the 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

In following lines, → is the charging reaction and ← is the discharging reaction.

Positive electrode:

PF−
6 + n C ⇄ C
n(PF
6) + e−

Negative electrode:

Li+
+ n C + e−
⇄ LiC
n

Patents

• Patent A US 3844837 A ; basic concept, awarded to U.S. Navy on 29 Oct 1974
• Patent A1 WO 2015132962 A1 ; commercially viable chemistry, awarded to Kyushu University and Power Japan Plus on 11 Sep 2015
• Patent A1 WO 2016021067 A1 ; construction technique, awarded to Power Japan Plus on 11 Feb 2016
• Patent A1 WO 2016021068 A1 ; fabrication technique, awarded to Power Japan Plus on 11 Feb 2016
• Patent A1 WO 2016046910 A1 ; medical application arising from their carbon research, awarded to Power Japan Plus on 31 Mar 2016
• Patent A JP 2016091984 A ; dendrite growth problem solved, awarded to Power Japan Plus on 23 May 2016

References