Introduction of graphite based high rate dual carbon battery
Hydrogen production from methane cracking produces no carbon dioxide emissions, and the carbon is fixed in solid carbon products. A large amount of natural gas and biogas can be used as reaction feedstock, and dual carbon battery is regarded as clean hydrogen production processes with great development potential.
For every ton of hydrogen produced with this process, there are 3 tons of solid carbon co-production. Effective use of solid carbon co-products produced in methane cracking can bring significant economic benefits and make the methane cracking hydrogen production process more competitive in the market.
Dual carbon battery introduction
Dual carbon battery is a new lithium ion battery types. Its cathode and anode energy storage materials are made of carbon. It has the advantages of low cost, environmental friendliness, and a high operating voltage (> 4.5 V).
However, in the repeated charging and discharging process, the traditional graphite material structure will be damaged and collapsed, resulting in a short cycle life and poor performance of the dual carbon battery (the energy storage capacity will decay rapidly during high-speed charging and discharging).
Using iron ore as catalyst, the onion graphite co-product of hydrogen produced by methane catalytic cracking has a moderate specific surface area (10-30 m2 g-1) and certain porosity, which can be used as an efficient electrode material for dual carbon batteries.
The production of dual carbon battery
Using graphite as the electrode material for cathode and anode, a dual carbon battery with excellent rate performance was realized. The work uses low-cost iron ore as a catalyst to produce hydrogen by catalytic cracking of methane. At the same time, graphite-carbon co-products with onion structure were obtained.
By using conventional high temperature heat treatment or electrochemical methods at room temperature to purify graphite carbon materials, the carbon purity of onion graphite can reach 99.32% and 97.59%, respectively.
Studies have found that purified onion graphite has a larger specific surface area and smaller lattice size than traditional natural graphite and synthetic graphite. This facilitates faster surface redox reactions and better structural stability.
● Cycle life
The assembled dual carbon battery can cycle stably for 300 cycles without significant capacity degradation, demonstrating excellent cycling performance.
Under high load and discharge conditions, there are still 79.2% and 93.4 % capacity retention rates.
● Energy density
The dual carbon battery also has higher energy densities (169 and 160 Wh kg-1) and power densities (10.6 and 10.8 kW kg-1). This achievement opens up a new direction of application for the large number of solid carbon co-products generated in the clean hydrogen production process based on methane cracking.
These two dual carbon graphite batteries have excellent cycling and speed performance. It can be stable for 300 cycles without significant capacity degradation. At large magnifications, capacity retention rates are as high.
In addition, compared to other recently reported dual carbon battery, this dual carbon battery also exhibits high energy density as the energy density of lithium ion battery.
Graphite materials in dual carbon battery
● High temperature heat purification
At 890 °C and 6 atmospheres, using iron ore as a catalyst, methane interacts with iron ore powder to crack and generate hydrogen and solid carbon. Iron ore particles are broken into nanoscale fragments, and solid carbon is deposited on the iron surface to form graphite with an onion structure.
Onion graphite can undergo conventional high-temperature purification to remove iron nanoparticles wrapped in carbon materials to obtain high-temperature purified onion graphite (TG).
● Electrochemical purification at room temperature
It is also possible to use a method of electrochemical purification at room temperature. Using purified onion graphite as the working electrode and platinum foil as the counter electrode, the encapsulated iron nanoparticles are leached into the electrolyte to obtain electrochemically purified onion graphite (EG).
In addition, two commercial graphite materials, natural graphite (NG) and synthetic graphite (SG), are also used as reference materials. The energy storage performance of anions and cations (PF6-, Li+) in the electrolyte when embedded as cathode and anode in dual carbon battery was compared.
The structural stability of dual carbon battery
The new TG and EG half cells have lower charge transfer resistance. At 2 and 5 C, the TG had a capacity of 78.4 mAh g-1 and at 50 C, the TG retained 88.3% of its capacity of 69.2 mAh g-1.
When the current returns to 1 C after 1-50 C charge and discharge, TG and EG capacities are 76.8 and 70.1 mAh g-1, showing capacity recovery rates of 98.0 and 96.8%, higher than 95.9% of NG.
It is observed that during loading and unloading at large magnifications, NG material will collapse and produce defects, resulting in irreversible peeling of the graphite layer and low cell efficiency. TG has good structural stability and can tolerate rapid anion intercalation, so it can recover quickly after large loads and discharges.
The dual carbon battery rate performance
Four graphite materials were used by the top 10 lithium battery anode material factories in China as anode materials to assemble lithium semi-batteries. At low current densities, TG and EG have energy storage capacities similar to NGs. From current densities above 0.35 C to the end, TG and EG have greater energy storage capacity.
By contrast, SG’s energy storage capacity is very low. There is obvious capacity decay at 0.2 C, indicating that the intercalation process of lithium ions between SG layers is very slow. This may be due to the smaller specific surface area, pore volume, larger crystal size, and fewer defects in its structure.
Dual carbon battery electrochemical property
At 5 C, the energy storage capacities of the EG and TG full batteries are 74.7 and 75.1 respectively. At 50 C, EG and TG exhibited high capacity retention of 93.4% and 79.2 %, respectively, demonstrating excellent rate performance.
At a current density of 5 C, TG and EG complete cells can cycle stably for 300 cycles without capacity decay, demonstrating excellent cycle stability. TG and EG dual carbon battery has high energy and power densities, surpassing traditional energy storage devices and other recently reported dual carbon battery.
The graphite co-product in the methane catalytic cracking hydrogen production process was used as cathode and anode electrode material to achieve a dual carbon battery with excellent performance.
Onion graphite is purified by high temperature heat purification or electrochemical purification at room temperature, respectively, and the carbon purity can reach 99.32 and 97.59%. Compared with commercial graphite, purified onion graphite has a larger specific surface area, faster kinetics and better structural stability in the electrochemical process.
This article explores the new application of onion graphite in energy storage, which brings new economic benefits to the methane cracking hydrogen production process, and is more conducive to promoting this clean hydrogen production process.