BU-309: How does Graphite Work in Li-ion?

In 2015, the media predicted heavy demand for graphite to satisfy the growth of Li-ion batteries used in electric vehicles. Speculation arose that graphite could be in short supply because a large EV battery requires about 25kg (55 lb) of graphite for the Li-ion anode. Although price and consumption has been lackluster, there are indications that the demand is tightening. China is the main producer of anode material.

Producing anode-grade graphite with 99.99 percent purity is expensive and the process creates waste. The end-cost is not so much the material but the purification process. Recycling old Li-ion to retrieve graphite will not solve this because of the tedious purification process.

Carbon and graphite are related substances. Graphite is an allotrope of carbon, a structural modification that occurs by bonding the elements together in a different manner. Graphite is the most stable form of carbon. The diamond, a metastable allotrope of carbon known for its excellent physical qualities, is less stable than graphite; yet graphite is soft and malleable.

Graphite comes from the Greek word “graphein.” It is heat-resistant, electrically and thermally conductive, chemically passive (corrosion-resistant) and lighter than aluminum. Beside Li-ion anodes, high-grade graphite is also used in fuel cells, solar cells, semiconductors, LEDs, and nuclear reactors.

A carbon fiber is a long, thin strand of about 5–10µm in diameter, one-tenth the thickness of a human hair. The carbon atoms are bonded together in microscopic crystals and are extremely strong. They are woven in a textile fashion and mixed with a polymer matrix, which is a hardened form of carbon fiber that is as strong as steel but lighter. These materials are used in golf clubs and bicycle frames, as well as body parts for cars and airplanes to replace aluminum. The Boeing 787 and Airbus 350X make extensive use of carbon fiber. Graphite for batteries currently accounts to only 5 percent of the global demand.

Graphite comes in two forms: natural graphite from mines and synthetic graphite from petroleum coke. Both types are used for Li-ion anode material with 55 percent gravitating towards synthetic and the balance to natural graphite.

Manufacturers preferred synthetic graphite because of its superior consistency and purity to natural graphite. This is changing and with modern chemical purification processes and thermal treatment, natural graphite achieves a purity of 99.9 percent compared to 99.0 percent for the synthetic equivalent.

Purified natural flake graphite has a higher crystalline structure and offers better electrical and thermal conductivity than synthetic material. Switching to natural graphite will lower production cost with same or better Li-ion performance. Synthetic graphite for Li-ion sells for around US $10,000 per ton whereas spherical graphite made from natural flake sells for US $7,000 (2015 prices).

Unprocessed natural graphite is much cheaper, and besides cost, natural graphite is more environmentally friendly than synthetic graphite; it also forms the base for graphene, a scientist’s dream. At the end of 2016, natural graphite accounts for 60-65% of the market share; synthetic is around 30% and alternatives such as lithium titanate, silicon and tin is around 5%.

A research lab reports improvements in cycle life using artificial graphite. Artificial graphite is similar to synthetic graphic but cost and manufacturability are not yet known. Test results released in 2019 reveal notable improvements in cycle life, an issue that is of large interest for the electric vehicle.

Environmental Concerns: The graphite industry is under pressure to reduce pollution levels. Processing natural flake graphite and synthetic graphite can contaminate the air with dangerous particles in the proximity of the plant. Reducing wastewater born by processing natural flake graphite into spherical graphite as part of purification is also a concern.

Spherical graphite is mainly refined from flake graphite reaching purity of 99.95%. With a rapid growth of Li-ion demand over the next decade, questions arise on the ability to supply enough spherical graphite to meet the demand. Spherical graphite costs 3-4 more than small- to medium-sized flake concentrate. Part of this cost is born by stringent environmental requirements because the refinement process uses strong acids.

These graphite materials are almost exclusively used for anodes in Li-ion batteries. India and China are large produces of graphite. As Li-ion improves, processes become more complex and this also involves environmental protection. (See BU-1002b: Environmental Benefit of the Electric Powertrain)

Current purification processes are mainly done in China and require a large quantity of chemicals that have a negative environmental impact. In the near future, purification can be done with new green technology, such as hydroelectricity.

While efforts are made to ease the environmental impact, supply is constrained for both the natural and synthetic graphite. This holdback reflects in the price of graphite material that started in 2017 and is expected to hold into 2020 as plants are being refurbished.

Graphene

Graphene is an allotrope of carbon in the form of a two-dimensional hexagonal lattice. Presented in a sheet of pure carbon, graphene is only one atom thick. It is flexible, transparent, impermeable to moisture, stronger than diamonds and more conductive than gold. Experts hint to graphene as a miracle material that will improve many products, including the battery.

Graphene anodes are said to hold energy better than graphite anodes and promise a charge time that is ten times faster than what is currently possible with Li-ion. Load capabilities should also improve; better longevity is another item on the wish-list that needs to be proven.

With traditional graphite anodes, lithium ions accumulate around the outer surface of the anode. Graphene has a more elegant solution by enabling lithium ions to pass through the tiny holes of the graphene sheets measuring 10–20nm. This promises optimal storage area and easy extraction. Once available, such a battery is estimated to store ten times more energy than Li-ion featuring regular graphite anodes.

Further improvements with graphene are achieved by adding vanadium oxide to the cathode. Experimental batteries with such an enhancement are said to recharge in 20 seconds and retain 90 percent capacity after 1,000 cycles. Graphene is also being tested in supercapacitors to improve the specific energy density, as well as in solar cells. Figure 1 illustrates the unique lattice of graphene made visible with scanning probe microscopy (SPM).

Graphene is a sheet of pure carbon that is one atom thick. It is flexible, transparent, impermeable to moisture, stronger than diamonds and more conductive than gold. Each carbon atom possesses three electrons that bind with the nearest neighbor atom electron, creating a chemical bond.

Scientists have theorized about the wonders of graphene for decades, but no commercial products exist that makes exclusive use of this apparent miracle material. It is likely that the marvel of graphene has been utilized unknowingly for centuries in pencils and other products. A better understanding of its mechanism will eventually lead to improved products.

Meanwhile we take the many wonderful breakthroughs published by academia and stock promoters with a grain of salt. We will embrace the super battery when it arrives but pledge to honor what we currently have by taking better care of it in the workforce. (See BU-104c: The Octagon Battery)

[1] Source: U.S. Army Materiel Command