[Complete Battery Mastery](27) Tire and Shoe Sole Materials Also Used in Batteries... What Are Conductive Additives?

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In January 2017, LG Electronics announced a new laptop model called the 'All-Day Gram,' which significantly increased usage time while reducing weight. A special material, previously unused, was applied to the battery inside this laptop.

The 'Gram' laptop, first introduced in 2014, gained great popularity due to its thinness and light weight, but there were many complaints about its short usage time. Users had to carry chargers or external batteries separately.

The LG Electronics PC development team began to explore ways to extend battery life without changing the weight. Initially, they considered reducing the thickness of the separator, but this was excluded due to fire risk concerns. After much deliberation, the team decided to apply carbon nanotubes (CNT), a new material gaining attention at the time, as a conductive additive. The result was a great success.

LG Electronics' 2017 model 'All Day Gram' with extended battery life by applying carbon nanotube (CNT) conductive material.

By applying CNT conductive additives, the battery's usable capacity was increased by 1.7 times compared to before. The battery had a capacity of 60 watt-hours (Wh), which allowed up to 24 hours of use on a single charge. Despite the increased battery capacity, the laptop's weight either decreased or only slightly increased. For the 13.3-inch model, the weight was reduced by 40g to 940g, and for the 14-inch model, it was reduced by 10g to 970g.

Conductive Additives: Helpers for Active Materials

Conductive additives (導電材) literally mean materials that conduct electricity. In lithium-ion batteries, conductive additives help electrons move between the active materials of the cathode and anode. They connect the active materials electrically.

Lithium-ion batteries operate by lithium ions and electrons moving between the cathode and anode, but the active materials themselves have low electrical conductivity, so conductive additives are added to enhance conductivity.

Additionally, conductive additives maintain spacing between active materials to reduce contact resistance and help the electrolyte penetrate easily.

In English, conductive additives are called "conductive additives," meaning substances added to provide conductivity. They are also referred to as "conductive agents."

Image source=LG Energy Solution

Conductive additives are used in the first stage of secondary battery manufacturing called the mixing process. The mixing process involves combining active materials, conductive additives, and binders into a slurry form. Active materials are the chemically reactive substances in the cathode and anode that generate electrical energy. Binders are a type of adhesive that helps active materials and conductive additives stick together.

The slurry made this way is coated onto the current collector to form the electrode. Although the proportion of conductive additives in the electrode is not large, they play a very important role in maximizing electrode performance. Conversely, if conductive additives are insufficient or do not function properly, the active materials cannot react effectively, reducing battery capacity.

In the entire electrode, the weight ratio of active materials, conductive additives, and binders is approximately 95:5:5. Recently, as the performance of conductive additives has improved, their proportion has decreased. Reducing the amount of conductive additives allows more active materials to be added, increasing energy capacity. Using high-performance conductive additives is why battery capacity can be increased.

Carbon Black, Previously Used in Tires and Shoe Soles, as a Conductive Additive

Good conductive additives must satisfy several conditions. First, since the main purpose of adding conductive additives is to improve electrical conductivity, they must fundamentally have excellent conductivity. At the same time, they should not cause unnecessary oxidation or reduction reactions with the electrolyte.

In the electrode process, after drying the slurry, it is compressed under high pressure. Therefore, conductive additives must maintain high strength to withstand high pressure.

Conductive additives used in secondary batteries include metal-based (silver powder, copper powder, nickel powder, etc.), metal oxide-based (tin oxide, iron oxide, zinc oxide, etc.), carbon-based (carbon black, graphite, carbon nanotubes, etc.), and composites (composite powders, composite fibers, etc.).

Among these, carbon-based conductive additives are the most widely used. Carbon-based additives have the advantages of low cost and light weight. Carbon-based conductive additives include carbon black, fine graphite, carbon nanotubes (CNT), and graphene-like materials. Sometimes two or more conductive additives are used together to improve conductivity and other properties.

So far, the most commonly used conductive additive material is carbon black. Literally translated, carbon black means "carbon blackness." It refers to soot produced by incomplete combustion of carbon-based substances. In the past, in China, soot was collected and used as a substitute for ink.

Carbon Black. Photo by Wikipedia

Nowadays, carbon black is produced by incomplete combustion or thermal decomposition of hydrocarbons such as petroleum or natural gas. Carbon black has unique properties and is used as an industrial material in various fields.

First, it is used as a pigment in inks and paints. Carbon black is also included in printer inks and toners. Especially, adding carbon black to rubber improves strength, abrasion resistance, and heat resistance, making it an essential material in the rubber industry for tires and shoe soles. In fact, the largest use of carbon black is in tires, accounting for about 70% of demand.

Carbon black produced by thermal decomposition has excellent electrical conductivity and is also used as a battery conductive additive. Currently, carbon black is generally added at 2-3% by total electrode weight in cathodes and 0.5-1% in anodes.

Recently, there is a trend to enhance conductive additive performance by adding graphene or graphite to carbon black. Graphene is a thin film made of carbon atoms arranged in a honeycomb-shaped two-dimensional plane of six carbon atoms. It has excellent electrical conductivity and strength, making it useful as a conductive additive.

CNT Rapidly Emerging as a Secondary Battery Conductive Additive

Recently, CNT has attracted attention as a conductive additive material. CNT has a structure where hexagonal graphene layers are rolled into tubes. CNT was discovered in 1991 by Dr. Sumio Iijima of the Japanese electronics company NEC.

Depending on the structure, if the carbon tube has a single wall, it is called SWCNT (Single Wall CNT), and if it has multiple walls, it is called MWCNT (Multi Wall CNT). Mechanical, electrical, and chemical properties vary depending on the structure. With technological advances, CNT structures can be artificially created, but SWCNT is more difficult to produce and much more expensive than MWCNT.

CNTs have diameters of several nanometers (nm) and lengths of several to tens of micrometers (μm). Their diameter is only about one hundred-thousandth the thickness of a human hair, but their strength is about 100 times that of steel, and they have electrical conductivity comparable to copper.

Types and Structures of Carbon Nanotubes (CNT). Image source=Electronics and Telecommunications Research Institute (ETRI)

Despite their excellent performance, CNTs faced difficulties in finding demand due to their high price for a considerable period. However, in recent years, as the secondary battery market has grown, CNTs have rapidly emerged as conductive additives. When used in secondary battery electrodes, CNTs reduce the amount used by about 30% compared to carbon black while improving conductivity by about 10%.

CNTs can be used in smaller amounts than carbon black as conductive additives. This allows more active materials to be added, enhancing battery performance. Another advantage is that the use of expensive binders can be reduced.

CNT conductive additives are also gaining attention as conductive additives for silicon anode materials. Silicon anodes can greatly increase energy capacity compared to conventional graphite anodes but have volume expansion issues, so they are used by adding small amounts, around 5%, to graphite. CNTs help suppress the expansion of silicon anodes, allowing increased additive amounts. SWCNTs are used as conductive additives for anodes. (For more on silicon anodes, see Complete Battery Mastery Episode 11.)

However, despite CNTs' excellent conductivity, heat resistance, and strength, they have the limitation of strong agglomeration. CNTs do not disperse well in solvents and tend to clump, so technologies to improve dispersion are necessary. The industry is understood to pre-disperse CNTs in solutions or create composites for use.

"$2.8 Trillion Market by 2030... MWCNT to Account for 60%"

As the lithium-ion battery market grows, the use and market for conductive additives are also expected to grow. Market research firm SNE Research forecasts that the lithium-ion battery conductive additive market will grow from $800 million in 2022 to $2.1 billion (about 2.8 trillion KRW) in 2030, with an average annual growth rate of 12%.

Among these, MWCNT is expected to grow from $290 million in 2022 to $1.25 billion in 2030, accounting for about 60% of the total market. Despite low demand, SWCNT is expected to account for 29% of the market in 2030 due to its high unit price.

Meanwhile, the market share of carbon black and fine graphite is expected to shrink to about 10% by 2030 due to reduced usage.

Major suppliers of carbon black include Cabot in the United States, Denka and Lion in Japan, and Imerys in Switzerland.

MWCNT suppliers fiercely competing include LG Chem and J-O in Korea, Cnano, Dazhan, Timesnano, and DHnano in China, and SUSN (a subsidiary of Cabot) in the United States.

LG Chem began researching CNT for secondary battery use in 2011 and independently developed related technology in 2014. It supplies CNT conductive additives to LG Energy Solution.

LG Chem researchers are examining CNT anode materials. Image courtesy of LG Chem

LG Chem first operated a 500-ton scale CNT plant (Plant 1) in 2017 and currently has a total production capacity of 2,900 tons across three plants as of 2023. When the fourth CNT plant in Daesan, Chungnam, is completed in 2025, production capacity will increase to 6,100 tons.

J-O succeeded in mass-producing MWCNT domestically for the first time in 2006 and developed thin wall carbon nanotubes (TWCNT) in 2014. It supplies CNT conductive additives to SK On and CATL and plans to expand production capacity to 5,000 tons annually by 2025.

SWCNT is dominated by OCSiAl, headquartered in Luxembourg, with over 90% market share. In Korea, Cobon and Nano New Materials have entered the SWCNT market.

iNews24, LG Gram's New Weapon is 'Battery'... No Need to Carry Charger, 2017.1.12
LG Business Research Institute, Accelerating Commercialization of Carbon Nanotubes, 2018.11.16
LG Energy Solution, Battery Inside - CNT Conductive Additives Cover Both Cathode and Anode, 2022.8.4
Hi Investment & Securities, Secondary Battery Industry Status and Outlook, 2022.11.28
SNE Research, Development Status and Mid-to-Long-Term Outlook of Lithium-ion Secondary Battery Conductive Additives, 2023.11.30