Cathode materials

In lithium-ion batteries, the cathode (positive electrode) is a major factor in the overall cost.

To evaluate cathode materials, we consider several key factors: energy, power density, lifespan and safety.

The more energy a battery can store, the longer it can be used. For example, in vehicles, a higher energy battery allows the vehicle to drive longer distances.

The amount of energy a battery can store depends on its voltage and capacity to achieve high energy density; cathode materials must have both high capacity (specific and volumetric) along with high voltage (Kim et al., 2012).

Cathode materials are generally categorised into two main types: oxide-based and phosphate-based compounds. The following are some of the most important cathode materials used in lithium-ion batteries (Dou, 2013).

Lithium cobalt oxide

In 1980, Prof. John B. Goodenough introduced the lithium cobalt oxide (LiCoO₂ or LCO) compound as a cathode material for lithium-ion batteries. Sony was the first company to commercialise lithium-ion batteries using LCO cathode material in 1991. The LCO cathode has been popular in portable electronics for nearly three decades due to its high lithium-ion conductivity and long cycle life (Lyu et al., 2021).

The high energy density of LCO (150 Watt-hour/kilogram (Wh/kg)) makes it ideal for use in portable electric devices (Wang et al., 2019). However, there are some drawbacks: for instance, LCO-based lithium-ion batteries can pose serious problems like overheating and thermal runaway, especially at high temperatures or under stress.

Moreover, the use of cobalt (Co) makes these batteries more expensive (Lyu et al., 2021). The largest volume of the world’s cobalt (65%) is produced in the Democratic Republic of Congo (DRC), and the market of LCO-based lithium-ion is dependent on it. However, cobalt mining in the DRC has created poverty and social problems like child labour, low wages, and gender-based violence in the war-torn eastern area of the country (Eskelinen et al., 2024).

_{Cobalt mining tunnels often reach lengths and depths far greater than the legal maximum of 30 metres (already an extreme and dangerous level). International Institute for Environment and Development; CC BY-NC-ND 2.0}

Lithium nickel manganese cobalt oxide

Lithium nickel manganese cobalt oxide (NMC) is another widely used cathode material. NMC provides an outstanding battery performance, including high specific power, long lifespan, safety, and especially high energy density (170 Wh/kg) (Malik et al., 2022).

_{Nickel: electrolytically refined pure (99.9%) nickel nodules, and a high purity (99.99% = 4N) 1 cm³ nickel cube for comparison. Crystallised nickel-electrolyte salts (green) can be seen in the pores of the nodules. Alchemist-hp; CC BY-NC-ND 3.0}

Each metal in the NMC compound plays a specific role: nickel improves capacity, manganese increases the operating voltage, and cobalt provides stability during the charge and discharge processes. Because of these advantages, NMC is a promising choice for electric vehicles (EVs).

_{Manganese: pure (99.99%) manganese chips, electrolytically refined, and a high purity (99.99% = 4N) 1 cm³ manganese cube for comparison. Alchemist-hp; CC BY-NC-ND 3.0}

Although NMC cathodes were first introduced to the market in 2004, they have since become dominant in markets such as EVs, power tools, medical devices, and portable electronics. However, NMC batteries do have some disadvantages, including relatively high cost; dependency on cobalt; complex manufacturing processes; and environmental concerns, most of which stem from the use of cobalt (Jeevanantham & Shobana, 2022).

Lithium iron phosphate

To address the issues of cost and environmental impact, a phosphate-based cathode material called lithium iron phosphate (LiFePO₄ or LFP) was developed. Prof. John B. Goodenough introduced this material in 1997, and it has since gained popularity in the market (Jugović & Uskoković, 2009).

With an energy density of about 130 Wh/kg, LFP-based lithium-ion batteries are used in a wide range of electronic devices. An LFP cathode offers good battery performance at a lower cost; replacing LCO with LFP can reduce cathode costs by up to 40% (Ritchie & Howard, 2006). More importantly, LFP cathode material passes all safety tests such as short-circuit, nail and rod penetration tests.

Research and share

In addition to the materials described above, several others can be used as cathodes in lithium-ion batteries. Research some other cathode materials and their properties, and share what you’ve found about one of them in the comments below.

References

Dou, S. (2013). Review and prospect of layered lithium nickel manganese oxide as cathode materials for Li-ion batteries. Journal of Solid State Electrochemistry, 17, 911-926.

Eskelinen, T., Khan, J., & Härri, A. (2024). Cobalt mining and responsibility: An analysis of the meaning of ethical products. Etikk i praksis-Nordic Journal of Applied Ethics(1), 65-82.

Jeevanantham, B., & Shobana, M. (2022). Enhanced cathode materials for advanced lithium-ion batteries using nickel-rich and lithium/manganese-rich LiNixMnyCozO2. Journal of Energy Storage, 54, 105353.

Jugović, D., & Uskoković, D. (2009). A review of recent developments in the synthesis procedures of lithium iron phosphate powders. Journal of Power Sources, 190(2), 538-544.

Kim, T. H., Park, J. S., Chang, S. K., Choi, S., Ryu, J. H., & Song, H. K. (2012). The current move of lithium ion batteries towards the next phase. Advanced Energy Materials, 2(7), 860-872.

Lyu, Y., Wu, X., Wang, K., Feng, Z., Cheng, T., Liu, Y., Wang, M., Chen, R., Xu, L., & Zhou, J. (2021). An overview on the advances of LiCoO₂ cathodes for lithium‐ion batteries. Advanced Energy Materials, 11(2), 2000982.

Malik, M., Chan, K. H., & Azimi, G. (2022). Review on the synthesis of LiNi_xMn_yCo_1-x-yO₂ (NMC) cathodes for lithium-ion batteries. Materials Today Energy, 28, 101066.

Nkumba-Umpula, E., Buxton, A., & Schwartz, B. (2021). Islands of responsibility? Corporate sourcing of artisanal cobalt in the Democratic Republic of Congo. IIED.

Ritchie, A., & Howard, W. (2006). Recent developments and likely advances in lithium-ion batteries. Journal of Power Sources, 162(2), 809-812.

Wang, X., Wang, X., & Lu, Y. (2019). Realizing high voltage lithium cobalt oxide in lithium-ion batteries. Industrial & Engineering Chemistry Research, 58(24), 10119-10139.

Cobalt. Alchemist-hp; CC BY-NC-ND 3.0