This blog is adapted from a research paper submitted to the Toshiba Exploravision Competition 2023. The paper was co-written with Ian Nicholson.
Lithium-ion batteries are secondary (rechargeable) batteries of unparalleled importance in today’s society. The lithium-ion battery has enabled a revolution in portable electronics and has created a rapidly growing market for energy storage that can help support the green economy. However, the manufacture of batteries is not without geopolitical and environmental problems. In this blog post, we explain the present technology of lithium-ion batteries and spotlight novel, innovative research being done to engineer a bioinspired battery (or rather a “Living Battery”) that is composed of the biological tools of nature to create a sustainable, efficient, and biodegradable alternative.
Current technology
Since its inception in the 1970s, the lithium-ion battery (LIB) has emerged to become the most important type of rechargeable (secondary) battery, helping shape and drive the global economy. Research and development have pushed the maximum gravimetric energy density to about 300 Wh kg-1, making the LIB invaluable in a wide range of electronic devices and electric vehicles. LIBs are used in practically all portable and consumer electronics, such as smartphones, laptops, cordless appliances, electric vehicles such as the Tesla, and many industrial applications. LIBs are not only an essential part of everyday modern life but also a critical technology to help chart the path to the green economy through their application to electric vehicles and reducing dependency on fuel.
The lithium-ion battery is charged and discharged by lithium ions (Li+) moving between the negative (anode) and positive (cathode) electrodes. The movement of Li+ between the anode and cathode generates an electrical current. The anode is made of graphite and the cathode is made of an oxide, such as cobalt oxide LiCoO2 (LCO). The cathode material is often more complex, containing manganese (Mn) and nickel (Ni) in addition. The movement of Li+ is facilitated by an electrolyte solution. When the battery is being charged, an external electrical current is applied to the battery, causing the Li+ ions to move from the cathode to the anode. When the battery is discharged, i.e., when it is powering your phone or electric car, the lithium ions return to the cathode. In addition to the anode, cathode, and electrolyte, the battery contains a separator, a thin, porous membrane placed between the anode and cathode. The primary function of the separator is to prevent physical contact between the anode and cathode, which would cause a short circuit of the battery. The separator also helps regulate the flow of lithium ions between the electrodes.
Environmental consequences of LIBs
With an understanding of how lithium-ion batteries function, the several problems associated with the manufacture and life cycle of LIBs become more clear. Mining of graphite causes human toxicity and marine life ecotoxicity. Lithium mining in South America, producing more than one-third of global lithium, requires millions of gallons of water and creates environmental problems such as soil degradation, biodiversity loss, and damage to ecosystems. In addition, there are also serious humanitarian impacts. One of the most prevalent components is cobalt (Co), a crucial part of the aforementioned LCO cathode (LiCoO2, or LiNixMnyCozO2). This combination creates a huge demand for cobalt, which is causing a surge in mining in Africa, and leads to unethical mining practices such as displacement of people from their homelands and child labor. Finally, lithium-ion batteries are not biodegradable, and not properly recycled. Disposal of these batteries results in millions of tons of wasted material in landfills, leaching into the environment and posing a hazard to the health of human, aquatic, and plant life.
Redesigning the LIB through the bioinspired lens
Researchers have been working to replace the 4 key components of the LIB with bioinspired materials to create a “Living Battery” that sustains the advancements of current technology (e.g., supports portable devices, electric vehicles, etc.), while also transforming the battery into an environmentally sustainable alternative: one that remains non-pollutive, humanitarian, efficient, cost-effective, and ideally better performing than the original LIB. While there is a wide variety of approaches being taken by scientists around the world, this blog post highlights a few innovative solutions that caught our eye, for each of the four parts of the battery that could potentially be engineered into a final version of the bioinspired LIB.
Bioinspired Anode
The anode (the negative electrode) requires several key properties such as a high surface area, a porous structure, high conductivity, and stability. Scientists have found that algae-based electrodes are a possibility (1). Through bioinspiration and the manipulation of the algae’s natural functions and processes, we can synthesize an effective Li+ containing anode with carbonization being a required outside step aside from the cultivating and harvesting of the algae. Algae has an extremely high surface area and is extremely light, allowing greater absorption and improvement of energy density, just as it would be necessary for increased diffusion in nature. The lithium ions will diffuse into the high surface, algae-derived anode, and improve efficiency over graphite.
Bioinspired Cathode
For the cathode, the electrochemical potential must allow the lithium ions to flow from the anode to the cathode during discharge and have the same criteria as the other electrode (porous, conductivity, stability, etc.). One solution is a cathode with embedded modified Nicotinamide adenine dinucleotide (NAD) molecules, with a conductive binder, that can grasp and release lithium ions during the charge-discharge cycle of the battery (2). NAD - nicotinamide cofactor - is one of the most common redox coenzymes present in living cells. The redox-active “NAD+” motif is involved in thousands of bio-transformations and electron-transfer reactions in natural systems. It is therefore a master molecule carrying charged ions and electrons from one place to another and a candidate for affixing Li+ during the electron transfer process.
Bioinspired Separator
Many important features of the battery, such as power density, cycle life, and safety strongly depend on the separator. The separator allows ions to flow but prevents physical contact between the electrodes which could short the battery. An ideal separator is electrically insulating, ionically conducting, thin, and porous. A plausible bioinspired substitute for the separator in an LIB is Cellulose ((C6H10O5)n), the most widely available organic polymer on the biosphere and a basic structural component of plants (3). Capacity, conductivity, and cycle life have been demonstrated for cellulose separators. Cellulose naturally has a porosity > 70%, which provides the appropriate amount to absorb the electrolyte and thus, creates a suitable environment for rapid ion diffusion across the separator for high ionic conductivity. Moreover, cellulose provides the right properties for the electrolyte as it is hydrophilic, meaning it will absorb the electrolyte solution easily.
Bioinspired Electrolyte
The electrolyte provides a medium to shuttle ions back and forth between positively and negatively charged terminals, which balances the electrical charge and extends the lifespan of the LIB. Electrolytes are usually liquids, but they can be gels, or more specifically a hydrogel. Hydrogels have a great capacity for water absorbance while still keeping a well-defined structure, which would provide a reliable electrolyte and avoid the use of flammable, corrosive, or toxic chemicals. An approach being explored is a gel electrolyte made from a biological material called chitosan, a derivative of chitin (4). Chitin can be readily obtained in vast quantities from its most abundant source, the exoskeletons of crustaceans (e.g., crab shells). Researchers found that a chitosan battery can have an energy efficiency of 99.7% and over 1000 cycles, an extremely successful outcome that paves the way for future green technology since it shows promising capabilities for large-scale energy storage for wind/solar energy.
The continued engineering going into producing a “Living Battery” is extremely exciting since it would produce a new type of Lithium-ion battery that sustains the advancements of current technology, while also transforming the battery into an environmentally sustainable alternative with groundbreaking developments in materials science. Given the right technological breakthroughs sure to come in the future, we will be able to bring this battery to life and have the ability to power our society to a greener future.
To learn more about these exciting technologies, see the links to their published journal articles:
Kovalenko, I.; Zdyrko, B.; Magasinski, A.; Hertzberg, B.; Milicev, Z.; Burtovyy, R.; Luzinov, I.; Yushin, G. A Major Constituent of Brown Algae for Use in High-Capacity Li-Ion Batteries. Science (1979) 2011, 334 (6052), 75–79. https://doi.org/10.1126/science.1209150.
J. Kim et al., Biological Nicotinamide Cofactor as a Redox-Active Motif for Reversible Electrochemical Energy Storage, Angew. Chem. Int. Ed. 2019, 58, 16764. https://doi.org/10.1002/anie.201906844; and Miroshnikov, M.; Mahankali, K.; Thangavel, N. K.; Satapathy, S.; Arava, L. M. R.; Ajayan, P. M.; John, G. Bioderived Molecular Electrodes for Next-Generation Energy-Storage Materials. ChemSusChem. NLM (Medline) May 8, 2020, pp 2186–2204. https://doi.org/10.1002/cssc.201903589.
Lizundia, E.; Costa, C. M.; Alves, R.; Lanceros-Méndez, S. Cellulose and Its Derivatives for Lithium Ion Battery Separators: A Review on the Processing Methods and Properties. Carbohydrate Polymer Technologies and Applications. Elsevier Ltd December 25, 2020. https://doi.org/10.1016/j.carpta.2020.100001.
Meiling Wu, Ye Zhang, Lin Xu, Chunpeng Yang, Min Hong, Mingjin Cui, Bryson C. Clifford, Shuaiming He, Shuangshuang Jing, Yan Yao, Liangbing Hu. A sustainable chitosan-zinc electrolyte for high-rate zinc-metal batteries. Matter, 2022; DOI: 10.1016/j.matt.2022.07.015
Comments