While the performance of lithium batteries has increased tremendously, there's still room for improvement to lower cost, increase sustainability and maximise their impact on decarbonisation, says Marcos Ierides, consultant and materials expert at innovation consultancy Bax & Company.
Driven by an ever-increasing world population as well as global economic growth, our energy needs have been rising rapidly, peaking 113,000TWh in 2017 according to the International Energy Agency. The impact of this growth on the environment and well-being of society is becoming more apparent, intensifying the need to decarbonise the transportation and power generation sectors – the two highest polluting sectors in the European Union (EU).
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Electromobility has become the prevalent solution for the decarbonisation of the transportation sector, with sales of EVs increasing by 60% in the last two years. In the power generation sector meanwhile, the harvesting of wind and solar is gaining pace, with a quarter of global electricity coming from renewable energy sources.
For these solutions to reach their full potential, they need to be coupled with efficient energy storage technologies. The performance of lithium-ion (Li-ion) batteries has increased tremendously as a result of significant investments in R&D; energy density has tripled since 2008, while cost has reduced by close to 85%. Still, further research is needed to decrease levelised cost of energy (LCOE), and ensure that the production and use of batteries does not generate a negative impact on the environment.
1. Find alternatives to scarce electrode materials to improve energy density and decrease the impact on the environment and society
Today’s batteries include REE (Rare Earth Elements), CRM (Critical Raw Materials), and other “sensitive” materials. The most crucial elements are perhaps Cobalt (Co), Nickel (Ni), Manganese (Mn), and Lithium (Li), due to their importance in the battery’s final electrochemical performance.
The EU’s Joint Research Centre estimates that demand for these materials will grow by up to 2,500% from 2015 to 2030, creating a scarcity issue. The fact that most such elements are unevenly distributed around the world does not make things easier either; one-third of nickel and lithium used in batteries globally are mined in China and Chile respectively, while two-thirds of cobalt supplies are sourced from the Democratic Republic of Congo, according to the European Commission. This creates significant supply chain risks and contributes to the huge short- and long-term price volatility. Adding to that is the questionable impact on the environment and society from the sourcing of such materials, with most infamously, the mining of cobalt in the Democratic Republic of Congo using artisanal mines and child labour.
Ongoing research and innovation (R&I) efforts around the world are oriented towards addressing those issues. Cobalt content in nickel-manganese-cobalt (NMC) cathodes, one of the most established cathode chemistries, is reduced from ~0.4kg/kWh for NMC111, to 0.03kg/kWh for NMC811 the IEA says.
These improvements are oriented towards enhanced performance as well, besides addressing raw materials issues; specific energy of NMC811 cathodes are 25% higher than those of NMC111, at 200mAh/gr according to work by Research Interfaces. Other approaches eliminate the use of Co completely. The collaborative EU-funded R&I project COBRA (CObalt-free Batteries for FutuRe Automotive Applications) is working on a lithium-ion manganese oxide (LMO) cathode chemistry with no cobalt content. To improve the performance, the partners are working on doping the cathode material with Li-rich oxides, to reach capacities of 250mAh/gr.
2. Implement self-healing mechanisms to improve battery life
Electrochemical phenomena that allow a battery to store and provide energy on demand are also responsible for the degradation mechanisms that reduce battery performance over time in battery cells. One example is the formation of the SEI layer, which, although vital for the cell’s performance, eventually contributes to lower capacity and power density.
An approach towards addressing such issues takes inspiration from living organisms that can heal injuries and recover the functionality of damaged body parts to survive. It can be broadly divided into preventive, meaning preventing or decelerating degradation mechanisms, or active, meaning reversing the damage after it has occurred. The approach uses self-healing polymers that repair damage via the reconstruction of the broken interface by reversible chemical bonds, or specific supramolecular interactions, such as hydrogen bonding, among others. These materials can be either directly incorporated in the battery components during their manufacturing or embedded in microcapsules which are then injected into the components – e.g. the electrolyte – and are released autonomously when a condition has been met, or on-demand, by external stimulus.
Ongoing research in the area is still in its infancy, although the area is gradually gaining attention. The European battery arena highlights self-healing as one of the key areas for future research, including through its collaborative initiative 'Battery 2030+' (which aims to “put Europe at the forefront of the race to develop the battery technologies of the future”).
3. Develop more efficient manufacturing lines to decrease cost
Although battery costs are decreasing rapidly, LCOE is still two to four times higher than for wind and solar energy, BloombergNEF recently said. This is partly due to the energy-intensive manufacturing processes for the production of components and cells. Particularly energy-intensive are the calcination and co-precipitation processes for the production of the electrodes, as they require the heating of kilns to temperatures of over 1000°C. For NMC111, the share of energy consumption for calcination and precipitation is around 35% of the total 1127MJ/kWh of battery [according to lifecycle analysis by Q. Dai]. Besides needing significant amounts of energy to reach such temperatures, the kilns typically remain operational around the clock (reaching such temperatures from “cold start” would require a lot of time), which further increases the energy consumption of manufacturing plants.
An “easy” solution for this would be to use energy from renewable energy sources, which is gradually becoming cheaper. Besides costs, this would also reduce greenhouse gas emissions (GHGs).
Other approaches look into more innovative solutions, such as the development of a water-based process for the production of electrodes. This comes hand in hand with the development of water-based formulations with soluble binders, which would eliminate the use of current n-methyl-2-pyrrolidone (NMP) binders that require long drying times in high temperatures.
Conclusion
These are just a few of the ways we can ensure the sustainability and commercial viability of battery systems.
Additional technological, societal, and policy innovations would be necessary to accelerate the deployment of batteries that address our needs without generating an adverse effect on society or the environment.
Cover Image: Ampere Energy battery energy storage system for residential use. Image: Andy Colthorpe / Solar Media.