Taking on the challenges of Li-ion batteries for a clean energy world
Li-ion batteries are complex systems, and so are the challenges that hinder their further development and deployment.
We need to make fundamental changes in the way we generate and use energy. Not only do we need to reduce our overall energy consumption, but we also need to shift towards renewable energy sources that generate clean energy. However, renewable energy sources often have a fluctuating capacity, e.g. the wind does not blow around the clock, and the sun is only up for an average of 12 hours. Therefore, high-performance energy storage devices that can balance this capacity – such as batteries – play a vital role in this transition to clean energy.
By Maarten Buysse and Marcos Ierides
Extensive research has been done on batteries in the past decade to improve their performance in capacity, flexibility, efficiency, cycling stability, as well as decreasing their cost and impact on the environment. As a result, the current market of rechargeable batteries is mainly dominated by high-energy-density Li-ion batteries. However, a drastically rising demand, largely driven by the electrification of mobility, has brought to light multiple issues that still need to be overcome.
Li-ion batteries are complex systems, and so are the challenges that hinder their further development and deployment. These range from the ethical sourcing of raw materials, to the proper collection and treatment of End-of-Life batteries. To achieve their full potential without creating adverse social, environmental or other impacts, three key challenges will need to be addressed.
CHALLENGE: The negative impact of battery degradation mechanisms on its performance, mainly manifested in a limited “useful” lifetime.
Even though current Li-ion batteries are being used in electric vehicles (EVs) and other applications, they still struggle to combine a long battery life with high energy density and fast charging abilities. This is mainly because of the degradation mechanisms that occur within the battery during operation. These mechanisms irreversibly damage components or even the whole battery during use. They can be triggered by the chemical composition of the battery, contributing to its internal ageing as well as by influencing factors such as light, heat or external forces.
Looking deeper into degradation mechanisms, the separator, one of the vital elements influencing the performance of the battery, is also one of the most critical components of a battery cell that often gets damaged or broken. A damaged separator leads directly to reduced lifetime and safety (increasing the likelihood of short circuits, fire/explosion and leakage). Damages to the separator are caused by multiple mechanisms such as the induced formation of undesirable Li dendrites at the interface between electrolyte and electrodes. Some of these same mechanisms that induce damage to the separator are actually responsible for the operation of the battery, such as the formation of a solid electrolyte interface. Therefore, eliminating them altogether would render the battery non-operational!
To overcome this challenge, innovative solutions that address such degradation mechanisms by preventing or reversing them, in combination with high-quality degradation monitoring and sensing systems, have the potential to drastically improve the battery’s performance, especially in terms of battery life.
All these solutions must work in the electrochemically stable environment of the battery cell without negatively impacting other aspects of the cell. For example, adding non-functional materials will reduce the energy density of the battery since they do not contribute to its operation.
CHALLENGE: The negative environmental and societal impact caused by the sourcing of certain materials currently used in batteries.
Many of today’s Li-ion technologies contain REE (Rare Earth Elements), CRM (Critical Raw Materials), and other sensitive materials. The mining and processing of these materials often have a negative impact on the environment, as well as society.
Considering that the increasing demand for batteries will only compound the issue, there is a pressing need to substitute such REEs and CRMs. Ideally, these new materials will also minimise or even prevent the degradation mechanisms mentioned above to improve battery performance at the same time.
Did you know that one-third of Ni (Nickel) and Li (Lithium) used in batteries globally are mined in China and Chile respectively, while two-thirds of Co (Cobalt) are sourced from the Democratic Republic of Congo?1
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 Co in the Democratic Republic of Congo using artisanal miners and child labour.
SOLUTION: Avoiding or reducing the use of REE, CRM or other materials.
NMC (Nickel-Manganese-Cobalt) is one of the most established cathode chemistries today. Its Cobalt content has reduced from ~0.4kg/kWh for NMC111 – one of the first generations – to 0.03kg/kWh for the latest generation NMC8112. Besides addressing raw materials issues, these improvements can enhance performance as well; energy generated by NMC811 cathodes are 25% higher than those of NMC111, at 200mAh/gr3. Future research is expected to look at the complete elimination of Co. The collaborative R&I project COBRA (CObalt-free Batteries for FutuRe Automotive Applications) is working on an LMO (Lithium-Manganese Oxide) cathode chemistry with zero Co content. To improve the performance, the partners are working on doping the cathode material with Li-rich oxides, to reach capacities of 250mAh/gr.
Other approaches are targeting the existing LFP (Lithium-Iron-Phosphate) cathodes which have already proven high stability and long cycle times and focus on addressing their drawbacks; mainly the low energy density compared to NMC cathodes.
CHALLENGE: The significant carbon footprint and high costs of current manufacturing processes.
Larger and more efficient gigafactories, as well as improvements in manufacturing and assembly technologies, have steadily made Li-ion battery production cheaper.
Did you know that in the last 10-12 years, Li-ion batteries’ energy density went from some 200Wh/l to close to 600Wh/l, while cost went from around €900/kWh to €150/kWh?
Nevertheless, the LCOE (Levelised Cost Of Energy) is still 2-4 times higher than wind and solar energy. This is mainly due to special conditions that cell manufacturing requires, adding to the costs; as well as high energy consumption during manufacturing.
The calcination and co-precipitation processes for the production of the electrodes are particularly energy-intensive, as they require the heating of kilns to temperatures of over 1000C. For NMC111, the share of energy consumption for calcination and precipitation is around 35% of the total 1127MJ/kWh of battery4. 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.
SOLUTION: Innovative manufacturing solutions and their coupling with renewable energy sources.
A “straightforward” solution towards reducing greenhouse gas emissions is to switch from fossil-based fuels to renewable energy sources for powering battery manufacturing plants. As renewable energy is becoming cheaper, this is gradually becoming a reality, contributing to cost reduction, as well as cutting emissions.
In addition, future developments are looking into more innovative solutions, such as a water-based process for the production of electrodes that aims at reducing emissions, besides costs. This comes hand in hand with the development of water-based formulations with soluble binders, which would eliminate the use of current NMP (N-Methyl-2-Pyrrolidone) binders that require long drying times in high temperatures.
Improved performance in terms of lifetime, energy density and fast charging capabilities, will have a significant impact on multiple sectors, notably mobility. Where range anxiety due to poor battery performance is still one of the main challenges for the uptake of EVs, a self-healing battery, in combination with a comprehensive monitoring system, will extend the lifetime of the current batteries significantly. This could potentially become one of the main catalysts for electric mobility uptake. The new materials that will be included in these batteries will have a more stable and transparent supply chain to improve their societal impact and avoid unethical practices within the battery value chain. At the same time, they will limit their impact on the environment during the extraction and processing of these materials. These measures will further reduce the overall lifecycle impact of batteries. Finally, reducing the costs of battery production will ensure the commercial viability of all the new technological developments in batteries, as mentioned earlier. This is a critical element for the competitiveness and uptake of batteries and, in a wider sense, the commercial viability of an energy system based on fluctuating renewable energy; which will minimise the need for a constant non-renewable energy source as back up.
It is encouraging to see major research initiatives in Europe such as BATTERY 2030+ reflect similar focus areas in their latest roadmap, where sensing in combination with self-healing, as well as materials and manufacturability, are considered main research areas.
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