Background

Climate change has emerged as a core challenge in humanity's pursuit of the Sustainable Development Goals (SDGs). To effectively address this global issue, accelerating the transition of the world's energy structure towards clean energy is more urgent than ever. In this context, lithium-ion batteries (LIBs) play a pivotal role. As the primary power source for electric vehicles, LIBs, with their relatively high energy density and broad range of power-to-energy ratios, have become the market's top choice. According to the International Energy Agency (IEA), global electric vehicle sales skyrocketed from 700,000 units in 2015 to 10 million units in 2022. This soaring demand has directly fueled the explosive growth of the LIBs industry, with global shipments reaching an astonishing 1,202.6 GWh in 2023. This upward trend is expected to continue, with projections suggesting that by 2030, shipments may surpass the 5,004.3 GWh threshold.

However, alongside this wave of the energy revolution and the boundless possibilities it inspires, we are also faced with a series of challenges and risks.

The surge in demand for LIBs inevitably leads to large-scale mining of critical metals such as lithium, manganese, nickel, and cobalt, a process that carries significant environmental consequences. For example, lithium salt production not only generates substantial solid waste but also requires enormous amounts of energy—extracting lithium from rock consumes the equivalent of six American households' annual electricity use (about 60 megawatt-hours), or, when extracted from brine, demands water resources equivalent to the volume of a small swimming pool (70 cubic meters). More concerning is the extraction of nickel and cobalt, which are essential for the production of the preferred NCM (nickel-cobalt-manganese) batteries used in electric vehicles. These elements are often found in low-grade ores, making their mining and processing even more complex and environmentally damaging. Furthermore, large-scale mining is closely linked to issues such as poor labor conditions, corruption, and human rights abuses. For instance, two-thirds of the world’s cobalt supply comes from the Democratic Republic of Congo, where mining operations are notorious for hazardous working conditions, inadequate health protections, and even the use of child labor.

Fig. 1 left: Pollution from mining, right: Pollution from used batteries.

On the other hand, as LIBs production continues to rise, the number of used batteries reaching the end of their life-cycle will also increase dramatically. In general, LIBs in consumer electronics last only 1-3 years, while those in electric vehicles last 8-10 years. Given that China is the world's largest consumer and producer of LIBs—accounting for a staggering 73.8% of global shipments in 2023—the environmental threat posed by waste batteries in China cannot be ignored. If not properly handled, the toxic and flammable fluorinated organic electrolytes, along with heavy metal ions such as nickel, cobalt, and copper within the batteries, will inevitably leak into the environment. Of particular concern are heavy metals like cobalt and nickel, which are highly toxic to ecosystems. These metals not only pose severe threats to aquatic organisms but can also bioaccumulate and infiltrate the food chain, ultimately affecting human health. In extreme cases, nickel poisoning can occur, carrying risks of cancer and potential damage to the reproductive system.

In the face of these dual environmental threats, recycling and reusing waste LIBs is undoubtedly the best solution. Unfortunately, less than 5% of LIBs are currently being recycled globally. This dismal figure is largely due to the immaturity of industrial-scale recycling technologies and the many challenges they face.

Therefore, this year, our project--OUROBOROS--aims to develop a biosystem to recycle waste LIBs, enabling the extraction of key metals and the regeneration of electrode materials.

Introduction

In order to realize the recycling of LIBs, Our project harnesses the power of synthetic biology to create a sustainable, eco-friendly solution for metal recovery, meticulously designed around three innovative modules: bioleaching, biosorption, and biomineralization. Each module plays a pivotal role, transforming batteries waste into valuable resources while minimizing environmental impact. Join us on a journey where nature meets technology in the quest for a circular, greener future!

Fig. 2 Project Flow Diagram

Module 1 Bioleaching

We harness the metabolic prowess of Aspergillus niger to produce citric acid, coupled with glucose oxidase (GOx) displayed on engineered yeast cells, which synergistically generate gluconic acid and hydrogen peroxide. This powerful combination drives the efficient co-extraction of metal components from battery waste, setting the stage for sustainable metal recovery.

Module 2 Biosorption

Through quantum chemical modeling, we assessed the metal-binding capabilities of a peptide library collected online, selecting metal ion-binding peptides with high affinity and specificity. Utilizing advanced yeast surface display technology, these metal-binding peptides effectively capture and separate four key metal ions from leachate. Additionally, using AlphaFold3, we modeled and evaluated a nickel-binding peptide with self-assembly potential, enhancing the system's adsorption capacity through the peptide's self-assembly ability. This biogenic approach ensures selective extraction, thereby improving the purity and efficiency of the recovery process.

Module 3 Biomineralization

Finally, we engineered an E. coli system with robust urease expression to drive biomineralization, precipitating the captured metal ions as stable carbonates, which can be used as raw materials for electrode materials. This innovative step transforms the separated metals into reusable forms, closing the loop on metal recycling with a sustainable and scalable solution.

Hardware

In addition to the biological components, we have developed the necessary hardware to support and integrate these processes, ensuring the scalability and practicality of the system.

Fig. 3 Hardware Diagram

This recycling method not only significantly reduces pollutant emissions and energy consumption in the treatment of spent lithium batteries but also improves resource recovery rates through an optimized and efficient resource utilization strategies.

Sustainable development impact & Sustainable future

OUROBOROS is closely linked to the United Nations Sustainable Development Goals. This year we have not only made efforts to identify the sustainable development impact of OUROBOROS, but when we have identified potential negative impact of the project, we reviewed the relative literature and consulted with specialists to understand how to minimize this negative impact in future industrialisation , so that OUROBOROS can be as sustainable as it can be.

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