Vietnamese scientist uses rice husk to create rechargeable batteries.

Việt Nam•03/08/2023

Utilizing rice husks, the research team led by Associate Professor Dr. Le My Loan Phung designed a material for manufacturing low-cost Li-ion batteries.

The research was led by Assoc. Prof. Dr. Le My Loan Phung, Faculty of Science , Vietnam National University Ho Chi Minh City (APCLab), and her colleagues since 2020.

She explained that rice husks contain an average silica (SiO2) content of about 10.6%. This is an important component that can be used to manufacture Li-ion rechargeable batteries. The group proposed, and received funding from the Vingroup Innovation Fund (VinIF), to research a process for synthesizing electrode materials from rice husks to produce trial 4V Li-ion rechargeable batteries in button cell and pouch cell forms. Button cell batteries are used in watches, heart rate monitors, personal computers, and pouch batteries for phones and other compact electronic devices.

*Dr. Phung works in a vacuum chamber, assembling button cell batteries. Photo: Provided by the interviewee.*

The research team sourced rice husks from Tan Tru district (Long An province), washed and dried them, then heated them for one hour under inert gas conditions. They were finely ground into rice husk ash and mixed with solid potassium hydroxide (KOH). This mixture was then heated again under inert gas conditions, ground, and washed. After drying, the final product is a dark gray dry powder, also known as carbon silicate (C/SiO2) composite material.

The team developed a synthesis process that can produce 350g of C/SiO2 material from 1 kg of rice husk, with a selling price of approximately $50/1000g. After two years of experimental production, the research team has mastered the technology for assembling complete button cell and pouch batteries using C/SiO2 material from rice husk.

*Diagram of the silica material fabrication process. Photo: Research team*

Associate Professor Phung explained that silica material has a porous structure that allows lithium ions to move and interlock within the structure to convert into electrical energy. APCLab utilizes this property of the material to design a suitable structure for various rechargeable battery applications. Depending on the energy type of each battery, the material is designed to calculate the amount needed. Typically, each button cell battery only requires a few tens of milligrams of rice husk, while larger batteries require about 10-20 grams.

Currently, most rechargeable batteries on the market are made from graphite, a material extracted and refined from coal ore. This material costs approximately $100 per 100 grams, and the sourcing process can cause environmental pollution.

Dr. Phung assessed that silica material has the potential to completely replace graphite material in terms of cost, efficiency, and environmental protection. This expands the potentially lucrative market for rice husks and brings significant profits to farmers.

In the future, the research team plans to optimize the product based on economic cost. According to current estimates, button batteries made from rice husks could sell for $7-8 each, and pouch batteries for $30 each.

*Button batteries made from rice husks are being produced on a trial basis. Photo: Research team*

Associate Professor Dr. Nguyen Dinh Quan, Head of the Biofuel and Biomass Laboratory at the University of Technology, Vietnam National University Ho Chi Minh City, assessed that silica is known to be an additive for Li-ion rechargeable battery electrodes due to its ability to increase battery capacity many times. Its drawback is that the electrodes are prone to volume expansion, but this can be overcome by using nano-sized silica particles. APCLab has adopted similar research worldwide to utilize shaped silica from rice husks as a battery electrode additive. Silica in rice husks is dispersed at low density; when the rice husks are thermally decomposed, they form a mixture of carbonized carbon with nano-sized silica.

"This method is simple yet highly effective, and it could help a rice-producing powerhouse like Vietnam create significant added value if the research project is successful," said Dr. Quan.

According to statistics, Vietnam is the world's second-largest rice producer, with an estimated average output of approximately 44 million tons per year, and a husk content of about 20-22%, or nearly 9 million tons.

Associate Professor Dr. Le My Loan Phung spent six years studying and researching in the field of rechargeable batteries in France and nine years working on projects related to electrochemical batteries. She was invited to participate in research at the Institute of Materials Chemistry and Engineering – Kyushu University, Japan, on electrolytes for batteries and advanced materials development for batteries (Consortium Battery Material Research) at the Pacific Northwest National Laboratory (USA). The female doctor has participated in and led nine research projects, published 80 international and 60 domestic articles, and received numerous valuable awards and scholarships from prestigious organizations.

vnexpress.net