This proposal presents the development of lignocellulose-based materials for a variety of applications, such as polymer electrolytes, binders for electrode powders, and organic current collectors in batteries, as well as polymer gels for the corrosion removal from historical artifacts. Lignocellulosic biomass is one of the most abundant and eco-friendly feedstocks on earth. The replacement of petroleum-based synthetic polymers with these bio-derived polymers is a promising approach to reduce environmental impacts during production of polymers.
In the growing lithium ion battery (LIB) industry, the sustainability of battery production has become a new concern in addition to the performance and safety of batteries, since many LIB components are classified as critical raw materials (CRM) that are at risk of depletion. Fluorinated polymers are widely used in LIBs because of their high stability. However, their raw material, fluorospar, is one such CRM. Therefore, alternative materials based on highly abundant and easily accessible elements need to be developed.
We have been working on the extraction of cellulose and lignin from industrial waste of cocoa husk from 2020. Although both materials are known to be barely soluble in any organic solvents due to their intermolecular interactions, the extraction of individual component from cocoa husk was achieved by employing a highly polar deep eutectic solvent (DES). This year I undertake the valorization of extracted biomasses by developing them as alternatives to fluorinated polymers in LIBs. Extracted cellulose will also be used as a matrix of hydrogels for the corrosion removal from historical artefacts. In addition, valorization of lignin will be carried out by using them as organic current collectors in LIBs. By carrying out all the synthesis with water as a solely solvent, I intend to propose a technology for safer and more sustainable production of LIBs.
The use of extracted biomass for the battery materials is unattempted, and a route of the circular economy from the extraction of biomass derived from food waste to the use of biomass as battery component will be innovative. In addition, as shown in the Figure 2 of the former section, the green battery materials are proposed in this study, and these have following three benefits.
Sustainable Production of LIBs for Future
In the growing battery industry, the sustainability of battery production has become a new concern in addition to the performance and safety of batteries. In the recent battery production technology, high amounts of energy are consumed due to high-temperature processes during material production (including metal refinery and synthesis of fluorinated polymers) and due to electrical energy-intensive processing steps during cell assembly (moisture control, electrode drying, etc.). The use of materials already existing in the nature, proposed in this project, is one of the most effective way to reduce the energy consumption during material production. At the same time, by using cocoa husk, which is inedible crop waste, we can reduce impacts on deforestation and food production, and can propose greener and more environmentally-friendly technology for LIB production.
Bio-derived Safe Polymer Electrolyte
The cellulose-based GPEs containing aqueous electrolytes are not only green but also safe and easy to handle. In general, carbonate-based electrolytes containing LiPF6 are used as a benchmark electrolyte in LIBs. However, they are known to present safety hazards such as flammability of carbonate-components, fear of leakage of the solution, and formation of toxic HF due to the presence of LiPF6. These electrolytes are also sensitive to humidity and need to be used in a dry condition. In contrast to this, aqueous electrolyte can be used in ambient atmosphere. In addition, the use of water as electrolyte solvent eliminates the possibility of explosion. Considering most accidents from LIBs are caused by flammable electrolyte solution, the development of aqueous polymer electrolyte no doubt contributes the improvement of thermal stability of the batteries.
Light and Extendable Polymer-based Batteries
In the traditional LIBs, metallic films of aluminum and copper are widely used as current collectors of cathode and anode, respectively. By using lignin as a matrix (density:1.5g/cm3), the weight of current collector will be save compared to aluminum foil (density 2.7/cm3) as well as copper foil (density 8.9 g/cm3). The reduction of the weight will leads the higher energy density of LIBs. In addition, the use of polymer as a matrix of current collector enhances the elasticity of current collector, which cannot be achieved only by using inorganic materials. This benefit can be extended to the development of elastic and shock resistive LIBs in future.
By taking advantages explained above, I conclude that LIBs composed of greener components proposed here are innovative and beneficial. I strongly deem that this battery composition provides significant benefits both in scientific- and industrial-level.