Carbon Dioxide Assist for Non-Aqueous Metal-Oxygen Batteries

Introduction

Growing interest in electrochemical energy storage for transportation and grid storage has resulted in an intensive search for alternative energy storage technologies that offer specific energies above those achievable (~200 Whkg⁻¹) with state-of-the-art lithium-ion batteries. More than a decade of research into such storage platforms has helped define the magnitude of the challenges that must be overcome for lithium-ion batteries to achieve specific energies in the 500–700 Whkg⁻¹range. In this context, metal–air batteries are gaining increasing attention because of their exceptionally high specific energies.

CO₂ is a greenhouse gas and has been implicated in global climate change. A variety of chemical and physical methodologies are under development for capturing and sequestering the thousands of metric tons of the gas emitted per annum. A metal–air battery that utilizes a mixed fuel of CO₂ and O₂ provides a potentially novel platform for electrical energy generation and carbon capture [1]. In 2011, researchers at Toyota reported that incorporation of CO₂ with O₂ improves the energy density of a Li–O₂ primary battery [2], indicating that there may be other benefits for incorporating CO₂in other metal–air batteries.

This talk reports a novel Na–CO₂/O₂ battery operated at room temperature and a high temperature Li-CO₂ battery.

Experimental and Results

The Na-CO₂/O₂ battery uses either tetraglyme or ionic liquid as the electrolyte. The discharge capacity of both cases depends strongly on the ratio of CO₂ and O₂ in the cathode feed gas.[3] The highest discharge capacity is reached at around 50% CO₂ content in the cathode feed gas.

Considering the rechargeability, replacing the electrolyte with a conventional PC electrolyte with a tethered ionic liquid particle additive would help recharge the battery stably for over 20 cycles at a capacity cutoff at 800mAh/g_carbon. [4]

The rechargeability of the battery has been studied via SEM. Before discharge, the cathode is composed by carbon particles aggregating together. After discharge, the inter particle space are occupied by discharge product, which make the structure of the cathode more sheet-like. After recharge, the carbon particles are separate again, meaning the discharge product is decomposed during the recharge, which is an indication of the rechargeability.

Besides the Na-CO₂/O₂ battery, using CO₂ gas only as the feed gas at the cathode has also been studied. However, based on the previous study, the capacity of the 100% CO₂ case is extremely low due to the inactivity of CO₂ gas at low temperatures. In our recent paper, we show that the temperature has a big influence on the performance of Li-O₂ battery. [5] Therefore, the high temperature Li-CO₂battery was studied.[6] The higher the temperature is, the higher the discharge potential and capacity is.

Reference

1. S. Xu, W. I. A. Al Sadat, S. K. Das and L. A. Archer, US Patent Application, No. PCT/US13/68469
2.  K. Takechi, T. Shiga and T. Asaoka, Chem. Commun., 2011, 47, 3463
3. S. K. Das, S. Xu and L. A. Archer, Electrochem. Commun., 2013, 27, 59
4. S. Xu and L. A. Archer, In Preparation
5. S. K. Das, S. Xu, A. Emwas, Y. Lu, S. Srivastava and L. A. Archer, Energy Environ. Sci., 2012, 5, 8927
6. S. Xu, S. K. Das and L. A. Archer, RSC Advances, 2013, 3, 6656