Concept and Advantages of Carbon/Air Secondary Battery System as a Fixed Compact Power Storage with Large Capacity
Authors: Ihara Manabu , Kameda Keisuke , Takagi Reimi , Wakamiya Taishiro , Kexin Chen , Manzhos Sergei 
Published: December 2024

Introduction

One of the critical technological isuues to constract carbon neutral society is the suppression of the impact of the volatility in power generation from inexpensive variable renewable energy power sources, such as solar cells and wind powers. It is necessary to maintain a balance between power generation, transmission, and consumption, and to maintain three types of stability in the power system: frequency stability, synchronization stability, and voltage stability. For this reason, energy storage technology is one of the most important issues for making up carbon neutral energy system. Among energy storage technologies, lithium-ion secondary batteries are superior in terms of both output density and energy density, but they present a cost challenge for large-capacity energy storage. Pumped storage power generation is the mainstay of long-term large-capacity energy storage in the current power system, but significant pumped storage expansion is subject to geopolitical constraints. Therefore, a compact, large-capacity energy storage system that can be installed in the power grid is required to expand the introduction of variable renewable energy power sources.
In this research, we first describe the operating mechanism and advantages of the "Carbon/Air Secondary Battery (CASB) system" [1,2], a compact power storage system that integrates the functions of a solid oxide fuel cell that generates electricity by producing CO2 through the oxidation reaction of carbon and a solid oxide electrolytic cell that produces carbon through the electrolysis of CO2. The operating mechanism and features of the CASB system are introduced. In addition, we report the calculation results of feasible system efficiency based on thermodynamic considerations compared to power storage system using H2/H2O-solid oxide fuel cells/electrolysis cells. In addition, the advantages/disadvantages of the two types of CASBs, integrated type of CASB between carbon deposition /electrochemical reaction, and the separated type of CASBs, as well as their representative charge/discharge characteristics will be presented.

Theoreticl advantage of CASB as a fixed compact power storage with large capacity

The theoretical charge/discharge efficiency of CASB, which is the ΔG/ΔH of reaction “C+O2→CO2” is 100%. This means that there is no heat input and output ideally in both carbon generation and CO2 electrolysis (in charge/discharge). Therefore, temperature control is simple and a heat exchanger can be minimized, which may allow the system to be compact. The feasible charge/discharge system efficiency of CASB including possible heat exchange were estimated as 92% based on thermodynamics, which is much higher than that of power storage system using H2/H2O-solid oxide fuel cells/electrolysis cells (63%). In addition, since CO2 can be liquefied at about 6.4 MPa at 25°C, its volumetric energy density to 1.62 × 103 Wh L-1, about four times higher than the volumetric energy density of hydrogen compressed at 20 MPa at 25°C, 3.79 × 102 Wh L-1.

A key technological point of CASB at its discharging , which is combination between electrochemical reaction (CO2→
CO+O2-) and thermochemical reaction (2CO→
C+CO2) by achiving at closed system

The discharge reaction of the CASB is the same as that of the Rechargeable Direct Carbon Fuel Cell [3,4,5]. The reason for the first successful demonstration of the CASB is that the combining electrochemical reaction with low overpotential (CO2
→CO+O2-) with the thermochemical reaction, the Boudouard equilibrium reaction (2CO
→ C+CO2) were achieved at the charging by making the system a closed system.

Two types of CASBs, (1) Integrated type of CASB between carbon deposition /electrochemical reaction, and (2) the separated type of CASBs

Since generally, the carbon deposition on the electrode cause its degradation [6], two type of CASBs can be designed and demonstrated (as shown in Fig.1). Both types of CASBs could be demonstrated.

References

[1] K. Kameda, S. Manzhos, and M. Ihara, J. Power Sources, 516, (2021) 230681.
[2] K. Kameda. T. Wakamiya, C. Kexin, S. Manzhos, and M. Ihara, SCEJ 89th Annual Meeting, (2024).
[3] M. Ihara, K. Matsuda, H. Sato and C. Yokoyama, Solid state fuel storage and utilization through reversible carbon deposition on an SOFC anode, Solid State Ionics, 175(1-4), (2004), 51-54
[4] M. Ihara and S. Hasegawa, Quickly Rechargeable Direct Carbon Solid Oxide Fuel Cell with Propane for Recharging, Journal of The Electrochemical Society, 153, (2006), A1544-A1546
[5] Gür, T. M. Critical Review of Carbon Conversion in“ Carbon Fuel Cells”. Chem. Rev. 113, 6179-6206 (2013).
[6] Y. Jin, H. Yasutake, K. Yamahara and M. Ihara, Suppressed carbon deposition behavior in Nickel / Yittria-stabilized zirconia anode with SrZr0.95Y0.05O3-α in dry methane fuel, Journal of The Electrochemical Society, 157(1), (2010), B130-B134

Figure 1