新型ナトリウム・アルミニウム電池、再生可能エネルギーとの融合で電力網の安定化を目指す(New Sodium, Aluminum Battery Aims to Integrate Renewables for Grid Resiliency)

低コストで地球上に豊富に存在する原料を利用した新しいグリッドエネルギー貯蔵ソリューションを開発。 Low-cost, Earth-abundant raw materials power a new grid energy storage solution

2023-02-07 パシフィック・ノースウェスト国立研究所(PNNL)

＜関連情報＞

• https://www.pnnl.gov/news-media/new-sodium-aluminum-battery-aims-integrate-renewables-grid-resiliency
• https://www.sciencedirect.com/science/article/pii/S2405829723000107?via%3Dihub

低コスト・長寿命のNa-Al電池を実現するNaCl-AlCl3相図の解明に成功 Unlocking the NaCl-AlCl3 phase diagram for low-cost, long-duration Na-Al batteries

J. Mark Weller, Minyuan M. Li, Evgueni Polikarpov, Kee Sung Han, Neil Kidner, Anant Patel, Mai Nguyen, Meghan Stout, Michael Gossett, Keeyoung Jung, David M. Reed, Vincent L. Sprenkle, Guosheng Li
Energy Storage Materials  Available online: 7 January 2023
DOI:https://doi.org/10.1016/j.ensm.2023.01.009

Highlights

•Extended sodium chloroaluminate chemistry from neutral (NaAlCl₄) to acidic (NaAl₂Cl₇) catholyte to increase specific capacity/energy.

•Demonstrated excellent reversibility of acidic chloroaluminate chemistry with purely inorganic catholyte.

•Raman and NMR spectroscopy confirms conversion to NaAl₂Cl₇ at end of charge.

•Liquid-solid reaction mechanism at the cathode allows higher areal capacity, suitable for long-duration energy storage.

•Based on inexpensive raw materials ($7.02 kWh⁻¹): promising for low-cost grid-scale storage to enable intermittent renewables.

Abstract

Sodium and aluminum are a natural combination of inexpensive, abundant elements as a redox pair for battery energy storage. Recent explorations pairing a sodium anode and aluminum cathode have demonstrated reversible, energy dense Na-Al cells with excellent rate capability using the electrochemical reaction between a molten Na anode and a NaAlCl₄/Al cathode. In this work, the NaAlCl₄/Al cathode is extended beyond the neutral NaAlCl₄ composition by unlocking the NaCl-AlCl₃ phase diagram to explore the extra accessible capacity hidden in acidic chloroaluminate melts up to and beyond the composition NaAl₂Cl₇. This enables higher specific capacity and average discharge voltages than previous Na-Al batteries, utilizing two distinct cell reaction mechanisms in one battery. Fundamental aspects of the NaAlCl₄-NaAl₂Cl₇ reaction chemistry are investigated, and Na-metal/chloroaluminate batteries with excellent reversibility and areal capacity are demonstrated. Increasing the voltage window of the chloroaluminate Na-Al battery takes advantage of the higher voltage (∼ 2 V vs ∼1.6 V for neutral NaAlCl₄) contributed by the acidic chloroaluminate cathode reaction, unlocking an additional specific energy of ∼119 Wh kg⁻¹ by utilizing the conversion of NaAlCl₄ to NaAl₂Cl₇, which adds to the neutral melt reaction between NaAlCl₄/Al and Na (∼493 Wh kg⁻¹ theoretical). By significantly increasing the cathode thickness and therefore accessible areal capacity up to 131.7 mAh cm⁻², a discharge duration of 28.2 h is achieved with an estimated raw active materials cost of $7.02 kWh⁻¹. These metrics show the great potential of this unlocked chloroaluminate battery for future low-cost, long-duration electrochemical energy storage.