Unlocking Sustainable Na-Ion Batteries into Industry,ACS Energy Letters

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Unlocking Sustainable Na-Ion Batteries into Industry
ACS Energy Letters ( IF 19.3 ) Pub Date : 2021-11-12 , DOI: 10.1021/acsenergylett.1c02292
Yong-Sheng Hu ₁ , Yuqi Li ₁

Affiliation

More than 170 nations have signed The Paris Agreement so far, committing to fight climate change by cutting carbon emissions with the proposal of “carbon peak and neutrality” goals. Rechargeable batteries, as the representative technologies of energy storage, play a key role for decarbonization. After 30 years of development, Li-ion batteries (LIBs) have already walked into thousands of families, making it possible to reduce the consumption of fossil fuels. (1) Due to the restriction of limited Li resources, a series of “beyond LIBs” research has sprung up all over the batteries field. However, most of it is still in the conceptual stage. Fortunately, Na-ion batteries (NIBs), which most closely resemble the technology of LIBs, have the greatest potential to achieve industrialization. (2–5) The development of NIBs is driven by the rapid growth of renewable energies such as solar and wind energy, which require large-scale energy storage systems. NIBs have been considered as a good choice due to the abundance and wide distribution of Na, and more unexpected properties of the material or system level of NIBs are being revealed with intensive in-depth studies, (6) including wide working temperature range, fast charge/discharge, high safety, etc. Recently, the start-up company HiNa launched their first 1 MWh NIB system for energy storage (Figure 1), which is a milestone of NIB development. CATL (a leading manufacturer of LIBs) recently announced their first-generation NIB technology, which attracted unprecedented attention. (7) At this critical moment, this Editorial aims to present some insights on the commercialization of NIBs. Figure 1. The world’s first 1 MWh Na-ion battery system for energy storage, combined with municipal electricity, photovoltaic, and charging facilities to form a microgrid, which can further interact smartly with public networks. Concerning the cathode side, there are three main technical routes, including the use of layered metal oxides, polyanionic compounds, and Prussian blue analogs. (8) For layered metal oxides, the O3-type materials with high sodium content are beneficial to improve the energy density, while the P2-type materials with favorable diffusion channels make it possible to achieve high power density. The design of these two different configurations can be directly realized by “cationic potential” prediction, which helps reduce experimental costs. (9) Compared with the Li-based layered metal oxides, Na-based layered metal oxides are very rich in transition metals with electrochemical activity, such as the Cu³⁺/Cu²⁺ redox couple. (10) Despite the fact that current research works mostly focus on the inhibition of phase transition via doping strategies, attention must also be paid to solving the air stability issue, (11) where magic coating needs to be further explored. Polyanionic compounds have higher safety than layered metal oxides due to the difficult oxygen release. They can also support fast charging, with a long cycle life over 10 000 times, owing to the three-dimensional open channels for Na⁺ diffusion. However, most of them contain the toxic and expensive element V, so it is more essential to replace V with cheaper transition metals, as proposed in Na₃MnTi(PO₄)₃. (12) Prussian blue analogs have a fast charging property similar to that of polyanionic compounds, but how to completely remove the interstitial water still remains challenging. Nevertheless, the high specific capacity and operating voltage plus easy large-scale preparation are common goals for the three types of cathodes. Na-ion batteries have been considered as a promising choice for industrialization of rechargeable batteries due to the abundance and wide distribution of Na, and more unexpected properties are being revealed with intensive in-depth studies. The anodes and electrolytes are discussed together, considering the solid–electrolyte interphase (SEI) formed between them. (13−16) Disordered carbons, with low insertion strain, suitable specific capacity, and low voltage hysteresis, are promising anode candidates. Even though some ultra-high-capacity (>400 mAh/g) disordered carbons have been reported, (17) elaboration on the design of the proper microstructure (e.g., pore shape, pore size, pore number, etc.) is still lacking because the Na storage mechanism in disordered carbons is unclear. (18) Moreover, initial and average Coulombic efficiencies (a presodiation technique can effectively offset the initial capacity loss (19)) are key parameters, induced by the different particle morphologies and electrolyte selections. Accurate SEI or solvation models in Na-based systems should be built to help guide functional protection layers on the anode and cathode. (20) The electrolyte concentration and formulation should be rationally regulated with overall considerations of the cost, high voltage application, compatibility with carbon anodes, etc. (21−23) Moreover, the influence of interactions among active materials, conductive additives, and binders for SEI formation should be further investigated. In addition, solid-state and aqueous NIBs also arouse wide research interest, given the intrinsic safety feature of aqueous and solid-state electrolytes, but the corresponding problems need to be solved before their practical application. In addition to the investigation of materials and interfaces, the full NIB system also deserves comprehensive study. Scientific research in laboratories usually uses coin cells to evaluate the battery performance; however, data from pouch cells assembled by electrodes with high loading mass are more realistic. Furthermore, a detailed failure analysis is still lacking, especially the thermal runaway model for NIBs. (24) For the pack level, how to achieve high-efficiency operation of thousands of integrated NIBs remains challenging, and the design of a battery management system (BMS) is the key. Actually, one advantage of NIBs lies in the fact that they can be discharged to 0 V (Al foil can be used as both cathode and anode current collectors of NIBs), indicating a convenient design of the BMS. To date, many start-up companies including Faradion (UK), Natron Energy (USA), HiNa (China), Tiamat (France), CATL (China), etc. have launched their first-generation NIB technology. For example, NIBs from HiNa demonstrated superior electrochemical performance of ∼145 Wh/kg energy density, 12 min charge/discharge,∼5000 cycles, and wide temperature operation (−40 to 80 °C). (6,25) Overall, the rapid development of NIBs will change the business landscape of the energy storage field, and related scale-up technologies need updates accordingly. Based on 30 years of rich experience with LIBs, actually, the commercialization path for NIBs seems smooth. Even so, more fundamental research should be conducted, with the focus on stability and consistency from the material or system level. Performance evaluation of NIBs should be approached from multiple perspectives, and successful industrialization also needs policy support from governments, for example, promoting the establishment of international standards for NIBs. The main direction for the development of NIBs still lies in improving energy density. Further optimization of the storage capacities of the cathode and anode as well as the operation voltage is still important and challenging to reach the goal of 200 Wh/kg (3) (Figure 2) and unlock more different application scenarios for NIBs in the near future. Figure 2. Relationship between the practical energy density of Na-ion batteries and the capacities of cathode and anode as well as the operation voltage, calculated based on a revised empirical model. (26) This article references 26 other publications.

更新日期：2021-11-12

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