Hard Carbon Anodes for Next-Generation Li-Ion Batteries: Review and Perspective

Sodium-ion batteries (SIBs) have shown promising prospects for complementarity to lithium-ion batteries (LIBs) in the field of grid-scale energy storage. After a decade of continuous fundamental research on SIBs, it's becoming increasingly urgent to advance the commercialization. For SIB anode materials, hard carbon is the most mature and currently the only material likely to be commercialized, but it is still far away from large-scale industrialization. Herein, we carry out a comprehensive overview of the current state of the art in terms of three main aspects. Firstly, a fundamental understanding of the microstructure and sodium storage mechanism of hard carbon is introduced, which can be categorized into three different processes: capacitive adsorption, nanopore filling, and intercalation in carbon interlayers. Then, based on an in-depth understanding of the sodium storage mechanism, optimization methods in terms of increasing the specific capacity, rate performance, initial coulombic efficiency (ICE), and long-cycling stability are comprehensively summarized and analyzed. Finally, potential methods and associated benefits for the design of carbon structures and the solid electrolyte interface (SEI) are discussed, hoping to provide useful guidelines for future research and commercialization.

Hard carbon for sodium storage: mechanism and optimization strategies toward commercialization

There is no doubt that rechargeable batteries will play a huge role in the future of the world. Sodium-ion (Na-ion) batteries might be the ideal middle-ground between high performance delivered by the modern lithium-ion (Li-ion) battery, desire for low costs and long-term sustainability. To commercialise the Na-ion technology, Faradion was founded in 2011 as the world's first non-aqueous Na-ion battery company. Over the years, we have made rapid progress in increasing the all-around performance of Na-ion batteries, benefitting from decades' worth of industry experience and prior Na-ion as well as Li-ion academic research. The Faradion Na-ion chemistry can now exceed the energy densities of LiFePO4//graphite Li-ion batteries with rapidly converging cycle lives, similar rate performance and charge acceptance. In addition, our technology makes use of lower materials costs, offers improved safety through the use of high flash point electrolytes and has the ability to be discharged to zero volts for storage and transportation. In this article, Faradion's step-by-step progress in the Na-ion technology will be discussed together with a general picture of how our Na-ion chemistry compares with other Na-ion systems and commercially available Li-ion technology. Finally, the importance of starting experimental testing on new materials, keeping commercially-relevant protocols in mind, will be illustrated by clearly highlighting the drastic effects of some crucial experimental factors. By sharing such industry know-how, Faradion hopes researchers worldwide will adopt such experimental protocols as routine methodology in the laboratory. These simple measures can significantly shorten the path from a new invention to commercial application, while also ensuring that the battery-related literature conveys the true commercial feasibility of an invention or discovery to the general public.

Commercialisation of high energy density sodium-ion batteries: Faradion's journey and outlook

Low-solvation electrolytes for high-voltage sodium-ion batteries

Hard carbon has the potential to serve as a high-capacity anode material for sodium-ion batteries (SIBs), however, its Na+ storage mechanism, particularly on the low potential plateau, remains controversial. To overcome this issue, two types of hard carbons with different microstructures are employed and the relationship between the microstructures and Na+ storage behaviors is evaluated. By the combination of operando X-ray diffraction, ex situ Raman spectroscopy, NMR, and theoretical calculation, it is found that the sodium storage capacities of the hard carbons in the low potential plateau region contain the concurrent contributions from both interlayer intercalation and micropores filling, and the ratio of the two contributors greatly depends on the microstructure of hard carbon materials. Moreover, an electrochemical pointer (potential inflection point at the end of the discharge curve) is found to distinguish the dominance of interlayer intercalation and the micropores filling processes of sodium ions in the low potential plateau region. Based on this new finding, a microstructure-dependent mechanism (“adsorption-intercalation/filling” hybrid mechanism) is proposed to achieve an overall understanding of the sodium storage behaviors in different hard carbon materials, which may provide deep insight into the rational design of hard carbon structures as high-performance anode materials for advanced SIBs. 

An Overall Understanding of Sodium Storage Behaviors in Hard Carbons by an “Adsorption‐Intercalation/Filling” Hybrid Mechanism

Extremely high capacity hard carbon for Na-ion battery, delivering 478 mAh g-1 , is successfully synthesized by heating a freeze-dried mixture of magnesium gluconate and glucose by a MgO-template technique. Influences of synthetic conditions and nano-structures on electrochemical Na storage properties in the hard carbon are systematically studied to maximize the reversible capacity. Nano-sized MgO particles are formed in a carbon matrix prepared by pre-treatment of the mixture at 600 °C. Through acid leaching of MgO and carbonization at 1500 °C, resultant hard carbon demonstrates an extraordinarily large reversible capacity of 478 mAh g-1 with a high Coulombic efficiency of 88 % at the first cycle.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/anie.202013951

MgO-Template Synthesis of Extremely High Capacity Hard Carbon for Na-Ion Battery

Potassium titanyl phosphate (KTiOPO4) is a well-known material for nonlinear optical device applications, but its electrochemical properties are not yet well understood. This study investigates sod...

https://pubs.acs.org/doi/pdf/10.1021/acs.jpcc.1c08339

Enhanced Electrochemical Properties of KTiOPO4–rGO Negative Electrode for Sodium and Potassium Ion Batteries

https://pubs.acs.org/doi/pdf/10.1021/acsphyschemau.1c00036

Daisuke Igarashi

Papers

MgO-Template Synthesis of Extremely High Capacity Hard Carbon for Na-Ion Battery

Enhanced Electrochemical Properties of KTiOPO4–rGO Negative Electrode for Sodium and Potassium Ion Batteries

Na Diffusion in Hard Carbon Studied with Positive Muon Spin Rotation and Relaxation