No abstract

Figure 4. HR-TEM images and FFTs after 50 cycles under 3.0-4.8 V conditions. a) Lattice image of the surface region where (b-e) correspond to the FFTs of Regions 1-4, respectively. (11-1) c is the diffraction spot of the rock salt phase of the metal monoxide.

The tremendous improvement in performance and cost of lithium-ion batteries (LIBs) have made them the technology of choice for electrical energy storage. While established battery chemistries and cell architectures for Li-ion batteries achieve good power and energy density, LIBs are unlikely to meet all the performance, cost, and scaling targets required for energy storage, in particular, in large-scale applications such as electrified transportation and grids. The demand to further reduce cost and/or increase energy density, as well as the growing concern related to natural resource needs for Li-ion have accelerated the investigation of so-called "beyond Li-ion" technologies. In this review, we will discuss the recent achievements, challenges, and opportunities of four important "beyond Li-ion" technologies: Na-ion batteries, K-ion batteries, all-solid-state batteries, and multivalent batteries. The fundamental science behind the challenges, and potential solutions toward the goals of a low-cost and/or high-energy-density future, are discussed in detail for each technology. While it is unlikely that any given new technology will fully replace Li-ion in the near future, "beyond Li-ion" technologies should be thought of as opportunities for energy storage to grow into mid/large-scale applications.

This work reports that natural graphite is capable of Na insertion and extraction with a remarkable reversibility using ether-based electrolytes. Natural graphite (the most well-known anode material for Li-ion batteries) has been barely studied as a suitable anode for Na rechargeable batteries due to the lack of Na intercalation capability. Herein, graphite is not only capable of Na intercalation but also exhibits outstanding performance as an anode for Na ion batteries. The graphite anode delivers a reversible capacity of ≈150 mAh g −1 with a cycle stability for 2500 cycles, and more than 75 mAh g −1 at 10 A g −1 despite its micrometer-size (≈100 µm). An Na storage mechanism in graphite, where Na + -solvent co-intercalation occurs combined with partial pseudocapacitive behaviors, is revealed in detail. It is demonstrated that the electrolyte solvent species signifi cantly affect the electrochemical properties, not only rate capability but also redox potential. The feasibility of graphite in a Na full cell is also confi rmed in conjunction with the Na 1.5 VPO 4.8 F 0.7 cathode, delivering an energy of ≈120 Wh kg −1 while maintaining ≈70% of the initial capacity after 250 cycles. This exceptional behavior of natural graphite promises new avenues for the development of cost-effective and reliable Na ion batteries.