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Originally sodium-ion batteries (SIBs) were studied together with Li-ion batteries (LIBs) in pioneering work on intercalation chemistry during the 1970s and 1980s, [1][2][3][4][5] and have recently While sodium-ion batteries (SIBs) represent a low-cost substitute for Li-ion batteries (LIBs), there are still several key issues that need to be addressed before SIBs become market-ready. Among these, one of the most challenging is the negligible sodium uptake into graphite, which is the keystone of the present LIB technology. Although hard carbon has long been established as one of the best substitutes, its performance remains below that of graphite in LIBs and its sodium storage mechanism is still under debate. Many other carbons have been recently studied, some of which have presented capacities far beyond that of graphite. However, these also tend to exhibit larger voltage and high first cycle loss, leading to limited benefits in terms of full cell specific energy. Overcoming this concerning tradeoff necessitates a deep understanding of the charge storage mechanisms and the correlation between structure, microstructure, and performance. This review aims to address this by drawing a roadmap of the emerging routes to optimization of carbon materials for SIB anodes on the basis of a critical survey of the reported electrochemical performances and charge storage mechanisms.

In this paper we examine the mechanism of Na insertion and extraction in the FePO 4 -NaFePO 4 system. Chemical preparation of the intermediate Na 1Àx FePO 4 phase has revealed the existence of a range of stable compositions with different Na + /vacancy arrangements. The mechano-chemical aspects of the charge and discharge reactions are also discussed.

Once lithium-ion battery (LIB) technology has reached a maturity level enough to be the battery of choice for consumer electronics and power tools, it will be very well positioned to take over transport applications while displacing, for instance, NiCd and Ni-MH technologies. However, a major challenge is waiting for us in the near term: large scale and low cost stationary energy storage. This will be crucial for boosting the efficiency, adaptability, and reliability of the next-generation power grid. The use of stationary energy storage systems coupled to the The urgent need for optimizing the available energy through smart grids and efficient large-scale energy storage systems is pushing the construction and deployment of Li-ion batteries in the MW range which, in the long term, are expected to hit the GW dimension while demanding over 1000 ton of positive active material per system. This amount of Li-based material is equivalent to almost 1% of current Li consumption and can strongly influence the evolution of the lithium supply and cost. Given this uncertainty, it becomes mandatory to develop an energy storage technology that depends on almost infinite and widespread resources: Na-ion batteries are the best technology for large-scale applications. With small working cells in the market that cannot compete in cost ($/W h) with commercial Li-ion batteries, the consolidation of Na-ion batteries mainly depends on increasing their energy density and stability, the negative electrodes being at the heart of these two requirements. Promising Na-based negative electrodes for large-scale battery applications are reviewed, along with the study of the solid electrolyte interphase formed in the anode surface, which is at the origin of most of the stability problems.

Assessment of Na-based battery technology: from materials to cell development. • Realistic comparison of key performance indicators for Na-ion and Li-ion cells. • Na-ion batteries can be considered as complementary alternatives to Li-ion batteries. • Fundamental research is the key enabler for future development of the Na-based technology.

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The reaction mechanism occurring during the (de)intercalation of sodium into the host olivine FePO4 structure is thoroughly analysed through a combination of structural and electrochemical methods. In situ XRD experiments have confirmed that the charge and discharge reaction mechanisms are different and have revealed the existence of a solid solution domain from 1 < x < 2/3 in Na(x)FePO4 upon charge. The second part of the charge proceeds through a 2-phase reaction between Na(2/3)FePO4 and FePO4 with strongly varying solubility limits. The strong cell mismatch between Na(2/3)FePO4 and FePO4 enhances the effects of the diffuse interface and therefore varying solubility limits are first observed here in micrometric materials.

Transition metal layered oxides are promising cathode materials for sodium‐ion batteries. Phase transitions involving different stacking sequences of the oxide layers often plague the electrochemistry of these materials during cycling, which strongly impacts in their electrochemical performance. However, the underlying mechanisms of these processes remain elusive. Interestingly, P2‐ and O3‐Na2/3Fe2/3Mn1/3O2 phases are the first transition metal layered oxide polymorphs that have been synthesized with exactly the same composition. This offers unprecedented access to the study of bistability in these systems as well as isolates the effect of local structure on Na ion mobility. Here, first‐principles calculations and experiments are combined to unveil the physical origin of such bistability and identify important differences in Na ion diffusion between these two phases. It has been found that electrostatic interactions between oxide layers control the bistable nature of P2 and O3 phases. It is also put forward that the interlayer distance between oxide layers may be a useful descriptor to rationalize the relative stability of other P and O phases in general. Furthermore, this study tracks down to the molecular level the differences regarding Na ion mobility in P2‐ and O3‐Na2/3Fe2/3Mn1/3O2 by computing activation energies and estimating diffusion coefficients.