Shuyin Xu

A zero-strain layered metal oxide as the negative electrode for long-life sodium-ion batteries

Room-temperature sodium-ion batteries have shown great promise in large-scale energy storage applications for renewable energy and smart grid because of the abundant sodium resources and low cost. Although many interesting positive electrode materials with acceptable performance have been proposed, suitable negative electrode materials have not been identified and their development is quite challenging. Here we introduce a layered material, P2-Na0.66[Li0.22Ti0.78]O2, as the negative electrode, which exhibits only ~0.77% volume change during sodium insertion/extraction. The zero-strain characteristics ensure a potentially long cycle life. The electrode material also exhibits an average storage voltage of 0.75 V, a practical usable capacity of ca. 100 mAh g(-1), and an apparent Na(+) diffusion coefficient of 1 × 10(-10) cm(-2) s(-1) as well as the best cyclability for a negative electrode material in a half-cell reported to date. This contribution demonstrates that P2-Na0.66[Li0.22Ti0.78]O2 is a promising negative electrode material for the development of rechargeable long-life sodium-ion batteries.

Prototype Sodium‐Ion Batteries Using an Air‐Stable and Co/Ni‐Free O3‐Layered Metal Oxide Cathode

A prototype rechargeable sodium-ion battery using an O3-Na0.90[Cu0.22 Fe0.30 Mn0.48]O2 cathode and a hard carbon anode is demonstrated to show an energy density of 210 W h kg(-1) , a round-trip energy efficiency of 90%, a high rate capability (up to 6C rate), and excellent cycling stability.

Amorphous monodispersed hard carbon micro-spherules derived from biomass as a high performance negative electrode material for sodium-ion batteries

Sodium-ion batteries (SIBs) are expected to be a promising commercial alternative to lithium-ion batteries (LIBs) for large-scale and low-cost electrical energy storage applications in the near future. Despite this, the absence of a suitable negative electrode material hinders their development. In this contribution, we synthesized monodispersed hard carbon spherules (HCS) from an abundant biomass of sucrose, and investigated the influence of the carbonization temperature on the microstructure and electrochemical performance. The initial coulombic efficiency of the HCS was increased to 83% by coating its surface with soft carbon through the pyrolysis of toluene. Interestingly, the plateau capacity at the low potential region increased with increasing carbonization temperature. The HCS carbonized at 1600 °C showed the highest plateau capacity (220 mA h g−1) and excellent cycling performance with a capacity retention of 93% after 100 cycles. When coupled with an air-stable P2-Na2/3Ni1/3Mn2/3O2 positive electrode, the full cell exhibited a high initial coulombic efficiency of 76%, a mean operating voltage of 3.5 V and excellent cycling performance. The theoretical energy density of this system was estimated to be 200 W h kg−1. These promising properties are believed to be close to the level required for practical applications.

Ti-substituted tunnel-type Na 0.44 MnO 2 oxide as a negative electrode for aqueous sodium-ion batteries

The aqueous sodium-ion battery system is a safe and low-cost solution for large-scale energy storage, because of the abundance of sodium and inexpensive aqueous electrolytes. Although several positive electrode materials, for example, Na₀.₄₄MnO₂, were proposed, few negative electrode materials, for example, activated carbon and NaTi₂(PO₄)₃, are available. Here we show that Ti-substituted Na₀.₄₄MnO₂ (Na₀.₄₄[Mn₁-xTix]O₂) with tunnel structure can be used as a negative electrode material for aqueous sodium-ion batteries. This material exhibits superior cyclability even without the special treatment of oxygen removal from the aqueous solution. Atomic-scale characterizations based on spherical aberration-corrected electron microscopy and ab initio calculations are utilized to accurately identify the Ti substitution sites and sodium storage mechanism. Ti substitution tunes the charge ordering property and reaction pathway, significantly smoothing the discharge/charge profiles and lowering the storage voltage. Both the fundamental understanding and practical demonstrations suggest that Na₀.₄₄[Mn₁-xTix]O₂ is a promising negative electrode material for aqueous sodium-ion batteries.

Air‐Stable Copper‐Based P2‐Na7/9Cu2/9Fe1/9Mn2/3O2 as a New Positive Electrode Material for Sodium‐Ion Batteries

An air‐stable copper‐based P2‐Na7/9Cu2/9Fe1/9Mn2/3O2 is designed and synthesized by a simple solid‐state method and investigated as a positive electrode material for sodium‐ion batteries. The attractive long cycling stability is demonstrated by the capacity retention of 85% after 150 cycles at 1 C rate without phase transformation. The reversible Cu2+/Cu3+ redox couple in P2 phase oxides is proved for the first time.

A spray drying approach for the synthesis of a Na2C6H2O4/CNT nanocomposite anode for sodium-ion batteries

Sodium-ion batteries have attracted extensive attention for large-scale energy storage applications for renewable energy and smart grids owing to their abundant sodium resources and potential low cost. Compared with the numerous available cathodes, very few anodes are viable for sodium-ion batteries. Here we report a highly safe and low-cost nanocomposite, disodium 2,5-dihydroxy-1,4-benzoquinone (Na2C6H2O4)/CNT, prepared by a simple spray drying method, as a high performance anode for sodium-ion batteries. The resulting nanocomposite exhibits a reversible capacity of 259 mA h g−1 with a first Coulombic efficiency of 88% and excellent rate performance. The average sodium storage voltage is 1.4 V, which prevents the formation of a solid electrolyte interphase layer and consequently ensures high safety, high first Coulombic efficiency and superior rate performance.

Suppressing the Voltage Decay of Low-Cost P2-Type Iron Based Cathode Materials for Sodium-ion Batteries

Rechargeable sodium-ion batteries with earth-abundant Fe/Mn based cathodes are a promising choice for grid-scale applications. However, the key candidate, P2-type Fe-based materials, suffers from severe voltage decay during battery operation due to Fe3+ migration to the neighboring tetrahedral sites. In this study, two Fe-based layered oxides, Na0.7[Cu0.15Fe0.3Mn0.55]O2 and Na0.7[Cu0.2Fe0.2Mn0.6]O2, were prepared. With a combination of in situ XRD, X-ray PDF, and hard and soft X-ray absorption, we demonstrate that the voltage decay in Fe-based layered oxides has dynamic origins. Drastic phase transition can be triggered by higher upper voltage limit, while partially irreversible Fe migration leads to voltage fading. With excess Cu doped into the crystal lattice, Fe migration can be considerably mitigated and therefore, structural stability can be maintained. Furthermore, Cu introduction brings about extra capacity via the correlation between transition metal elements and ligand oxygen, which may well compensate for capacity loss from inert impurity doping. Possible strategies for suppressing the detrimental voltage decay in battery cathodes can be proposed accordingly.