Yuhao Lu

Rhombohedral Prussian White as Cathode for Rechargeable Sodium-Ion Batteries

A novel air-stable sodium iron hexacyanoferrate (R-Na1.92Fe[Fe(CN)6]) with rhombohedral structure is demonstrated to be a scalable, low-cost cathode material for sodium-ion batteries exhibiting high capacity, long cycle life, and good rate capability. The cycling mechanism of the iron redox is clarified and understood through synchrotron-based soft X-ray absorption spectroscopy, which also reveals the correlation between the physical properties and the cell performance of this novel material. More importantly, successful preparation of a dehydrated iron hexacyanoferrate with high sodium-ion concentration enables the fabrication of a discharged sodium-ion battery with a non-sodium metal anode, and the manufacturing feasibility of low cost sodium-ion batteries with existing lithium-ion battery infrastructures has been tested.

Removal of Interstitial H2O in Hexacyanometallates for a Superior Cathode of a Sodium-Ion Battery

Sodium is globally available, which makes a sodium-ion rechargeable battery preferable to a lithium-ion battery for large-scale storage of electrical energy, provided a host cathode for Na can be found that provides the necessary capacity, voltage, and cycle life at the prescribed charge/discharge rate. Low-cost hexacyanometallates are promising cathodes because of their ease of synthesis and rigid open framework that enables fast Na(+) insertion and extraction. Here we report an intriguing effect of interstitial H2O on the structure and electrochemical properties of sodium manganese(II) hexacyanoferrates(II) with the nominal composition Na2MnFe(CN)6·zH2O (Na2-δMnHFC). The newly discovered dehydrated Na2-δMnHFC phase exhibits superior electrochemical performance compared to other reported Na-ion cathode materials; it delivers at 3.5 V a reversible capacity of 150 mAh g(-1) in a sodium half cell and 140 mAh g(-1) in a full cell with a hard-carbon anode. At a charge/discharge rate of 20 C, the half-cell capacity is 120 mAh g(-1), and at 0.7 C, the cell exhibits 75% capacity retention after 500 cycles.

Aqueous cathode for next-generation alkali-ion batteries.

The lithium-ion batteries that ushered in the wireless revolution rely on electrode strategies that are being stretched to power electric vehicles. Low-cost, safe electrical-energy storage that enables better use of alternative energy sources (e.g., wind, solar, and nuclear) requires an alternative strategy. We report a demonstration of the feasibility of a battery having a thin, solid alkali-ion electrolyte separating a water-soluble redox couple as the cathode and lithium or sodium in a nonaqueous electrolyte as the anode. The cell operates without a catalyst and has high storage efficiency. The possibility of a flow-through mode for the cathode allows flexibility of the cell design for safe, large-capacity electrical-energy storage at an acceptable cost.

Low-surface-area hard carbon anode for na-ion batteries via graphene oxide as a dehydration agent.

Na-ion batteries are emerging as one of the most promising energy storage technologies, particularly for grid-level applications. Among anode candidate materials, hard carbon is very attractive due to its high capacity and low cost. However, hard carbon anodes often suffer a low first-cycle Coulombic efficiency and fast capacity fading. In this study, we discover that doping graphene oxide into sucrose, the precursor for hard carbon, can effectively reduce the specific surface area of hard carbon to as low as 5.4 m(2)/g. We further reveal that such doping can effectively prevent foaming during caramelization of sucrose and extend the pyrolysis burnoff of sucrose caramel over a wider temperature range. The obtained low-surface-area hard carbon greatly improves the first-cycle Coulombic efficiency from 74% to 83% and delivers a very stable cyclic life with 95% of capacity retention after 200 cycles.

Rechargeable alkali-ion cathode-flow battery

We provide a proof of concept of a lithium battery configuration containing an aqueous cathode in a flow-through mode. A room-temperature, rechargeable alkali-ion battery with a commercially available Li+-ion solid–electrolyte separating a Li0 anode and an organic liquid–carbonate electrolyte on one side and, on the other, an aqueous cathode containing 0.1 M K3Fe(CN)6 has been demonstrated to give high efficiency electrical energy storage at 3.40 V; it is capable of matching the capacity of the Li0 anode if operated with the aqueous cathode in a flow-through mode. The resistance of the solid electrolyte rather than the flow rate of the cathode determined the power density of the test cell. The concept can be used with a more-abundant Na0 anode and a Na+-ion solid electrolyte. The results call for the development of an alkali-ion solid–electrolyte separator with a smaller resistance.

Rate Properties and Elevated-Temperature Performances of LiNi0.5 − x Cr2x Mn1.5 − x O4 ( 0 ≤ 2x ≤ 0.8 ) as 5 V Cathode Materials for Lithium-Ion Batteries

A series of Cr-substituted spinel cathodes LiNi 0.5-x Cr 2x Mn 1.5-x O 4 (0 ≤ 2x ≤ 0.8) has been prepared and their electrochemical properties were characterized at different C rates and temperatures. Although the pristine Li[Ni 0.5 Mn 1.5 ]O 4 showed a capacity loss from ~ 130 mAh g -1 at 0.2C to ~ 10 mAh g -1 at 10C at room temperature, LiNi 0.4 Cr 0.2 Mn 1.4 O 4 showed capacity retention ~93.8% after 400 cycles under the same conditions and LiNi 0.45 Cr 0.1 Mn 1.45 O 4 gave the best rate property. At 55°C, LiNi 0.5 Mn 1.5 O 4 retained ~80.5% of its capacity after 50 cycles; 98, 92.1, and 91.7% capacities were still observed for LiNi 0.475 Cr 0.05 Mn 1.475 O 4 , LiNi 0.45 Cr 0.1 Mn 1.45 O 4 , and LiNi 04 Cr 0.2 Mn 1.4 O 4 , respectively. Structural analyses and surface morphology changes show that although no second phase was detected during cycling, there is a surface rearrangement on the electrodes. Elemental analyses indicated that the Cr substitution helps to suppress the surface atomic rearrangement, which improves the electrochemical performance.

Aluminum-stabilized NASICON-structured Li3V2(PO4)3

The redox couple, V4+/V3+, exhibits a potential of 3.76 V in NASICON-structured Li3Al0.1V1.9(PO4)3, which is suitable for a cathode material of a lithium-ion battery. The rhombohedral NASICON framework provides a large interstitial space for fast lithium transport, but the structure has to be prepared by the lithium ion-exchange method from NASICON-structured Na3V2(PO4)3. We used a LiNO3 aqueous solution to treat Na3V2(PO4)3 for two weeks; a mixture of rhombohedral and monoclinic Li3V2(PO4)3 was obtained in the final product. Therefore, we introduced aluminum into the NASICON framework. Results from phase analysis and electrochemical evaluation have concluded that the aluminum stabilizes the NASICON framework of V2(PO4)3 in the lithium ion-exchange process. The aluminum-stabilized Li3Al0.1V1.9(PO4)3 showed a reversible capacity of 70 mA h g−1 compared to 15 mA h g−1 for the non-aluminum-doped n-LVP at 5C rate.

Antimony/Graphitic Carbon Composite Anode for High-Performance Sodium-Ion Batteries.

Although the room-temperature rechargeable sodium-ion battery has emerged as an attractive alternative energy storage solution for large-scale deployment, major challenges toward practical sodium-ion battery technology remain including identification and engineering of anode materials that are both technologically feasible and economical. Herein, an antimony-based anode is developed by incorporating antimony into graphitic carbon matrices using low-cost materials and scalable processes. The composite anode exhibits excellent overall performance in terms of packing density, fast charge/discharge capability and cyclability, which is enabled by the conductive and compact graphitic network. A full cell design featuring this composite anode with a hexacyanometallate cathode achieves superior power output and low polarization, which offers the potential for realizing a high-performance, cost-effective sodium-ion battery.

Modification of Transition-Metal Redox by Interstitial Water in Hexacyanometalate Electrodes for Sodium-Ion Batteries

A sodium-ion battery (SIB) solution is attractive for grid-scale electrical energy storage. Low-cost hexacyanometalate is a promising electrode material for SIBs because of its easy synthesis and open framework. Most hexacyanometalate-based SIBs work with aqueous electrolyte, and interstitial water in the material has been found to strongly affect the electrochemical profile, but the mechanism remains elusive. Here we provide a comparative study of the transition-metal redox in hexacyanometalate electrodes with and without interstitial water based on soft X-ray absorption spectroscopy and theoretical calculations. We found distinct transition-metal redox sequences in hydrated and anhydrated NaxMnFe(CN)6·zH2O. The Fe and Mn redox in hydrated electrodes are separated and are at different potentials, leading to two voltage plateaus. On the contrary, mixed Fe and Mn redox in the same potential range is found in the anhydrated system. This work reveals for the first time how transition-metal redox in batteries is strongly affected by interstitial molecules that are seemingly spectators. The results suggest a fundamental mechanism based on three competing factors that determine the transition-metal redox potentials. Because most hexacyanometalate electrodes contain water, this work directly reveals the mechanism of how interstitial molecules could define the electrochemical profile, especially for electrodes based on transition-metal redox with well-defined spin states.