Cathode Dependence of Liquid-Alloy Na–K Anodes

Alkali ions can be plated dendrite-free into a liquid alkali-metal anode. Commercialized Na–S battery technology operates above 300 °C. A low-cost Na–K alloy is liquid at 25 °C from 9.2 to 58.2 wt% of sodium; sodium and/or potassium can be plated dendrite-free in the liquid range at room temperature. The co-existence of two alkali metals in an anode raises a question: whether the liquid Na–K alloy acts as a Na or a K anode. Here we show the alkali-metal that is stripped from the liquid Na–K anode is dependent on the preference of the cathode host. It acts as the anode of a sodium rechargeable cell if the cathode host structure selectively accepts only Na⁺ ions; as the anode of a potassium rechargeable cell if the cathode accepts K⁺ ions in preference to Na⁺ ions. This dual-anode behavior means the liquid Na–K alkali-alloy can be applied as a dendrite-free anode in Na-metal batteries as well as K-metal batteries

Graphene Sandwiched by Sulfur-Confined Mesoporous Carbon Nanosheets: A Kinetically Stable Cathode for Li–S Batteries

The practical use of lithium–sulfur batteries for the next-generation energy storage, especially the automobiles, was hindered by low electronic conductivity of sulfur and the resulting poor rate capabilities. Here, we report a sulfur–carbon composite by confining S into a graphene sandwiched in mesoporous carbon nanosheets with a two-dimensional ultrathin morphology, suitable mesopore size and large pore volume, and excellent electronic conductivity. Serving as cathode material for a Li–S battery, the elaborately designed S/C composite leads to “kinetically stable” transmissions of Li ions and electrons, triggering a stable electrochemistry and a record-breaking rate performance. In this way, the S/C composite has been proved a promising cathode material for high-rate Li–S batteries targeted at automobile storage

Low-Cost High-Energy Potassium Cathode

Potassium has as rich an abundance as sodium in the earth, but the development of a K-ion battery is lagging behind because of the higher mass and larger ionic size of K⁺ than that of Li⁺ and Na⁺, which makes it difficult to identify a high-voltage and high-capacity intercalation cathode host. Here we propose a cyanoperovskite K_<i>x</i>MnFe­(CN)₆ (0 ≤ <i>x</i> ≤ 2) as a potassium cathode: high-spin Mn^III/Mn^II and low-spin Fe^III/Fe^II couples have similar energies and exhibit two close plateaus centered at 3.6 V; two active K⁺ per formula unit enable a theoretical specific capacity of 156 mAh g^–1; Mn and Fe are the two most-desired transition metals for electrodes because they are cheap and environmental friendly. As a powder prepared by an inexpensive precipitation method, the cathode delivers a specific capacity of 142 mAh g^–1. The observed voltage, capacity, and its low cost make it competitive in large-scale electricity storage applications

Low-Cost High-Energy Potassium Cathode

Potassium has as rich an abundance as sodium in the earth, but the development of a K-ion battery is lagging behind because of the higher mass and larger ionic size of K⁺ than that of Li⁺ and Na⁺, which makes it difficult to identify a high-voltage and high-capacity intercalation cathode host. Here we propose a cyanoperovskite K_<i>x</i>MnFe­(CN)₆ (0 ≤ <i>x</i> ≤ 2) as a potassium cathode: high-spin Mn^III/Mn^II and low-spin Fe^III/Fe^II couples have similar energies and exhibit two close plateaus centered at 3.6 V; two active K⁺ per formula unit enable a theoretical specific capacity of 156 mAh g^–1; Mn and Fe are the two most-desired transition metals for electrodes because they are cheap and environmental friendly. As a powder prepared by an inexpensive precipitation method, the cathode delivers a specific capacity of 142 mAh g^–1. The observed voltage, capacity, and its low cost make it competitive in large-scale electricity storage applications

Na_<i>x</i>MV(PO₄)₃ (M = Mn, Fe, Ni) Structure and Properties for Sodium Extraction

NASICON (Na⁺ super ionic conductor) structures of Na_<i>x</i>MV­(PO₄)₃ (M = Mn, Fe, Ni) were prepared, characterized by aberration-corrected STEM and synchrotron radiation, and demonstrated to be durable cathode materials for rechargeable sodium-ion batteries. In Na₄MnV­(PO₄)₃, two redox couples of Mn³⁺/Mn²⁺ and V⁴⁺/V³⁺ are accessed with two voltage plateaus located at 3.6 and 3.3 V and a capacity of 101 mAh g^–1 at 1 C. Furthermore, the Na₄MnV­(PO₄)₃ cathode delivers a high initial efficiency of 97%, long durability over 1000 cycles, and good rate performance to 10 C. The robust framework structure and stable electrochemical performance makes it a reliable cathode materials for sodium-ion batteries