No abstract

A cross-linked polymer containing pendant molecules attached to the polymer framework is shown to form flexible and low-cost membranes, to be a solid Li(+) electrolyte up to 270 °C, much higher than those based on poly(ethylene oxide), to be wetted by a metallic lithium anode, and to be not decomposed by the metallic anode if the anions of the salt are blocked by a ceramic electrolyte in a polymer/ceramic membrane/polymer sandwich electrolyte (PCPSE). In this sandwich architecture, the double-layer electric field at the Li/polymer interface is reduced due to the blocked salt anion transfer. The polymer layer adheres/wets the lithium metal surface and makes the Li-ion flux at the interface more homogeneous. This structure integrates the advantages of the ceramic and polymer. With the PCPSE, all-solid-state Li/LiFePO4 cells showed a notably high Coulombic efficiency of 99.8-100% over 640 cycles.

The garnet-related oxides with the general formula Li 7Àx La 3 Zr 2Àx Ta x O 12 (0 # x # 1) were prepared by conventional solid-state reaction. X-ray diffraction (XRD), neutron diffraction and AC impedance were used to determine phase formation and the lithium-ion conductivity. The lattice parameter of Li 7Àx La 3 Zr 2Àx Ta x O 12 decreased linearly with increasing x. Optimum Li-ion conductivity in the Li-ion garnets Li 7Àx La 3 Zr 2Àx Ta x O 12 is found in the range 0.4 # x # 0.6 for samples fired at 1140 C in an alumina crucible. A room-temperature s Li z 1.0 Â 10 À3 S cm À1 for x ¼ 0.6 with an activation energy of 0.35 eV in the temperature range of 298-430 K makes this Li-ion solid electrolyte attractive for a new family of Li-ion rechargeable batteries.

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 KMnFe(CN) (0 ≤ x ≤ 2) as a potassium cathode: high-spin Mn/Mn and low-spin Fe/Fe 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; 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. The observed voltage, capacity, and its low cost make it competitive in large-scale electricity storage applications.

Garnet-structured LiLaZrO is a promising solid Li-ion electrolyte for all-solid-state Li-metal batteries and Li-redox-flow batteries owing to its high Li-ion conductivity at room temperature and good electrochemical stability with Li metal. However, there are still three major challenges unsolved: (1) the controversial electrochemical window of garnet, (2) the impractically large resistance at a garnet/electrode interface and the fast lithium-dendrite growth along the grain boundaries of the garnet pellet, and (3) the fast degradation during storage. We have found that these challenges are closely related to a thick LiCO layer and the Li-Al-O glass phase on the surface of garnet materials. Here we introduce a simple method to remove LiCO and the protons in the garnet framework by reacting garnet with carbon at 700 °C; moreover, the amount of the Li-Al-O glass phase with a low Li-ion conductivity in the grain boundary on the garnet surface was also reduced. The surface of the carbon-treated garnet pellets is free of LiCO and is wet by a metallic lithium anode, an organic electrolyte, and a solid composite cathode. The carbon post-treatment has reduced significantly the interfacial resistances to 28, 92 (at 65 °C), and 45 Ω cm at Li/garnet, garnet/LiFePO, and garnet/organic-liquid interfaces, respectively. A symmetric Li/garnet/Li, an all-solid-state Li/garnet/LiFePO, and a hybrid Li-S cell show small overpotentials, high Coulombic efficiencies, and stable cycling performance.