Juan Miguel López del Amo

Structural evolution during sodium deintercalation/intercalation in Na2/3[Fe1/2Mn1/2]O2

Among the various possible earth abundant electrode materials, P2-Na2/3[Fe1/2Mn1/2]O2 is one of the most promising cathode materials for sodium ion batteries. Most transition metal oxide materials undergo various structural transitions during the sodiation/desodiation process and it is crucial to understand such transitions for further development of these materials. In the present research, in situ X-ray diffraction (XRD), in situ Raman spectroscopy and ex situ solid-state Nuclear Magnetic Resonance (NMR) were used as tools to understand such transitions for the specific case of P2-Na2/3[Fe1/2Mn1/2]O2. Both in situ Raman spectroscopy and X-ray diffraction measurements, together with ex situ solid-state NMR studies revealed that the synthesized P2-Na2/3[Fe1/2Mn1/2]O2 hexagonal crystal structure undergoes P2–OP4 reversible phase transitions at the end of the charge process and at the end of the discharge process a biphasic mechanism follows. Moreover, ex situ solid state NMR measurements revealed the fast diffusion of Na+ ions in the 2D layers of P2-Na2/3[Fe1/2Mn1/2]O2, which led to an average 23Na NMR signal that reflects very accurately the average oxidation state of the metal centres. Solid state NMR data also shows that the diffusion of sodium ions is frozen at high levels of sodiation, at low voltages and that at the end of the charge process the prismatic coordinated sites are preferentially populated in the OP4 phase.

Investigating the dendritic growth during full cell cycling of garnet electrolyte in direct contact with Li metal.

All-solid-state batteries including a garnet ceramic as electrolyte are potential candidates to replace the currently used Li-ion technology, as they offer safer operation and higher energy storage performances. However, the development of ceramic electrolyte batteries faces several challenges at the electrode/electrolyte interfaces, which need to withstand high current densities to enable competing C-rates. In this work, we investigate the limits of the anode/electrolyte interface in a full cell that includes a Li-metal anode, LiFePO4 cathode, and garnet ceramic electrolyte. The addition of a liquid interfacial layer between the cathode and the ceramic electrolyte is found to be a prerequisite to achieve low interfacial resistance and to enable full use of the active material contained in the porous electrode. Reproducible and constant discharge capacities are extracted from the cathode active material during the first 20 cycles, revealing high efficiency of the garnet as electrolyte and the interfaces, but prolonged cycling leads to abrupt cell failure. By using a combination of structural and chemical characterization techniques, such as SEM and solid-state NMR, as well as electrochemical and impedance spectroscopy, it is demonstrated that a sudden impedance drop occurs in the cell due to the formation of metallic Li and its propagation within the ceramic electrolyte. This degradation process is originated at the interface between the Li-metal anode and the ceramic electrolyte layer and leads to electromechanical failure and cell short-circuit. Improvement of the performances is observed when cycling the full cell at 55 °C, as the Li-metal softening favors the interfacial contact. Various degradation mechanisms are proposed to explain this behavior.

All-Solid-State Lithium-Ion Batteries with Grafted Ceramic Nanoparticles Dispersed in Solid Polymer Electrolytes

Lithium-based rechargeable batteries offer superior specific energy and power, and have enabled exponential growth in industries focused on small electronic devices. However, further increases in energy density, for example for electric transportation, face the challenge of harnessing the lithium metal as negative electrode instead of limited-capacity graphite and its heavy copper current collector. All-solid-state batteries utilize solid polymer electrolytes (SPEs) to overcome the safety issues of liquid electrolytes. We demonstrate an all-solid-state lithium-ion battery by using plasticized poly(ethylene oxide)-based SPEs comprising anions grafted or co-grafted onto ceramic nanoparticles. This new approach using grafted ceramic nanoparticles enables the development of a new generation of nanohybrid polymer electrolytes with high ionic conductivity as well as high electrochemical and mechanical stability, enabling Li-ion batteries with long cycle life.

Layered P2–O3 sodium-ion cathodes derived from earth abundant elements

Sodium layered oxide materials show excellent performance as cathodes in sodium ion batteries, leading to considerable interest in routes to improving their properties. A manganese-rich P2/O3-phase Na2/3Li0.18Mn0.8Fe0.2O2 material is synthesized, from earth abundant precursors, via a solid state-reaction. Its biphasic nature is confirmed by X-ray diffraction and transmission electron microscopy, and the inclusion of Li by solid state NMR. The pristine electrode delivers a capacity of 125 and 105 mA h g−1 at C/10 and 1C rates, respectively, with a coulombic efficiency of ca. 95 to 99.9% over 100 cycles. In addition, the influence of mechanical post-treatment is explored and shows an increased energy density and capacity retention over 50 cycles when compared to the pristine compound. The strategies outlined in this work not only apply to popular sodium manganese-based layered oxides, but also to the wider family of sodium layered oxide cathode materials in general – providing an additional facile and exploitable route to optimization.