Dual-ion batteries (DIBs) generally operate beyond 4.7 V vs Li + /Li 0 and rely on the intercalation of both cations and anions in graphite electrodes. Major challenges facing the development of DIBs are linked to electrolyte decomposition at the cathode–electrolyte interface (CEI), graphite exfoliation, and corrosion of Al current collectors. In this work, X-ray photoelectron spectroscopy (XPS) is employed to gain a broad understanding of the nature and dynamics of the CEI built on anion-intercalated graphite cycled both in highly concentrated electrolytes (HCEs) of common lithium salts (LiPF 6 , LiFSI, and LiTFSI) in carbonate solvents and in a typical ionic liquid. Though Al metal current collectors were adequately stable in all HCEs, the Coulombic efficiency was substantially higher for HCEs based on LiFSI and LiTFSI salts. Specific capacities ranging from 80 to 100 mAh g –1 were achieved with a Coulombic efficiency above 90% over extended cycling, but cells with LiPF 6 -based electrolytes were characterized by <70% Coulombic efficiency and specific capacities of merely ca. 60 mAh g –1 . The poor performance in LiPF 6 -containing electrolytes is indicative of the continual buildup of decomposition products at the interface due to oxidation, forming a thick interfacial layer rich in Li x PF y , PO x F y , Li x PO y F z , and organic carbonates as evidenced by XPS. In contrast, insights from XPS analyses suggested that anion intercalation and deintercalation processes in the range from 3 to 5.1 V give rise to scant or extremely thin surface layers on graphite electrodes cycled in LiFSI- and LiTFSI-containing HCEs, even allowing for probing anions intercalated in the near-surface bulk. In addition, ex situ Raman, SEM and TEM characterizations revealed the presence of a thick coating on graphite particles cycled in LiPF 6 -based electrolytes regardless of salt concentration, while hardly any surface film was observed in the case of concentrated LiFSI and LiTFSI electrolytes.

V2O5·0.55H2O nanosheets synthesizedviaa water based technique, and showing promising lithium-ion storage capacity.

High surface area carbon foams were prepared and characterized for use in 3D structured batteries. Two potential applications exist for these foams: firstly as an anode and secondly as a current collector support for electrode materials. The preparation of the carbon foams by pyrolysis of a high internal phase emulsion polymer (polyHIPE) resulted in structures with cage sizes of $25 mm and a surface area enhancement per geometric area of approximately 90 times, close to the optimal configuration for a 3D microstructured battery support. The structure was probed using XPS, SEM, BET, XRD and Raman techniques; revealing that the foams were composed of a disordered carbon with a pore size in the <100 nm range resulting in a BET measured surface area of 433 m 2 g À1 . A reversible capacity exceeding 3.5 mA h cm À2 at a current density of 0.37 mA cm À2 was achieved. SEM images of the foams after 50 cycles showed that the structure suffered no degradation. Furthermore, the foams were tested as a current collector by depositing a layer of polyaniline cathode over their surface. High footprint area capacities of 500 mA h cm À2 were seen in the voltage range 3.8 to 2.5 V vs. Li and a reasonable rate performance was observed.

P2-type NaMO sodiated layered oxides with mixed transition metals are receiving considerable attention for use as cathodes in sodium-ion batteries. A study on solid solution (1 - y)P2-NaCoO-(y)P2-NaMnNiO (y = 0, 1/3, 1/2, 2/3, 1) reveals that changing the composition of the transition metals affects the resulting structure and the stability of pure P2 phases at various temperatures of calcination. For 0 ≤ y ≤ 1.0, the P2-NaCoMnNiO solid-solution compounds deliver good electrochemical performance when cycled between 2.0 and 4.2 V versus Na/Na with improved capacity stability in long-term cycling, especially for electrode materials with lower Co content (y = 1/2 and 2/3), despite lower discharge capacities being observed. The (1/2)P2-NaCoO-(1/2)P2-NaMnNiO composition delivers a discharge capacity of 101.04 mAh g with a capacity loss of only 3% after 100 cycles and a Coulombic efficiency exceeding 99.2%. Cycling this material to a higher cutoff voltage of 4.5 V versus Na/Na increases the specific discharge capacity to ≈140 mAh g due to the appearance of a well-defined high-voltage plateau, but after only 20 cycles, capacity retention declines to 88% and Coulombic efficiency drops to around 97%. In situ X-ray absorption near-edge structure measurements conducted on composition NaCoMnNiO (y = 1/2) in the two potential windows studied help elucidate the operating potential of each transition metal redox couple. It also reveals that at the high-voltage plateau, all of the transition metals are stable, raising the suspicion of possible contribution of oxygen ions in the high-voltage plateau.

Sustainable battery materials and chemistries are required to complement the growing demand for renewable energy from solar farms, wind mills, and hydroelectric power stations which are characterized by either demand fluctuations or periodic supply interruptions. [1] To keep a balance between supply and demand at all times, the intermittent nature of renewables should be leveled using stationary batteries deploying abundant, inexpensive, and nontoxic materials. [2,3] Current stationary batteries rely heavily on expensive transition metals (e.g., nickelcadmium or nickel-metal hydride batteries, and vanadium redox flow batteries), toxic elements (e.g., nickelcadmium and lead-acid batteries), or require high temperature to operate (e.g., sodium-sulfur batteries operating at 300À350 C). [3,4] In the interest of avoiding toxic and expensive minerals, there is a pressing need for sustainable battery materials that can provide comparable performance and cycle life. In this regard, the dual-ion battery (DIB) concept has emerged as a promising chemistry for future energy storage applications. In contrast to the "rocking chair" model in lithium-ion batteries, the energy storage mechanism in an archetype of a DIB is underpinned by the simultaneous intercalation of cations and anions from the electrolyte into, respectively, negative and positive electrodes containing graphite. [5,6] In a lithium DIB, anion intercalation and extraction require an operating voltage window ranging from 3 to 5.2 V versus Li þ /Li with the extent of reversibility ultimately depending on the type of graphite, electrolyte-salt concentration, type of electrolyte solvent, type of anion in the electrolyte, working temperature, and amount of electrolyte in the cell. [7,8] Reported gravimetric capacities for half-cells generally vary between 80 and 140 mAh g À1 with discharge voltages averaging 4.5 V. [6,9] On the basis of these metrics, lithium metal DIBs can be optimized to deliver cell-level energy density and specific energy above 200 Wh L À1 and 100 Wh kg À1 , respectively, better than lead-acid batteries (50-80 Wh L À1 or 20-55 Wh kg À1 ) and comparable with Ni-metal hydride batteries (150-220 Wh L À1 or 50-70 Wh kg À1 ) or Na-S batteries (150-300 Wh L À1 or 80-150 Wh kg À1 ). [6,10] Using graphite as the anion-hosting electrode, a wide selection of materials can be utilized in the negative electrode, which allows for increasingly diverse electrodeelectrolyte combinations in the design of DIBs. In addition, the fact that the negative and positive electrodes host different ions during cell operation relaxes the requirements on the type of electrolytes used. Thus, a stationary battery based on a DIB technology presents significant strategic advantages such as the likelihood of replacing transition metal-containing cathodes with graphite or organic materials and a broad choice of electrolytes. [11][12][13] These benefits are, in turn, anticipated to facilitate the transition to beyond Li-ion technologies harnessing more abundant Na þ -, K þ -, Ca 2þ...