Using molecular dynamics simulations, small-angle neutron scattering, and a variety of spectroscopic techniques, we evaluated the ion solvation and transport behaviors in aqueous electrolytes containing bis(trifluoromethanesulfonyl)imide. We discovered that, at high salt concentrations (from 10 to 21 mol/kg), a disproportion of cation solvation occurs, leading to a liquid structure of heterogeneous domains with a characteristic length scale of 1 to 2 nm. This unusual nano-heterogeneity effectively decouples cations from the Coulombic traps of anions and provides a 3D percolating lithium-water network, via which 40% of the lithium cations are liberated for fast ion transport even in concentration ranges traditionally considered too viscous. Due to such percolation networks, superconcentrated aqueous electrolytes are characterized by a high lithium-transference number (0.73), which is key to supporting an assortment of battery chemistries at high rate. The in-depth understanding of this transport mechanism establishes guiding principles to the tailored design of future superconcentrated electrolyte systems.

Narrow electrochemical stability window (1.23 V) of aqueous electrolytes has always been the key obstacle preventing aqueous sodium ion chemistry of practical energy density and cycle life. The sodium ion Water-in-Salt Electrolyte (NaWiSE) eliminates this barrier by offering a 2.5 V window through suppressing hydrogen evolution on anode with the formation of a Na + -conducting solidelectrolyte-interphase (SEI) and reducing the overall electrochemical activity of water on cathode. A full aqueous Na-ion battery constructed on Na 0.66 [Mn 0.66 Ti 0.34 ]O 2 as cathode and NaTi 2 (PO 4 ) 3 as anode exhibits superior performance at both low and high rates, as exemplified by extraordinarily high coulombic efficiency (> 99.2%) at a low rate (0.2 C) for >350 cycles, and excellent cycling stability with negligible capacity losses (0.006 % per cycle) at a high rate (1C) for >1200 cycles. Molecular modeling revealed some key difference between Li-ion and Na-ion WiSE, and identified a more pronounced ion aggregation with frequent contacts between the sodium cation and fluorine of anion in the latter as one main factor responsible for the formation of a dense SEI at lower salt concentration than its Li cousin.

A new super-concentrated aqueous electrolyte is proposed by introducing a second lithium salt. The resultant ultra-high concentration of 28 m led to more effective formation of a protective interphase on the anode along with further suppression of water activities at both anode and cathode surfaces. The improved electrochemical stability allows the use of TiO2 as the anode material, and a 2.5 V aqueous Li-ion cell based on LiMn2 O4 and carbon-coated TiO2 delivered the unprecedented energy density of 100 Wh kg(-1) for rechargeable aqueous Li-ion cells, along with excellent cycling stability and high coulombic efficiency. It has been demonstrated that the introduction of a second salts into the "water-in-salt" electrolyte further pushed the energy densities of aqueous Li-ion cells closer to those of the state-of-the-art Li-ion batteries.

4.0 V aqueous LIBs of both high energy density and high safety are made possible by a new interphase formed from an ''inhomogeneous additive'' approach that effectively stabilizes graphite or lithium-metal anode materials.

Efforts were made to differentiate the contributions to the so-called "ion transfer" barrier at the electrolyte/graphite junction from two distinct processes: (1) desolvation of Li(+) before it enters graphene interlayer and (2) the subsequent migration of bare Li(+) through the ad hoc interphase. By leveraging a scenario where no substantial interphase was formed on Li(+) intercalation hosts, we were able to quantify the distribution of "ion transfer" activation energy between these two interfacial processes and hence identify the desolvation process of Li(+) as the major energy-consuming step. The result confirmed the earlier belief that the rate-determining step in the charging of a graphitic anode in Li(+) intercalation chemistry relates to the stripping of solvation sheath of Li(+), which is closely interwoven with the interphasial resistance to Li(+) migration.

Aqui.Onde a terra termina e o mar j a não começa -A poetic definition of a binary liquid/solid interface by Lu ıs de Camões (1572). Since its birth in early 1990s, Li ion battery technology has been powering the rapid digitization of our daily life and finally made its debut in 2010 into the large format application for electrified vehicles such as the Nissan Leaf and GM Chevrolet Volt; however, much of the chemistry and processes underneath this amazing energy storage device still remain to be understood, among which is the interphase between electrolyte and electrodes. Interphases are formed in situ on electrode surfaces from sacrificial decomposition of electrolytes. Their ad hoc chemistry supports the reversible Li + -intercalation in both anode and cathode materials at extreme potentials, while preventing parasitic reductions/oxidations on the reactive surfaces of those electrodes; but their existence places restrictions on energy and power densities of the device by impeding Li + -transport and setting operating voltage limits, respectively. It has been the dream of battery engineers to maximize the former and minimize the latter. This review summarizes the most recent knowledge about the chemistry and formation mechanism of this elusive battery component on both anode and cathode surfaces. The attempts to tailor a desired interphasial chemistry via diversified means were also discussed.

To understand how Li(+) interacts with individual carbonate molecules in nonaqueous electrolytes, we conducted natural abundance (17)O NMR measurements on electrolyte solutions of 1 M LiPF6 in a series of binary solvent mixtures of ethylene carbonate (EC) and dimethyl carbonate (DMC). It was observed that the largest changes in (17)O chemical shift occurred at the carbonyl oxygens of EC, firmly establishing that Li(+) strongly prefers EC over DMC in typical nonaqueous electrolytes, while mainly coordinating with carbonyl rather than ethereal oxygens. Further quantitative analysis of the displacements in (17)O chemical shifts renders a detailed Li(+)-solvation structure in these electrolyte solutions, revealing that maximum six EC molecules can coexist in the Li(+)-solvation sheath, while DMC association with Li(+) is more "noncommittal" but simultaneously prevalent. This discovery, while aligning well with previous fragmental knowledge about Li(+)-solvation, reveals for the first time a complete picture of Li(+) solvation structure in nonaqueous electrolytes.

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