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Chemical pre-lithiation is carried out using lithium naphthalene to incorporate excess lithium into lithium manganese spinel (LiMn2O4). Pre-lithiated LiMn2O4 powder is collected and processed under ambient air conditions, demonstrating its seamless integration into current lithium-ion manufacturing. Precise control of the lithiation content in LiMn2O4 allows tuning of the first cycle efficiency, and when demonstrated in a full-cell configuration comprising a silicon anode, can achieve a projected specific energy of ∼216 W h kg−1. [ABSTRACT FROM AUTHOR]

We demonstrate that an ionic liquid 1-ethyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide combined with propylene carbonate and lithium bis(trifluoromethanesulfonyl)imide yields a hybrid electrolyte that enables a wide operational temperature window (−20 °C to 60 °C). When integrated into a lithium titanate‖lithium cobalt oxide full-cell configuration, high-rate capability is achieved at −20 °C with >40% retention at a C/2 cycling rate, and negligible capacity fade is observed during rate capability tests and long-term cycling at 60 °C. [ABSTRACT FROM AUTHOR]

Lithium-ion (Li+) batteries are considered the most attractive for low temperature operation. Though Li+-conducting electrolytes predominately use carbonate solvents, we show that nitriles, such as 3-methoxypropyionitrile (MPN), are promising candidates for use at low temperatures. At a high salt concentration (2.5 molal), and combined with a fluoroethylene carbonate additive, this electrolyte enables −40 °C operation when configured in a graphite‖lithium cobalt oxide cell. We leverage molecular dynamics simulations and experimentally validate Li+ diffusivity/conductivity measurements to bolster our understanding of the MPN electrolyte in comparison with carbonates. At room temperature, cells demonstrate high rate capability (100 mA h g−1 discharge capacity at 2C), and also maintain >75% of their initial capacity up to 100 cycles when cycled at 0.2C. At −40 °C, >50% of the cell's room temperature discharge capacity is sustained, showing exemplary low temperature performance. By performing an impedance-based distribution of relaxation times analysis, we identify that interfacial kinetics at the anode surface and the cathode electrolyte interphase are the two underlying factors limiting low temperature operation. The results presented herein offer an exciting direction for the discovery and implementation of nitrile-based solvents that can withstand low temperatures. [ABSTRACT FROM AUTHOR]

Directing the morphology of lithium metal deposits during electrodeposition is crucial to the development of safe, high energy density batteries with long cycle life. Towards this end, mechanistic insight is imperative to understand the impact of electrolyte components and cycling conditions on lithium morphologies. In this work, we used a standard carbonate-based electrolyte while systematically adding water (0–250 ppm, corresponding to 0–500 ppm HF) in Li‖Cu cells to study the links between electrolyte composition, initial solid electrolyte interphase (SEI) formation, and morphology of electroplated lithium metal using electrochemical characterization, X-ray scattering, X-ray photoelectron spectroscopy, and electron microscopy. Under conditions in which the electrolyte contains several hundred ppm added HF and applied constant currents on the order of 0.5 mA cm−2, this system yields electrodeposited lithium metal with a highly monodispersed columnar morphology. Systematic experimental investigation of the HF reduction process, nature of the initial SEI, and the structure of the electrodeposited lithium metal enable insights to be drawn concerning the underlying mechanisms of columnar lithium formation. This morphology arises from an SEI layer comprising crystalline LiF deposits on the copper current collector surface, formed through selective reduction of HF at high potential, embedded in an amorphous matrix of solvent reduction products. This interphase structure contains fast lithium-ion diffusion pathways which lead to a high nucleation density and uniform growth of lithium metal deposits. The mechanism proposed herein will help to inform future electrolyte additive design and formation cycling protocols for lithium metal batteries. [ABSTRACT FROM AUTHOR]

Metal phosphate compounds are considered promising candidates as positive electrode materials for Na-ion batteries because they offer higher cation-insertion potentials than analogous metal oxides. One such example is sodium iron fluorophosphate (Na2FePO4F), a compound that is typically synthesized by high-temperature solid-state routes. In this study, we prepare phase-pure Na2FePO4F using the polyol route, a low-temperature process that allows for the synthesis of nanoparticles (15–25 nm), a form that enhances Na-ion insertion kinetics and cycling stability. We then apply two methods to enhance the electronic conductivity of Na2FePO4F: (i) converting residual organic byproducts of the polyol synthesis to conductive carbon coatings; and (ii) preparing a nanocomposite with reduced graphene oxide. The resulting electrode materials are characterized in nonaqueous Na-ion electrolytes, assessing such metrics as specific capacity, rate capability, and cycling stability. A thorough electrochemical kinetics analysis is performed to deconvolve surface-vs.-bulk Na-ion insertion as a function of composite structure. Specific capacities between 60–110 mA h g−1 were achieved in galvanostatic charge–discharge tests when cycling in the range from 10C to C/10, respectively. [ABSTRACT FROM AUTHOR]

Vanadium-substituted iron oxide aerogels (2 : 1 Fe : V ratio; VFe2Ox) are synthesized using an epoxide-initiated sol–gel method to form high surface-area, mesoporous materials in which the degree of crystallinity and concentration of defects are tuned via thermal treatments under controlled atmospheres. Thermal processing of the X-ray amorphous, as-synthesized VFe2Ox aerogels at 300 °C under O2-rich conditions removes residual organic byproducts while maintaining a highly defective γ-Fe2O3-like local structure with minimal long-range order and vanadium in the +5 state. When as-synthesized VFe2Ox aerogels are heated under low partial pressure of O2 (e.g., flowing argon), a fraction of vanadium sites are reduced to the +4 state, driving crystallization to a Fe3O4-like cubic phase. Subsequent thermal oxidation of this nanocrystalline VFe2Ox aerogel re-oxidizes vanadium +4 to +5, creating additional cation vacancies and re-introducing disordered oxide domains. We correlate the electrochemical charge-storage properties of this series of VFe2Ox aerogels with their degree of order and chemical state, as verified by X-ray diffraction, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. We find that the disordered O2-heated VFe2Ox aerogel yields the highest Li+- and Na+-insertion capacities among this series, approaching 130 mA h g−1 and 70 mA h g−1, respectively. Direct heat-treatment of the VFe2Ox aerogel in flowing argon to yield the partially reduced, nanocrystalline form results in significantly lower Li+-insertion capacity (77 mA h g−1), which improves to 105 mA h g−1 by thermal oxidation to create additional vacancies and structural disorder. [ABSTRACT FROM AUTHOR]