aThe electrochemical kinetics of battery electrodes at the single-particle scale are measured as a function of state-of-charge, and interpreted with the aid of concurrent transmission X-ray microscopy (TXM) of the evolving particle microstructure. An electrochemical cell operating with near-picoampere current resolution is used to characterize single secondary particles of two widely-used cathode compounds, NMC333 and NCA. Interfacial charge transfer kinetics are found to vary by two orders of magnitude with state-of-charge (SOC) in both materials, but the origin of the SOC dependence differs greatly. NCA behavior is dominated by electrochemically-induced microfracture, although thin binder coatings significantly ameliorate mechanical degradation, while NMC333 demonstrates strongly increasing interfacial reaction rates with SOC for chemical reasons. Micro-PITT is used to separate interfacial and bulk transport rates, and show that for commercially relevant particle sizes, interfacial transport is rate-limiting at low SOC, while mixed-control dominates at higher SOC. These results provide mechanistic insight into the mesoscale kinetics of ion intercalation compounds, which can guide the development of high performance rechargeable batteries. Broader contextThe performance of high performance Li-ion batteries, central to both electric transportation and grid scale storage, is ultimately reliant on the performance of critical components such as their cathode and anode compounds. For ease of manufacturing, the prevailing technological forms of these materials are secondary particles of nearly spherical morphology containing many nanocrystallites. The electrochemical kinetics at this critical length scale have been difficult to assess; particle-level behavior has primarily been deduced from macroscale cell measurements. Thus the microelectrode technique developed in this work, combined with state-of-the-art TXM imaging, allows for the first time the direct measurement of electrochemical kinetics of particles as they are charged and discharged. Surprising behavior is revealed -interfacial charge transfer kinetics are found to vary greatly with state-of-charge and cycling history, both for intrinsic chemical reasons (in NMC333) and because of massively damaging ''electrochemical shock'' (in NCA). Moreover, a thin coating of polymer binder is found to ameliorate fracture damage. These results, and the techniques demonstrated, provide a bridge between macroscopic battery function and microscale electrode kinetics as influenced by electrochemomechanical stress and charging history.

The dropping cost of wind and solar power intensifies the need for low-cost, efficient energy storage, which together with renewables can displace fossil fuels. While batteries for transportation and portable devices emphasize energy density as a primary consideration, here, low-cost, ultra-abundant reactants deployable at massive (TWh) scale are essential. An air-breathing aqueous sulfur flow battery approach with ultralow energy cost is demonstrated at laboratory scale and shown to have economics similar to pumped hydroelectric storage without its geographical and environmental limitations.

Lithium-sulfur (Li-S) batteries have high theoretical energy density and low raw materials cost compared to present lithium-ion batteries and are thus promising for use in electric transportation and other applications. A major obstacle for Li-S batteries is low rate capability, especially at the low electrolyte/sulfur (E/S) ratios required for high energy density. Herein, we investigate several potentially rate-limiting factors for Li-S batteries. We study the ionic conductivity of lithium polysulfide solutions of varying concentration and in different ether-based solvents and their exchange current density on glassy carbon working electrodes. We believe this is the first such investigation of exchange current density for lithium polysulfide in solution. Exchange current densities are measured using both electrochemical impedance spectroscopy and steady-state galvanostatic polarization. In the range of interest (1-8 M [S]), the ionic conductivity monotonically decreases with increasing sulfur concentration while exchange current density shows a more complicated relationship to sulfur concentration. The electrolyte solvent dramatically affects ionic conductivity and exchange current density. The measured ionic conductivities and exchange current densities are also used to interpret the overpotential and rate capability of polysulfide-nanocarbon suspensions; this analysis demonstrates that ionic conductivity is the rate-limiting property in the solution regime (i.e. between Li 2 S 8 and Li 2 S 4 ). The widespread adoption of electric vehicles requires energy storage systems with higher energy density and lower cost than currently available batteries. The US Department of Energy's 2020 pack-level targets to enable widespread commercialization of electric vehicles are cost < $125/kWh, energy density > 400 Wh/L, specific energy >250 Wh/kg, and specific power >2000 W/kg.1 Sulfur is of interest as a cathode material for next-generation batteries because of its very low cost (as a by-product of oil and gas production, ∼$60 ton −1 ) and high natural abundance. Moreover, its theoretical capacity of 1670 mAh/g as a lithium host (upon full reaction to Li 2 S) is almost an order of magnitude higher than incumbent transition metal-based intercalation cathode active materials and may enable batteries with very high active materials-only theoretical specific energy (up to 2500 Wh/kg).2,3 The low cost of active materials for the Li-S couple makes it an attractive option for large-scale grid energy storage applications as well, which are essential for the large-scale deployment of intermittent renewable energy sources such as wind and solar. 4 Several technical barriers have limited the advancement of lithiumsulfur (Li-S) batteries, including rapid capacity fade, low rate capability, and low materials utilization.5-9 During discharge of a Li-S cell, elemental S is initially reduced to form soluble polysulfide species Li 2 S x (4 ≤ x ≤ 8) which exist in complex solution-phase equilibria. Upon further discharge, the short chain po...

Wide deployment of electric vehicles (EVs) would greatly facilitate global de-carbonization, but achieving the emission targets depends on future battery prices. Conventional learning curves for manufacturing costs, used in many battery projections, unrealistically predict battery prices will fall below $100/kWh by 2030, pushing EVs to hit price parity with internal combustion engine vehicles (ICEVs) in the absence of incentives. However, in reality, essential materials costs set practical lower bounds on battery prices.Our 2-stage learning curve model projects the active material costs and NMC-based lithium-ion battery pack price with mineral and material costs as the respective price floors. The improved model predicts NMC battery prices will fall only to about $124/kWh by 2030 -much cheaper than today, but still too expensive to truly compete with ICEVs, due primarily to the high prices of cobalt, nickel, and lithium. Our results suggest that stabilizing raw materials prices and/or stimulating R&D activities on alternative battery chemistries will be important to achieve environmentally sustainable EV-based ground transportation at an attractive price.