Fast charging of most commercial lithium-ion batteries is limited due to fear of lithium plating on the graphite anode, which is difficult to detect and poses significant safety risk. Here we demonstrate the power of simple, accessible, and high-throughput cycling techniques to quantify irreversible Li plating spanning data from over 200 cells. We first observe the effects of energy density, charge rate, temperature, and State-of-Charge (SOC) on lithium plating, use the results to refine mature physicsbased electrochemical models, and provide an interpretable empirical equation for predicting the plating onset SOC. We then explore the reversibility of lithium plating for varied deposition rates, amounts, and electrolyte compositions, applying our understanding towards development of electrolytes that reduce irreversible Li formation. Finally, we provide the first quantitative comparison of lithium plating in the experimentally convenient Graphite|Li cell configuration compared with commercially relevant Graphite|LiNi0.5Mn0.3Co0.2O2 (NMC). The hypotheses and abundant data herein were generated primarily with equipment universal to the battery researcher, encouraging further development of innovative testing methods and data processing that enable rapid battery IntroductionThe urgent need to combat climate change has sparked extreme growth in demand for lithium-ion batteries (LIB). Rapid innovation in battery materials and cell design is critical to meet this demand for diverse applications from electronics to vehicles and utility-scale energy storage. Composite graphite electrodes remain a universal component of the LIB and are expected to dominate anode market share through 2030 despite the introduction of silicon and lithium-based materials 1 . The design space for graphite electrodes is immense, with parameters such as the loading, porosity, particle size, binder composition, and electrolyte being carefully selected to meet requirements for lifetime, operating temperature, charge time, and manufacturing. Regardless of design and application, the lithium plating reaction on graphite is a performance and safety concern due to the formation of noncyclable 'dead' lithium metal and salts. While recent studies have focused on Li plating during fast charging, the phenomenon is also pertinent to other operating extremes such as low temperature 2 , overcharge 3 , or system malfunction 4 . Electrochemical (EChem) modeling is an important tool for understanding design tradeoffs that improve graphite performance while avoiding plating. Over decades, Newman-based models that relate cell current density, voltage, temperature, and material properties to graphite intercalation have been enhanced to also estimate lithium plating. [5][6][7][8][9][10] This has led to initial insight into the effect of charge rate, electrode loading, and temperature on lithium plating onset/amount, but simulations rely on debated parameters such as the plating exchange current density or reversibility and are frequently not verified with direct ex...

Ultraviolet (UV) light can trigger a plethora of useful photochemical reactions for diverse applications, including photocatalysis, photopolymerization, and drug delivery. These applications typically require penetration of high energy photons deep into materials, yet delivering these photons beyond the surface is extremely challenging due to absorption and scattering effects. Triplet-triplet annihilation upconversion (TTA-UC) shows great promise to circumvent this issue by generating high energy photons from incident lower energy photons. However, molecules that facilitate TTA-UC usually have poor water solubility, limiting their deployment in aqueous environments. To address this challenge, we leverage a nanoencapsulation method to fabricate water-compatible UC micelles, enabling on-demand UV photon generation deep into materials. We present two iridium-based complexes for use as TTA-UC sensitizers with increased solubilities that facilitate the formation of highly emissive UV-upconverting micelles. Furthermore, we show this encapsulation method is generalizable to nineteen UV-emitting UC systems, accessing a range of upconverted UV emission profiles with wavelengths as low as 350 nm. As a proof-of-principle demonstration of precision photochemistry at depth, we use UV-emitting UC micelles to photolyze a fluorophore at a focal point nearly a centimeter beyond the surface, revealing opportunities for spatially controlled manipulation deep into UV-responsive materials.

Long charge times and battery safety remain two of the largest hurdles for widespread adoption of electric vehicles. It is well known that the deposition of lithium metal on the graphite electrode, or ‘lithium plating’, can cause capacity fade and catastrophic cell shorting, so recent studies have focused on its detection and evolution throughout cycling. While many specialty lithium plating detection techniques have been reported, few are well suited for robust characterization of electrode and electrolyte materials for fast charging. We have developed cycling protocols that use coulombic efficiencies to estimate the evolving amount of irreversible Li plating during a single fast charge in graphite/lithium cells. The technique was applied to over 50 coin cells with varying electrode thicknesses (x), temperatures (T), and C-rates (C), and the results agree well with models developed a priori. Defining 0.1% of the graphite capacity of irreversible lithium plating as a threshold, we identify plating onset states-of-charge (SOC) for each condition and map the plating onsets as a function of x, T, and C. We contribute novel insights about the importance of these variables on the lithium plating onset and demonstrate this technique as one of the most sensitive, accessible, and reproducible methods for lithium plating detection.

Fast charging of most commercial lithium-ion batteries is limited due to fear of lithium plating on the graphite anode, which is difficult to detect and poses significant safety risk. Here we demonstrate the power of simple, accessible, and high-throughput cycling techniques to quantify irreversible Li plating spanning data from over 200 cells. We first observe the effects of energy density, charge rate, temperature, and State-of-Charge (SOC) on lithium plating, use the results to refine mature physics-based electrochemical models, and provide an interpretable empirical equation for predicting the plating onset SOC. We then explore the reversibility of lithium plating for varied deposition rates, amounts, and electrolyte compositions, applying our understanding towards development of electrolytes that reduce irreversible Li formation. Finally, we provide the first quantitative comparison of lithium plating in the experimentally convenient Graphite|Li cell configuration compared with commercially relevant Graphite|LiNi0.5Mn0.3Co0.2O2 (NMC). The hypotheses and abundant data herein were generated primarily with equipment universal to the battery researcher, encouraging further development of innovative testing methods and data processing that enable rapid battery engineering.