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Fast-charging lithium-ion batteries in 15 min or less is an important capability that may lead to greater electric vehicle adoption but remains challenging to implement. Heating to moderate temperature (40–50 °C) during the fast-charge step has been introduced as one method to mitigate the loss of lithium inventory by enhancing transport and kinetics. Unfortunately, this edge has two sides as even moderate temperature elevation will accelerate capacity fade due to interface and electrolyte degradation. While the thermal enhancement of transport and degradation is intuitive, the mechanistic effects of various temperature ranges on fast-charging capabilities are under-reported. The present work examines the balance between aging, temperature, and charge rate and describes cycling protocols in combination with high-temperature ranges that may enable fast-charging capabilities. A galvanostatic intermittent titration technique (GITT) analysis reveals non-Arrhenius diffusion behavior at the cell level. This shift is attributed to a mechanistic difference in graphite staging at temperatures above and below 40 °C. Coupled with differential capacity and voltage analysis, we indicate the specific phase transition that is kinetically sluggish at low temperatures relative to the other phase transitions but is comparable to the other phase transitions at high temperatures. This reduction of the transport bottleneck, in addition to the benefits of thermal activation of diffusion, further minimizes the likelihood of lithium plating that is triggered by particle scale transport challenges well before full lithiation of the graphite. This helps to explain recently described outsized successes of elevated temperature fast-charge protocols, but also questions the temperature at which fast-charge should take place, as the diffusivity gains for 55 vs 45 °C are less dramatic than 45 vs 35 °C, and side reactions may deter operation above 50 °C. These diffusivity studies are connected with long-term aging studies which indicate improved high-temperature aging at lower states-of-charge rather than higher states-of-charge. Taken together, we introduce a cycling protocol utilizing a constant current fast-charge at high temperature to take advantage of lower overpotentials, shorter duration at high states-of-charge, and improved cell diffusivity.

Activated carbon plays a pivotal role in achieving critical functions, such as separation, catalysis, and energy storage. A remaining question of carbon activation is which substructures in amorphous carbon are preferentially removed during activation. Herein, we report the first structure–activation correlation elucidated on the basis of unprecedented comprehensive characterization on carbon activation. We discover that activation under CO2preferentially removes graphenic layers that are more defective. Therefore, the resulting activated carbon contains thinned turbostratic nanodomains that are of a higher local graphenic order. The mechanistic insights explain why more defective soft carbon is “burned” under CO2at a much faster rate than hard carbon. The mechanism leads to an activation-based design principle of mesoporous carbon. Guided by this principle, a bimodal micromesoporous carbon is prepared simply by CO2activation. Our findings may cause a paradigm shift for the rational design of nanoporous carbon.

This paper utilizes density functional theory calculations to explore amorphous carbon materials, and concludes that the theoretical capacity is between 300 and 400 mAh g–1, depending on the degree of defects. This conclusion arises from a comprehensive number of simulations used to validate the experimentally determined storage mechanism, with these results then being extrapolated to elucidate a theoretical capacity limit. Through investigating the breadth of structures, with multiple Na configurations, the studies lead to four major conclusions. First, we found that the nature of Na storage in carbon materials changes with increasing Na concentrations in a continuum from ionic storage to metallic plating. Second, we revealed the critical role of the intersheet spacing, stacking misalignment, and effects of spacing expansion on the feasibility of Na intercalation into graphitic structures. This leads to the third and fourth conclusion, which stipulates that the results provided here offer compelling support towards an earlier experimentally derived Na ion storage for hard carbon materials, along with the existence of a theoretical limit of sodium ion storage in hard carbon materials. Moreover, the techniques and scope of the work involved are highly relevant to future simulations exploring amorphous carbon as an active material, whether it should be for Li-ion battery anodes, supercapacitors, or catalysts.

We report the electrochemical anion storage properties of a group of molecular solids of polycyclic aromatic hydrocarbons (PAHs): coronene, perylene, and triphenylene. We discover an interesting trend of progressively lower potentials for these three molecular solids. Our DFT calculations reveal that the inserted PF6–anions preferably bind with the edge sites of the coronene molecules as opposed to being sandwiched between two coronene molecular planes. For smaller PAHs, the more edge sites in the solids may facilitate higher capacity values. However, small PAHs do face a greater challenge of dissolution in the nonaqueous electrolyte, which affects the cycling stability.

The confined, sealed design of a commercial lithium-ion battery makes it difficult to probe and understand how the system evolves during cycling. In this work, we investigate the full-cell evolution of lithium-ion batteries using two complementary techniques, electrochemical impedance spectroscopy (EIS) and ultrasonic time-of-flight analysis, which make it possible to couple electrochemical and material property changes during cycling. It is found that there is a post-formation “break-in” period before full-cell behavior stabilizes. This period is signified by an increased swelling of the graphite anode, likely caused by side reactions, which increases the pressure within the cell. The increased pressure forces electrolyte to wet previously inactive portions of the lithium cobalt oxide cathode, lowering the cell impedance. The results demonstrate how the full-cell performance can be greatly affected by non-chemical crosstalk between the two electrodes and indicates the importance of using multiple complementary experimental techniques.

Na-ion batteries (NIBs) have attracted great attention for scalable electrical energy storage considering the abundance and wide availability of Na resources. However, it remains elusive whether carbon anodes can achieve the similar scale of successes in Na-ion batteries as in Li-ion batteries. Currently, much attention is focused on hard carbon while soft carbon is generally considered a poor choice. In this study, we discover that soft carbon can be a high-rate anode in NIBs if the preparation conditions are carefully chosen. Furthermore, we discover that the turbostratic lattice of soft carbon is electrochemically expandable, where d-spacing rises from 3.6 to 4.2 Å. Such a scale of lattice expansion only due to the Na-ion insertion was not known for carbon materials. It is further learned that portions of such lattice expansion are highly reversible, resulting in excellent cycling performance. Moreover, soft carbon delivers a good capacity at potentials above 0.2 V, which enables an intrinsically dendrite-free anode for NIBs.

Current synthetic methods of biomass-derived activated carbon call for a costly chemical or physical activation process. Herein, we report a simple one-step annealing synthesis yielding a high surface area cellulose-derived activated carbon. We discover that simply varying the flow rate of Argon during pyrolysis enables ‘self-activation’ reactions that can tune the specific surface areas of the resulting carbon, ranging from 98m2/g to values as high as 2600m2/g. Furthermore, we, for the first time, observe a direct evolution of H2from the pyrolysis, which gives strong evidence towards an in situ self-activation mechanism. Surprisingly, the obtained activated carbon is a crumbled graphene nanostructure composed of interconnected sheets, making it ideal for use in an electrochemical capacitor. The cellulose-derived nanoporous carbon exhibits a capacitance of 132Fg−1at 1Ag−1, a performance comparable to the state-of-the-art activated carbons. This work presents a fundamentally new angle to look at the synthesis of activated carbon, and highlights the importance of a controlled inert gas flow rate during synthesis in general, as its contributions can have a very large impact on the final material properties.

Na-ion batteries are emerging as one of the most promising energy storage technologies, particularly for grid-level applications. Among anode candidate materials, hard carbon is very attractive due to its high capacity and low cost. However, hard carbon anodes often suffer a low first-cycle Coulombic efficiency and fast capacity fading. In this study, we discover that doping graphene oxide into sucrose, the precursor for hard carbon, can effectively reduce the specific surface area of hard carbon to as low as 5.4 m2/g. We further reveal that such doping can effectively prevent foaming during caramelization of sucrose and extend the pyrolysis burnoff of sucrose caramel over a wider temperature range. The obtained low-surface-area hard carbon greatly improves the first-cycle Coulombic efficiency from 74% to 83% and delivers a very stable cyclic life with 95% of capacity retention after 200 cycles.

Studies related to battery performance and long-term health of commercial Li-ion batteries (LIBs) typically have a fixed temperature parameter. However, commercial LIBs are subject to temperature fluctuations due to their local environment and operating conditions, and these transient temperatures are well known to impact long-term stability. Herein, we demonstrate the adverse effects of temperature shifts, and show that transitioning from low temperature to higher temperature can lead to catastrophic failure within practical temperature ranges experienced by commercial LIBs. We show there exists an Arrhenius relationship between the rate of acoustic attenuation and the magnitude of the temperature shift. A combination of acoustic attenuation, which marks gassing occurrence during cycling, and post mortem chemical analyses provides further mechanistic insight into the Li-rich solid electrolyte interphase (SEI) formation at low temperatures and subsequent reactions with the electrolyte at higher temperatures. Further, several strategies to prevent or mitigate catastrophic failure are introduced. On a broader scale, this research further highlights the importance of temperature and current controls integration into battery management systems (BMS) for both safety and extension of cycle life as battery systems move toward fast charge (>3 C) capability.

Studies related to battery performance and long-term health of commercial Li-ion batteries (LIBs) typically have a fixed temperature parameter. However, commercial LIBs are subject to temperature fluctuations due to their local environment and operating conditions, and these transient temperatures are well known to impact long-term stability. Herein, we demonstrate the adverse effects of temperature shifts, and show that transitioning from low temperature to higher temperature can lead to catastrophic failure within practical temperature ranges experienced by commercial LIBs. We show there exists an Arrhenius relationship between the rate of acoustic attenuation and the magnitude of the temperature shift. A combination of acoustic attenuation, which marks gassing occurrence during cycling, and post mortem chemical analyses provides further mechanistic insight into the Li-rich solid electrolyte interphase (SEI) formation at low temperatures and subsequent reactions with the electrolyte at higher temperatures. Further, several strategies to prevent or mitigate catastrophic failure are introduced. On a broader scale, this research further highlights the importance of temperature and current controls integration into battery management systems (BMS) for both safety and extension of cycle life as battery systems move toward fast charge (>3 C) capability.

Stable long-term cycling and solid-electrolyte-interphase (SEI) formation are key challenges in the design of Si/graphite composites as Li-ion battery (LIB) anode materials. Typically, these long-term cycling properties are examined in flooded half-cell settings making use of a Li-metal counter electrode and a Si/graphite working electrode. This form factor has the advantage of offering an unlimited supply of Li-ions and electrolyte, thus isolating performance degradation to the passivation of the working electrode. However, half-cell studies are ineffective in revealing performance and degradation mechanisms of the Si/graphite composite in a more commercially realistic full cell setting. This paper outlines an operando acoustic technique that can offer insights on SEI formation and capacity degradation of Si/graphite composites in a full cell setting. Through a combination of electrochemical and chemical analyses, we show that increasing passivation of the silicon particles in the Si/graphite composite anode is correlated with an increase in the acoustic time-of-flight shift. We further show that temporary loss of the acoustic signal during the first cycle is associated with significant gassing of the cell. The operando acoustic technique outlined here is low-cost, simple to setup and has the potential for localized resolution, indicating usefulness in commercial-scale Si/graphite cell quality control and diagnosis.