Electrode Packing Research Articles

Designing a High-Energy Dry-Processed Electrode for Li-Ion Batteries By Layering Single-Walled Carbon Nanotubes Onto the Ni-Rich Cathode Material

With the growing need for lithium-ion batteries (LIBs) in the context of carbon-neutral policies, the requirements for high safety and high energy density in LIBs have gained importance. High-nickel-content (Ni≥90%) cathodes offer a means of increasing both volumetric and gravimetric energy densities, but they also increase the risk of structural instability, which jeopardizes the battery system's overall safety. Thus, it makes more sense to maximize electrode packing density while using stable cathode materials. To mitigate these issues, we apply a coating material of single walled carbon nanotubes (SWCNTs) on the surface of the LiNi0.85Mn0.07Co0.05Al0.03O2 cathode, thereby significantly increasing its electronic conductivity. Furthermore, to increase ionic conductivity of the SWCNT-coated NCMA cathode, we also adopted a solvent-free electrode fabrication procedure. Our SWCNT-dry electrode showed sustained electrochemical characteristics in addition to a notably high cathode material weight ratio (99. x (x=0.5, 0.7, 0.9) wt.%) and increased electrode density (4.0 g cm−3). Their superior volumetric capacity of 860 mAh cm−3 allowed them to surpass traditional wet-processed electrodes (The first group consists of NCMA, CB, and PVDF, mixed in a ratio of 96:2:2, achieving an electrode density ≈ 3.4 g cm−3 and second group consists of NCMA, CB, and PVDF, mixed in a ratio of 98:1:1 achieving an electrode density ≈ 3.6 g cm−3). SWCNT coating combined with a solvent-free electrode is a novel technique that could lead to significant improvements in LIBs' high energy density, industrial scalability, and cell safety.

Influence of Cathode Calendering Density on the Cycling Stability of Li-Ion Batteries Using NMC811 Single or Poly Crystalline Particles

Calendering of battery electrodes is a commonly used manufacturing process that enhances electrode packing density and therefore improves the volumetric energy density. While calendering is standard industrial practice, it is known to crack cathode particles, thereby increasing the electrode surface area. The latter is particularly problematic for new Ni-rich layered transition metal oxide cathodes, such as NMC811, which are known to have substantial surface-driven degradation processes. To establish appropriate calendering practices for these new cathode materials, we conducted a comparative analysis of uncalendered electrodes with electrodes that have a 35% porosity (industrial standard), and 25% porosity (highly calendered) for both single crystal (SC) and polycrystalline (PC) NMC811. PC cathodes show clear signs of cracking and decrease in rate capability when calendered to 25% porosity, whereas SC NMC811 cathodes, achieve better cycling stability and no penalty in rate performance at these high packing densities. These findings suggest that SC NMC811 cathodes should be calendered more densely, and we provide a comprehensive overview of both electrochemical and material characterisation methods that corroborate why PC and SC electrodes show such different degradation behaviour. Overall, this work is important because it shows how new single-crystal cathode materials can offer additional advantages both in terms of rate performance and cycling stability by calendaring them more densely.

Evaluating the feasibility of carbon fiber brush for improving biohydrogen production in acidogenic dark fermentation

Dark fermentation is a promising technology for biohydrogen (bioH2) production. Augmenting the dark fermentation process with conductive materials has drawn significant research interests improving the bioH2 yield. This study evaluated the feasibility of using carbon fiber brush (CB) as an additive to increase the efficiency of mesophilic dark fermentation using glucose as substrate and heat-shock pretreated anaerobic sludge as inoculum. Effect of electrode packing density on bioH2 yield, soluble metabolite product formation, and substrate degradation was investigated. Maximal bioH2 yield of 334.6 mL/g-glucose was obtained using medium-sized CB with 72.5% higher than the control (194 mL/g-glucose) and butyrate-type fermentation was the dominant metabolic pathway. Further, enhanced concentrations of proteins and polysaccharides on CB biofilm suggested the critical role of extracellular polymeric substances in microbial electron transfer. This was supported via electron transport activity in CB biofilm. Finally, microbial community analysis revealed a selective enrichment of the potentially electroactive Clostridium_sensu_stricto_1 on the CB (56.6%) compared to 40.9% abundance in control. Insights gained from this study demonstrated that CB aided dark fermentation can be an economical and environmentally benign strategy for improving bioH2 yield.

Engendering High Energy Density LiFePO4 Electrodes with Morphological and Compositional Tuning.

Improving the energy density of Li-ion batteries is critical to meet the requirements of electric vehicles and energy storage systems. In this work, LiFePO4 active material was combined with single-walled carbon nanotubes as the conductive additive to develop high-energy-density cathodes for rechargeable Li-ion batteries. The effect of the morphology of the active material particles on the cathodes' electrochemical characteristics was investigated. Although providing higher packing density of electrodes, spherical LiFePO4 microparticles had poorer contact with an aluminum current collector and showed lower rate capability than plate-shaped LiFePO4 nanoparticles. A carbon-coated current collector helped enhance the interfacial contact with spherical LiFePO4 particles and was instrumental in combining high electrode packing density (1.8 g cm-3) with excellent rate capability (100 mAh g-1 at 10C). The weight percentages of carbon nanotubes and polyvinylidene fluoride binder in the electrodes were optimized for electrical conductivity, rate capability, adhesion strength, and cyclic stability. The electrodes that were formulated with 0.25 wt.% of carbon nanotubes and 1.75 wt.% of the binder demonstrated the best overall performance. The optimized electrode composition was used to formulate thick free-standing electrodes with high energy and power densities, achieving the areal capacity of 5.9 mAh cm-2 at 1C rate.

Spectroscopy vs. Electrochemistry: Catalyst Layer Thickness Effects on Operando/In Situ Measurements

AbstractIn recent years, operando/in situ X‐ray absorption spectroscopy (XAS) has become an important tool in the electrocatalysis community. However, the high catalyst loadings often required to acquire XA‐spectra with a satisfactory signal‐to‐noise ratio frequently imply the use of thick catalyst layers (CLs) with large ion‐ and mass‐transport limitations. To shed light on the impact of this variable on the spectro‐electrochemical results, in this study we investigate Pd‐hydride formation in carbon‐supported Pd‐nanoparticles (Pd/C) and an unsupported Pd‐aerogel with similar Pd surface areas but drastically different morphologies and electrode packing densities. Our in situ XAS and rotating disk electrode (RDE) measurements with different loadings unveil that the CL‐thickness largely determines the hydride formation trends inferred from spectro‐electrochemical experiments, therewith calling for the minimization of the CL‐thickness in such experiments and the use of complementary thin‐film control measurements.

Spectroscopy vs. Electrochemistry: Catalyst Layer Thickness Effects on Operando/In Situ Measurements.

In recent years, operando/in situ X-ray absorption spectroscopy (XAS) has become an important tool in the electrocatalysis community. However, the high catalyst loadings often required to acquire XA-spectra with a satisfactory signal-to-noise ratio frequently imply the use of thick catalyst layers (CLs) with large ion- and mass-transport limitations. To shed light on the impact of this variable on the spectro-electrochemical results, in this study we investigate Pd-hydride formation in carbon-supported Pd-nanoparticles (Pd/C) and an unsupported Pd-aerogel with similar Pd surface areas but drastically different morphologies and electrode packing densities. Our in situ XAS and rotating disk electrode (RDE) measurements with different loadings unveil that the CL-thickness largely determines the hydride formation trends inferred from spectro-electrochemical experiments, therewith calling for the minimization of the CL-thickness in such experiments and the use of complementary thin-film control measurements.

Engineering CoP Alloy Foil to a Well-Designed Integrated Electrode Toward High-Performance Electrochemical Energy Storage.

Nanostructured integrated electrodes with binder-free design show great potential to solve the ever-growing problems faced by currently commercial lithium-ion batteries such as insufficient power and energy densities. However, there are still many challenging problems limiting practical application of this emerging technology, in particular complex manufacturing process, high fabrication cost, and low loading mass of active material. Different from existing fabrication strategies, here using a CoP alloy foil as a precursor a simple neutral salt solution-mediated electrochemical dealloying method to well address the above issues is demonstrated. The resultant freestanding mesoporous np-Co(OH)x /Co2 P product possesses not only active compositions of high specific capacity and large electrode packing density (>3.0g cm-3 ) to meet practical capacity requirements, high-conductivity and well-developed nanoporous framework to achieve simultaneously fast ion and electron transfer, but also interconnected ligaments and suitable free space to ensure strong structural stability. Its comprehensively excellent electrochemical energy storage (EES) performances in both lithium/sodium-ion batteries and lithium-ion capacitors can further illustrate the effectiveness of the integrated electrode preparation strategy, such as remarkable reversible specific capacities/capacitances, dominated pseudo-capacitive EES mechanism, and ultra-long cycling life. This study provides new insights into preparation and design of high-performance integrated electrodes for practical applications.

Moisture behavior of lithium-ion battery components along the production process

With the ongoing development of producing high-quality lithium-ion batteries (LIB), the influence of moisture on the individual components and ultimately the entire cell is an important aspect. It is well known that water can lead to significant aging effects on the components and the cell itself. Therefore it is urgent to understand the moisture behavior of the most important components anode, cathode and separator along the entire cell production as precisely as possible. This work is intended to realize just that, by creating application-related references, point out and explain difficulties as well as challenges and finally work out and provide solutions. At first it describes the amount of moisture these components can adsorb and desorb and which components of the electrodes take up particularly much or little moisture. On this basis the adsorption kinetics of anode, cathode and separator material are investigated, showing how quickly the described equilibrium moisture contents are achieved under typical manufacturing conditions. A linear time dependency was observed which shows that all components adsorb a high share of the equilibrium moisture in the first minutes. To give the reader a better impression for the overall process, real values of the various moisture contents of anode, cathode and separator material along the entire process chain during a production campaign are shown. Since moisture in the components cannot be completely avoided during manufacturing, a total of five different process variants for minimizing residual moisture are finally described, analyzed and compared with each other. General advantages and disadvantages, impact of the individual process parameters, residual moisture contents as well as energy and media consumption of electrode pack baking, coil baking, roll-to-roll baking, cell stack baking or pure exposure to dry room atmosphere are discussed. Finally an overall strategy to minimize water content in LIB components along the entire production is proposed regarding all established results.

Enhancing nanostructured nickel-rich lithium-ion battery cathodes via surface stabilization

Layered, nickel-rich lithium transition metal oxides have emerged as leading candidates for lithium-ion battery (LIB) cathode materials. High-performance applications for nickel-rich cathodes, such as electric vehicles and grid-level energy storage, demand electrodes that deliver high power without compromising cell lifetimes or impedance. Nanoparticle-based nickel-rich cathodes seemingly present a solution to this challenge due to shorter lithium-ion diffusion lengths compared to incumbent micrometer-scale active material particles. However, since smaller particle sizes imply that surface effects become increasingly important, particle surface chemistry must be well characterized and controlled to achieve robust electrochemical properties. Moreover, residual surface impurities can disrupt commonly used carbon coating schemes, which result in compromised cell performance. Using x-ray photoelectron spectroscopy, here we present a detailed characterization of the surface chemistry of LiNi0.8Al0.15Co0.05O2 (NCA) nanoparticles, ultimately identifying surface impurities that limit LIB performance. With this chemical insight, annealing procedures are developed that minimize these surface impurities, thus improving electrochemical properties and enabling conformal graphene coatings that reduce cell impedance, maximize electrode packing density, and enhance cell lifetime fourfold. Overall, this work demonstrates that controlling and stabilizing surface chemistry enables the full potential of nanostructured nickel-rich cathodes to be realized in high-performance LIB technology.

Scalable Synthesis of Microsized, Nanocrystalline Zn0.9 Fe0.1 O-C Secondary Particles and Their Use in Zn0.9 Fe0.1 O-C/LiNi0.5 Mn1.5 O4 Lithium-Ion Full Cells.

Conversion/alloying materials (CAMs) are a potential alternative to graphite as Li‐ion anodes, especially for high‐power performance. The so far most investigated CAM is carbon‐coated Zn0.9Fe0.1O, which provides very high specific capacity of more than 900 mAh g−1 and good rate capability. Especially for the latter the optimal particle size is in the nanometer regime. However, this leads to limited electrode packing densities and safety issues in large‐scale handling and processing. Herein, a new synthesis route including three spray‐drying steps that results in the formation of microsized, spherical secondary particles is reported. The resulting particles with sizes of 10–15 μm are composed of carbon‐coated Zn0.9Fe0.1O nanocrystals with an average diameter of approximately 30–40 nm. The carbon coating ensures fast electron transport in the secondary particles and, thus, high rate capability of the resulting electrodes. Coupling partially prelithiated, carbon‐coated Zn0.9Fe0.1O anodes with LiNi0.5Mn1.5O4 cathodes results in cobalt‐free Li‐ion cells delivering a specific energy of up to 284 Wh kg−1 (at 1 C rate) and power of 1105 W kg−1 (at 3 C) with remarkable energy efficiency (>93 % at 1 C and 91.8 % at 3 C).

A new method for urine electrofiltration and long term power enhancement using surface modified anodes with activated carbon in ceramic microbial fuel cells

This work is presenting for the first time the use of inexpensive and efficient anode material for boosting power production, as well as improving electrofiltration of human urine in tubular microbial fuel cells (MFCs). The MFCs were constructed using unglazed ceramic clay functioning as the membrane and chassis. The study is looking into effective anodic surface modification by applying activated carbon micro-nanostructure onto carbon fibres that allows electrode packing without excessive enlargement of the electrode. The surface treatment of the carbon veil matrix resulted in 3.7 mW (52.9 W m−3 and 1626 mW m−2) of power generated and almost a 10-fold increase in the anodic current due to the doping as well as long-term stability in one year of continuous operation. The higher power output resulted in the synthesis of clear catholyte, thereby i) avoiding cathode fouling and contributing to the active splitting of both pH and ions and ii) transforming urine into a purified catholyte - 30% salt reduction - by electroosmotic drag, whilst generating - rather than consuming – electricity, and in a way demonstrating electrofiltration. For the purpose of future technology implementation , the importance of simultaneous increase in power generation, long-term stability over 1 year and efficient urine cleaning by using low-cost materials, is very promising and helps the technology enter the wider market.

Novel Multi-Material 3-Dimensional Low-Temperature Co-Fired Ceramic Base

This paper proposes a novel multi-material 3D low-temperature co-fired ceramic base called NeuroStone. It employs 3D inkjet printing with ceramic and copper particle suspension, followed by co-firing. This technology provides both free-form and non-planar electrodes not only on the surface but also inside the device. NeuroStone makes it possible to enhance the directional freedom and electrode packing density in the field of miniature interconnection devices. This report demonstrates that the proposed technology can realize sophisticated shapes of interconnection devices fabricated by additive manufacturing, which can significantly enhance the scope of electronics.

Effects of Electrode Structure and Packing Materials on Conversion of Methane and Carbon Dioxide into Synthesis Gas

Effects of Electrode Structure and Packing Materials on Conversion of Methane and Carbon Dioxide into Synthesis Gas

A flexible 3D nitrogen-doped carbon foam@CNTs hybrid hosting TiO2 nanoparticles as free-standing electrode for ultra-long cycling lithium-ion batteries

Free-standing electrodes have stood out from the electrode pack, owing to their advantage of abandoning the conventional polymeric binder and conductive agent, thus increasing the specific capacity of lithium-ion batteries. Nevertheless, their practical application is hampered by inferior electrical conductivity and complex manufacturing process. To this end, we report here a facile approach to fabricate a flexible 3D N-doped carbon foam/carbon nanotubes (NCF@CNTs) hybrid to act as the current collector and host scaffold for TiO2 particles, which are integrated into a lightweight free-standing electrode (NCF@CNTs-TiO2). In the resulting architecture, ultra-fine TiO2 nanoparticles are homogeneously anchored in situ into the N-doped NCF@CNTs framework with macro- and meso-porous structure, wrapped by a dense CNT layer, cooperatively enhances the electrode flexibility and forms an interconnected conductive network for electron/ion transport. As a result, the as-prepared NCF@CNTs-TiO2 electrode exhibits excellent lithium storage performance with high specific capacity of 241 mAh g−1 at 1 C, superb rate capability of 145 mAh g−1 at 20 C, ultra-long cycling stability with an ultra-low capacity decay of 0.0037% per cycle over 2500 cycles, and excellent thermal stability with ∼94% capacity retention over 100 cycles at 55 °C.

High-Frequency Nanocapacitor Arrays: Concept, Recent Developments, and Outlook.

We have developed a measurement platform for performing high-frequency AC detection at nanoelectrodes. The system consists of 65 536 electrodes (diameter 180 nm) arranged in a sub-micrometer rectangular array. The electrodes are actuated at frequencies up to 50 MHz, and the resulting AC current response at each separately addressable electrode is measured in real time. These capabilities are made possible by fabricating the electrodes on a complementary metal-oxide-semiconductor (CMOS) chip together with the associated control and readout electronics, thus minimizing parasitic capacitance and maximizing the signal-to-noise ratio. This combination of features offers several advantages for a broad range of experiments. First, in contrast to alternative CMOS-based electrical systems based on field-effect detection, high-frequency operation is sensitive beyond the electrical double layer and can probe entities at a range of micrometers in electrolytes with high ionic strength such as water at physiological salt concentrations. Far from being limited to single- or few-channel recordings like conventional electrochemical impedance spectroscopy, the massively parallel design of the array permits electrically imaging micrometer-scale entities with each electrode serving as a separate pixel. This allows observation of complex kinetics in heterogeneous environments, for example, the motion of living cells on the surface of the array. This imaging aspect is further strengthened by the ability to distinguish between analyte species based on the sign and magnitude of their AC response. Finally, we show here that sensitivity down to the attofarad level combined with the small electrode size permits detection of individual 28 nm diameter particles as they land on the sensor surface. Interestingly, using finite-element methods, it is also possible to calculate accurately the full three-dimensional electric field and current distributions during operation at the level of the Poisson-Nernst-Planck formalism. This makes it possible to validate the interpretation of measurements and to optimize the design of future experiments. Indeed, the complex frequency and spatial dependence of the data suggests that experiments to date have only scratched the surface of the method's capabilities. Future iterations of the hardware will take advantage of the higher frequencies, higher electrode packing densities and smaller electrode sizes made available by continuing advances in CMOS manufacturing. Combined with targeted immobilization of targets at the electrodes, we anticipate that it will soon be possible to realize complex biosensors based on spatial- and time-resolved nanoscale impedance detection.

Fabrication of macroporous Si alloy anodes using polystyrene beads for lithium ion batteries

In this work, macroporous Si alloy anodes were manufactured using polystyrene (PS) spheres as a pore-forming agent. The PS spheres were easily eliminated by heat treatment, and the porosity and pore size of the electrodes were controllable by adjusting the content and size of the PS aggregates. Following heat treatment, the electrode packing density of the Si alloy anodes with 10–20 % PS decreased by 9–26 % due to removal of the PS, whereas the control electrode without PS displayed only a 1.3 % decrease. The porous electrode prepared using 10 or 15 % PS showed improved cyclic performances with capacities of 1110–1210 mAh g−1 after 100 cycles at 0.5 C. Although the macroporous Si alloy anode fabrication process using the PS beads reduced the electrode adhesion strength, the electrode performance improvements were attributed to the presence of macropores in the Si alloy electrode, which significantly reduced the changes in electrode thickness during lithiation/delithiation. The manufacture of macroporous electrodes using an appropriate PS content offers an effective strategy for applying Si-based anodes in advanced lithium ion batteries.

Two-Dimensional Porous Carbon: Synthesis and Ion-Transport Properties.

Their chemical stability, high specific surface area, and electric conductivity enable porous carbon materials to be the most commonly used electrode materials for electrochemical capacitors (also known as supercapacitors). To further increase the energy and power density, engineering of the pore structures with a higher electrochemical accessible surface area, faster ion-transport path and a more-robust interface with the electrolyte is widely investigated. Compared with traditional porous carbons, two-dimensional (2D) porous carbon sheets with an interlinked hierarchical porous structure are a good candidate for supercapacitors due to their advantages in high aspect ratio for electrode packing and electron transport, hierarchical pore structures for ion transport, and short ion-transport length. Recent progress on the synthesis of 2D porous carbons is reported here, along with the improved electrochemical behavior due to enhanced ion transport. Challenges for the controlled preparation of 2D porous carbons with desired properties are also discussed; these require precise tuning of the hierarchical structure and a clarification of the formation mechanisms.

High Density Sodium and Lithium Ion Battery Anodes from Banana Peels

Banana peel pseudographite (BPPG) offers superb dual functionality for sodium ion battery (NIB) and lithium ion battery (LIB) anodes. The materials possess low surface areas (19 - 217 m2 g-1) and a relatively high electrode packing density (0.75 g cm-3 vs. ~ 1 g cm-3 for graphite). Tested against Na, BPPG delivers a gravimetric (and volumetric) capacity of 355 mAhg-1 (by active material ~ 700 mAh cm-3, by electrode volume ~ 270 mAh cm-3) after 10 cycles at 50 mAg-1. A nearly flat ~ 200 mAhg-1 plateau that is below 0.1 V, and a minimal charge/discharge voltage hysteresis, makes BPPG a direct electrochemical analogue to graphite but with Na. A charge capacity of 221 mAhg-1 at 500 mAg-1 is degraded by 7% after 600 cycles, while a capacity of 336 mAhg-1 at 100 mAg-1 is degraded by 11% after 300 cycles, in both cases with ~ 100% cycling coulombic efficiency. For LIB applications BPPG offers a gravimetric (volumetric) capacity of 1090 mAhg-1 (by material ~ 2200 mAh cm-3, by electrode ~ 900 mAh cm-3) at 50 mAg-1. The reason that BPPG works so well for both NIBs and LIBs is that it uniquely contains three essential features: a) dilated intergraphene spacing for Na intercalation at low voltages; b) highly accessible near-surface nanopores for Li metal filling at low voltages; and c) substantial defect content in the graphene planes for Li adsorption at higher voltages. The < 0.1 V charge storage mechanism is fundamentally different for Na versus for Li. A combination of XRD and XPS demonstrates highly reversible Na intercalation rather than metal underpotential deposition. By contrast, the same analysis proves the presence of metallic Li in the pores, with intercalation being much less pronounced.

Low Temperature Performance of Electrochemical Double-Layer Capacitor based on Electrospun Half-Cells

Electrochemical characteristics of the two identical electrospun microporous-mesoporous carbon electrodes deposited onto the electrospun nanofibrous polymer membrane layer have been studied in 1 M triethylmethylammonium tetrafluoroborate solution in acetonitrile at room and low temperature, 24°C and −30°C, respectively, by using cyclic voltammetry, constant current charge/discharge, electrochemical impedance spectroscopy and constant power discharge methods. The electrochemical double-layer capacitor (EDLC) half-cells have been prepared using a two step process: at first the nanowire polymer separator layer has been created by the electrospinning method, and thereafter the electrode material layer (microporous-mesoporous carbon powder with binder) has been directly electrospun onto the separator layer. Applying the electrospun half-cell preparation method we are able to prepare composite electrodes for EDLC with lower density and thickness of electrode pack than using the widely used traditional roll-pressing method. The wide region of ideal polarizability, high specific capacitance, low equivalent series resistance, short characteristic time constant and high specific energy and specific power values have been obtained and discussed for the completed EDLC working at 24°C and −30°C. The electrochemical characteristics of EDLC based on electrospun half-cells have been compared with those for EDLC completed using the roll-pressed thin (∼80 μm) electrodes.

High-density sodium and lithium ion battery anodes from banana peels.

Banana peel pseudographite (BPPG) offers superb dual functionality for sodium ion battery (NIB) and lithium ion battery (LIB) anodes. The materials possess low surface areas (19-217 m(2) g(-1)) and a relatively high electrode packing density (0.75 g cm(-3) vs ∼1 g cm(-3) for graphite). Tested against Na, BPPG delivers a gravimetric (and volumetric) capacity of 355 mAh g(-1) (by active material ∼700 mAh cm(-3), by electrode volume ∼270 mAh cm(-3)) after 10 cycles at 50 mA g(-1). A nearly flat ∼200 mAh g(-1) plateau that is below 0.1 V and a minimal charge/discharge voltage hysteresis make BPPG a direct electrochemical analogue to graphite but with Na. A charge capacity of 221 mAh g(-1) at 500 mA g(-1) is degraded by 7% after 600 cycles, while a capacity of 336 mAh g(-1) at 100 mAg(-1) is degraded by 11% after 300 cycles, in both cases with ∼100% cycling Coulombic efficiency. For LIB applications BPPG offers a gravimetric (volumetric) capacity of 1090 mAh g(-1) (by material ∼2200 mAh cm(-3), by electrode ∼900 mAh cm(-3)) at 50 mA g(-1). The reason that BPPG works so well for both NIBs and LIBs is that it uniquely contains three essential features: (a) dilated intergraphene spacing for Na intercalation at low voltages; (b) highly accessible near-surface nanopores for Li metal filling at low voltages; and (c) substantial defect content in the graphene planes for Li adsorption at higher voltages. The <0.1 V charge storage mechanism is fundamentally different for Na versus for Li. A combination of XRD and XPS demonstrates highly reversible Na intercalation rather than metal underpotential deposition. By contrast, the same analysis proves the presence of metallic Li in the pores, with intercalation being much less pronounced.