Electrode Current Collector Research Articles

Effects of Electrolytic Copper Foil Roughness on Lithium-Ion Battery Performance

Improving the interfacial properties between the electrode materials and current collectors plays a significant role in lithium-ion batteries. Here, four kinds of electrolytic copper foils with roughness (Rz) values of 1.2, 1.5, 2.2, and 2.8 μm were prepared via an electropolishing technique. Reducing the roughness of the electrolytic copper foil can effectively improve the wettability of the anode slurry. The electrolytic copper foil with a roughness value of 1.2 μm shows the best coating uniformity of the graphite anode slurry. The battery with this electrolytic copper foil (Rz = 1.2 μm) as the current collector exhibits fifth-cycle capacities of 358.7 and 102.5 mAh g−1 at 0.2 and 3.0 C, respectively, showing excellent rate capability. In addition, at 0.5 C, the battery exhibits an initial discharge capacity of 319.5 mAh g−1 and a 100th-cycle capacity retention rate of 98.1%, demonstrating a high level of cycling performance. These results indicate that reducing the roughness of electrolytic copper foil can provide a feasible route to improve the performance of lithium-ion batteries.

Hybrid carbon nanofiller/polymer composites as self-healable current collector electrodes for use in high-performance flexible metal-free supercapacitors

Supercapacitors with multiple features, such as high capacitance, high-rate capability, high flexibility, and self-healing properties, are regarded as good candidates for powering portable and wearable electronics. Herein, a symmetric supercapacitor with multiple functions is fabricated by sandwiching a highly conductive self-healable composite current collector electrode with an active material, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)/multiwalled carbon nanotubes (PEDOT:PSS/MWNTs), and a poly(vinyl alcohol)/ phosphoric acid (PVA/H3PO4) electrolyte. The novelty of this work lies in the synergy arising from the combination of two conducting carbon nanofillers, referred to as hybrid carbon nanofiller (HCF), coupled with healable polymer matrices (HCF/HPU) to fabricate self-healing high-conductivity composite current collector electrodes. These can be used in flexible metal-free supercapacitors, which have not been specifically considered previously. The use of two geometrically varied nanofillers with proper selection of the nanofiller content ratio can induce the formation of an effectively conductive co-supporting network, which drastically enhances the electrical properties and mechanical strength of the composite current collector compared to that of single nanofillers. More importantly, the supercapacitor assembled by the HCF/HPU composite current collector delivers high specific capacitance and energy density. In addition, noticeable cycling stability with only ∼ 10 % capacitance loss was observed after 20,000 consecutive charge/discharge cycles at a high current density of 10 mA cm–2. Furthermore, at a medium temperature of 60 °C, supercapacitors with this HCF/HPU composite current collector restore at least 96.2 % of their capacitance properties even after 5 cycles of severing/healing. The capacitive retention rate after 2000 bending cycles was 97.4 % at a bending radius of 4.0 mm. These properties indicate this HCF/HPU composite current collector is a promising candidate for use in high-performance flexible energy storage devices.

Research for Electrochemical & Structural Properties of Recycling Cathode Materials for End of Life Lib

Demand for lithium-ion batteries (LIBs) has increased dramatically over the years due to the rapid market expansion of electric vehicles. However, many of the essential components of cathode materials, such as cobalt, nickel, manganese and lithium, are resource-limited and expensive[1]. Therefore, recycling of used LIB cathode materials is very important to conserve resources and the environment. Currently, the lithium secondary battery recycling technology mainly uses wet and dry smelting, but there is a disadvantage of high energy consumption due to the use of strong acid and the smelting process[2-3].In this study, the cathode active material was separated from a pouch-type lithium secondary battery separated from a portable tablet that was over 10 years old and the chemical, structural, and electrochemical characteristics thereof were investigated. The cathode active materials were dismantled from a pouch-type LIB, which was removed from the tablet produced in 2011. The pouch cell was in a swelling state and the OCV was 0V due to internal short is expected. As a result of TGA analysis, the electrode composition was confirmed to be 92wt% of the cathode active material, 3wt% of the conductive agent, and 3wt% of the binder, respectively. The recovery rate of the active material is the best when a mixed solvent including NMP, heating, and ultrasonic, respectively. Through SEM and EDS analysis, copper metal due to dissolution of the negative electrode current collector was found on the surface of the positive electrode. As shown in Fig. 1, It can be seen that the positive electrode active material recovered using the composite solvent is a positive electrode active material that is a mixture of NCM active material and LMO active material. The XRD results shows a well layered structure and a Co3O4 phase due to lithium deficiency. In order to examine the electrochemical characteristics of the recovered electrode, it was reassembled into a 2032 coin type cell and evaluated, and the discharge capacity of approximately 150mAh/g was recovered as shown in Fig. 2. The positive active material recovered according to the experimental results is estimated to be in a state of insufficient lithium, and a lithium compensation process is planned to be additionally performed in the future.

Facile dynamic current deposition of high tensile gradient Cu foil with (110) preferred orientation

The conductive copper (Cu) foil is an important raw material in the electronic industry. However, the traditional Cu foil with low tensile strength (∼350 MPa) and poor toughness is prone to breakage during production and usage, which is not conducive to its application in high-density printed circuit boards and high-energy-density batteries. In this work, we report a facile dynamic current deposition (DCD) method for preparing a gradient Cu foil with adjustable thickness (9–50 µm) and a highly preferred crystal orientation of Cu (110). The gradient Cu foil transitions gradually from micron-scale coarse grains to nano-scale fine grains, which promotes its tensile strength (∼840 MPa) while maintaining toughness (∼3.6%). Particularly, the gradient Cu foil shows a high conductivity of 3.3 × 107 S m−1, indicating its promising application in negative electrode current collectors of lithium-ion batteries and printed circuit boards. The facile DCD method can also provide guidance for the fabrication of other metallic materials.

Tensile Property and Corrosion Performance of Ag Microalloying of Al-Cu Alloys for Positive Electrode Current Collectors of Li-Ion Batteries.

The development of a current collector for Li-ion batteries is of great significance for improving the performance of Li-ion batteries. Tensile property and corrosion performance of the positive electrode current collectors are an indispensable prerequisite for the realization of high-performance Li-ion batteries. In our study, the effects of Ag alloying on the microscopic structure, electrical conductivity, tensile property and corrosion resistance of Al-xCu (x = 0.1–0.15%) alloy foils were investigated. Moderate Ag addition on the Al-Cu alloy could reduce the size of second phases and promote the formation of second phases. The tensile strength of the Al-0.1Cu-0.1Ag alloy was higher than that of the Al-0.1Cu alloy at both room and high temperatures. All of the alloy foils demonstrated high electrical conductivity around 58% ICAS. The corrosion potential and corrosion current density of the Al-0.1Cu alloy were demonstrated by Tafel polarization to be −873 mV and 37.12 μA/cm2, respectively. However, the Al-0.1Cu-0.1Ag alloy showed enhanced corrosion resistance after the Ag element was added to the Al-0.1Cu alloy, and the Al-0.1Cu-0.1Ag alloy had a greater positive corrosion potential of −721 mV and a lower corrosion current density of 1.52 μA/cm2, which suggests that the Ag element could significantly improve the corrosion resistance of the Al-Cu alloy.

Current Collector-Free Interdigitated Nb2O5//LiFePO4 Micro-Batteries Prepared by a Simple Laser-Writing Process

The recent development of the internet of things (IoT) raises new needs in energy storage micro-devices to power implantable and wearable applications. Conventional battery components, including electrode materials and current collectors, have to be miniaturized and integrated onto flexible substrates while keeping their electrochemical performance. Although numerous micro-fabrication processes were successfully adapted to prepare lithium-ion micro-batteries (Li-ion μBs), they often rely on wet processing routes such as electrochemical deposition, which does not allow the preparation of energy micro-sources at a large scale. Laser-writing processes are among the most practical and versatile methods to deposit active materials as thin films on flexible substrates. Here, we report about the integration of positive LiFePO4 (LFP)-based and negative pseudocapacitive niobium pentoxide (Nb2O5)-based electrodes onto flexible current collector-free polyimide foils, through laser-writing of a mixture of HAuCl4, cellulose acetate, and active material coated on polyimide. The influence of the laser energy during the laser-writing step on the electrochemical performance of the as-prepared electrodes was studied. Laser-scribed (LS) Nb2O5 flexible electrodes exhibit a typical pseudocapacitive behavior, and deliver up to 114 μAh.cm−2 (205 mF.cm−2), while 76 μAh.cm−2 were recorded for LS-LiFePO4 battery electrodes prepared with the optimized laser parameters. Nb2O5//LiFePO4 micro-devices were assembled in a parallel-plate configuration, providing a 32 μAh.cm−2 areal capacity, despite the absence of any underlying current collectors. Finally, interdigitated planar micro-batteries were realized by this simple laser-writing procedure, thus paving the path towards the facile fabrication of micro-batteries at a large scale.

Self-healing action of Bi in high-performance Sb–Bi–Sn positive electrodes for liquid metal batteries

Li||Sb–Bi–Sn liquid metal batteries (LMBs) have comprehensive advantages of a high energy density, excellent rate capability, low material costs, and high cycle performance. However, the corrosion of the positive electrode to the current collector at high temperatures cannot be neglected over the long term. Here, we investigate the corrosion behavior of SS304 in two types of Sb–Bi–Sn alloys under static and cell cycling conditions. Interestingly, we find that the cell performance of Li||Sb–Bi–Sn LMBs are not affected by corrosion between the positive electrode and stainless-steel current collector. The corrosion products and their participation in the cell reaction process are determined using ex situ analyses and electrochemical measurements. Bi not only inhibits the dissolution of SS304 in Sb–Bi–Sn alloy but also spontaneously promotes the decomposition of Fe–Sb and Fe–Cr–Sb corrosion products during lithiation, releasing the active component Sb, and Sb–Bi–Sn alloy is recovered. Encouragingly, even in the event of corrosion, the cell capacity, efficiency, and cycle stability remain almost unaffected due to this self-healing action of Bi. This study represents a new direction toward inhibiting the corrosion of positive electrode and stabilizing cell performance for practical application and commercialization by alloying.

Quinone Electrodes for Alkali-Acid Hybrid Batteries.

Aqueous batteries are promising candidates for large-scale energy storage but face either limited energy density (lead-acid batteries), cost/resource concerns (Ni-MH batteries), or safety issues due to metal dendrite growth at high current densities (zinc batteries). We report that through designing electrochemical redox couples, quinones as intrinsic dendrite-free and sustainable anode materials demonstrate the theoretical energy density of 374 W h kg-1 coupling with affordable Mn2+/MnO2 redox reactions on the cathode side. Due to the fast K-ion diffusion in the electrolyte, low K-ion desolvation energy at the interface, and fast quinone/phenol reaction, the optimized poly(1,4-anthraquinone) in the KOH electrolyte shows specific capacities of 295 mA h g-1 at 300 C-rate and 225 mA h g-1 at 240 mA cm-2. Further constructed practical aqueous batteries exhibit an output voltage of 2 V in alkali-acid hybrid electrolyte systems with exceptional electrochemical kinetics, which can release/store over 95% of the theoretical capacity in less than 40 s (25 000 mA g-1). The scaled Ah level aqueous battery with the upgradation of interfacial chemistry on the electrode current collector exhibits an overall energy density of 92 W h kg-1, exceeding commercial aqueous lead-acid and Ni-MH batteries. The rapid response, intrinsic dendrite-free existence, and cost efficiency of quinone electrodes provide promising application interests for regulating the output of the electricity grid generated by intermittent solar and wind energy.

3D-printed flexible flow-field plates for bendable polymer electrolyte membrane fuel cells

3D-printed flexible flow-field plates are employed in this study to realize a bendable polymer electrolyte membrane fuel cell (PEMFC). The prepared bendable PEMFC consists of a membrane electrode assembly (MEA), current collectors, and flow-field plates. The performance of the fuel cell is measured in the flat and bent positions. Polarization curves and impedance plots are analyzed to assess the fuel cell performance. A peak power density of 87.1 mW cm−2 is obtained for the fuel cell with the maximum bending, while a power density of 30.2 mW cm−2 is obtained in the flat position. The enhanced performance is attributed to the compressive stress applied to the reaction sites of the MEA during bending of the fuel cell. The compressive stress is calculated using finite element analysis (FEA). According to the FEA results, the compressive stress occurring at the MEA intensifies as the curvature of the fuel cell increases, resulting in significantly decreased ohmic and charge transfer resistances. The successfully realized bendable fuel cell with 3D-printed flexible flow-field plates exhibits flexibility, decent performance, and a simple structure. It is also competitive in terms of the cost of manufacturing owing to the use of 3D printing.

A composite electrode model for lithium-ion batteries with silicon/graphite negative electrodes

Silicon is a promising negative electrode material with a high specific capacity, which is desirable for commercial lithium-ion batteries. It is often blended with graphite to form a composite anode to extend lifetime, however, the electrochemical interactions between silicon and graphite have not been fully investigated. Here, an electrochemical composite electrode model is developed and validated for lithium-ion batteries with a silicon/graphite anode. The continuum-level model can reproduce the voltage hysteresis and demonstrate the interactions between graphite and silicon. At high states-of-charge, graphite provides the majority of the reaction current density, however this rapidly switches to the silicon phase at deep depths-of-discharge due to the different open circuit voltage curves, mass fractions and exchange current densities. Furthermore, operation at high C-rates leads to heterogeneous current densities in the through-thickness direction, where peak reaction current densities for silicon can be found at the current collector–electrode side as opposed to the separator–electrode side for graphite. Increasing the mass fraction of silicon also highlights the beneficial impacts of reducing the peak reaction current densities. This work, therefore, gives insights into the effects of silicon additives, their coupled interactions and provides a platform to test different composite electrodes for better lithium-ion batteries.

On-demand solid-state artistic ultrahigh areal energy density microsupercapacitors

Practical application of microsupercapacitors (MSCs) has been plagued by challenging task of achieving high energy density, shape/configuration diversity, and mechanical flexibility. Here, we present on-demand solid-state artistic ultrahigh areal energy density MSCs (a-MSCs). Direct-ink-writing (DIW) printing of rheology-tuned electrode inks and ultraviolet-curable gel polymer electrolyte inks allows the construction of thick electrodes with microscale features/arbitrary form factors and ionic isolation between unit cells (enabling electrochemical tailoring of voltages and capacitances in a single a-MSC). A nickel/gold-plated polyimide substrate is introduced as a flexible current collector that allows an increase in areal mass loading of electrodes. A DIW-printed polydimethylsiloxane layer shifts the location of a neutral plane to electrode-current collector interface to improve flexibility. The resulting a-MSC exhibits high areal energy density (61.34 µWh cm−2) and on-demand (in-series/in-parallel) cell configuration with artistic versatility. Moreover, the a-MSC is aesthetically unitized with complex-shaped electronic devices, acting as a customized practical monolithic power source.

Alkaline hydrogel electrolyte from biosourced chitosan to enhance the rate capability and energy density of carbon-based supercapacitors

A green biodegradable hydrogel electrolyte was developed from chitosan biopolymer and KOH. This allows one to increase the energy density of carbon-based supercapacitors and to prevent the electrode degradation and current collector corrosion.

Efficient separation of electrode active materials and current collector metal foils from spent lithium-ion batteries by a green deep eutectic solvent

The opposite electrostatic potential between the oxygen atoms on the carbonate ion and the hydrogen atoms on PVDF makes the potassium carbonate–ethylene glycol deep eutectic solvent suitable for electrode material separation.

A low-cost and sustainable cross-linked dextrin as aqueous binder for silicon anodes in lithium-ion batteries

Silicon is a promising anode material for lithium-ion batteries (LIBs) because of its impressive theoretical capacity. However, it undergoes severe volume changes in the lithiated state thus limiting its development in LIBs. Herein, a cross-linked dextrin binder is created through in-situ thermal cross-linking of dextrin and the inorganic cross-linker sodium tetraborate decahydrate, which is a cost-effective, “greener” water-soluble binder. This binder can significantly strengthen the adhesion between Si electrode and copper current collector, which is almost three times more effective in adhesion than commercially available CMC binder. Meanwhile, the cross-linked dextrin binder also has superior mechanical properties and is able to well mitigate the huge volume changes upon cycling, consequently achieving an excellent cycling stability and superior rate capability. It is believed that this aqueous binder has the potential to utilize in silicon anodes for high-energy-density LIBs, as well as providing a new idea in the design of binders for other electrode materials which suffer from volume change during cycling.

Ultrafast Nonvolatile Ionic Liquids-Based Supercapacitors with Al Foam-Enhanced Carbon Electrode.

The ultrafast frequency response supercapacitor is a promising candidate for alternating current line filtering. We report the fabrication of a special structured ionic liquid-based supercapacitor with an ultrafast response of only 1.5 ms. The three-dimensional aluminum (Al) foam in situ coated with carbon layer (∼500 nm) serves as the novel, highly efficient electrode-current collector. The high porosity (95%) of Al foam allows the rapid ion diffusion and the as-obtained Al/C interface with atomic-level mixing allows the fast electron transfer, two crucial factors for ultrafast response. Hence, it possesses an excellent specific mass capacitance of 68 mF g-1 at 120 Hz, as well as an ultrahigh rate of up to 3000 V s -1. The supercapacitors exhibit frequency modulation performance in the range of 20 kHz to 16 MHz. They exhibit the similar even better alternating current filtering performance, as compared to the commercial aluminum electrolytic capacitors, detected at 10 Hz, 60 Hz, 100 Hz and 1 M Hz. These results suggest that, although ILs have high viscosity and low ion mobility, the IL-based supercapacitor has a great potential to be used as a device for alternating current line filtering, as well as providing nonvolatile and nonflammability safety.

Flexible, Transparent and Highly Conductive Polymer Film Electrodes for All-Solid-State Transparent Supercapacitor Applications.

Lightweight energy storage devices with high mechanical flexibility, superior electrochemical properties and good optical transparency are highly desired for next-generation smart wearable electronics. The development of high-performance flexible and transparent electrodes for supercapacitor applications is thus attracting great attention. In this work, we successfully developed flexible, transparent and highly conductive film electrodes based on a conducting polymer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The PEDOT:PSS film electrodes were prepared via a simple spin-coating approach followed by a post-treatment with a salt solution. After treatment, the film electrodes achieved a high areal specific capacitance (3.92 mF/cm2 at 1 mA/cm2) and long cycling lifetime (capacitance retention >90% after 3000 cycles) with high transmittance (>60% at 550 nm). Owing to their good optoelectronic and electrochemical properties, the as-assembled all-solid-state device for which the PEDOT:PSS film electrodes were utilized as both the active electrode materials and current collectors also exhibited superior energy storage performance over other PEDOT-based flexible and transparent symmetric supercapacitors in the literature. This work provides an effective approach for producing high-performance, flexible and transparent polymer electrodes for supercapacitor applications. The as-obtained polymer film electrodes can also be highly promising for future flexible transparent portable electronics.

Degeneration of Key Structural Components Resulting in Ageing of Supercapacitors and the Related Chemical Ageing Mechanism.

The research on supercapacitors (SCs) is one of the hot topics in the field of energy storage, and the intrinsic ageing mechanism of SCs is significant from both the economic and the scientific point of view. In this paper, the negative effects of decay of the key structural components on ageing of SCs were investigated by factorial design and analysis of variance (ANOVA). The ANOVA results showed that the degree of the negative influence on ageing of SCs could be ranked in descending order as anode > separator > cathode. The ageing would be accelerated due to the interaction between the electrode and separator, especially at a high charge-discharge current density. Further, the intrinsic chemical ageing mechanism of SCs was revealed by the morphology, microstructure, and chemical composition analyses of the fresh and aged key components (the electrode carbon materials, current collectors, and separators) with scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectra (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR), etc. Moreover, the minimum pore width of electrode carbon materials suitable for electrolyte ion diffusion was obtained by density functional theory (DFT) calculations, which corroborated the assumption that the pore structure deterioration was one of the direct causes of capacitance loss for aged SCs. Generally, the ageing mechanism of key components of SCs could be a reference to develop advanced electrode materials and separators for SCs.

First Prototype 18650 Aqueous Supercapacitors Using Graphite Coated Al Foil As Low Cost and Anti-Corrosion Current Collector

Supercapacitors have been attached much attention for power supplies due to their high-power density and excellent cycling stability. Up to now, the study of aqueous supercapacitors is increasing continuously due to their low-cost and high safety with non-flammable. Especially, it provides a high-power density up to 10 kW kg-1 (refers to the fast charge/discharge capability) which is higher than other electrolytes such as organic and ionic liquid electrolytes.(1) However, the major problem of the aqueous electrolyte system is the corrosion of metal current collector, especially aluminium (Al) foil. Even the Al foil is a promising current collector due to its low-cost, it can be corroded easily in aqueous solutions. Additionally, the resistive oxide film is spontaneously formed on the surface of Al foil, leading to low conductivity of the electrode.(2) To address this issue, we chose the graphite material for coating on the top and bottom of Al foil surface as a hydrophobic layer to prevent a penetration of the aqueous solution into Al foil surface that can be confirmed by contact angle measurement. In addition, we further studied the electrochemical performance of the as-prepared electrode in a half-cell configuration. Overall, not only protection of corrosion but also improvement of interfacial contact between electrode material layer and current collector are resulted from graphite protective layer, leading to low internal resistance and high-rate capability of the electrode. Moreover, the corrosion suppression of the current collector can enhance the cycling stability of the electrode. Finally, we fabricated the first prototype of cylindrical aqueous supercapacitor with the standardized size of 18650 for commercial-scale using the as-modified current collector which achieves capacitance of 18.9 F/cell at 50 mA and excellent cycling stability with almost 100% over 8,000 cycles at 250 mA. KEYWORDS: Aqueous supercapacitors, anti-corrosion, hydrophobic protective layer REFERENCES C. Zhong, Y. Deng, W. Hu, J. Qiao, L. Zhang and J. Zhang, Chem. Soc. Rev., 44, 7484 (2015). 2. P. Chomkhuntod, M. Sawangphruk and K. Kongsawatvoragul, ECS Transactions, 97, 3 (2020). Figure 1

Reliable Lab-Scale Evaluation of Solid Oxide Fuel Cells Electrode Performance – the Effect of Electrode Thickness and Current Collecting Spacing

Understanding and optimizing electrochemically active zone for oxygen reduction reaction in solidoxide fuel cells (SOFCs) cathodes are indispensable to maximize device’s performance. For mixed ionicand electronic conductors, the range of this zone depends on the oxygen surface exchange and solid-stateoxygen/electron transport properties of materials [1]. This aspect is also critical to realize validcharacterization of the electrode’s electrochemical activities. For instance, when a material’s electronicconductivity is low or the electrical contact points are spaced beyond a critical distance, the electrodepolarization resistance measured by electrochemical impedance spectroscopy will be controlled by the sheetresistance not the oxygen exchange resistance [2]. The situation becomes more complicated as the electricalconductivity of porous layer, which is an advantageous structure with large surface area and facile gas phasetransport, considerably deviates from the material’s intrinsic property. It is expected that porosity,connectivity, and impurity contents can have significant impact on porous electrode’s electronic conduction[3].In this context, we have studied effective in-plane electronic conductivity of lanthanum strontiumcobalt ferrite (LSCF) porous layers. The in-plane conductivity was measured by four-line probeconfiguration [4], modified from the widely used four-point probe technique to be applied for a porouslayer. We have confirmed that the in-plane electrical conductivity of screen-printed LSCF porous layers isone or two orders of magnitude lower than the material’s bulk property in ambient air, depending ontemperatures. This electronic conductivity deviation was taken into account to rationally designcombination of electrode thickness and current collector spacing and, in turn, to guarantee a validassessment of electrode performance. In addition, we found that electrical conductivity of LSCF porouslayers decreases by 20~30 %, within relatively short period of time (250~400 hours) upon repeated thermalcycles (500 ℃ to 700 ℃). Furthermore, we found that in-plane conductivity of thin (<10 µm) electrodes isstrongly dependent on the measurement time and the local atmospheric environment relative to thickerelectrodes. Special attention is required to use a thin electrode to evaluate electrode performance.This work was supported by the US Department of Energy (DOE), Office of Fossil Energy, (Officeof Clean Coal & Carbon Management), “Solid Oxide Fuel Cell Manufacturing in Support of Office ofFossil Energy” program through Argonne National Laboratory under FWP No. 27327.1.[1] S.B. Adler et al. J. Electrochem. Soc. 143 (1996) 3554-3564; S.B. Alder Solid State Ionics 111 (1998)125-134.[2] B.A. Boukamp et al. Solid State Ionics 192 (2011) 404-408; B.A. Boukamp et al. Solid State Ionics 283(2015) 81-90.[3] L. Holzer et al. J. Mater. Sci. 48 (2013) 2934-2952.[4] S.W. Peterson et al. J. Electrochem. Soc. 161 (2014) A2175-A2181.

Analysis of Germanium Nanoparticle Composites with an Aluminum Current Collector toward Li-ion Battery Anodes with High Capacity and Broad Potential Stability Range

Reduction reactions with lithium at >0.3 V vs Li/Li+ make germanium prospectively compatible with aluminum current collectors to form a copper-free lithium-ion cell anode that may enable lithium-ion cells that are more tolerant to overdischarge. Targeted 2.0 mAh/cm2 germanium nanoparticle electrodes with an aluminum foil (Ge–Al electrode) current collector were fabricated and tested versus lithium from 0.3 to 1.5 V vs Li/Li+ in 1.0 M LiPF6 1:1 ethylene carbonate/diethyl carbonate (v/v) electrolyte and demonstrated a peak reversible capacity of 342 mAh/gGe at a targeted C/10 rate. A targeted 2.0 mAh/cm2 germanium nanoparticle electrode with a copper current collector (Ge–Cu electrode) was also tested from 0.005 to 1.5 V vs Li/Li+, the results of which are utilized as a representative comparison of germanium tested in a conventional lithium-ion anode potential range. Compared to the Ge–Cu electrode, after 50 cycles at a targeted C/10 rate the Ge–Al electrode showed 90% vs 18% capacity retention. Post-mortem analysis with XPS, SEM/EDS, Raman spectroscopy, and FTIR showed that compared to the Ge–Cu electrode the Ge–Al electrode had (1) less oxygen, fluorine, and carbon deposition, (2) less germanium amorphization, (3) formation of LixCy and Ge–H, and (4) less Li2O formation. After 150 cycles at equivalent targeted rates, the Ge–Al electrode also had significantly less mid-frequency impedance growth than the Ge–Cu electrode. Modeling of 18650 format LiNiCoAlO2-cathode lithium-ion cells with a Ge–Al anode predicted an achievable energy density and specific energy of up to 491 Wh/L and 198 Wh/kg. A germanium dissolution potential of 4.2 V vs Li/Li+ was assigned based on voltammetry and post-mortem SEM/EDS. Cycling of a Ge–Al electrode with an upper potential cutoff of 4.2 V vs Li/Li+ every tenth cycle showed 30% capacity retention after 50 cycles, an increased capacity fade attributed to solid electrolyte interphase instability up to 4.2 V vs Li/Li+ based on impedance and post-mortem analysis.