Amorphous Electrodes Research Articles

Surfactant-Assisted NiCo2S4 for Redox Supercapacitors

Until now, crystalline NiCo2S4 and its composites have demonstrated improved performance in supercapacitor applications compared to their oxide analogues due to their relatively higher electrical conductivity and multifaceted redox reaction. However, amorphous phase materials have recently shown promise in electrochemical energy storage systems. This work reports on amorphous NiCo2S4 with the help of urea via the hydrothermal method. It was noted that urea not only aided the amorphous formation but also served as a nitrogen precursor. In comparison, amorphous NiCo2S4 demonstrated a higher nitrogen atom% of 5.9 compared to 4.49 for crystalline NiCo2S4. Furthermore, the amorphous NiCo2S4 electrode exhibited superior electrochemical performance, with a specific capacitance of ~3506 F g−1, which was higher than the cNCS electrode’s specific capacitance of ~2185 F g−1 at 2 A g−1. Additionally, aNCS in a two-electrode asymmetric supercapacitor exhibited a specific capacitance and an energy density of ~196 F g−1 and 56 Wh kg−1, respectively.

Enhanced Cycling Stability of Amorphous MgNi-Based Alloy Electrodes through Corrosion Prevention by Incorporating Al2(SO4)3·18H2O into the Electrolyte

Mg-based alloy anodes suffer from severe corrosion in alkaline electrolytes, which substantially impedes their cycle life and thereby limits their suitability as anode materials for nickel–metal hydride (Ni-MH) batteries. This work modifies the conventional 6 M KOH electrolyte by adding 0.1 M Al2(SO4)3·18H2O. The electrochemical hydrogen storage properties of Mg0.45Ti0.05Ni0.50 alloy in this electrolyte and its microstructural evolution during cycling are studied. In the 6 M KOH + 0.1 M Al2(SO4)3·18H2O electrolyte, a protective layer consisting of Mg2Al(OH)7 is formed on the surface of the Mg0.45Ti0.05Ni0.50 alloy anode during charge/discharge cycling instead of Mg(OH)2, effectively preventing further corrosion and improving its cycle life. The Mg0.45Ti0.05Ni0.50 alloy anode delivers a maximum discharge capacity of 479.0 mAh g−1 and maintains 318.4 mAh g−1 after 30 cycles in the 6 M KOH + 0.1 M Al2(SO4)3·18H2O electrolyte, which is significantly superior to that achieved in the 6 M KOH electrolyte (471.1 mAh g−1 and 201.8 mAh g−1, respectively). This work provides a new strategy for improving the cycle stability of Mg-based alloy anodes.

Performance and mechanism of electrocatalytic oxidation of urea based on carbon-doped FeCoNiCrMn high entropy alloy film

The application and research of high entropy alloy electrodes in urea oxidation reactions (UOR) are significant. In this study, FeCoNiCrMn, FeCoNiCrMnO, and FeCoNiCrMnC high entropy alloy thin films were prepared by magnetron sputtering by controlling the sputtering power, varying the sputtering atmosphere, and using double target co-sputtering, respectively. The microstructure and surface morphology of the electrode were observed and analyzed by X-ray diffraction, scanning electron microscope, transmission electron microscope, and atomic force microscope. In addition, the chemical state of the elements on the electrode surface was analyzed by X-ray photoelectron spectroscopy (XPS) to clarify the mechanism related to the excellent UOR performance of the electrode. The study found that a small amount of carbon doping can greatly improve the UOR performance of this type of electrode. The amorphous FeCoNiCrMnC electrode has more potential UOR active sites than the face-centered cubic FeCoNiCrMn electrode. After cyclic voltammetry (CV), the potential active sites of the electrode are activated, and the active substances of these electrodes are increased, furthermore, the UOR performance of these electrodes has improved. Since it has 200 cycles of CV, the 10 mA cm−2 potential of FeCoNiCrMnC electrode for UOR is only 1.337 V. After 100 days of natural aging, the catalytic ability of the electrode not only did not decrease but slightly improved, with a potential of 1.321 V at 10 mA cm−2, reflecting the good stability of the catalytic electrode.

Achieving Non-Interfacial Blocking Zinc Ion Transport Based on MOF Derived Manganese Oxides and Amorphous Carbon Hybrid Materials.

How to coordinate electron and ion transport behavior across scales and interfaces within ion battery electrodes? The exponential increase in surface area observed in nanoscale electrode materials results in an incomprehensibly vast spatial interval. Herein, to address the problems of volume expansion, dissolution of cathode material, and the charge accumulation problem existing in manganiferous materials for zinc ion batteries, metal organic framework is utilized to form the architecture of non-interfacial blocking ~10 nm Mn2O3 nanoparticles and amorphous carbon hybrid electrode materials, demonstrating a high specific capacity of 361 mAh g-1 (0.1 A g-1), and excellent cycle stability of 105 mAh g-1 after 2000 cycles under 1 A g-1. The uniform and non-separated disposition of Mn and C atoms constitutes an interconnected network with high electronic and ionic conductivity, minimizing issues like structural collapse and volume expansion of the electrode material during cycling. The cooperative insert mechanism of H+ and Zn2+ are analyzed via ex-situ XRD and in-situ Raman tests. The model battery is assembled to present practical possibilities. The results indicate that MOF-derived carbonization provides an effective strategy for exploring Mn-based electrode materials with high ion and electron transport capacity.

Enhancing Methylated Amorphous Silicon Anode Performances in Li-Ion Batteries By Boron Doping

Methylated amorphous silicon has already demonstrated some advantages as compared to silicon in terms of mechanical properties and cyclability for Li-ion batteries (LIB) [1]. However, the conductivity of methylated amorphous silicon drops by several orders of magnitude when increasing the methyl content in the material, which prevents investigating methyl contents higher than 10%. It is well known that doping significantly improves the conductivity of crystalline or amorphous silicon, and has sometimes been reported to improve the material cyclability when used as a LiB anode [2].Here, boron-doped methylated amorphous silicon electrodes with different methyl contents were investigated as anodes for LiB in half-cell configuration. Boron doped methylated silicon thin films (100nm thick) with various methyl content were cycled in the range 0.025V – 1V at C/2 rate (electrolyte: LP30 with 5%FEC). 10% methylated amorphous silicon with 2% boron doping performs a capacity retention of 77% after 1000 cycles (exhibiting a capacity around 1800 mAh.g-1) of full lithiation/delithiation. Figure 1a shows a clearly improved performance as compared to the undoped material. The stability upon cycling of higher methyl contents (15% and 20%) electrodes is further increased, with a capacity retention exceeding 80% over 1000 cycles of full lithiation/delithiation.The evolution of the SEI thickness can be quantitatively determined from IR spectra during cycling. The thickness in the delithiated state is found to increase from cycle to cycle, but with a lower rate for the doped 10% methylated electrodes (thickness lower than 25 nm after 40 cycles and 30 nm after 80 cycles) than for the undoped ones (thickness larger than 35 nm after 40 cycles), see Figure 1b. The SEI evolution upon cycling for higher methyl content is currently under investigation. Reference [1] L. Touahir, A. Cheriet, D. A. D. Corte, J.-N. Chazalviel, C. H. Villeneuve, F. Ozanam, I. Solomon, A. Keffous, N. Gabouze et M. Rosso, «Methylated silicon: A longer cycle-life material for Li-ion batteries,» Journal of Power Sources, vol. 240, pp. 551-557, 10 2013. [2] M. Salah, C. Hall, P. Murphy, C. Francis, R. Kerr, B. Stoehr, S. Rudd et M. Fabretto, «Doped and reactive silicon thin film anodes for lithium ion batteries: A review,» Journal of Power Sources, vol. 506, p. 230194, 9 2021. Figure 1

Facile top-down fabrication of integrated amorphous NiFe-based electrocatalytic electrodes for high current and long-life oxygen evolution

Developing an industrially relevant electrode with high catalytic activity, stability, and tunable composition/size for large-scale water electrolysis is a significant challenge. We have created an integrated electrode (NFM30-N) for the oxygen evolution reaction (OER) using a facile top-down approach that combines arc melting with dealloying-oxidation. Due to the dealloying-oxidation effect, the as-derived porous amorphous M–O, M–OH, and M–OOH (M = Ni, Fe) nanocones cover the basic NiFeMn alloy. This integrated design enables NFM30-N to exhibit outstanding OER performance at high current densities, requiring low overpotentials of only 282 and 323 mV to achieve large current densities of 100 and 500 mA cm−2, respectively. It also displays a small Tafel slope of 44.1 mV dec−1 and remarkable stability for over 100 h at 100 and 500 mA cm−2. When used as an anode, a two-electrode electrolyzer cell with NFM30-N at 500 mA cm−2 only requires a cell voltage of 1.619 V and exhibits excellent stability, with almost no performance degradation after continuous chronopotentiometry test for each 100 h at 500 and 100 mA cm−2. This exceptional OER electrocatalytic performance is attributed to the integrated structure providing high electrical conductivity and stability, the presence of numerous active sites due to dealloying and the amorphous structure, and the promotion of the OER process by M–O, M–OH, and M–OOH species. This work offers a novel idea for fabricating integrated, industrially relevant electrocatalytic electrodes through traditional metallurgy combined with dealloying-oxidation.

A novel efficient three-stage electrochemical pre-lithiation method for the amorphous carbon negative electrodes of lithium-ion capacitors

Electrochemical pre-lithiation stands as a practical and widely adopted technique for precisely controlling the degree of pre-lithiation, but the process is usually time-consuming. Herein, we introduce a novel three-stage electrochemical pre-lithiation method, comprising an initial stage of a high current density, a second stage of a low current density, and an additional stage of constant voltage to ensure the complete formation of solid electrolyte interphase (SEI) on the amorphous carbons: soft carbon (SC) and hard carbon (HC). Lithium-ion capacitors (LICs) are configured with the pre-lithiated SC or HC as the negative electrode and activated carbon as the positive electrode to assess the efficacy and adaptability of this three-stage pre-lithiation approach. Our findings demonstrate that this method can reduce the pre-lithiation time from 1114 to 604 min for SC, and from 1913 to 1080 min for HC, achieving nearly 46 % and 44 % decreases, respectively. Furthermore, the three-stage pre-lithiation method can simultaneously increase reversible Li-ion storage capacity within the same operating potential window, thereby enhancing the electrochemical performance of the LIC cells. Specifically, the LIC cell employing the three-stage pre-lithiated SC exhibits an energy density of 96.5 Wh kg-1 at 0.15 kW kg-1 and 76.5 Wh kg-1 at 5.98 kW kg-1. These cells demonstrate remarkable reversibility, retaining 89.6 % charge capacity after 10,000 cycles. Similarly, the LIC with the three-stage pre-lithiated HC achieves even higher energy densities of 105.3 Wh kg-1 at 0.15 kW kg-1 and 86.42 Wh kg-1 at 5.98 kW kg-1 with a retention of 85.2 % after 5000 cycles. The successful implementation and validation of this three-stage pre-lithiation method pave the way for further development of LICs.

Inhibition of Phase Transition in Amorphous Niobium Oxide by Covalent Carbon Reinforcement Enables Fast‐Charge and Long‐Duration Lithium Storage

AbstractNiobium oxides are potential anode materials for ultrafast and safe lithium‐ion batteries due to their high ionic conductivity and relatively high operation voltage. However, the electrochemically induced phase transformations that involve multi‐electron redox reactions in a wide voltage window cause rapid capacity degradation and poor rate capability. Here, a novel carbon‐covalent amorphous niobium oxide anode is reported to greatly suppress the phase transition during cycling via formation of strong Nb─O─C bonds, achieving high‐capacity, fast‐charge and long‐duration lithium storage. This amorphous structure and forming covalent carbon contribute to good volume accommodation and high electron conductivity. The carbon‐covalent amorphous Nb2O5 displays a high reversible capacity of 361.5 mAh g−1 at 0.1 A g−1 and excellent cycling stability with a capacity of 189.8 mAh g−1 at a high rate of 10 A g−1 after 9000 cycles. Structure characterizations reveal that the well‐preserved amorphous structure without phase transition during repeated Li+ insertion/desertion is responsible for the superior performance. This work opens a new avenue on rational design of high‐performance amorphous electrode materials for next‐generation batteries.

Amorphous Iridium Oxide-Integrated Anode Electrodes with Ultrahigh Material Utilization for Hydrogen Production at Industrial Current Densities

HighlightsElectrodeposited amorphous IrOx thin electrodes are first developed for proton exchange membrane electrolyzer cells.An ultralow loading of 0.075 mg cm−2 archives superior performance to catalyst-coated membrane (2 mg cm−2).> 96% of catalyst savings and > 42-fold higher catalyst utilization are demonstrated.

Accurate identification of glass crystallization helps in selecting high electronic conductivity materials

Though the current research on vanadium-based glass electrodes has made great progress, the conductivity theory of V-based glasses has not been obviously improved and crystals cannot be positioned precisely. The changes in the valence state of V3+, V4+ and V5+ are regulated by the strong reducing agent Fe2P to realize valence bond transformation of the amorphous electrode, explore the redox process of multi-electron reactions and further optimize the conductivity of electrode materials. VPFe2 and VPFe3 precipitate VO2 crystals and VPFe4 precipitates VO2 and V6O11 crystals. Electron back-scattered diffraction was used to accurately identify the distribution and specific positions of both types of crystals. V6O11 crystals exhibit a strong texture according to pole figure and inverse pole figure. XPS reveals that Fe2P and V2O5, undergo a redox reaction during the high-temperature melting process, where V5+ is reduced to V4+ and V3+ and V4+ renders a positive influence on conductivity. The addition of Fe2P increases the content of V4+ in the glass and VPFe3 glass contains the highest content of V4+, leading to the highest electronic conductivity. V2O5 transforms into VO2 crystals and VO2 transforms into V6O11 with the increase of Fe2P content. The type of nanocrystal precipitation in glass affects electronic conductivity.

Function‐Oriented Design of Amorphous MoS2 with Abundant Active Sites for High‐Efficiency Hydrogen Evolution Reaction

AbstractMolybdenum disulfide (MoS2) has received great interest as a highly active and cost‐effective electrocatalyst for hydrogen evolution reaction (HER). However, a main challenge for developing high‐efficiency electrocatalysts is to tailor the factors affecting the HER performance, such as composition, structure, and morphology. Herein, amorphous MoS2 electrodes with different Mo and S contents are successfully synthesized by the chemical bath deposition method using different molar ratios of Mo/S precursors (Mo/S: 4 : 1, 1 : 1 and 1 : 4) at various growth times. Experimental results indicate that the composition and the surface morphology of MoS2 are strongly sensitive to the Mo and S contents, which can create different surface roughness at the interface induced by growth times. The as‐prepared MoS2 electrode with a molar ratio of 1 : 4 exhibits superior HER activity in 1 M KOH, only requiring low overpotentials of 220 mV at 20 mA cm−2, which is much lower than those of MoS2 with a molar ratio of 1 : 1 (253 mV), and 4 : 1 (290 mV), respectively. This outstanding electrochemical performance of MoS2 (Mo/S, 1 : 4) with excellent long‐term stability can be attributed to its unique sulfur‐rich MoS2 nanosheet array structure with exposed abundant active sites, a high electrochemical active surface area (ECSA: 955.50 cm2) and superior roughness factor (RF: 3822).

Operando Nanomechanical Mapping of Amorphous Silicon Thin Film Electrodes in All-Solid-State Lithium-Ion Battery Configuration during Electrochemical Lithiation and Delithiation.

An operando bimodal atomic force microscopy system was constructed to perform nanomechanical mapping of an amorphous Si thin film electrode deposited on a Li6.6La3Zr1.6Ta0.4O12 solid electrolyte sheet during electrochemical lithiation/delithiation. The evolution of Young's modulus maps of the Si electrode was successfully tracked as a function of apparent Li content x in lithium silicide (LixSi) simultaneously with real-time surface topography observation. At the initial stage of lithiation, the average modulus steeply decreased due to the generation of LixSi from intrinsic Si, followed by a moderate modulus reduction until the electrode capacity reached 3300 mAh g-1 (Li content x = 3.46). In the following delithiation, the gradual recovery of the average modulus of LixSi was observed up to 1467 mAh g-1 (Li content x = 1.54) at which delithiation stopped due to the significant volume change induced by phase transformation of LixSi.

Электроискровое модифицирование поверхности аддитивного сплава ВТ6 высокоэнтропийным и аморфным электродами

Unsatisfactory quality of the surface layer of additive products, in particular increased surface roughness, prevents the widespread use of electron beam powder bed fusion (EBPBF). Electrospark treatment (EST) is one of the methods for smoothing and hardening the surface layer. The work shows the possibility of modifying the surface of additive VT6 alloy samples by reactive EST with multicomponent electrodes. For this purpose, the authors used electrodes made of the Fe48Cr15Mo14Y2C15B6 bulk metallic glass forming alloy and the FeCoCrNi2 high-entropy alloy. Based on the results of scanning electron microscopy, it was identified that after EST, both modified layers have a thickness of about 16 μm. X-ray diffraction phase analysis showed that in the case of treatment with an amorphous electrode they contain carboborides of the Ti(B,C) type, and in the case of treatment with a high-entropy electrode – intermetallic of the Ti2(Fe,Ni) type. The modified layers have average hardness values of 19 and 10 GPa and elastic modulus of 234 and 157 GPa, respectively, which significantly exceeds the values of these parameters for the EBPBF-grown VT6 alloy. Electric discharge modification of the surface with multicomponent electrodes led to a decrease in roughness by 8...11 times due to the melting of the protrusions and filling of the dimples with the melt to a depth of more than 50 μm. A comparative analysis of the results of tribological tests showed a change in the wear mechanism as a result of EST of the additive VT6 alloy. Wear resistance increased by 4 and 3 orders of magnitude when using electrodes made of a bulk metallic glass and high-entropy alloy, respectively.

In Situ Formed Amorphous Bismuth Sulfide Cathodes with a Self-Controlled Conversion Storage Mechanism for High Performance Hybrid Ion Batteries.

Conversion-type electrodes offer a promising multielectron transfer alternative to intercalation hosts with potentially high-capacity release in batteries. However, the poor cycle stability severely hinders their application, especially in aqueous multivalence-ion systems, which can fundamentally impute to anisotropic ion diffusion channel collapse in pristine crystals and irreversible bond fracture during repeated conversion. Here, an amorphous bismuth sulfide (a-BS) formed in situ with unprecedentedly self-controlled moderate conversion Cu2+ storage is proposed to comprehensively regulate the isotropic ion diffusion channels and highly reversible bond evolution. Operando synchrotron X-ray diffraction and substantive verification tests reveal that the total destruction of the Bi─S bond and unsustainable deep alloying are fully restrained. The amorphous structure with robust ion diffusion channels, unique self-controlled moderate conversion, and high electrical conductivity discharge products synergistically boosts the capacity (326.7 mAh g-1 at 1 A g-1 ), rate performance (194.5 mAh g-1 at 10 A g-1 ), and long-lifespan stability (over 8000 cycles with a decay rate of only 0.02 ‰ per cycle). Moreover, the a-BS Cu2+ ‖Zn2+ hybrid ion battery can well supply a stable energy density of 238.6Wh kg-1 at 9760W kg-1 . The intrinsically high-stability conversion mechanism explored on amorphous electrodes provides a new opportunity for advanced aqueous storage.

Amorphous nanosphere self-supporting electrode based on filter paper for efficient water splitting

Given its superior structure, the abundance of surface functional groups, and low cost, cotton fiber filtration paper can be used as the support for hydrogen evolution reaction (HER) and oxygen evolution reaction catalysts (OER) instead of copper foam (CF), nickel foam (NF), or carbon cloth (CC). Herein, the chemical plating method was used to create thin self-supporting electrodes based on cotton fiber filtration paper (FP). The Co-Ni-P amorphous nanospheres can be uniformly dispersed on the self-supporting FP due to its porous structure and oxygen functional groups. The Co-Ni-P/FP electrode has an overpotential as low as 125 mV for HER and 320 mV for OER at the current density of 10 mA cm−2. Additionally, according to density functional theory (DFT) calculations, the Co atom added to the Ni-P nanosphere can lead to considerably more charge accumulation around the Co and Ni active sites, which greatly encourages the HER and OER processes. The novel porous support, FP, provides a fresh way the preparation of self-supporting electrodes.

Manganese oxides as positive electrode materials for rechargeable aluminum batteries

Three composites of carbon and amorphous MnO2, crystalline α-MnO2, or Mn2O3 were synthesized and investigated as the positive electrode materials for rechargeable Al batteries. For amorphous MnO2 and crystalline Mn2O3, the maximum discharge capacity was about 300 mAh g−1, which is the highest capacity among nonaqueous rechargeable Al batteries using manganese oxide positive electrodes. The amorphous MnO2 electrode showed a discharge capacity of more than 150 mAh g−1 even after 10 charge-discharge cycles. Crystal structure analysis and electronic state analysis suggested that crystalline Mn2O3 changed to amorphous MnO2 during the first charge process. These results suggest that the amorphous MnO2/carbon composite can be an excellent positive electrode material for rechargeable Al batteries.

In-situ reconstruction of self-supported amorphous Ni-Mo electrode for stable hydrogen evolution at large and intermittent current density

Solar power drived water splitting for hydrogen production is pivotal for sustainable energy conversion. Yet, it is challenging to develop earth abundant, high active, and durable electrodes to catalyzing hydrogen evolution reaction (HER) under fluctuating solar electricity. Herein we report self-supprted NiMo phosphate (NiMo-Pi) electrodes, where amorphous NiMo-Pi with nanosheets-like structure grow directly on conductive Ni foam by a facile one-step hydrothermal treatment. The electronic structures of Ni and Mo are tuned by O and P in NiMo-Pi electrodes, resulting the down-shift of their d-band centers. NiMo-Pi electrodes offer high activity and stability for HER, delivering -100 and -500 mA cm−2 mgcat−1 with overpotentials of 343 and 461 mV, repectively. They also sustain long-term electrolysis at a constant industrial-level current density of 500 mA cm−2 and at dynamic current densities ranging from -10 to -1 000 mA cm−2. Their HER activity become higher after stability tests, benefitting from in-situ surface reconstruction. This reconstruction makes the surface rich in active higher-lying d-band centers. This work suggests that tuning the electronic structure of electrodes is an efficient way to design efficient and stable electrodes for HER under harsh conditions.

Two-step electrodeposition to achieve durable IrOx electrode with a semi-crystalline structure for efficient OER

The Development of highly catalytically active and stable anodes for oxygen evolution reaction (OER) in acidic media remains a great challenge. Herein, we proposed a two-step electrodeposition method to optimize an amorphous electrodeposited IrOx electrode (eⅡ-IrOx/Ti). The introduction of a pre-deposition layer, prepared by triangular wave electrodeposition, contributes to the enhancement of surface oxygen vacancies, resulting in a semi-crystalline structure. Compared to directly potentiostatic electrodeposited IrOx electrode (e-IrOx/Ti) and industrially thermally decomposed IrO2 electrode (IrO2–Ta2O5/Ti) at the same iridium loading level, eⅡ-IrOx/Ti exhibited superior OER performance, with a Tafel slope of 52.85 mV/dec and an overpotential as low as 218 mV at 10 mA/cm2. Moreover, eⅡ-IrOx/Ti demonstrates remarkable stability while continuously catalyzing OER at 250 mA/cm2 for 100 h, with little performance decay and a stability number of 3.397 × 106 (comparable to crystal IrO2). The semi-crystalline structure of eII-IrOx/Ti, rich in oxygen vacancies, facilitates the synergistic effect of amorphous and crystalline phases, indicating the potential of electrodeposited IrOx electrodes for sustained and efficient OER in acidic environments.

Silicon-Based Solid-State Batteries: Electrochemistry and Mechanics to Guide Design and Operation.

Solid-state batteries (SSBs) are promising alternatives to the incumbent lithium-ion technology; however, they face a unique set of challenges that must be overcome to enable their widespread adoption. These challenges include solid-solid interfaces that are highly resistive, with slow kinetics, and a tendency to form interfacial voids causing diminished cycle life due to fracture and delamination. This modeling study probes the evolution of stresses at the solid electrolyte (SE) solid-solid interfaces, by linking the chemical and mechanical material properties to their electrochemical response, which can be used as a guide to optimize the design and manufacture of silicon (Si) based SSBs. A thin-film solid-state battery consisting of an amorphous Si negative electrode (NE) is studied, which exerts compressive stress on the SE, caused by the lithiation-induced expansion of the Si. By using a 2D chemo-mechanical model, continuum scale simulations are used to probe the effect of applied pressure and C-rate on the stress-strain response of the cell and their impacts on the overall cell capacity. A complex concentration gradient is generated within the Si electrode due to slow diffusion of Li through Si, which leads to localized strains. To reduce the interfacial stress and strain at 100% SOC, operation at moderate C-rates with low applied pressure is desirable. Alternatively, the mechanical properties of the SE could be tailored to optimize cell performance. To reduce Si stress, a SE with a moderate Young's modulus similar to that of lithium phosphorous oxynitride (∼77 GPa) with a low yield strength comparable to sulfides (∼0.67 GPa) should be selected. However, if the reduction in SE stress is of greater concern, then a compliant Young's modulus (∼29 GPa) with a moderate yield strength (1-3 GPa) should be targeted. This study emphasizes the need for SE material selection and the consideration of other cell components in order to optimize the performance of thin film solid-state batteries.

Effect of Stress on the Electrochemical Response of Amorphous Silicon Electrodes

Silicon electrodes for lithium-ion batteries exhibit a theoretical capacity ten times higher than that of the graphite electrodes currently used in commercial systems. When lithiated/delithiated, silicon experiences stresses on the order of one GPa, inducing the damage of the material, which results in poor cyclability. Concurrently, irreversible continuum thermodynamics predicts that these stresses affect the lithiation itself in different ways for monophasic and biphasic lithiation (progressive invasion of the electrode by a lithiated phase of given composition) [1,2]. When lithiation takes place homogeneously (without phase transformation), mechanical stresses affect lithiation through their effect on the chemical potential of diffusing lithium (Larché-Cahn theory). On the other hand, when lithiation is biphasic, mechanical stresses affect lithiation through an effect on both chemical potential of lithium and thermodynamic driving force acting on the phase boundary. This coupling has first been probed experimentally in homogeneous lithiation using a method where the stress state of silicon is modified indirectly through incremental delithiation [3].In this work, we investigate the interplay between the electrochemical state (electrode potential and current density) of an amorphous silicon electrode and its stress state. The electrochemical response of the amorphous silicon thin film deposited on a stainless steel substrate has been recorded under varying mechanical loading during lithiation and delithiation cycles. The mechanical loading is applied by deforming elastically the steel substrate of the amorphous silicon thin film, which allows us to directly probe the contribution of mechanics to the lithiation/delithiation processes. When carried out under galvanostatic conditions, incremental changes in stress lead to instantaneous change in the electrode potential. Experimental results from uniaxial tensile tests show that an applied strain of 0.3%, resulting in changes in stress in silicon of ~ 200-300 MPa, induces a potential variation on the order of 2.5 mV. Stress-induced changes in the potential are measured for the biphasic first lithiation, as well as subsequent monophasic lithiation and delithiation sequences at different states of charge. These results are discussed within the context of continuum thermodynamic theories of the coupling between transport of chemical species and mechanical stress.[1] A. F. Bower, E. Chason, P. R. Guduru, B. W. Sheldon, Acta Mater. 98 (2015) 229-241.[2] A. F. Bower, P. R. Guduru, E. Chason, Int. J. Solids Struct. 69 (2015) 328-342.[3] V. A. Sethuraman, V. Srinivasan, A. F. Bower, P. R. Guduru, J. Electrochem. Soc. 157 (2010) A1253.