Use Of Solid Electrolytes Research Articles

Interphase Control for Electrodeposition of Thin Lithium Films for Lithium Metal Batteries

Rechargeable lithium metal batteries including Li-S batteries, need a thin lithium anode with high purity for high energy density and long cycle life. Today, lithium metal is typically produced from Li2CO3. In contrast to the price of Li2CO3, which is often used for benchmarking, pure lithium metal is actually a costly component. In addition, it has quite some CO2 footprint as it needs significant amounts of energy to produce. Lithium foils of few hundred micron thick are produced by lithium extrusion and cold rolling. To limit cost and to increase energy density, maximum only a few tens of microns is. However, due to the soft nature of lithium, foils of few tens of micrometers are very difficult to manufacture at large volumes and too expensive for cost competitive high energy density Li-metal based cells. Hence, the production of thin lithium foils is currently a bottleneck.The electrodeposition of thin lithium films directly on copper current collector foils could be a cost effective and elegant method, where it not for the high reactivity of lithium with the electrolyte solution and the poor control of lithium morphology. Recently, several approaches have been pursued on lithium electrodeposition by stabilizing the lithium metal-electrolyte interface with the use of solid electrolytes and polymer coatings on electrode [1], however a poor quality of solid electrolyte interphase (SEI) and lithium metal deposition remain as a challenge.Among the various solid-state electrolytes, nitrogen doped lithium phosphate glass or LiPON has been evaluated as solid-electrolyte coatings on electrode particles as buffer layer between active material and the bulk electrolyte [2]. Previously, we investigated the stability of 100 nm down to 10 nm LiPON thin-films as artificial solid-electrolyte interphase for lithium plating and stripping on copper current collectors. We demonstrated the reversible plating/stripping of 150 nm lithium layer for over 100 cycles, indicating formation of a uniform lithium metal layer in-between substrate and LiPON layer [3].In the present work, we further investigated the effect of artificial solid electrolyte interphase, such as LiPON and poly(ethylene) glycol (PEG) coatings, on the deposition behavior of lithium to fabricate micro-meter thick lithium layer which is desirable for negative electrode in next-generation battery application. With a thin LiPON (<150 nm) layer, lithium layer uniformly grew up to 1 μm between substrate and LiPON without breaking of LiPON layer. However, the breakage of the thin LiPON layer was observed with further growth of lithium layer leading to dendrite growth. On the other hand, with a thick PEG coating (> 1 μm) dendrite growth was mitigated by increasing the molar mass of PEG from 8000 to 600,000 g/mol. Furthermore, addition of PEG into the carbonate-based electrolyte resulted in a denser lithium film with a thickness of 2-5 μm without dendrites. In the presentation, effect of molar mass, concentration of PEG on growth behavior of lithium will be further discussed.

Research Progress and Application of PEO-Based Solid State Polymer Composite Electrolytes

As a high-efficiency energy storage and conversion device, lithium-ion batteries have high energy density, and have received widespread attention due to their good cycle performance and high reliability. However, currently commercial lithium batteries usually use organic solutions containing various lithium salts as liquid electrolytes. In practical applications, liquid electrolytes have many shortcomings and shortcomings, such as poor chemical stability, flammability, and explosion. Therefore, the liquid electrolyte has a great safety hazard. The use of solid electrolyte ensures the safety of lithium-ion batteries, and has the advantages of high energy density, good cycle performance, long life, and wide electrochemical window, making the battery safer and more durable, with higher energy density and simple battery Structural design. Solid electrolytes mainly include inorganic solid electrolytes and organic polymer solid electrolytes. Although both inorganic solid electrolytes and polymer solid electrolytes have their own advantages, as far as the existing research work is concerned, whether it is an inorganic system or a polymer system, a single-system solid electrolyte can never achieve the full performance of an ideal solid electrolyte. The composite solid electrolyte composed of active or passive inorganic filler and polymer matrix is considered as a promising candidate electrolyte for all-solid-state lithium batteries. Among many polymer systems, PEO-based is considered to be the most ideal polymer substrate. In this review article, we first introduced the structure, properties, and preparation methods of PEO-based polymer electrolytes. Furthermore, the researches related to the modification of PEO-based polymer solid electrolytes in recent years are summarized. The contribution of polymer structural modification and the introduction of additives to the ionic conductivity, electrochemical stability and mechanical properties of PEO-based solid electrolytes is described. Examples of different composite solid electrolyte design concepts were extensively discussed, such as inorganic inert nanoparticles/PEO, oxide/PEO, and sulfide/PEO. Finally, the future development direction of composite solid electrolytes was prospected.

Editors’ Choice—Quantification of the Impact of Chemo-Mechanical Degradation on the Performance and Cycling Stability of NCM-Based Cathodes in Solid-State Li-Ion Batteries

The use of solid electrolytes in lithium batteries promises to increase their power and energy density, but several challenges still need to be overcome. One critical issue is capacity-fading, commonly ascribed to various degradation reactions in the composite cathode. Chemical, electrochemical as well as chemo-mechanical effects are discussed to be the cause, yet no clear understanding of the mechanism of capacity fading is established. In this work, a model is proposed to interpret the low-frequency impedance of the cathode in terms of lithium diffusion within an ensemble of LiNi1−x−y Co x Mn y O2 (NCM) cathode active material particles with different particle sizes. Additionally, an electrochemical technique is developed to determine the electrochemically active mass in the cathode, based on the estimation of the state-of-charge via open circuit potential-relaxation. Tracking the length of lithium diffusion pathways and active mass over 40 charge-discharge cycles demonstrates that the chemo-mechanical evolution in the composite cathode is the major cause for cell capacity fading. Finally, it is shown that single-crystalline NCM is far more robust against chemo-mechanical degradation compared to polycrystalline NCM and can maintain a high cycling stability.

SO2 Gas Sensor Based on LATP Solid Electrolyte

The emission of SO2 mainly comes from the burning of fossil fuels such coal and sulfur-containing oil. Thus, the source of SO2 emission may be contributed from power plants or steel making factories.Exposures to SO2 can harm the human respiratory system and make breathing difficult. People suffered by asthma are sensitive to these effects of SO2. To improve air quality, the concentration of SO2 is typically limited by national and/or regional standards to reduce emissions of SO2. Therefore, the accurate detection of SO2 is important. Electrochemical solid state sensors are known to provide reliable and stable signals based on the use of solid electrolytes. Oxygen sensors based on oxygen-conducting yittria-stabilized zirconia have shown their wide applications. In this study, a solid state SO2 sensor are developed using Li-conducting Li1.3Al0.3Ti1.7(PO4)3 (LATP). Li2SO4 is used as electrode. With the application of adequate voltage, Li2SO4 may be formed at the surface exposed to SO2-containing atmosphere. Thus, the current measured from the sensors is expected to be proportional to the concentration of SO2. The dependence of SO2 concentration, temperature, and electrode microstructure will be analyzed and discussed.

Switching Response of Hydrogen-Terminated-Diamond-Based All-Solid-State Electric-Double-Layer Transistor

INTRODUCTION High-density electronic carrier control using an electric double layer (EDL) at electrolyte/electrode interfaces has been attracting attention for the application in various electronic devices. Specifically, the use of solid electrolyte is advantageous for practical use owing to its high compatibility with other peripheral devices.Recently, we have achieved an in situ modulation of hole density in hydrogen-terminated diamond (H-terminated diamond) using an all-solid-state electric double layer transistor (EDLT) [1]. The hole density increased from 1010 cm-2 to 1013 cm-2, a 3-order-of-magnitude difference, applying a negative gate voltage (V G). This indicates that the two-dimensional hole gas was electrostatically modulated by EDL charging at the solid electrolyte/H-terminated diamond interface. Then, we focus on a switching response speed, which is an important parameter for EDLTs. Towards further development of all-solid-state EDLTs for practical use, high switching response is desired. Because diamond is suitable for high-frequency electronic device owing to its high carrier mobility, diamond-based all-solid-state EDLT is a candidate to exceed the response speed of conventional all-solid-state EDLTs EXPERIMENTAL An H-terminated diamond thin film was homoepitaxially grown on the surface of an Ib-type HPHT diamond single crystal (100) using microwave plasma chemical vapor deposition. The channel area was fabricated by photolithography, and O2 plasma ashing. Source and drain electrodes were made of Pt/Pd. Gate electrode was made of LiCoO2 (LCO) and Pt films. We chose a Li+ conducting Li2O-ZrO2-SiO2 (LZSO) amorphous thin film as a solid-state-electrolyte. To compare response speed, we also fabricated EDLT with the same structure except for the gate electrode. The gate electrode of another EDLT was made of Au. Electrochemical measurements were performed using a Keithley 4200-SCS parameter analyzer and an atmosphere/temperature tunable prober system (Nagase). RESULTS AND DISCUSSION Figure 1 shows the switching characteristics of EDLTs measured at the drain voltage of 0.5 V. The measurements were performed in steps of 2 K. When a pulse (V G) is applied, drain current (i D) instantaneously decreases from the 10 microampere order to less than 10 nanoampere order. Thus, EDLTs are switched from an on-state to off-state. As explained in the introduction, this is attributed to the effect of EDL charging at the LZSO solid electrolyte/H-terminated diamond interface. In both EDLTs, the response time is shorter than 50 ms at 298 K. Because the speed is not affected even when the type of the gate electrode was changed, the effect of EDL charge and discharge at the LZSO/LCO interface can be ignored. Therefore, this response speed mainly resulted from EDL charge and discharge processes at the LZSO/H-terminated diamond interface. The response speed becomes faster with an increase in the temperature. This is attributed to an increase in the Li+ conductivity of LZSO. The conductivity of LZSO exhibited a thermally activated behavior with an activation energy of 0.66 eV; the conductivity of LZSO increased from 8×10-9 S/cm at 298 K to 2×10-7 S/cm at 340 K. Although the conductivity of the H-terminated diamond channel changed with an increase in the temperature, the variation was about 25%, which is sufficiently small compared to the variation in that of LZSO. Therefore, the rate of the response speed in EDLTs is determined by the conductivity of LZSO. At 340 K (Li+ conductivity: 2×10-7 S/cm), EDLTs show the response time of less than 800 μs. Thus, H-terminated diamond-based all-solid-state EDLT has a potential for ultrafast switching even at room temperature if an electrolyte with better conductivity is used. Since RbAg4I5 Ag+ superionic conductor (0.12 S/cm at RT [2]) was previously reported as an electrolyte for EDL capacitors [3], RbAg4I5 is a good candidate for ultrafast EDLTs, of which the response speed is expected to exceed 1 GHz.In the presentation, we will show the switching characteristics for H-terminated diamond-based all-solid-state EDLTs using various solid electrolytes. Acknowledgements This work was in part supported by JSPS KAKENHI Grant Number JP20H05816 (Grant-in-Aid for Scientific Research on Innovative Areas “Interface Ionics”), JP19K05279 and JP19J22244 (Grant-in-Aid for JSPS Fellows). REFERENCES [1] T. Tsuchiya, M. Takayanagi, M. Imura, Y. koide, T. Higuchi, and K. Terabe, Abstr. 22nd Intl. Conf. on Solid State Ionics, 2019, P-TUE-108.[2] J.N. Bradley and P.D. Greene, Trans. Faraday Soc., 63 (1967) 424.[3] J. E. Oxley, Proc. Power Sources Symp., 24, 20 (1970)Fig. 1. Switching characteristics of H-terminated diamond-based all-solid-state EDLTs in the temperature range of 298-340 K. The gate electrodes are (a) Pt/LCO and (b) Au. Figure 1

Insight into Electrical and Dielectric Relaxation of Doped Tellurite Lithium-Silicate Glasses with Regard to Ionic Charge Carrier Number Density Estimation.

We investigate the role of tellurite on a lithium-silicate glass 0.1 TeO2 − 0.9 (Li2O-2SiO2) (LSTO) system proposed for the use in solid electrolyte for lithium ion batteries. The measurements of electrical impedance are performed in the frequency 100 Hz–30 MHz and temperature from 50 to 150 °C. The electrical conductivity of LSTO glass increases compared with that of Li2O-2SiO2 (LSO) glass due to an increase in the number of Li+ ions. The ionic hopping and relaxation processes in disordered solids are generally explained using Cole–Cole, power law and modulus representations. The power law conductivity analysis, which is driven by the modified Rayleigh equation, presents the estimation of the number of ionic charge carriers explicitly. The estimation counts for direct contribution of about a 14% increase in direct current conductivity in the case of TeO2 doping. The relaxation process by modulus analysis confirms that the cations are trapped strongly in the potential wells. Both the direct current and alternating current activation energies (0.62–0.67 eV) for conduction in the LSO glass are the same as those in the LSTO glass.

Polymer‐Clay Nanocomposite Solid‐State Electrolyte with Selective Cation Transport Boosting and Retarded Lithium Dendrite Formation

AbstractCommercialized lithium‐ion batteries (LIBs) with a liquid electrolyte have a high potential for combustion or explosion. The use of solid electrolytes in LIBs is a promising way to overcome the drawbacks of conventional liquid electrolyte‐based systems, but they generally have a lower ionic conductivity and lithium ion mobility. Here, a UV‐crosslinked composite polymer‐clay electrolyte (U‐CPCE) that is composed of a durable semi‐interpenetrating polymer network (semi‐IPN) ion transportive matrix (ETPTA/PVdF‐HFP) and 2D ultrathin clay nanosheets that are fabricated by a one‐step in situ UV curing method, are reported. The U‐CPCE exhibits robust and flexible properties with an ionic conductivity of more than 10−3 S cm−1 at room temperature with the help of exfoliated clay nanosheets. As a result, the U‐CPCE‐based LIBs show an initial discharge capacity of 152 mAh g−1 (at 0.2 C for a LiCoO2 half‐cell), which is comparable to that of conventional liquid electrolyte‐based cells. In addition, they show excellent cycling performance (96% capacity retention after 200 cycles at 0.5 C) due to a significantly enhanced Li+ transference number (tLi+ = 0.78) and inhibition of lithium dendrite formation on the lithium metal surface. Furthermore, a molecular dynamics (MD) study is conducted to elucidate the mechanism of improving ionic conductivity. The U‐CPCE design can offer opportunities for future all‐solid‐state Li‐ion batteries.

Electrochemically Enhancing Nanostructured Fe-Oxide/Co3O4 for the Reverse Water Gas Shift Reaction

The abundant amount of CO2 in the atmosphere is a valuable resource that when managed correctly can replace energy from the fossil fuel industry and provide a carbon-neutral solution that will reduce the impacts of the climate and ecological crisis[1]. This is achieved by reducing CO2 with hydrogen (H2) through the reverse water gas shift (RWGS) reaction to produced carbon monoxide (CO). CO then acts as a source molecule in the Fischer-Tropsch synthesis to manufacture hydrocarbon fuels. Due to the high stability of the CO2 molecule, significant thermal energy is required to undertake the reaction. Iron-oxide (FeOx) has been shown to be an active and thermally stable catalysts towards the RWGS reaction. FeOx (iron-oxide) nanowires are fabricated through the polyol reduction method and have been characterized through scanning transmission electron microscopy (STEM) analysis[2]. Following the wet deposition method, the Fe nanowires are finely dispersed on cobalt-oxide (Co3O4) to act as a support and semi-conductor. The dispersion of Fe on Co3O4 enhances the electronic properties of the catalyst through the metal-support interaction (MSI) effect[3]. The MSI entails the back spillover of promoting oxygen (Oδ-) ionic species from Co3O4 to FeOx by an increase in temperature, altering the work function of FeOx and allowing to cycle oxygen from the breaking of CO2. Through the Electrochemical Promotion of Catalysis (EPOC) phenomenon the catalytic activity can be enhanced by altering the binding energy of the reactant and intermediate species on the catalytic surface[4]. The MSI and EPOC phenomena have been shown to be functionally equivalent in terms of the change in work function. The difference between them is that in EPOC the movement of ions can be controlled through the application of an electrical current or potential difference, while the MSI effect is controlled by a thermal input. EPOC entails the use of solid electrolytes, for instance yttria-stabilized zirconia (YSZ) and barium zirconate yttrium-doped (BZY) which are oxygen and proton conductors, respectively. The catalyst-working electrodes (i.e. FeOx nanowires) are deposited on one side of the electrolyte and on the opposite side, inert gold counter and reference electrodes. Through the application of a potential difference between the electrodes, promoting species migrate through the three-phase (solid-gas-catalyst) boundary in order to interact with the exposed-catalyst surface. In the case of BZY, when a potential difference is applied between the counter and working electrode, H+ are removed from the surface through the three-phase boundary (tpb) towards BZY, referred to as positive polarization. When the polarization is reversed from the working to counter electrode, H+ migrate from BZY through the tpb towards the catalytic surface. Utilizing YSZ, results in the opposite migration with O2- ions. Regardless of the type of solid electrolyte used the catalyst is oxidized under positive polarization and reduced under negative polarization. The use of the Co3O4 semiconductor allows to combine both the MSI and EPOC effect at 350°C, by finely dispersing the Fe nanowires on Co3O4 to expose active sites and lowering the rate of sintering while being conductive to close the circuit[5]. As opposed to using other supports that do not display fully conductive properties, this approach provides an electronic path for the promoters to follow. Results have shown the working-catalyst FeOx/Co3O4 on YSZ and BZY to be highly selective to CO formation under oxidizing (3CO2:H2) and reducing (CO2:7H2) conditions, with a superior activity experienced under rich reducing conditions. Furthermore, alteration in work function from the EPOC effect, has led to a promotional response for both YSZ and BZY. Combining the MSI and EPOC effect allows for high RWGS activity, establishing a promising solution in utilizing CO2 as a resource while using transition metals. Additionally, the EPOC effect will be elucidated through Fourier-Transform Infrared (FTIR) spectroscopy to provide insight on the promoting mechanism occurring during polarization. 1. Porosoff, M. D., Yan, B. & Chen, J. G. Catalytic reduction of CO2 by H2 for synthesis of CO, methanol and hydrocarbons: challenges and opportunities. Energy Environ. Sci. 2, 303 (2015).1. Baranova, E. A., Bock, C., Ilin, D., Wang, D. & MacDougall, B. Infrared spectroscopy on size-controlled synthesized Pt-based nano-catalysts. Surf. Sci. 600, 3502–3511 (2006).2. Panaritis, C., Edake, M., Couillard, M., Einakchi, R. & Baranova, E. A. Insight towards the role of ceria-based supports for reverse water gas shift reaction over RuFe nanoparticles. J. CO2 Util. 26, 350–358 (2018).3. Vayenas, C. G., Bebelis, S., Pliangos, C., Brosda, S. & Tsiplakides, D. Electrochemical Activation of Catalysis. (Springer US, 2001).4. Zagoraios, D. et al. Electrochemical promotion of methane oxidation over nanodispersed Pd/Co3O4 catalysts. Catal. Today (2019). doi:10.1016/j.cattod.2019.02.030

Evaluation of Porous Ni(Zn) Materials As 3D Matrices for Li Metal Electrodes

Due to its very high theoretical capacity (3861 mAh g-1 or 2062 mAh cm-3) and low redox potential (-3.04 V vs standard hydrogen electrode), lithium metal is one of the most attractive anode materials for batteries. However, its use in rechargeable batteries such as Li-S and Li-air batteries is problematic due to the uncontrolled formation of lithium dendrites during charge/discharge cycling, which can induce cell short circuit, aggravated adverse reactions, dead Li formation, polarization increase and large volume changes, resulting in safety concerns and low coulombic efficiencies. Various strategies have been evaluated to prevent the growth of Li dendrites such as: (i) electrolyte engineering for modifying the physicochemical properties of the solid electrolyte interphase and better regulating the current distribution during Li deposition; (ii) interface engineering by covering the Li surface with a protective coating before cycling; (iii) use of solid electrolyte or reinforced separator to mechanically block Li dendrite propagation and (iv) development of 3D substrates inducing a more uniform Li-ion flux in addition to act as stable hosts that guide Li plating and minimize the electrode volume variation upon cycling [1-3].According to this latter strategy, the present study is focused on porous Ni and Ni-Zn electrodes elaborated by the dynamic hydrogen bubble template (DHBT) method [4]. The Li wettability of these electrodes as a function of their porosity and composition will be presented. Their ability to better control lithium dendritic growth will be discussed on the basis of cycling experiments in Li/S batteries, electrochemical dilatometry experiments and operando optical microscopy analyses. References [ 1 ] X.B. Cheng, R. Zhang, C.Z. Zhao, Q. Zhang, Toward safe lithium metal anode in rechargeable batteries: a review, Chem. Rev 117 (2017) 10403-10473. [ 2 ]X.B. Cheng, J.Q. Huang, Q. Zhang, Review-Li metal anode in working lithium-sulfur batteries, J. Electrochem. Soc. 165 (2018) A6058-A6071. [ 3 ] D. Lin, Y. Liu, Y. Cui, Reviving the lithium metal anode for high-energy batteries, Nat. Nanotechnol. 12 (2017) 194-206. [ 4 ] M. Hao, V. Charbonneau, N. N. Fomena, J. Gaudet, D. R. Bruce, S. Garbarino, D. A. Harrington, D. Guay, . Hydrogen Bubble Templating of Fractal Ni Catalysts for Water Oxidation in Alkaline Media. ACS Appl. Energy Mater. 2 (2019) 5734-5743.

The Role of Interlayer Chemistry in Li‐Metal Growth through a Garnet‐Type Solid Electrolyte

AbstractSecuring the chemical and physical stabilities of electrode/solid‐electrolyte interfaces is crucial for the use of solid electrolytes in all‐solid‐state batteries. Directly probing these interfaces during electrochemical reactions would significantly enrich the mechanistic understanding and inspire potential solutions for their regulation. Herein, the electrochemistry of the lithium/Li7La3Zr2O12‐electrolyte interface is elucidated by probing lithium deposition through the electrolyte in an anode‐free solid‐state battery in real time. Lithium plating is strongly affected by the geometry of the garnet‐type Li7La3Zr2O12 (LLZO) surface, where nonuniform/filamentary growth is triggered particularly at morphological defects. More importantly, lithium‐growth behavior significantly changes when the LLZO surface is modified with an artificial interlayer to produce regulated lithium depositions. It is shown that lithium‐growth kinetics critically depend on the nature of the interlayer species, leading to distinct lithium‐deposition morphologies. Subsequently, the dynamic role of the interlayer in battery operation is discussed as a buffer and seed layer for lithium redistribution and precipitation, respectively, in tailoring lithium deposition. These findings broaden the understanding of the electrochemical lithium‐plating process at the solid‐electrolyte/lithium interface, highlight the importance of exploring various interlayers as a new avenue for regulating the lithium‐metal anode, and also offer insight into the nature of lithium growth in anode‐free solid‐state batteries.

Structural and electrochemical features of (Li2S)x(SiS2)100–x superionic glasses

Silicon is easily available and thus its use in solid electrolytes in all-solid-state lithium-ion batteries can reduce the cost of the system. Thus, significant research attention is focused on (Li2S)x(SiS2)100−x glasses as solid electrolytes because they exhibit the highest ionic conductivities among Li ion conducting glasses. However, there is a paucity of details on how Li ions actually travel through an operating device. In the present work, four-probe AC impedance measurements, synchrotron X-ray diffraction experiments, and time-of-flight neutron diffraction experiments were performed using 7Li-enriched (7Li2S)x(SiS2)100−x glasses (x = 40, 50, and 60). We demonstrated the three-dimensional atomic configurations and conduction pathways of Li ions for (7Li2S)x(SiS2)100−x glasses via reverse Monte Carlo (RMC) modeling and bond valence sum (BVS) imaging. Specifically, BVS imaging indicated that the frameworks of the (Li2S)x(SiS2)100−x glasses facilitate high mobility of the conducting Li ions when compared with those of (Li2S)x(GeS2)100−x glasses and (Li2S)x(P2S5)100−x glasses.

Optimization of the Compositions of Solid Electrolytes Cd1 – xRxF2 + x (R = La–Lu, Y) with a Fluorite-Type Structure for Conductivity and Thermal Stability

Optimization of the compositions of Cd1–xRxF2+x nonstoichiometric phases (CaF2 type, R is a rare-earth element) for the ionic conductivity and thermal stability is based on the temperature measurements of the electrical conductivity of single crystals depending on the R3+ ionic radii and RF3 content and on the investigation of phase diagrams of the CdF2–RF3 systems. It is shown that the conductivity of 20 compositions out of 30 studied Cd1–xRxF2+x crystals exceeds the conditional limit σ500K = 10–5 S/cm, below which the use of solid electrolytes in electrochemical devices is believed to be undesirable because of low conductivity. The maximum conductivities σ500K = (3.0–3.2) × 10–4 S/cm and σ293K = (1.5–2.3) × 10–8 S/cm are observed for solid electrolytes with R = Ho, Er, Tm, or Yb and x = 0.22–0.27.

A Facile and Scalable Processing Method for 3-D Nanostructured Copper Current Collectors to Enable High Energy Li-Metal Batteries

Lithium metal is a promising anode for high-energy-density batteries owing to its high theoretical capacity and highly negative electrochemical potential. However, its commercial application is stalled by the undesired dendritic growth of lithium during cycling.[1]Among all kinds of promising approaches (e.g. electrolyte engineering, interfacial engineering, use of solid electrolyte and use of 3-D structured current collectors, etc. ) [2], 3-D structured current collectors represent some new promises as they can effectively increase Li nucleation sites and reduce local current. However, most of these successes are at lab-scale with coin cells and most of the methods are sophisticated and expensive, not scalable and compatible with the roll-to-roll manufacturing processes of current Li-ion battery industry. Here we report a facile electrodeposition process for low- cost, scalable fabrication of copper current collectors with 3-D architected porous structures composed of interconnected Cu nanoparticles.[3]Compared to flat foil current collectors, the deposited 3-D nanostructured Cu current collector has much larger active surfaces area, thus effectively reduces the actual current density for the same apparent current and lowers the possibility of triggering dendritic growth. During Li plating process, Li can be accommodated in the porous structure and on the top surface of the 3-D nanostructured Cu current collector, which effectively suppresses Li dendrite formation and provides a very high practical Li storage areal capacity. The nanoporous electrodeposition coated Cu foil can be produced with very low cost and this foil can be seamlessly incorporated into current Li-ion battery production with no major modifications required. The electrodeposition method also provides great flexibility and tunability of the deposited structure, which suggests more Li may be accommodated and ultrahigh energy density batteries may be developed along this promising approach. Harry, K.J., et al., Detection of subsurface structures underneath dendrites formed on cycled lithium metal electrodes.Nat. Mater., 2014. 13(1): p. 69-73. Lin, D., Y. Liu, and Y. Cui, Reviving the lithium metal anode for high-energy batteries.Nat. Nanotechnol, 2017. 12(3): p. 194-206. Ma, X., Z. Liu, and H. Chen, Facile and scalable electrodeposition of copper current collectors for high-performance Li-metal batteries.Nano Energy, 2019. 59: p. 500-507.

Understanding the Effect of Interlayer on the Performance of All-Solid-State Li2s Batteries

Li−S batteries are considered a promising technology for next generation batteries, due to their high energy density and low cost of sulfur. The traditional liquid Li−S batteries, however, suffer from severe capacity fading and low Coulombic efficiency owing to processes occurring at the sulfur cathode. The electrochemical conversion reaction between S8 and Li2S involves a phase change where soluble lithium polysulfide intermediates are produced, causing so-called polysulfide shuttle phenomena. In order to mitigate the issues related to polysulfides, various approaches such as physical confinement of polysulfides or fabricating protective layer on Li anode were employed. However, the shuttle reaction still remains, affecting the cycling performance of the battery. One promising approach to proceed the Li−S battery chemistry without producing polysulfide intermediates is to utilize non-solvating electrolyte such as inorganic solid electrolytes (SE). The use of solid electrolyte eliminates the possibility of polysulfide dissolution, improving the energy efficiency of Li−S batteries. In addition, sulfide solid electrolyte such as Li7P­3S­11­ exhibits an ionic conductivity of ~10-3 S cm-1 comparable to that of the conventional 1 M ethereal electrolytes. Despite these advantages, the performance of all-solid-state Li−S battery (ASSLSB) incorporating inorganic solid electrolyte is much worse than Li−S cells with liquid electrolytes in terms of active material utilization and rate capability. The biggest challenge lies in constructing sufficient Li+ ion transport channel within the composite cathode, since SEs do not infiltrate into cathodes as liquid electrolytes. There have been considerable research efforts to improve the ionic conductivity of the cathode, such as ball-milling S8 (or Li2S), conductive carbon, and SE to prepare the composite cathode. However, only limited improvement was achieved on increasing active material utilization by simply ball-milling the three components. This is likely due to the poor physical contact between SE and cathode active material, leaving the active material electrochemically inactive (Figure 1a). In an effort to improve the interfacial contact and increase the capacity, we report a strategy of using an interlayer between the electrode/electrolyte interfaces (Figure 1b). Our solid-state cell with interlayers exhibits much higher capacity compared to that of bare sample without interlayers, achieving ~80% active material utilization at cycle 60 with dramatically reduced impedance relative to the bare cell. The interlayer in ASSLSB infiltrates into void space in composite cathode creating contact between the active material and SE resulting in high active material utilization. This increased contact leads to smaller cell impedance due to the decreased interfacial resistance. Additionally, the interlayer provides buffer space for volume contraction and expansion during electrochemical cycling, thereby preventing the physical delamination of cathode components. Figure 1

Bipolar All-Solid-State Battery Enabled By a Perovskite-Based Hybrid Solid Electrolyte

The increasing number of fire/explosion incidents related to lithium-ion batteries (LIBs) for mobile devices and electric vehicles (EVs) in the recent years have raised significant concerns regarding their safety and reliability. The use of solid electrolytes provides a technical solution to address the safety issues of lithium-ion batteries and enables a bipolar design of high-voltage and high-energy battery modules. The bipolar design avoids unnecessary components and parts for packaging and electrical connection; therefore, it facilitates an increase in the volumetric energy density of the battery, while enabling easy build-up of total output voltage. Here, we report the design and construction of a multi-layered bipolar ASSB using a hybrid solid electrolyte (HSE) membrane. The HSE membrane proposed in this work consists of inorganic Li0.29La0.57TiO3 (LLTO) perovskite and poly(ethylene oxide) (PEO). The perovskite-structured LLTO was selected as an inorganic solid electrolyte specifically as a result of its high Li+ conductivity, excellent mechanical strength, and high chemical stability against moisture. The hybridization of LLTO with PEO allows for the fabrication of thin and large-area electrolyte membranes with high ionic conductivity, without the need for high-temperature sintering. Moreover, the soft and adhesive PEO improves the interfacial contact between the electrolyte and electrode, resulting therefore in enhanced electrochemical performance of the prepared ASSBs. Although the concept of hybridization between inorganic material (garnet-Li7La3Zr2O12 and NASICON-Li1.5Al0.5Ge1.5(PO4)3) and polymer has been proposed previously, the focus in these earlier studies has been predominantly on optimizing the electrolytes to improve their Li+-conducting and/or mechanical properties and/or demonstrating their applications in the monopolar-type, small-sized ASSB. By contrast, little attention has been given to the design and fabrication of bipolar ASSBs with HSEs, which is essential for demonstrating the feasibility of HSEs in large-scale ASSBs with high voltage and energy. In this study, the HSE membranes based on LLTO and PEO were synthesized in the form of flexible and freestanding sheets with a thickness of ~30 mm using a simple casting method. The optimized HSE membrane exhibits remarkably enhanced Li+ conductivity, electrochemical window, and thermal stability when compared to a solid PEO-only membrane, facilitating reversible charge–discharge operations of ASSBs. Finally, a proof-of-concept bipolar ASSB comprising three unit cells connected in series was designed and constructed using the HSE membrane, and its electrochemical performance was investigated.

On the Way to Elucidate Reaction Mechanisms that Involve Metallic Lithium and Atmospheric Gases Using In Situ Ambient Pressure X-Ray Photoelectron Spectroscopy

Metallic lithium, which would be the ideal anode for Li-ion rechargeable batteries, has not reached yet the commercial stage because of safety issues related to instabilities arising on the Li surface during electrochemical cycling. When metallic lithium is in contact with the electrolyte, a surface layer called SEI (Solid Electrolyte Interface) is formed. In a conventional Li-ion battery with graphite-based anode, the SEI layer is a passivation interface that will help to stabilize the battery. However, when considering Li metal anodes, the SEI is unable to maintain a uniform plating and stripping of Li. During charge/discharge processes the SEI breaks, continuously exposing fresh lithium surface to the electrolyte, leading to an irreversible capacity loss and the formation of dendrites. The latter are nanostructured formations that can grow on the anode surface until reaching the cathode surface and originating the fatal failure of the cell [1]. There are many approaches that aim to improve the stabilization of the Li metal surface. The use of solid electrolytes can inhibit the growth of dendrites while electrolyte additives are used to form a more stable SEI. An alternatively approach is the direct modification of the metallic Li surface to form a designed passivation layer before being in contact with the electrolyte [2]. However, despite all these efforts, the interfacial chemistry of these surfaces and interfaces are currently still not well understood. In order to find a suitable solution for the stabilization of the lithium surface, it is essential to have a full understanding of the nature and characteristics of its high reactivity. For this purpose, one of the preliminary steps is to analyze the effects that atmospheric gases, such as carbon dioxide gas, oxygen gas and water, have on the surface of Li metal. Although there are a lot of studies from the last decades analyzing these interactions using a wide range of tools of both theoretical and experimental methods that propose interesting reaction mechanisms [3], little has been done using in situ experiments. There is still a lack of knowledge in terms of understanding the mechanism behind the reaction of metallic lithium with atmospheric gases. Ambient Pressure X-Ray Photoelectron Spectroscopy (APXPS) is an ideal tool to explore this phenomenon. Being a chemically specific surface sensitive technique, it allows determining which components are present on the first nanometers of the surface of the metal. Furthermore, ambient pressure studies make it possible to follow the reactions in situ. The possibility to perform experiments using a synchrotron based facility will add crucial information about the distribution of the components on the surface by non-destructive deep profiling experiments. APXPS from beamline 9.3.2 at the Advanced Light Source, Lawrence Berkeley National Laboratory (California, United States), fulfill all this criteria. Thanks to the use of soft X-rays (hv < 800 eV), it is an extremely surface sensitive technique that can operate from Ultra High Vacuum (UHV) conditions up to pressure < 1 Torr. Our recent studies done were focused on the effect that carbon dioxide gas, oxygen gas and water vapor produce on the surface of UHV cleaned metallic lithium. We clearly observe two regimens in the growth of the layer for the three gases, a reaction controlled regime and a diffusion controlled regime, in good agreement with recent studies [4]. These two regimens can be observed in the Figure 1 for CO2 gas at 10 mTorr and at 0.1 mTorr. These experiments are supplemented with previous ex-situ studies in conditions using a laboratory based XPS at CIC Energigune research center (Álava, Spain), where the effect of CO2, O2 and N2 gases were studied on a UHV cleaned lithium surface. The various gas exposure conditions created different surface final states of metallic lithium, which will affect the composition of the SEI layer that will influence the stability of the interface between metallic lithium anode and electrolyte. APXPS technique is proving to be an essential tool to bring more insight into the mechanisms that lead to the formation of this specific surface layer. [1] Langa J. et al., Energy Storage Materials 7, 115 (2017) [2] Cheng X.-B et al., Journal of Materials Chemistry A 3, 7207 (2015) [3] Zhuang et al., Surface Science, 418, 139 (1998) [4] Li Y. et al, Nano Letters, 17, 5171 (2017) Figure 1

Toward a Fundamental Understanding of the Lithium Metal Anode in Solid-State Batteries-An Electrochemo-Mechanical Study on the Garnet-Type Solid Electrolyte Li6.25Al0.25La3Zr2O12.

For the development of next-generation lithium batteries, major research effort is made to enable a reversible lithium metal anode by the use of solid electrolytes. However, the fundamentals of the solid-solid interface and especially the processes that take place under current load are still not well characterized. By measuring pressure-dependent electrode kinetics, we explore the electrochemo-mechanical behavior of the lithium metal anode on the garnet electrolyte Li6.25Al0.25La3Zr2O12. Because of the stability against reduction in contact with the lithium metal, this serves as an optimal model system for kinetic studies without electrolyte degradation. We show that the interfacial resistance becomes negligibly small and converges to practically 0 Ω·cm2 at high external pressures of several 100 MPa. To the best of our knowledge, this is the smallest reported interfacial resistance in the literature without the need for any interlayer. We interpret this observation by the concept of constriction resistance and show that the contact geometry in combination with the ionic transport in the solid electrolyte dominates the interfacial contributions for a clean interface in equilibrium. Furthermore, we show that-under anodic operating conditions-the vacancy diffusion limitation in the lithium metal restricts the rate capability of the lithium metal anode because of contact loss caused by vacancy accumulation and the resulting pore formation near the interface. Results of a kinetic model show that the interface remains morphologically stable only when the anodic load does not exceed a critical value of approximately 100 μA·cm-2, which is not high enough for practical cell setups employing a planar geometry. We highlight that future research on lithium metal anodes on solid electrolytes needs to focus on the transport within and the morphological instability of the metal electrode. Overall, the results help to develop a deeper understanding of the lithium metal anode on solid electrolytes, and the major conclusions are not limited to the Li|Li6.25Al0.25La3Zr2O12 interface.

The role of glass crystallization processes in preparation of high Li-conductive NASICON-type ceramics

One of the approaches to tackle the problem of limited electrolyte electrochemical stability, which controls the development of novel electrochemical storage devices, is the use of solid electrolytes.

Multilayered, Bipolar, All-Solid-State Battery Enabled by a Perovskite-Based Biphasic Solid Electrolyte.

The use of solid electrolytes provides a technical solution to address the safety issues of lithium-ion batteries and enables a bipolar design of high-voltage and high-energy battery modules. The bipolar design avoids unnecessary components and parts for packaging and electrical connection; therefore, it facilitates an increase in the volumetric energy density of the battery, while enabling easy build-up of total output voltage. Herein, the design and construction of a multilayered, bipolar-type, all-solid-state battery (ASSB) from a biphasic solid electrolyte (BSE) based on inorganic Li0.29 La0.57 TiO3 perovskite and poly(ethylene oxide) (PEO) are reported. A flexible and freestanding BSE membrane exhibits high Li+ conductivity of about 1.2×10-4 S cm-1 , and shows enhanced electrochemical/thermal stability, in comparison to a PEO-only solid electrolyte. A single-layered ASSB assembled with a BSE shows promising electrochemical performance, as evidenced by a high reversible capacity of about 123 mA h g-1 and excellent cycling stability over 100 cycles. Furthermore, a proof-of-concept bipolar ASSB comprising three unit cells connected in series is constructed by using the BSE membrane and Al/Cu-cladded bipolar plates. The bipolar ASSB shows high thermal stability and operates reversibly without any internal short circuit or current leakage during charge-discharge cycles; this demonstrates that BSEs provide a promising approach to the design and fabrication of bipolar ASSBs with improved safety and high energy density.

Machine Learning Enabled Computational Screening of Inorganic Solid Electrolytes for Suppression of Dendrite Formation in Lithium Metal Anodes.

Next generation batteries based on lithium (Li) metal anodes have been plagued by the dendritic electrodeposition of Li metal on the anode during cycling, resulting in short circuit and capacity loss. Suppression of dendritic growth through the use of solid electrolytes has emerged as one of the most promising strategies for enabling the use of Li metal anodes. We perform a computational screening of over 12 000 inorganic solids based on their ability to suppress dendrite initiation in contact with Li metal anode. Properties for mechanically isotropic and anisotropic interfaces that can be used in stability criteria for determining the propensity of dendrite initiation are usually obtained from computationally expensive first-principles methods. In order to obtain a large data set for screening, we use machine-learning models to predict the mechanical properties of several new solid electrolytes. The machine-learning models are trained on purely structural features of the material, which do not require any first-principles calculations. We train a graph convolutional neural network on the shear and bulk moduli because of the availability of a large training data set with low noise due to low uncertainty in their first-principles-calculated values. We use gradient boosting regressor and kernel ridge regression to train the elastic constants, where the choice of the model depends on the size of the training data and the noise that it can handle. The material stiffness is found to increase with an increase in mass density and ratio of Li and sublattice bond ionicity, and decrease with increase in volume per atom and sublattice electronegativity. Cross-validation/test performance suggests our models generalize well. We predict over 20 mechanically anisotropic interfaces between Li metal and four solid electrolytes which can be used to suppress dendrite growth. Our screened candidates are generally soft and highly anisotropic, and present opportunities for simultaneously obtaining dendrite suppression and high ionic conductivity in solid electrolytes.