Making Better Batteries: Following Electrochemistry at the Nano Scale with Electron Microscopy

With the focus in automobile industry to switch from petroleum-based vehicles to all electric vehicles, the increasing demand on harvesting energy from renewable sources for a safer and greener future and the ever-increasing demand of the portable electronics systems, the need for better batteries is eminent. The ultimate aim of battery research is to develop a low cost, light and small battery that can deliver high-capacity and/or high power. Lithium and sodium batteries are the frontrunners in achieving this ultimate battery. A macro battery is composed of thousands of millions of nanoparticles. Thus, to prepare a better battery we must determine the respective effects of electrode nanoparticle size, shape, structure, grain–grain boundary, defects and doping on the battery performance. To do so electrode nanoparticles need to be probed at the nano-scale to find out the correlation between their morphology, structure and chemical properties and their evolution due to the battery charging-discharging with battery performance. In this thesis we have utilized the unique capability of electron microscope to resolve the microstructural and chemical information at the (sub)nanometer scale to probe the electrode nanoparticles for making better batteries.Casimir PhD series, Delft-Leiden 2017-09QN/Zandbergen La

Improving reversible capacities of high-surface lithium insertion materials – the case of amorphous TiO2

Chemisorbed water and solvent molecules and their reactivity with components from the electrolyte in high-surface nano-structured electrodes remains a contributing factor toward capacity diminishment on cycling in lithium ion batteries due to the limit in maximum annealing temperature. Here, we report a marked improvement in the capacity retention of amorphous TiO2 by the choice of preparation solvent, control of annealing temperature, and the presence of surface functional groups. Careful heating of the amorphous TiO2 sample prepared in acetone under vacuum lead to complete removal of all molecular solvent and an improved capacity retention of 220 mAh/g over 50 cycles at a C/10 rate. Amorphous TiO2 when prepared in ethanol and heated under vacuum showed an even better capacity retention of 240 mAh/g. From Fourier transform infra-red spectroscopy and electron energy loss spectroscopy measurements, the improved capacity is attributed to the complete removal of ethanol and the presence of very small fractions of residual functional groups coordinated to oxygen-deficient surface titanium sites. These displace the more reactive chemisorbed hydroxyl groups, limiting reaction with components from the electrolyte and possibly enhancing the integrity of the solid electrolyte interface. The present research provides a facile strategy to improve the capacity retention of nano-structured electrode materials.RST/Radiation, Science and TechnologyApplied Science

Nano-Workbench: A Combined Hollow AFM Cantilever and Robotic Manipulator

To manipulate liquid matter at the nanometer scale, we have developed a robotic assembly equipped with a hollow atomic force microscope (AFM) cantilever that can handle femtolitre volumes of liquid. The assembly consists of four independent robots, each sugar cube sized with four degrees of freedom. All robots are placed on a single platform around the sample forming a nano-workbench (NWB). Each robot can travel the entire platform and has a minimum position resolution of 5 nm both in-plane and out-of-plane. The cantilever chip was glued to the robotic arm. Dispensing was done by the capillarity between the substrate and the cantilever tip, and was monitored visually through a microscope. To evaluate the performance of the NWB, we have performed three experiments: clamping of graphene with epoxy, mixing of femtolitre volume droplets to synthesize gold nanoparticles and accurately dispense electrolyte liquid for a nanobattery.QN/Quantum NanoscienceApplied Science

Accessing the bottleneck in all-solid state batteries, lithium-ion transport over the solid-electrolyte-electrode interface

Solid-state batteries potentially offer increased lithium-ion battery energy density and safety as required for large-scale production of electrical vehicles. One of the key challenges toward high-performance solid-state batteries is the large impedance posed by the electrode-electrolyte interface. However, direct assessment of the lithium-ion transport across realistic electrode-electrolyte interfaces is tedious. Here we report two-dimensional lithium-ion exchange NMR accessing the spontaneous lithium-ion transport, providing insight on the influence of electrode preparation and battery cycling on the lithium-ion transport over the interface between an argyrodite solid-electrolyte and a sulfide electrode. Interfacial conductivity is shown to depend strongly on the preparation method and demonstrated to drop dramatically after a few electrochemical (dis)charge cycles due to both losses in interfacial contact and increased diffusional barriers. The reported exchange NMR facilitates non-invasive and selective measurement of lithium-ion interfacial transport, providing insight that can guide the electrolyte-electrode interface design for future all-solid-state batteries.RST/Fundamental Aspects of Materials and EnergyQN/Zandbergen La

Operando Transmission Electron Microscopy Study of All-Solid-State Battery Interface: Redistribution of Lithium among Interconnected Particles

With operando transmission electron microscopy visualizing the solid-solid electrode-electrolyte interface of silicon active particles and lithium oxide solid electrolyte as a model system, we show that (de)lithiation (battery cycling) does not require all particles to be in direct contact with electrolytes across length scales of a few hundred nanometers. A facile lithium redistribution that occurs between interconnected active particles indicates that lithium does not necessarily become isolated in individual particles due to loss of a direct contact. Our results have implications for the design of all-solid-state battery electrodes with improved capacity retention and cyclability. ©RST/Storage of Electrochemical EnergyApplied SciencesInstrumenten groepRST/Technici Poo

Use of Nano Seed Crystals to Control Peroxide Morphology in a Nonaqueous Li-O₂ Battery

The high theoretical energy density of Li-O2 batteries as required for electrification of transport has pushed Li-O2 research to the forefront. The poor cyclability of this system due to incomplete Li2O2 oxidation is one of the major hurdles to be crossed if it is ever to deliver a high reversible energy density. Here we present the use of nano seed crystallites to control the size and morphology of the Li2O2 crystals. The evolution of the Li2O2 lattice parameters during operando X-ray diffraction demonstrates that the hexagonal NiO nanoparticles added to the activated carbon electrode act as seed crystals for equiaxed growth of Li2O2, which is confirmed by scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM-EDX) elemental maps also showing preferential formation of Li2O2 on the NiO surface. Even small amounts of NiO (∼5 wt %) particles act as preferential sites for Li2O2 nucleation, effectively reducing the average size of the primary Li2O2 crystallites and promoting crystalline growth. This is supported by first principle calculations, which predict a low interfacial energy for the formation of NiO-Li2O2 interfaces. The eventual cell failure appears to be the consequence of electrolyte side reactions, indicating the necessity of more stable electrolytes. The demonstrated control of the Li2O2 crystallite growth by the rational selection of appropriate nano seed crystals appears to be a promising strategy to improve the reversibility of Li-air electrodes.RST/Fundamental Aspects of Materials and EnergyQN/Zandbergen LabChemE/Materials for Energy Conversion & Storag

Revealing the relation between the structure, Li-ion conductivity and solid state battery performance for the argyrodite Li6PS5Br solid electrolyte

Based on its high Li-ion conductivity, argyrodite Li6PS5Br is a promising solid electrolyte for all-solid-state batteries. However, more understanding is required on the relation between the solid electrolyte conductivity and the solid-state battery performance with the argyrodite structure, crystallinity and particle size that depend on the synthesis conditions. In the present study, this relationship is investigated using neutron and X-ray diffraction to determine the detailed structure and impedance as well as 7Li solid state NMR spectroscopy to study the Li-ion kinetics. It is found that depending on the synthesis conditions the distribution of the Br dopant over the crystallographic sites in Li6PS5Br is inhomogeneous, and that this may be responsible for a larger mobile Li-ion fraction at the interface regions in the annealed argyrodite materials. Comparing the bulk and interface properties of the differently prepared Li6PS5Br materials, it is proposed that optimal solid-state battery performance requires a different particle size for the solid electrolyte only region and the solid electrolyte in the cathode mixture. In the electrolyte region, the grain boundary resistance is minimized by annealing the argyrodite Li6PS5Br resulting in relatively large crystallites. In the cathode mixture however, additional particle size reduction of the Li6PS5Br is required to provide abundant Li6PS5Br-Li2S interfaces that reduce the resistance of this rate limiting step in Li-ion transport. Thereby the results give insight in how to improve solidstate battery performance by controlling the solid electrolyte structure.RST/Fundamental Aspects of Materials and EnergyRST/Neutron and Positron Methods in MaterialsQN/Zandbergen La

Facile Synthesis toward the Optimal Structure-Conductivity Characteristics of the Argyrodite Li₆PS₅Cl Solid-State Electrolyte

The high Li-ion conductivity of the argyrodite Li6PS5Cl makes it a promising solid electrolyte candidate for all-solid-state Li-ion batteries. For future application, it is essential to identify facile synthesis procedures and to relate the synthesis conditions to the solid electrolyte material performance. Here, a simple optimized synthesis route is investigated that avoids intensive ball milling by direct annealing of the mixed precursors at 550 °C for 10 h, resulting in argyrodite Li6PS5Cl with a high Li-ion conductivity of up to 4.96 × 10-3 S cm-1 at 26.2 °C. Both the temperature-dependent alternating current impedance conductivities and solid-state NMR spin-lattice relaxation rates demonstrate that the Li6PS5Cl prepared under these conditions results in a higher conductivity and Li-ion mobility compared to materials prepared by the traditional mechanical milling route. The origin of the improved conductivity appears to be a combination of the optimal local Cl structure and its homogeneous distribution in the material. All-solid-state cells consisting of an 80Li2S-20LiI cathode, the optimized Li6PS5Cl electrolyte, and an In anode showed a relatively good electrochemical performance with an initial discharge capacity of 662.6 mAh g-1 when a current density of 0.13 mA cm-2 was used, corresponding to a C-rate of approximately C/20. On direct comparison with a solid-state battery using a solid electrolyte prepared by the mechanical milling route, the battery made with the new material exhibits a higher initial discharge capacity and Coulombic efficiency at a higher current density with better cycling stability. Nevertheless, the cycling stability is limited by the electrolyte stability, which is a major concern for these types of solid-state batteries.RST/Fundamental Aspects of Materials and EnergyRST/Storage of Electrochemical EnergyApplied SciencesRST/Neutron and Positron Methods in Material

Green manufacturing of metallic nanoparticles: A facile and universal approach to scaling up

High-yield and continuous synthesis of ultrapure inorganic nanoparticles (NPs) of well-defined size and composition has invariably been one of the major challenges in nanotechnology. Employing green techniques that avoid the use of poisonous and expensive chemicals has been realized as a necessity for manufacturing NPs on an industrial scale. In this communication, we show that a newly developed high-frequency spark (HFS) quenched by a high-purity gas yields a series of monometallic and bimetallic NPs in large quantities, with well-defined (primary) particle size (sub-10 nm) and chemical composition. The mass production rate is linearly dependent on the operating frequency, and can reach up to 1 g h−1, providing a universal and facile technology for producing multicomponent hybrid NPs. Considering also that the methodology requires neither any specialized machinery, nor any chemical reagents, product purification, or any further waste processing, it provides a green, sustainable and versatile platform for manufacturing key building blocks toward industrial scale production.ChemE/Materials for Energy Conversion & StorageQN/Zandbergen LabAtmospheric Remote Sensin

Accessing lithium−oxygen battery discharge products in their native environments via transmission electron microscopy grid electrode

High-fidelity and facile ex situ transmission electron microscopy (TEM) characterization of lithium−oxygen (Li−O2) batteries is still limited by challenges in preserving the native environment of Li−O2 discharge products. The extreme reactivity and moisture sensitivity of the discharge products means that they are quickly altered during sample retrieval from cycled batteries and transfer for TEM analysis, resulting in loss of original information. We here demonstrate that by using a TEM specimen grid directly in Li−O2 batteries as both support electrode and sample collector overlaid on a standard oxygen diffusion electrode, discharge products that are formed on the grid can be kept pristine.Instrumenten groepRST/Storage of Electrochemical EnergyQN/Zandbergen La