Designing Polymer-in-Salt Electrolyte and Fully Infiltrated 3D Electrode for Integrated Solid-State Lithium Batteries.

Solid-state lithium batteries (SSLBs) are promising owing to enhanced safety and high energy density but plagued by the relatively low ionic conductivity of solid-state electrolytes and large electrolyte-electrode interfacial resistance. Herein, we design a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)-based polymer-in-salt solid electrolyte (PISSE) with high room-temperature ionic conductivity (1.24×10-4  S cm-1 ) and construct a model integrated TiO2 /Li SSLB with 3D fully infiltration of solid electrolyte. With forming aggregated ion clusters, unique ionic channels are generated in the PISSE, providing much faster Li+ transport than common polymer electrolytes. The integrated device achieves maximized interfacial contact and electrochemical and mechanical stability, with performance close to liquid electrolyte. A pouch cell made of 2 SSLB units in series shows high voltage plateau (3.7 V) and volumetric energy density comparable to many commercial thin-film batteries.

Self-Standing 3D Cathodes for All-Solid-State Thin Film Lithium Batteries with Improved Interface Kinetics.

3D all-solid-state thin film batteries (TFBs) are proposed as an attractive power solution for microelectronics. However, the challenge in fabricating self-supported 3D cathodes constrains the progress in developing 3D TFBs. In this work, 3D LiMn2 O4 (LMO) nanowall arrays are directly deposited on conductive substrates by magnetron sputtering via controlling the thin film growth mode. 3D TFBs based on the 3D LMO nanowall arrays and 2D TFBs based on the planar LMO thin films are successfully fabricated using a lithium phosphorous oxynitride (LiPON) electrolyte and Li anode. In comparison, the 3D TFB significantly outperforms the 2D TFB, exhibiting large specific capacity (121 mAh g-1 at 1 C), superior rate capability (83 mAh g-1 at 20 C), and good cycle performance (over 90% capacity retention after 500 cycles). The superior electrochemical performance of the 3D TFB can be attributed to the 3D architecture, which not only greatly increases the cathode/electrolyte interface and shortens the Li+ diffusion length, but also effectively enhances the structural stability. Importantly, the vertically aligned nanowall array architecture of the cathode can significantly mitigate disordered LMO formation at the cathode surface compared to the 2D planar thin film, resulting in a greatly reduced interface resistance and improved rate performance.

PVA-assisted spray deposited porous Li4Ti5O12 thin film as high-rate and long-cycle anode for lithium-ion thin-film batteries.

Spinel Li4Ti5O12 (LTO), a zero-strain material, is a promising anode material for solid-state thin-film lithium-ion batteries (TFB). However, the preparation of high-performance Li4Ti5O12 thin-film electrodes through facile methods remains a significant challenge. Herein, we present a novel approach to prepare a binder- and conductor-free porous Li4Ti5O12 (P-LTO) thin-film. This approach polyvinyl alcohol (PVA)-assisted spray deposition and does not require the use of complex or expensive methods. Adding PVA to the precursor solution effectively prevents thin-film cracking during high-temperature annealing, enhances adhesion, and forms a highly interconnected porous structure. This unique structure shortens the lithium-ion diffusion pathways and facilitates electron transport. Therefore, P-LTO thin film electrodes demonstrate exceptional rate capacity of 104.1 mAh/g at a current density of 100C. In addition, the electrodes exhibit ultra-long cycle stability, retaining 80.9 % capacity after 10,000 cycles at 10C. This work offers a novel approach for the preparation of high-performance thin-film electrodes for TFBs.

Dynamic Electrode-Electrolyte Intermixing in Solid-State Sodium Nano-Batteries.

Nanostructured solid-state batteries (SSBs) are poised to meet the demands of next-generation energy storage technologies by realizing performance competitive to their liquid-based counterparts while simultaneously offering improved safety and expanded form factors. Atomic layer deposition (ALD) is among the tools essential to fabricate nanostructured devices with challenging aspect ratios. Here, we report the fabrication and electrochemical testing of the first nanoscale sodium all-solid-state battery (SSB) using ALD to deposit both the V2O5 cathode and NaPON solid electrolyte followed by evaporation of a thin-film Na metal anode. NaPON exhibits remarkable stability against evaporated Na metal, showing no electrolyte breakdown or significant interphase formation in the voltage range of 0.05-6.0 V vs Na/Na+. Electrochemical analysis of the SSB suggests intermixing of the NaPON/V2O5 layers during fabrication, which we investigate in three ways: in situ spectroscopic ellipsometry, time-resolved X-ray photoelectron spectroscopy (XPS) depth profiling, and cross-sectional cryo-scanning transmission electron microscopy (cryo-STEM) coupled with electron energy loss spectroscopy (EELS). We characterize the interfacial reaction during the ALD NaPON deposition on V2O5 to be twofold: (1) reduction of V2O5 to VO2 and (2) Na+ insertion into VO2 to form NaxVO2. Despite the intermixing of NaPON-V2O5, we demonstrate that NaPON-coated V2O5 electrodes display enhanced electrochemical cycling stability in liquid-electrolyte coin cells through the formation of a stable electrolyte interphase. In all-SSBs, the Na metal evaporation process is found to intensify the intermixing reaction, resulting in the irreversible formation of mixed interphases between discrete battery layers. Despite this graded composition, the SSB can operate for over 100 charge-discharge cycles at room temperature and represents the first demonstration of a functional thin-film solid-state sodium-ion battery.

All-Solid-State Thin-Film Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) system coupled with thin-film solid electrolyte as a novel high-energy micro-battery has enormous potential for complementing embedded energy harvesters to enable the autonomy of the Internet of Things microdevice. However, the volatility in high vacuum and intrinsic sluggish kinetics of S hinder researchers from empirically integrating it into all-solid-state thin-film batteries, leading to inexperience in fabricating all-solid-state thin-film Li-S batteries (TFLSBs). Herein, for the first time, TFLSBs have been successfully constructed by stacking vertical graphene nanosheets-Li2S (VGs-Li2S) composite thin-film cathode, lithium-phosphorous-oxynitride (LiPON) thin-film solid electrolyte, and Li metal anode. Fundamentally eliminating Li-polysulfide shuttle effect and maintaining a stable VGs-Li2S/LiPON interface upon prolonged cycles have been well identified by employing the solid-state Li-S system with an "unlimited Li" reservoir, which exhibits excellent long-term cycling stability with a capacity retention of 81% for 3,000 cycles, and an exceptional high temperature tolerance up to 60 °C. More impressively, VGs-Li2S-based TFLSBs with evaporated-Li thin-film anode also demonstrate outstanding cycling performance over 500 cycles with a high Coulombic efficiency of 99.71%. Collectively, this study presents a new development strategy for secure and high-performance rechargeable all-solid-state thin-film batteries.

A review: Learning from the flight of beetles.

Some Coleoptera (popularly referred to as beetles) can fly at a low Reynolds number with their deployable hind wings, which directly enables a low body weight-a good bioinspiration strategy for miniaturization of micro-air vehicles (MAVs). The hind wing is a significant part of the body and has a folding/unfolding mechanism whose unique function benefits from different structures and materials. This review summarizes the actions, factors, and mechanisms of beetle flight and bioinspired MAVs with deployable wings. The elytron controlled by muscles is the protected part for the folded hind wing and influences flight performance. The resilin, the storage material for elasticity, is located in the folding parts. The hind wings' folding/unfolding mechanism and flight performance can be influenced by vein structures of hollow, solid and wrinkled veins, the hemolymph that flows in hollow veins and its hydraulic mechanism, and various mechanical properties of veins. The action of beetle flight includes flapping flight, hovering, gliding, and landing. The hind wing is passively deformed through force and hemolymph, and the attack angle of the hind wing and the nanomechanics of the veins, muscles and mass body determine the flight performance. Based these factors, bioinspired MAVs with a new deployable wing structure and new materials will be designed to be much more effective and miniaturized. The new fuels and energy supply are significant aspects of MAVs.

Ensemble Design of Electrode-Electrolyte Interfaces: Toward High-Performance Thin-Film All-Solid-State Li-Metal Batteries.

In accordance with the fourth industrial revolution (4IR), thin-film all-solid-state batteries (TF-ASSBs) are being revived as the most promising energy source to power small electronic devices. However, current TF-ASSBs still suffer from the perpetual necessity of high-performance battery components. While every component, a series of a TF solid electrolyte (i.e., lithium phosphorus oxynitride (LiPON)) and electrodes (cathode and Li metal anode), has been considered vital, the lack of understanding of and ability to ameliorate the cathode (or anode)-electrolyte interface (CEI) (or AEI) has impeded the development of TF-ASSBs. In this work, we suggest an ensemble design of TF-ASSBs using LiPON (500 nm), an amorphous TF-V2O5-x cathode with oxygen vacancies (Ovacancy), a thin evaporated Li anode (evp-Li) with a thickness of 1 µm, and an artificial ultrathin Al2O3 layer between evp-Li and LiPON. Well-defined Ovacancy sites, such as O(II)vacancy and O(III)vacancy, in amorphous TF-V2O5-x not only allow isotropic Li+ diffusion at the CEI but also enhance both the ionic and electronic conductivities. For the AEI, we employed protective Al2O3, which was specially sputtered using the facing target sputtering (FTS) method to form a homogeneous layer without damage from plasma. In regard to the contact with evp-Li, interfacial stability, electrochemical impedance, and battery performance, the nanometric Al2O3 layers (1 nm) were optimized at different temperatures (40, 60, and 80 °C). The TF-ASSB cell containing Al2O3 (1 nm) delivers a high specific capacity of 474.01 mAh cm-3 under 60 °C at 2 C for the 400th cycle, and it achieves a long lifespan as well as ultrafast rate capability levels, even at 100 C; these results were comparable to those of TF Li-ion battery cells using a liquid electrolyte. We demonstrated the reaction mechanism at the AEI utilizing time-of-flight secondary ion mass spectrometry (TOF-SIMS) and molecular dynamics (MD) simulations for a better understanding. Our design provides a signpost for future research on the rational structure of TF-LIBs.

Tunnel Intergrowth Lix MnO2 Nanosheet Arrays as 3D Cathode for High-Performance All-Solid-State Thin Film Lithium Microbatteries.

All-solid-state thin film lithium batteries (TFBs) are proposed as the ideal power sources for microelectronic devices. However, the high-temperature (>500 °C) annealing process of cathode films, such as LiCoO2 and LiMn2 O4, restricts the on-chip integration and potential applications of TFBs. Herein, tunnel structured Lix MnO2 nanosheet arrays are fabricated as 3D cathode for TFBs by a facile electrolyte Li+ ion infusion method at very low temperature of 180 °C. Featuring an interesting tunnel intergrowth structure consisting of alternating 1 × 3 and 1 × 2 tunnels, the Lix MnO2 cathode shows high specific capacity with good structural stability between 2.0 and 4.3 V (vs. Li+ /Li). By utilizing the 3D Lix MnO2 cathode, all-solid-state Lix MnO2 /LiPON/Li TFB (3DLMO-TFB) has been successfully constructed with prominent advantages of greatly enriched cathode/electrolyte interface and shortened Li+ diffusion length in the 3D structure. Consequently, the 3DLMO-TFB device exhibits large specific capacity (185 mAh g-1 at 50 mA g-1 ), good rate performance, and excellent cycle performance (81.3% capacity retention after 1000 cycles), outperforming the TFBs using spinel LiMn2 O4 thin film cathodes fabricated at high temperature. Importantly, the low-temperature preparation of high-performance cathode film enables the fabrication of TFBs on various rigid and flexible substrates, which could greatly expand their potential applications in microelectronics.

Hybrid Thin-Film Encapsulation for All-Solid-State Thin-Film Batteries.

All-solid-state thin-film batteries have been actively investigated as a power source for various microdevices. However, insufficient research has been conducted on thin-film encapsulation, which is an essential element of these batteries as solid electrolytes and Li anodes are vulnerable to moisture in the atmosphere. In this study, a hybrid thin-film encapsulation structure of hybrid SiOy/SiNxOy/a-SiNx:H/Parylene is suggested and investigated. The water-vapor transmission rate of hybrid thin-film encapsulation is estimated to be 4.9 × 10-3 g m-2·day-1, a value that is applicable to batteries as well as flexible solar cells, thin-film transistor liquid-crystal display, and E-papers. As a result of hybrid thin-film encapsulation, it is confirmed that the all-solid-state thin-film batteries are stable even after 100 charge/discharge cycles in the air atmosphere for 30 days and present a Coulombic efficiency of 99.8% even after 100 cycles in the air atmosphere. These results demonstrate that the thin-film encapsulation structure of hybrid SiOy/SiNxOy/a-SiNx:H/Parylene can be employed in thin-film batteries while retaining long-term stability.

Atomic Layer Deposition of Sodium Phosphorus Oxynitride: A Conformal Solid-State Sodium-Ion Conductor.

The development of novel materials that are compatible with nanostructured architectures is required to meet the demands of next-generation energy-storage technologies. Atomic layer deposition (ALD) allows for the precise synthesis of new materials that can conformally coat complex 3D structures. In this work, we demonstrate a thermal ALD process for sodium phosphorus oxynitride (NaPON), a thin-film solid-state electrolyte (SSE), for sodium-ion batteries (SIBs). NaPON is analogous to the commonly used lithium phosphorus oxynitride SSE in lithium-ion batteries. The ALD process produces a conformal film with a stoichiometry of Na4PO3N, corresponding to a sodium polyphosphazene structure. The electrochemical properties of NaPON are characterized to evaluate its potential in SIBs. The NaPON film exhibited a high ionic conductivity of 1.0 × 10-7 S/cm at 25 °C and up to 2.5 × 10-6 S/cm at 80 °C, with an activation energy of 0.53 eV. In addition, the ionic conductivity is comparable and even higher than the ionic conductivities of ALD-fabricated Li+ conductors. This promising result makes NaPON a viable SSE or passivation layer in solid-state SIBs.

Flat Monolayer Graphene Cathodes for Li-Oxygen Microbatteries.

Miniature batteries can accelerate the development of mobile electronics by providing sufficient energy to power small devices. Typical microbatteries commonly use thin-film inorganic electrodes based on Li-ion insertion reaction. However, they rely on the complicated thin-film synthesis method of inorganics containing many elements. Graphene, one atomic layer thick carbon sheet, has diverse physical and chemical properties and is compatible with conventional micron-scale device fabrication. Here, we study the use of chemical vapor deposition (CVD) grown monolayer graphene in a two-dimensional configuration, as a future Li-oxygen microbattery cathode. By maximizing the dissolution of discharge intermediates, we obtain 2610 Ah/ggraphene of capacity corresponding to 20% higher areal cathode energy density and 2.7 times higher cathode specific energy than that can be derived from the same volume or mass of conventional Li-ion battery cathode material. Furthermore, a clear observation on the discharge reaction on composite electrodes and their role in the charging reaction was made, thanks to the two-dimensional monolayer graphene Li-oxygen battery cathode. We demonstrate an easy integration of two-dimensional CVD graphene cathode into microscale devices by simply transferring or coating the target device substrate with flexible graphene layers. The ability to integrate and use monolayer graphene on arbitrary device substrates as well as precise control over a chemical derivation of the carbon interface can have a radical impact on future energy-storage devices.

Nanoscale electrochemical response of lithium-ion cathodes: a combined study using C-AFM and SIMS.

The continuous demand for improved performance in energy storage is driving the evolution of Li-ion battery technology toward emerging battery architectures such as 3D all-solid-state microbatteries (ASB). Being based on solid-state ionic processes in thin films, these new energy storage devices require adequate materials analysis techniques to study ionic and electronic phenomena. This is key to facilitate their commercial introduction. For example, in the case of cathode materials, structural, electrical and chemical information must be probed at the nanoscale and in the same area, to identify the ionic processes occurring inside each individual layer and understand the impact on the entire battery cell. In this work, we pursue this objective by using two well established nanoscale analysis techniques namely conductive atomic force microscopy (C-AFM) and secondary ion mass spectrometry (SIMS). We present a platform to study Li-ion composites with nanometer resolution that allows one to sense a multitude of key characteristics including structural, electrical and chemical information. First, we demonstrate the capability of a biased AFM tip to perform field-induced ionic migration in thin (cathode) films and its diagnosis through the observation of the local resistance change. The latter is ascribed to the internal rearrangement of Li-ions under the effect of a strong and localized electric field. Second, the combination of C-AFM and SIMS is used to correlate electrical conductivity and local chemistry in different cathodes for application in ASB. Finally, a promising starting point towards quantitative electrochemical information starting from C-AFM is indicated.

Ultrafast Dischargeable LiMn2O4 Thin-Film Electrodes with Pseudocapacitive Properties for Microbatteries.

LiMn2O4 (LMO) thin films are deposited on Si-based substrates with Pt current collector via multi-layer pulsed-laser-deposition technique. The LMO thin films feature unique kinetics that yield outstanding electrochemical cycling performance in an aqueous environment. At extremely high current densities of up to 1880 µA cm-2 (≈ 348 C), a reversible capacity of 2.6 µAh cm-2 is reached. Furthermore, the electrochemical cycling remains very stable for over 3500 cycles with a remarkable capacity retention of 99.996% per cycle. We provide evidence of significant nondiffusion-controlled, pseudocapacitive-like storage contribution of the LMO electrode.

Atomic Layer Deposition of MnS: Phase Control and Electrochemical Applications.

Manganese sulfide (MnS) thin films were synthesized via atomic layer deposition (ALD) using gaseous manganese bis(ethylcyclopentadienyl) and hydrogen sulfide as precursors. At deposition temperatures ≤150 °C phase-pure γ-MnS thin films were deposited, while at temperatures >150 °C, a mixed phase consisting of both γ- and α-MnS resulted. In situ quartz crystal microbalance (QCM) studies validate the self-limiting behavior of both ALD half-reactions and, combined with quadrupole mass spectrometry (QMS), allow the derivation of a self-consistent reaction mechanism. Finally, MnS thin films were deposited on copper foil and tested as a Li-ion battery anode. The MnS coin cells showed exceptional cycle stability and near-theoretical capacity.