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

Customization of Manganese Oxide Cathodes via Precise Electrochemical Lithium-Ion Intercalation for Diverse Zinc-Ion Batteries

Manganese oxide-based aqueous zinc-ion batteries (ZIBs) are attractive energy storage devices, owing to their good safety, low cost, and ecofriendly features. However, various critical issues, including poor conductivity, sluggish reaction kinetics, and unstable structure still restrict their further development. Oxygen defect engineering is an effective strategy to improve the electrochemical performance of manganese oxides, but challenging in the accurate regulation of oxygen defects. In this work, an effective and controllable defect engineering strategy-controllable electrochemical lithium-ion intercalation - is proposed to tackle this issue. The incorporation of lithium ions and oxygen defects can promote the conductivity, lattice spacing, and structural stability of Mn2O3 (MO), thus improving its capacity (232.7 mAh g-1), rate performance, and long-term cycling stability (99.0% capacity retention after 3000 cycles). Interestingly, the optimal ratio of intercalated lithium-ion varies at different temperature or mass-loading of MO, which provides the possibility to customize diverse ZIBs to meet different application conditions. In addition, the fabricated ZIBs present good flexibility, superior safety, and admirable adaptability under extreme temperatures (-20-100 °C). This work provides an inspiration on the structural customization of metal oxide nanomaterials for diverse ZIBs, and sheds light on the construction of future portable electronics.

Vanadium pentoxide interfacial layer enables high performance all-solid-state thin film batteries

Lithium cobalt oxide (LiCoO2) is considered as one of the promising building blocks that can be used to fabricate all-solid-state thin film batteries (TFBs) because of its easy accessibility, high working voltage, and high energy density. However, the slow interfacial dynamics between LiCoO2 and LiPON in these TFBs results in undesirable side reactions and severe degradation of cycling and rate performance. Herein, amorphous vanadium pentoxide (V2O5) film was employed as the interfacial layer of a cathode-electrolyte solid-solid interface to fabricate all-solid-state TFBs using a magnetron sputtering method. The V2O5 thin film layer assisted in the construction of an ion transport network at the cathode/electrolyte interface, thus reducing the electrochemical redox polarization potential. The V2O5 interfacial layer also effectively suppressed the side reactions between LiCoO2 and LiPON. In addition, the interfacial resistance of TFBs was significantly decreased by optimizing the thickness of the interfacial modification layer. Compared to TFBs without the V2O5 layer, TFBs based on LiCoO2/V2O5/LiPON/Li with a 5 nm thin V2O5 interface modification layer exhibited a much smaller charge transfer impedance (Rct) value, significantly improved discharge specific capacity, and superior cycling and rate performance. The discharge capacity remained at 75.6% of its initial value after 1000 cycles at a current density of 100 μA cm-2. This was mainly attributed to the enhanced lithium ion transport kinetics and the suppression of severe side reactions at the cathode-electrolyte interface in TFBs based on LiCoO2/V2O5/LiPON/Li with a 5 nm V2O5 thin layer.

Boosting the Energy Density of Bowl-Like MnO2@Carbon Through Lithium-Intercalation in a High-Voltage Asymmetric Supercapacitor with "Water-In-Salt" Electrolyte

Highly concentrated "'water-in-salt"' (WIS) electrolytes are promising for high-performance energy storage devices due to their wide electrochemical stability window. However, the energy storage mechanism of MnO2 in WIS electrolytes-based supercapacitors remains unclear. Herein, MnO2 nanoflowers are successfully grown on mesoporous bowl-like carbon (MBC) particles to generate MnO2/MBC composites, which not only increase electroactive sites and inhibit the pulverization of MnO2 particles during the fast charging/discharging processes, but also facilitate the electron transfer and ion diffusion within the whole electrode, resulting in significant enhancement of the electrochemical performance. An asymmetric supercapacitor, assembled with MnO2/MBC and activated carbon (AC) and using 21 m LiTFSI solution as the WIS electrolyte, delivers an ultrahigh energy density of 70.2 Wh kg-1 at 700 W kg-1, and still retains 24.8 Wh kg-1 when the power density is increased to 28 kW kg-1. The ex situ XRD, Raman, and XPS measurements reveal that a reversible reaction of MnO2 + xLi+ + xe-↔LixMnO2 takes place during charging and discharging. Therefore, the asymmetric MnO2/MBC//AC supercapacitor with LiTFSI electrolyte is actually a lithium-ion hybrid supercapacitor, which can greatly boost the energy density of the assembled device and expand the voltage window.

Investigation on the mechanical integrity of a PEO-based polymer electrolyte in all-solid-state lithium batteries

Polyethylene oxide (PEO)-based solid polymer electrolytes (SPEs) have good ionic conductivity and flexibility, and is a key component of all-solid-state lithium batteries (ASSLBs). Therefore, the mechanical integrity of PEO-based SPEs during cell operation needs to be urgently evaluated. Here, we conducted a series of tensile and shear adhesion performance tests on PEO16-LiTFSI electrolyte and LiFePO4 electrode adhesion samples at various temperatures and quenching rates. Based on the interface performance data and the elastic-viscoplastic material model of the PEO-LiTFSI electrolyte, a comprehensive electrochemical-mechanical model was established to analyze the stress in the cell and evaluate the mechanical integrity of the PEO16-LiTFSI electrolyte and SPE/cathode interface. The experimental results show that the adhesion strength of the SPE and cathode decreases significantly with increasing operating temperature and quenching rate. The simulation study indicates that the mechanical properties of the SPE can be fully utilized to a certain extent by increasing the quenching rate. In addition, appropriately increasing the operating temperature helps maintain the mechanical integrity of the SPE during cell operation. However, increasing the quenching rate and operating temperature will reduce the interface bonding properties between the SPE and the cathode, resulting in an increased probability of mechanical failure at the SPE/cathode interface. To suppress this negative effect, a design scheme to maintain the structural integrity of the PEO-based polymer electrolyte is proposed by using the C-rate and the SPE thickness as control parameters, which can assist in engineering design and safe operation of Li/PEO16-LiTFSI/LiFePO4 for ASSLBs.

Highly Efficient Aligned Ion-Conducting Network and Interface Chemistries for Depolarized All-Solid-State Lithium Metal Batteries

Improving the long-term cycling stability and energy density of all-solid-state lithium (Li)-metal batteries (ASSLMBs) at room temperature is a severe challenge because of the notorious solid-solid interfacial contact loss and sluggish ion transport. Solid electrolytes are generally studied as two-dimensional (2D) structures with planar interfaces, showing limited interfacial contact and further resulting in unstable Li/electrolyte and cathode/electrolyte interfaces. Herein, three-dimensional (3D) architecturally designed composite solid electrolytes are developed with independently controlled structural factors using 3D printing processing and post-curing treatment. Multiple-type electrolyte films with vertical-aligned micro-pillar (p-3DSE) and spiral (s-3DSE) structures are rationally designed and developed, which can be employed for both Li metal anode and cathode in terms of accelerating the Li+ transport within electrodes and reinforcing the interfacial adhesion. The printed p-3DSE delivers robust long-term cycle life of up to 2600 cycles and a high critical current density of 1.92 mA cm-2. The optimized electrolyte structure could lead to ASSLMBs with a superior full-cell areal capacity of 2.75 mAh cm-2 (LFP) and 3.92 mAh cm-2 (NCM811). This unique design provides enhancements for both anode and cathode electrodes, thereby alleviating interfacial degradation induced by dendrite growth and contact loss. The approach in this study opens a new design strategy for advanced composite solid polymer electrolytes in ASSLMBs operating under high rates/capacities and room temperature.

Lattice pinning in MoO3 via coherent interface with stabilized Li+ intercalation

Large lattice expansion/contraction with Li+ intercalation/deintercalation of electrode active materials results in severe structural degradation to electrodes and can negatively impact the cycle life of solid-state lithium-based batteries. In case of the layered orthorhombic MoO3 (α-MoO3), its large lattice variation along the b axis during Li+ insertion/extraction induces irreversible phase transition and structural degradation, leading to undesirable cycle life. Herein, we propose a lattice pinning strategy to construct a coherent interface between α-MoO3 and η-Mo4O11 with epitaxial intergrowth structure. Owing to the minimal lattice change of η-Mo4O11 during Li+ insertion/extraction, η-Mo4O11 domains serve as pin centers that can effectively suppress the lattice expansion of α-MoO3, evidenced by the noticeably decreased lattice expansion from about 16% to 2% along the b direction. The designed α-MoO3/η-Mo4O11 intergrown heterostructure enables robust structural stability during cycling (about 81% capacity retention after 3000 cycles at a specific current of 2 A g-1 and 298 ± 2 K) by harnessing the merits of epitaxial stabilization and the pinning effect. Finally, benefiting from the stable positive electrode-solid electrolyte interface, a highly durable and flexible all-solid-state thin-film lithium microbattery is further demonstrated. This work advances the fundamental understanding of the unstable structure evolution for α-MoO3, and may offer a rational strategy to develop highly stable electrode materials for advanced batteries.

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.

All-Solid-State Thin Film Lithium/Lithium-Ion Microbatteries for Powering the Internet of Things

As the world steps into the era of Internet of Things (IoT), numerous miniaturized electronic devices requiring autonomous micropower sources will be connected to the internet. All-solid-state thin-film lithium/lithium-ion microbatteries (TFBs) combining solid-state battery architecture and thin-film manufacturing are regarded as ideal on-chip power sources for IoT-enabled microelectronic devices. However, unlike commercialized lithium-ion batteries, TFBs are still in the immature state, and new advances in materials, manufacturing, and structure are required to improve their performance. In this review, the current status and existing challenges of TFBs for practical application in internet-connected devices for the IoT are discussed. Recent progress in thin-film deposition, electrode and electrolyte materials, interface modification, and 3D architecture design is comprehensively summarized and discussed, with emphasis on state-of-the-art strategies to improve the areal capacity and cycling stability of TFBs. Moreover, to be suitable power sources for IoT devices, the design of next-generation TFBs should consider multiple functionalities, including wide working temperature range, good flexibility, high transparency, and integration with energy-harvesting systems. Perspectives on designing practically accessible TFBs are provided, which may guide the future development of reliable power sources for IoT devices.

Sputter-Deposited Amorphous Li3PO4 Solid Electrolyte Films

This paper reports the thin-film synthesis of Li₃PO₄ solid electrolytes by RF magnetron sputtering. A relatively high ionic conductivity of more than 1 × 10^-6 S cm^-1 is achieved. It is revealed that the crystallization of Li₃PO₄ impedes ionic conduction, and a moderate amount of O₂ addition to Ar suppresses the crystallization and guarantees long-term deposition. Another important finding in this study is that when Li₃PO₄ is deposited on a LiCoO₂ film to construct a thin-film battery, the LiCoO₂ film can be damaged depending on the substrate bias potential relative to the cathode potential propagated through the sputtering plasma. Active control of the bias potential to avoid the damage realizes negligible interface resistance in the thin-film battery.

2D Materials for All-Solid-State Lithium Batteries

Although one of the most mature battery technologies, lithium-ion batteries still have many aspects that have not reached the desired requirements, such as energy density, current density, safety, environmental compatibility, and price. To solve these problems, all-solid-state lithium batteries (ASSLB) based on lithium metal anodes with high energy density and safety have been proposed and become a research hotpot in recent years. Due to the advanced electrochemical properties of 2D materials (2DM), they have been applied to mitigate some of the current problems of ASSLBs, such as high interface impedance and low electrolyte ionic conductivity. In this work, the background and fabrication method of 2DMs are reviewed initially. The improvement strategies of 2DMs are categorized based on their application in the three main components of ASSLBs: The anode, cathode, and electrolyte. Finally, to elucidate the mechanisms of 2DMs in ASSLBs, the role of in situ characterization, synchrotron X-ray techniques, and other advanced characterization are discussed.

Flexible FeVOx porous nanorods on carbon cloth for long-life aqueous energy storage

We report the FeVO_x porous nanorods on carbon cloth as a novel cathode material for flexible aqueous energy storage. It exhibits excellent electrochemical properties and cycling stability in supercapacitors and zinc-ion batteries. Moreover, this work makes significant progress for developing high-performance electrodes and provides a foundation for future research.

Atomic-Level Changes during Electrochemical Cycling of Oriented LiMn2O4 Cathodic Thin Films

Spinel LiMn₂O₄ is an attractive lithium-ion battery cathode material that undergoes a complex series of structural changes during electrochemical cycling that lead to rapid capacity fading, compromising its long-term performance. To gain insights into this behavior, in this report we analyze changes in epitaxial LiMn₂O₄ thin films during the first few charge-discharge cycles with atomic resolution and correlate them with changes in the electrochemical properties. Impedance spectroscopy and scanning transmission electron microscopy are used to show that defect-rich LiMn₂O₄ surfaces contribute greatly to the increased resistivity of the battery after only a single charge. Sequences of {111} stacking faults within the films were also observed upon charging, increasing in number with further cycling. The atomic structures of these stacking faults are reported for the first time, showing that Li deintercalation is accompanied by local oxygen loss and relaxation of Mn atoms onto previously unoccupied sites. The stacking faults have a more compressed structure than the spinel matrix and impede Li-ion migration, which explains the observed increase in thin-film resistivity as the number of cycles increases. These results are used to identify key factors contributing to conductivity degradation and capacity fading in LiMn₂O₄ cathodes, highlighting the need to develop techniques that minimize defect formation in spinel cathodes to improve cycle performance.

Controllable 3D Porous Ni Current Collector Coupled with Surface Phosphorization Enhances Na Storage of Ni3 S2 Nanosheet Arrays

3D porous Ni is fabricated via an easily scalable electroless plating method using a dynamic template formed through in-situ hydrogen bubbles. The pore size in the range of several micrometers is controllable through adjusting the Ni²⁺ depositing rate and hydrogen bubbles releasing rate. The Ni₃ S₂ nanosheet arrays anode is then grown on the unique 3D porous Ni current collector followed by subsequent surface phosphorization. The tremendous interconnected pores and rich voids between the Ni₃ S₂ nanosheet arrays cannot only provide rapid transferring channels for Na⁺ , but also accommodate volumetric changes of the Ni₃ S₂ electrode during cycling, guaranteeing the integrity of the active material. In addition, the surface phosphorized layer enhances the electronic conductivity through providing an electron transport highway along the 3D Ni₃ S₂ , NiP₂ layer, and 3D porous Ni current collector, and simultaneously stabilizes the electrode/electrolyte interphase as a protecting layer. Because of these merits, the phosphorized 3D porous Ni₃ S₂ (3D P-Ni₃ S₂ ) electrode is capable of delivering an ultra-stable capacity of 387.5 mAh g^-1 at 0.1 A g^-1 , and a high capacity retention of 85.3% even at a high current density of 1.6 A g^-1 .

Enhancing Moisture and Electrochemical Stability of the Li5.5PS4.5Cl1.5 Electrolyte by Oxygen Doping

Chlorine-rich argyrodite-type solid electrolyte Li_5.5PS_4.5Cl_1.5 has been a promising choice for solid-state batteries (SSBs) because of its ultrafast Li-ion conduction. However, the poor air/moisture stability and low electrochemical stability with pristine high-voltage cathodes hinder their applications. Herein, O-substituted Li_5.5PS_4.5-xO_xCl_1.5 (x = 0, 0.075, 0.175, and 0.25) solid electrolytes are successfully synthesized. Among them, Li_5.5PS_4.425O_0.075Cl_1.5 delivers high ionic conductivity, improved moisture resistance, and enhanced electrochemical stability in higher voltage windows. SSBs using Li_5.5PS_4.425O_0.075Cl_1.5 show higher capacities and superior cyclability than those using Li_5.5PS_4.5Cl_1.5 combined with a pristine LiNi_0.8Mn_0.1Co_0.1O₂ cathode when operated at a high end-of-charge voltage of 4.5 V (vs Li⁺/Li⁰). Moreover, the batteries exhibit outstanding performance in a wide temperature range. This work provides a strategy to modify the inherent drawbacks of sulfide electrolytes, promoting their practical applications.

Boosting Oxygen Reduction Activity of Manganese Oxide Through Strain Effect Caused By Ion Insertion

Transition-metal oxides with a strain effect have attracted immense interest as cathode materials for fuel cells. However, owing to the introduction of heterostructures, substrates, or a large number of defects during the synthesis of strain-bearing catalysts, not only is the structure-activity relationship complicated but also their performance is mediocre. In this study, a mode of strain introduction is reported. Transition-metal ions with different electronegativities are intercalated into the cryptomelane-type manganese oxide octahedral molecular sieves (OMS-2) structure with K ions as the template, resulting in the octahedral structural distortion of MnO₆ and producing strains of different degrees. Experimental studies reveal that Ni-OMS-2 with a high compressive strain (4.12%) exhibits superior oxygen reduction performance with a half-wave potential (0.825 V vs RHE) greater than those of other reported manganese-based oxides. This result is related to the increase in the covalence of MnO₆ octahedral configuration and shifting down of the e_g band center caused by the higher compression strain. This research avoids the introduction of new chemical bonds in the main structure, weakens the effect of e_g electron filling number, and emphasizes the pure strain effect. This concept can be extended to other transition-metal-oxide catalysts.

Updated Insights into 3D Architecture Electrodes for Micropower Sources

Microbatteries (MBs) and microsupercapacitors (MSCs) are primary on-chip micropower sources that drive autonomous and stand-alone microelectronic devices for implementation of the Internet of Things (IoT). However, the performance of conventional MBs and MSCs is restricted by their 2D thin-film electrode design, and these devices struggle to satisfy the increasing IoT energy demands for high energy density, high power density, and long lifespan. The energy densities of MBs and MSCs can be improved significantly through adoption of a 2D thick-film electrode design; however, their power densities and lifespans deteriorate with increased electrode thickness. In contrast, 3D architecture electrodes offer remarkable opportunities to simultaneously improve MB and MSC energy density, power density, and lifespan. To date, various 3D architecture electrodes have been designed, fabricated, and investigated for MBs and MSCs. This review provides an update on the principal superiorities of 3D architecture electrodes over 2D thick-film electrodes in the context of improved MB and MSC energy density, power density, and lifespan. In addition, the most recent and representative progress in 3D architecture electrode development for MBs and MSCs is highlighted. Finally, present challenges are discussed and key perspectives for future research in this field are outlined.

Response and Implication of NASICON Solid-State Electrolytes to Local Electrical Stimulation: From Surface Engineering to Interfacial Manipulation

The surface feature of solid electrolytes fundamentally governs their own physical properties and significantly affects the interaction with the electrode materials. The evaluation of interfacial contact between the electrolyte and the metallic anode is largely relied on the macroscopic contact angle measurement, which is influenced by the intrinsic wettability and the microstructure of the electrolyte. In this work, the surface chemistry of the solid electrolyte is first regulated via facile thermal treatments. Then, scanning probe microscopy (SPM)-based techniques are comprehensively adopted to study the interaction between the electrolyte and metallic anode at the nanoscale. By manipulating the overpotential applied on the SPM tip, the mobile sodium ions at the subsurface of the solid electrolyte can be extracted toward the surface, and the eventual topography of the products is deliberately correlated with the sodium wettability. In this context, the impact of surface treatment on the sodium wettability of the surface layer is systematically evaluated based on the topographic evolution at the nanoscale. Furthermore, the local electrochemical reaction dynamics is revealed by correlating the surface ionic activity and current-voltage (I-V) curves. This work presents a new methodology to effectively evaluate the sodium wettability of the solid electrolyte, and these findings can provide meaningful implications to the surface engineering of ceramic electrolytes for high-performance solid-state batteries.

Low Temperature Deposition of Highly Cyclable Porous Prussian Blue Cathode for Lithium-Ion Microbattery

Small dimension Li-ion microbatteries are of great interest for embedded microsystems and on-chip electronics. However, the deposition of fully crystallized cathode thin film generally requires high temperature synthesis or annealing, incompatible with microfabrication processes of integrated Si devices. In this work, a low temperature deposition process of a porous Prussian blue-based cathode on Si wafers is reported. The active material is electrodeposited under aqueous conditions using a pulsed deposition protocol on a porous dendritic metallic current collector that ensures good electronic conductivity of the composite. The high voltage cathodes exhibit a huge areal capacity of ≈650 μAh cm^-2 and are able to withstand more than 2000 cycles at 0.25 mA cm^-2 rate. The application of these electrode composites with porous Sn based alloying anodes is also demonstrated for the first time in full cell configuration, with high areal energy of 3.1 J cm^-2 and more than 95% reversible capacity. This outstanding performance can be attributed to uniform deposition of Prussian blue materials on conductive matrix, which maintains electronic conductivity while simultaneously providing mechanical integrity to the electrode. This finding opens new horizons in the monolithic integration of energy storage components compatible with the semiconductor industry for self-powered microsystems.

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.