Enhanced Cycling Stability of All-Solid-State Lithium-Sulfur Battery through Nonconductive Polar Hosts.

All-solid-state lithium-sulfur batteries (ASSLSBs) are promising next-generation battery technologies with a high energy density and excellent safety. Because of the insulating nature of sulfur/Li2S, conventional cathode designs focus on developing porous hosts with high electronic conductivities such as porous carbon. However, carbon hosts boost the decomposition of sulfide electrolytes and suffer from sulfur detachment due to their weak bonding with sulfur/Li2S, resulting in capacity decays. Herein, we propose a counterintuitive design concept of host materials in which nonconductive polar mesoporous hosts can enhance the cycling life of ASSLSBs through mitigating the decomposition of adjacent electrolytes and bonding sulfur/Li2S steadily to avoid detachment. By using a mesoporous SiO2 host filled with 70 wt % sulfur as the cathode, we demonstrate steady cycling in ASSLSBs with a capacity reversibility of 95.1% in the initial cycle and a discharge capacity of 1446 mAh/g after 500 cycles at C/5 based on the mass of sulfur.

Stable Photoelectrochemical Reactions at Solid/Solid Interfaces toward Solar Energy Conversion and Storage.

Electrochemistry has extended from reactions at solid/liquid interfaces to those at solid/solid interfaces. However, photoelectrochemistry at solid/solid interfaces has been hardly reported. In this study, we achieve a stable photoelectrochemical reaction at the semiconductor-electrode/solid-electrolyte interface in a Nb-doped anatase-TiO2 (a-TiO2:Nb)/Li3PO4 (LPO)/Li all-solid-state cell. The oxidative currents of a-TiO2:Nb/LPO/Li increase upon light irradiation when a-TiO2:Nb is located at a potential that is more positive than its flat-band potential. This is because the photoexcited electrons migrate to the current collector due to the bending of the conduction band minimum toward the negative potential. The photoelectrochemical reaction at the semiconductor/solid-electrolyte interface is driven by the same principle as those at semiconductor/liquid-electrolyte interfaces. Moreover, oxidation under light irradiation exhibits reversibility with reduction in the dark. Thus, we extend photoelectrochemistry to all-solid-state systems composed of solid/solid interfaces. This extension would enable us to investigate photoelectrochemical phenomena uncleared at solid/liquid interfaces because of low stability and durability.

In Situ Formation of Stable Dual-Layer Solid Electrolyte Interphase for Enhanced Stability and Cycle Life in All-Solid-State Lithium Metal Batteries.

All-solid-state lithium metal batteries have emerged as a promising solution to overcoming the energy density and safety challenges associated with conventional lithium-ion batteries. Solid polymer electrolytes, particularly those based on poly(vinylidene fluoride) (PVDF) and dimethylformamide (DMF), demonstrate significant potential. However, interfacial side reactions between residual DMF solvents and lithium metal present substantial challenges. In this study, we investigate the in situ formation of solid electrolyte interphase protective layers to mitigate these side reactions. By incorporating F-rich additives, such as fluoroethylene carbonate and lithium difluorophosphate, we successfully establish a dual-layer inorganic SEI structure characterized by an outer LiF layer and an inner Li2O layer. Consequently, our approach extends the cycle life of lithium symmetric batteries to 3000 h. Additionally, the Li||LiFePO4 solid-state battery demonstrates exceptional stability, enduring 400 cycles at a 1C rate with an impressive capacity retention of 84%. This strategic methodology effectively leverages the benefits of residual solvents, ensuring both enhanced battery efficiency and long-term operational stability for PVDF-based all-solid-state lithium metal batteries.

Li Dynamics in Mixed Ionic-Electronic Conducting Interlayer of All-Solid-State Li-metal Batteries.

Lithium-metal (Li0) anodes potentially enable all-solid-state batteries with high energy density. However, it shows incompatibility with sulfide solid-state electrolytes (SEs). One strategy is introducing an interlayer, generally made of a mixed ionic-electronic conductor (MIEC). Yet, how Li behaves within MIEC remains unknown. Herein, we investigated the Li dynamics in a graphite interlayer, a typical MIEC, by using operando neutron imaging and Raman spectroscopy. This study revealed that intercalation-extrusion-dominated mechanochemical reactions during cell assembly transform the graphite into a Li-graphite interlayer consisting of SE, Li0, and graphite-intercalation compounds. During charging, Li+ preferentially deposited at the Li-graphite|SE interface. Upon further plating, Li0-dendrites formed, inducing short circuits and the reverse migration of Li0. Modeling indicates the interface has the lowest nucleation barrier, governing lithium transport paths. Our study elucidates intricate mechano-chemo-electrochemical processes in mixed conducting interlayers. The behavior of Li+ and Li0 in the interlayer is governed by multiple competing factors.

Double-Layered Perovskite Oxyfluoride Cathodes with High Capacity Involving O-O Bond Formation for Fluoride-Ion Batteries.

Developing electrochemical high-energy storage systems is of crucial importance toward a green and sustainable energy supply. A promising candidate is fluoride-ion batteries (FIBs), which can deliver a much higher volumetric energy density than lithium-ion batteries. However, typical metal fluoride cathodes with conversion-type reactions cause a low-rate capability. Recently, layered perovskite oxides and oxyfluorides, such as LaSrMnO4 and Sr3Fe2O5F2, have been reported to exhibit relatively high rate performance and cycle stability compared to typical metal fluoride cathodes with conversion-type reactions, but their discharge capacities (∼118 mA h/g) are lower than those of typical cathodes used in lithium-ion batteries. Here, we show that double-layered perovskite oxyfluoride La1.2Sr1.8Mn2O7-δF2 exhibits (de) intercalation of two fluoride ions to rock-salt slabs and further (de) intercalation of excess fluoride ions to the perovskite layer, leading to a reversible capacity of 200 mA h/g. The additional fluoride-ion intercalation leads to the formation of O-O bond in the structure for charge compensation (i.e., anion redox). These results highlight the layered perovskite oxyfluorides as a new class of active materials for the construction of high-performance FIBs.

Interphase Stabilization of LiNi0.5 Mn1.5 O4 Cathode for 5 V-Class All-Solid-State Batteries.

Employing high voltage cobalt-free spinel LiNi0.5 Mn1.5 O4 (LNMO) as a cathode is promising for high energy density and cost-effectiveness, but it has challenges in all-solid-state batteries (ASSBs). Here, it is revealed that the limitation of lithium argyrodite sulfide solid electrolyte (Li6 PS5 Cl) with the LNMO cathode is due to the intrinsic chemical incompatibility and poor oxidative stability. Through a careful analysis of the interphase of LNMO, it is elucidated that even the halide solid electrolyte (Li3 InCl6 ) with high oxidative stability can be decomposed to form resistive interphase layers with LNMO in ASSBs. Interestingly, with Fe-doping and a Li3 PO4 protective layer coating, LNMO with Li3 InCl6 displays stable cycle performance with a stabilized interphase at a high voltage (≈4.7 V) in ASSBs. The enhanced interfacial stability with the extended electrochemical stability window through doping and coating enables high electrochemical stability with LNMO in ASSBs. This work provides guidance for employing high-voltage cathodes in ASSBs and highlights the importance of stable interphases to enable stable cycling in ASSBs.

Enhanced Electrochemical Stability and Extended Cycle Life in Sulfide-Based All-Solid-State Batteries: The Role of Li10 SnP2 S12 Coating on Ni-Rich NCM Cathode.

Recently, sulfide-based all-solid-state batteries (ASSBs) have attracted great attention because of their excellent safety and high energy density. However, by-products formed from side-reactions between the oxide-based cathodes and sulfide-based solid electrolytes (SEs) increase the interfacial resistance and degrade the cell performance. Suppression of this interfacial resistance is thus critical. In this study, the extraordinarily high stability of the cathode/SE interface is discovered when a Li10 SnP2 S12 (LSnPS) is applied to a cathode buffer layer. The electrochemical properties of the cathode interface at high potential are improved by synthesizing a core-shell structure cathode using LSnPS. The synthesized LSnPS is uniformly coated on a Li2 ZrO3 -coated LiNi0.8 Co0.1 Mn0.1 O2 (LZO-NCM) surface using the cost-efficient mechano-fusion method. The ASSB with LSnPS-coated LZO-NCM as the cathode and Li6 PS5 Cl (argyrodite, LPSCl) as the SE exhibited a capacity of 192 mAh g-1 and excellent cycle retention of ≈75% after 500 charge/discharge cycles. In addition, the degradation mechanism at the cathode/SE interface is investigated. The results indicated that LSnPS stabilizes the interface between NCM and argyrodite, thereby inhibiting the decomposition of the SE. This technology is expected to contribute to the commercialization of cathode materials for sulfide-based ASSBs due to its enhanced cycle performance, low-cost material application, and eco-friendly process.

Exploring the Cathode Active Materials for Sulfide-Based All-Solid-State Lithium Batteries with High Energy Density.

All-solid-state lithium batteries (ASSLBs) are considered promising alternatives to current lithium-ion batteries that employ liquid electrolytes due to their high energy density and enhanced safety. Among various types of solid electrolytes, sulfide-based electrolytes are being actively studied, because they exhibit high ionic conductivity and high ductility, which enable good interfacial contacts in solid electrolytes without sintering at high temperatures. To improve the energy density of the sulfide-based ASSLBs, it is essential to increase the loading of active material in the composite cathode. In this study, the Ni-rich LiNix Coy Mn1-x-y O2 (NCM) materials are explored with different Ni content, particle size, and crystalline form to probe suitable cathode active materials for high-performance ASSLBs with high energy density. The results reveal that single-crystalline LiNi0.82 Co0.10 Mn0.08 O2 material with a small particle size exhibits the best cycling performance in the ASSLB assembled with a high mass loaded cathode (active mass loading: 26 mg cm-2 , areal capacity: 5.0 mAh cm-2 ) in terms of discharge capacity, capacity retention, and rate capability.

PEO-Based Solid Composite Polymer Electrolyte for High Capacity Retention All-Solid-State Lithium Metal Battery.

The limited ionic conductivity at room temperature and the constrained electrochemical window of poly(ethylene oxide) (PEO) pose significant obstacles that hinder its broader utilization in high-energy-density lithium metal batteries. The garnet-type material Li6.4 La3 Zr1.4 Ta0.6 O12 (LLZTO) is recognized as a highly promising active filler for enhancing the performance of PEO-based solid polymer electrolytes (SPEs). However, its performance is still limited by its high interfacial resistance. In this study, a novel hybrid filler-designed SPE is employed to achieve excellent electrochemical performance for both the lithium metal anode and the LiFePO4 cathode. The solid composite membrane containing hybrid fillers achieves a maximum ionic conductivity of 1.9 × 10-4 S cm-1 and a Li+ transference number of 0.67 at 40 °C, respectively. Additionally, the Li/Li symmetric cells demonstrate a smooth and stable process for 2000 h at a current density of 0.1 mA cm-2 . Furthermore, the LiFePO4 /Li battery delivers a high-rate capacity of 159.2 mAh g-1 at 1 C, along with a capacity retention of 95.2% after 400 cycles. These results validate that employing a composite of both active and inactive fillers is an effective strategy for achieving superior performance in all-solid-state lithium metal batteries (ASSLMBs).

Constructing Nano-Interlayer Inhibiting Interfacial Degradation toward High-Voltage PEO-Based All-Solid-State Lithium Batteries.

The interfacial instability between PEO-based solid electrolyte (SPE) and high-voltage cathode materials inhibits the longevity of high-energy-density all-solid-state polymer lithium metal batteries (ASSPLBs). Herein, for the first time it is demonstrated, that contact loss caused by gas generation from interfacial side reactions between the high-voltage cathode and solid polymer electrolyte (SPE) can also arise in ASSPLBs. To alleviate the interfacial side reactions, a LiNb0.6Ti0.5O3 (LNTO) layer is well coated on LiNi0.83Co0.07Mn0.1O2 (NCM83), denoted as (CNCM83). The LNTO layer with low electronic conductivity reduces the decomposition drive force of SPE. Furthermore, Ti and Nb in the LNTO layer spontaneously migrate inside the NCM83 surface to form a strong Ti/Nb─O bond, stalling oxygen evolution in high-voltage cathodes. The interfacial degradation phenomena, including SPE decomposition, detrimental phase transition and intragranular cracks of NCM83, and void formation between cathode and SPE, are effectively mitigated by the LNTO layer. Therefore, the growth rate of interfacial resistance (RCEI) decreases from 37.6 Ω h-0.5 for bare NCM83 to 2.4 Ω h-0.5 for CNCM83 at 4.2 V. Moreover, 4.2 V PEO-based ASSPLBs achieve impressive cyclability with high capacity retention of 135 mAh g-1 (75%) even after 300 cycles at 0.5 C.

Activating Redox Kinetics of Li2S via Cu+, I- Co-Doping Toward High-Performance All-Solid-State Lithium Sulfide-Based Batteries.

All-solid-state lithium sulfide-based batteries (ASSLSBs) have drawn much attention due to their intrinsic safety and excellent performance in overcoming the polysulfide shuttle effect. However, the sluggish kinetics of Li2S cathode severely impede commercial utilization. Here, a Cu+, I- co-doping strategy is employed to activate the kinetics of Li2S to construct high-performance ASSLSBs. The electronic conductivity and Li-ion diffusion coefficient of the co-doped Li2S are increased by five and two orders of magnitude, respectively. Cu+ as a redox medium greatly improves the reaction kinetics, which is supported by ex situ X-ray photoelectron spectroscopy. Density functional theory calculation (DFT) shows that Cu+, I- co-doping reduces the Li-ions diffusion energy barrier. The co-doped Li2S exhibits a remarkable improvement in capacity (1165.23 mAh g-1 (6.65 times that of pristine Li2S) at 0.02 C and 592.75 mAh g-1 at 2 C), and excellent cycling stability (84.58% capacity retention after 6200 cycles at 2 C) at room temperature. Moreover, an ASSLSB, fabricated with a lithium-free (Si─C) anode, obtains a high specific capacity of 1082.7 mAh g-1 at 0.05 C and 97% capacity retention after 400 cycles at 0.5 C. This work provides a broad prospect for the development of ASSLSBs with practical energy density exceeding that of traditional lithium-ion batteries.

Boron Quantum Dots Pillared Ti3 C2 Tx Membrane Electrode with High Rate Performance for Supercapacitor.

A sonication-assisted liquid-phase preparation technique is developed to prepare boron quantum dots (BQDs) with a lateral size of 3 nm in a solution of NMP and NBA; it shows a direct bandgap semiconductor with a bandgap of 3 eV and a specific capacitance of 41 F g-1 . A BQDs(10)-Ti3 C2 Tx membrane electrode with excellent capacitance and high flexibility is prepared by using Ti3 C2 Tx nanosheets (NSs) as assembled units and BQDs as pillar; it gives a specific capacitance of 524 F g-1 at 1 A g-1 in 6 m H2 SO4 electrolyte, a high capacity retention of 75%, and a minimum relaxation time of 0.51 s. An all-solid-state BQDs(10)-Ti3 C2 Tx flexibility supercapacitor is assembled by using a BQDs(10)-Ti3 C2 Tx membrane as electrodes and PVA/H2 SO4 hydrogel as electrolyte; it not only shows an area specific capacitance of 552 mF cm-2 at 1.25 mA cm-2 , a retention rate of 75%, a capacity retention of 93% after 5000 cycles, and an energy density of 40.4 Wh cm-3 at a volume power density of 416 W cm-3 , but also provides superior flexibility and can be bent to different degrees, showing that the assembled BQDs(10)-Ti3 C2 Tx membrane electrode and BQDs(10)-Ti3 C2 Tx flexible supercapacitor display broad application prospects in field of portable/wearable electronic devices.

Low-cost BPO4 In Situ Synthetic Li3PO4 Coating and B/P-Doping to Boost 4.8 V Cyclability for Sulfide-Based All-Solid-State Lithium Batteries.

Structural damage of Ni-rich layered oxide cathodes such as LiNi0.8Co0.1Mn0.1O2 (NCM811) and serious interfacial side reactions and physical contact failures with sulfide electrolytes (SEs) are the main obstacles restricting ≥4.6 V high-voltage cyclability of all-solid-state lithium batteries (ASSLBs). To tackle this constraint, here, a modified NCM811 with Li3PO4 coating and B/P co-doping using inexpensive BPO4 as raw materials via the one-step in situ synthesis process is presented. Phosphates have good electrochemical stability and contain the same anion (O2-) and cation (P5+) as in cathode and SEs, respectively, thus Li3PO4 coating precludes interfacial anion exchange, lessening side reactivity. Based on the high bond energy of B─O and P─O, the lattice O and crystal texture of NCM811 can be stabilized by B3+/P5+ co-doping, thereby suppressing microcracks during high-voltage cycling. Therefore, when tested in combination with Li─In anode and Li6PS5Cl solid electrolytes (LPSCl), the modified NCM811 exhibits extraordinary performance, with 200.36 mAh g-1 initial discharge capacity (4.6 V), cycling 2300 cycles with decay rate as low as 0.01% per cycle (1C), and 208.26 mAh g-1 initial discharge capacity (4.8 V), cycling 1986 cycles with 0.02% per cycle decay rate. Simultaneously, it also has remarkable electrochemical abilities at both -20 °C and 60 °C.

In Situ Characterization of Interface Evolution in Argyrodite-Based All-Solid-State Li Batteries.

Interfacial stability is one of the critical challenges in all-solid-state Li metal batteries. Multiple processes such as solid electrolyte (SE) decomposition and lithium dendrite growth take place at the solid interfaces during cycling, leading to the overall cell failure. To deconvolute these complex processes, in situ characterization is of paramount importance to elucidate the interfacial evolution on the SE upon Li plating/stripping. Herein, an all-solid-state asymmetric in situ cell is developed that allows the direct visualization of the highly localized Li plating/stripping processes under the optical microscope. Moreover, this cell configuration enables reliable post-mortem chemical and morphological analysis of the intact SE/Li interface. Using combined scanning electron microscopy and energy-dispersive X-ray spectroscopy, the study reveals that the evolution of the Li argyrodite interface is strongly influenced by the current density, particularly in terms of chemical distribution and Li plating morphology. More specifically, the solid interface is LiCl-rich with the formation of Li cubes at low current densities, while high currents result in more uniform elemental distribution and filament morphology. These findings elucidate the dynamic evolution mechanism at solid interfaces and offer valuable guidance for developing stable solid interfaces in all-solid-state Li metal batteries.

Pressure Tuning and Sn Particle Size Optimization for Enhanced Performance in PbSnF4-Based All-Solid-State Fluoride Ion Batteries.

All-solid-state fluoride ion batteries (ASSFIBs) show remarkable potential as energy storage devices due to their low cost, superior safety, and high energy density. However, the poor ionic conductivity of F- conductor, large volume expansion, and the lack of a suitable anode inhibit their development. In this work, PbSnF4 solid electrolytes in different phases (ß- and γ-PbSnF4) are successfully synthesized and characterized. The ASSFIBs composed of ß-PbSnF4 electrolytes, a BiF3 cathode, and micrometer/nanometer size (µ-/n-) Sn anodes, exhibit substantial capacities. Compared to the µ-Sn anode, the n-Sn anode with nanostructure exhibits superior battery performance in the BiF3/ß-PbSnF4/Sn battery. The optimized battery delivers a high initial discharge capacity of 181.3 mAh g-1 at 8 mA g-1 and can be reversibly cycled at 40 mA g-1 with a high discharge capacity of over 100.0 mAh g-1 after 120 cycles at room temperature. Additionally, it displays high discharge capacities over 90.0 mAh g-1 with excellent cyclability over 100 cycles under -20 °C. Detailed characterization has confirmed that reducing Sn particle size and boosting external pressure are crucial for achieving good defluorination/fluorination behaviors in the Sn anode. These findings pave the way to designing ASSFIBs with high capacities and superior cyclability under different operating temperatures.

An Effective Catholyte for Sulfide-Based All-Solid-State Batteries Utilizing Gas Absorbents.

All-solid-state batteries (ASSBs) possess the advantage of ensuring safety while simultaneously maximizing energy density, making them suitable for next-generation battery models. In particular, sulfide solid electrolytes (SSEs) are viewed as promising candidates for ASSB electrolytes due to their excellent ionic conductivity. However, a limitation exists in the form of interfacial side reactions occurring between the SSEs and cathode active materials (CAMs), as well as the generation of sulfide-based gases within the SSE. These issues lead to a reduction in the capacity of CAMs and an increase in internal resistance within the cell. To address these challenges, cathode composite materials incorporating zinc oxide (ZnO) are fabricated, effectively reducing various side reactions occurring in CAMs. Acting as a semiconductor, ZnO helps mitigate the rapid oxidation of the solid electrolyte facilitated by an electronic pathway, thereby minimizing side reactions, while maintaining electron pathways to the active material. Additionally, it absorbs sulfide-based gases, thus protecting the lithium ions within CAMs. In this study, the mass spectrometer is employed to observe gas generation phenomena within the ASSB cell. Furthermore, a clear elucidation of the side reactions occurring at the cathode and the causes of capacity reduction in ASSB are provided through density functional theory calculations.

Intercepting Dendrite Growth With a Heterogeneous Solid Electrolyte for Long-Life All-Solid-State Lithium Metal Batteries.

The application of lithium metal anode in all-solid-state batteries has the potential to achieve both high energy density and safety performance. However, the presence of serious dendrite issues hinders this potential. Here, the ion transport pathways and orientation of dendrite growth are regulated by utilizing the differences of ionic conductivity in heterogeneous electrolytes. The in situ formed Li-Ge alloy phases from the spontaneous reaction between Li10GeP2S12 and the attracted dendrites greatly enhance the ability to resist dendrite growth. As an outcome, the heterogeneous electrolyte achieves a high critical current density of 2.1 mA cm-2 and long-term stable symmetrical battery operation (0.3 mA cm-2 for 17 000 h and 1.0 mA cm-2 for 2000 h). Besides, due to the superior interfacial stability and low interface impedance between the heterogeneous electrolyte and lithium anode, the Li||LiNi0.8Co0.1Mn0.1O2 full battery exhibits great cycling stability (80.5% after 500 cycles at 1.0 mA cm-2) and rate performance (125.4 mAh g at 2.0 mA cm-2). This work provides a unique strategy of interface regulation via heterogeneous electrolytes design, offering insights into the development of state-of the-art all-solid-state batteries.

Vertically-Aligned Card-House Structure for Composite Solid Polymer Electrolyte with Fast and Stable Ion Transport Channels.

All-solid-state lithium batteries (ASSLBs) are highly promising as next-generation energy storage devices owing to their potential for great safety and high energy density. This work demonstrates that composite solid polymer electrolyte with vertically-aligned card-house structure can simultaneously improve the high rate and long-term cycling performance of ASSLBs. The vertical alignment of laponite nanosheets creates fast and uniform Li+ ion transport channels at the nanosheets/polymer interphase, resulting in high ionic conductivity of 8.9 × 10-4 S cm-1 and Li+ transference number of 0.32 at 60 °C, as well as uniformly distributed solid electrolyte interphase. Such electrolyte is characterized by high mechanical strength, low flammability, excellent structural stability and stable ion transport channels. In addition, the ASSLB cell with the electrolyte and LiFePO4 cathode delivers a high discharge specific capacity of 124.8 mAh g-1, which accounts for 85.6% of its initial capacity after 500 cycles at 1C. The reasonable design through structural control strategy by interconnecting the vertically-aligned nanosheets open a way to fabricate high performance composite solid polymer electrolytes.

Highly Conductive and Stable Composite Polymer Electrolyte with Boron Nitride Nanotubes for All-Solid-State Lithium Metal Batteries.

All-solid-state lithium metal batteries (ASSLMBs) have emerged as the most promising next-generation energy storage devices. However, the unsatisfactory ionic conductivity of solid electrolytes at room temperature has impeded the advancement of solid-state batteries. In this work, a multifunctional composite solid electrolyte (CSE) is developed by incorporating boron nitride nanotubes (BNNTs) into polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP). BNNTs, with a high aspect ratio, trigger the dissociation of Li salts, thus generating a greater population of mobile Li+, and establishing long-distance Li+ transport pathways. PVDF-HFP/BNNT exhibits a high ionic conductivity of 8.0 × 10-4 S cm-1 at room temperature and a Li+ transference number of 0.60. Moreover, a Li//Li symmetric cell based on PVDF-HFP/BNNT demonstrates robust cyclic performance for 3400 h at a current density of 0.2 mA cm-2. The ASSLMB formed from the assembly of PVDF-HFP/BNNT with LiFePO4 and Li exhibits a capacity retention of 93.2% after 850 cycles at 0.5C and 25 °C. The high-voltage all-solid-state LiCoO2/Li cell based on PVDF-HFP/BNNT also exhibits excellent cyclic performance, maintaining a capacity retention of 96.4% after 400 cycles at 1C and 25 °C. Furthermore, the introduction of BNNTs is shown to enhance the thermal conductivity and flame retardancy of the CSE.

All-Solid-State Mg-Air Battery Enhanced with Free-Standing N-Doped 3D Nanoporous Graphene.

Nitrogen (N) doping of graphene with a three-dimensional (3D) porous structure, high flexibility, and low cost exhibits potential for developing metal-air batteries to power electric/electronic devices. The optimization of N-doping into graphene and the design of interconnected and monolithic graphene-based 3D porous structures are crucial for mass/ion diffusion and the final oxygen reduction reaction (ORR)/battery performance. Aqueous-type and all-solid-state primary Mg-air batteries using N-doped nanoporous graphene as air cathodes are assembled. N-doped nanoporous graphene with 50-150 nm pores and ≈99% porosity is found to exhibit a Pt-comparable ORR performance, along with satisfactory durability in both neutral and alkaline media. Remarkably, the all-solid-state battery exhibits a peak power density of 72.1 mW cm-2 ; this value is higher than that of a battery using Pt/carbon cathodes (54.3 mW cm-2 ) owing to the enhanced catalytic activity induced by N-doping and rapid air breathing in the 3D porous structure. Additionally, the all-solid-state battery demonstrates better performances than the aqueous-type battery owing to slow corrosion of the Mg anode by solid electrolytes. This study sheds light on the design of free-standing and catalytically active 3D nanoporous graphene that enhances the performance of both Mg-air batteries and various carbon-neutral-technologies using neutral electrolytes.