Stable Cycling Behavior Research Articles

In-Depth Study of Li4Ti5O12 Performing beyond Conventional Operating Conditions.

Lithium-ion batteries (LIBs) are nowadays widely used in many energy storage devices, which have certain requirements on size, weight, and performance. State-of-the-art LIBs operate very reliably and with good performance under restricted and controlled conditions but lack in efficiency and safety when these conditions are exceeded. In this work, the influence of outranging conditions in terms of charging rate and operating temperature on electrochemical characteristics was studied on the example of lithium titanate (Li4Ti5O12, LTO) electrodes. Structural processes in the electrode, cycled with ultrafast charge and discharge, were evaluated by operando synchrotron powder diffraction and ex situ X-ray absorption spectroscopy. On the basis of the Rietveld refinement, it was shown that the electrochemical storage mechanism is based on the Li-intercalation process at least up to current rates of 5C, meaning full battery charge within 12 min. For applications at temperatures between -30 and 60 °C, four carbonate-based electrolyte systems with different additives were tested for cycling performance in half-cells with LTO and metallic lithium as electrodes. It was shown that the addition of 30 wt % [PYR14][PF6] to the conventional LP30 electrolyte, usually used in LIBs, significantly decreases its melting point, which enables the successful low-temperature application at least down to -30 °C, in contrast to LP30, which freezes below -10 °C, making battery operation impossible. Moreover, at elevated temperatures up to 60 °C, batteries with the LP30/[PYR14][PF6] electrolyte exhibit stable long-term cycling behavior very close to LP30. Our findings provide a guideline for the application of LTO in LIBs beyond conventional conditions and show how to overcome limitations by designing appropriate electrolytes.

High-performance CoSbS-based Na-ion battery anodes

CoSbS and its hard carbon-containing nanocomposite (CoSbS@hard-C) are prepared via simple solid-state reactions, and their potential as Na-ion battery (NIB) anode materials is investigated. The electrochemical phase change mechanism of CoSbS during Na insertion/extraction is thoroughly investigated using various ex situ analytical tools. During Na insertion, the CoSbS undergoes a topotactic transformation owing to the formation of a NaxCoSbS (x ≤ 1.6), and then, it is converted into Na3Sb, Na2S, and Co in the fully Na-inserted state via a conversion reaction. Conversely, during Na extraction, Na3Sb transforms to Sb, which alloys with Co to form CoSb. In the fully Na-extracted state, CoSb and S from Na2S are recombined into CoSbS. Owing to the interesting reaction mechanism of CoSbS, the electrochemical performance of the CoSbS and CoSbS@hard-C anodes is excellent. Specifically, when CoSbS is used as a NIB anode, the topotactic transformation between CoSbS and NaxCoSbS (x ≤ 1.6) leads to stable cycling behavior of the NIB and a volumetric capacity of ~480 mAh cm−3 is retained after 100 cycles. Additionally, the NIB with the CoSbS@hard-C anode presents highly reversible and stable capacity (~570 mAh cm−3 after 150 cycles) and fast rate capability (~500 and ~450 mAh cm−3 at 2C and 5C, respectively), which can be attributed to the presence of uniformly dispersed small (5–8 nm) CoSbS nanocrystallites in the hard carbon matrix. Therefore, CoSbS can be utilized as a new anode material for high-performance NIBs.

Stabilizing lithium metal anode by molecular beam epitaxy grown uniform and ultrathin bismuth film

Abstract Lithium metal anode is regarded as an attractive option for next-generation high-energy-density rechargeable batteries. However, the unstable solid-electrolyte interphases between lithium anode and electrolyte lead to uncontrolled growth of lithium dendrites. Herein, we describe the surface reconstruction of Li anode by molecular beam epitaxy deposition of an ultrathin and compact bismuth film. During Li plating process, the electrochemical active bismuth film is prone to form a close-knit lithiophilic lithium-bismuthide (LixBi) alloy layer through electrochemical alloying with lithium metal. Benefiting from its high ionic conductivity, lithiophilic characteristics, high chemical stability, good mechanical properties and air/moisture tolerance, the LixBi-rich layer efficiently inhibit the parasitic reactions between Li anode and electrolyte, and thus favor a dendrite-free Li plating/stripping process, as verified by electrochemical tests and in-depth analyses. Symmetric cells with Bi-coated Li electrodes show a stable and dendrite-free cycling behavior at 1.0 mAh cm−2 for 300 h and superior rate performance up to 5.0 mA cm−2. When Bi-coated lithium anodes are paired with a LiNi0.5Co0.2Mn0.3O2 cathode, a stable cycling life for over 300 cycles at 0.5C with a high capacity retention rate of 97% is obtained. This work provides new insights and strategies for the construction of Li-rich alloy layers on lithium metal surface via molecular beam epitaxy that enables dendrite-free and high-performance lithium metal batteries.

Dicyandiamide-formaldehyde and Borassus Flabellifer inflorescence assisted preparation of low surface area nitrogen-doped carbon as high-performance anode for lithium-ion batteries

The heteroatom-doped disordered and nanostructured carbon materials have gained significant attention due to their enormous potential to improve the performance of energy applications. In this context, we have successfully developed a sustainable green synthesis of disordered and nanostructured nitrogen-doped carbon using pre-carbonized Borassus Flabellifer Male Inflorescence biomass coated with Dicyandiamide and Formaldehyde polymer, which subsequently subjected to thermal activation at 1000 °C for 6 hrs in nitrogen environment and it has lower surface area (30.76 m2 g−1). The prepared N-doped carbon, when used as an anode in Li-ion batteries, delivered an outstanding reversible specific capacity of 655.8 mAh g−1 at a current density of 100 mA g−1 with the stable cycling behaviour for 1500 cycles. Even at a higher current rate (1000 mA g−1), the prepared carbon displayed a reversible capacity of 351.9 mAh g−1, thus making it a promising anode candidate for the next generation of high power lithium-ion batteries (LIBs).

Enabling ultrafast ionic conductivity in Br-based lithium argyrodite electrolytes for solid-state batteries with different anodes

One of the primary obstacles that has inhibited the development of solid-state batteries is the lower conductivity of solid electrolytes compared to liquid electrolytes. Li6PS5Br is a promising solid electrolyte for solid-state batteries due to its high ionic conductivity and low cost. Herein, we enhance the lithium conductivity by replacing S with Br and systematically tailor the composition and synthesis parameters to optimize the conductivity. Li5.5PS4.5Br1.5 exhibits higher ionic conductivity and better lithium compatibility than the bare Li6PS5Br. Although lithium metal is chemically unstable with Li5.5PS4.5Br1.5, stable cycling behavior in lithium symmetrical cells with small overpotential and resistance after 2500 ​h are achieved. Both the bare NCM622 and LiNbO3-coated NCM622 shows long cycling life with Li5.5PS4.5Br1.5 electrolyte in combination with In or lithium metal anodes. The LiNbO3 layer can effectively improve the capacity and cycling behavior of the solid-state battery using different anodes. Moreover, the electrochemical performances of Li5.5PS4.5Br1.5-based solid-state batteries are influenced by the charge/discharge voltage windows.

Compatibility of Porous Silicon with Lithium Polysulfides for Full Cell Lithium Ion Battery Applications with Sulfur Cathodes

Crystalline silicon is an ideal anode candidate for lithium ion batteries as it offers a high Li+ ion storage capacity, direct current pathway and is a stable and earth abundant element. In order to match the high theoretical energy density of silicon in lithium ion batteries a suitable cathode material is required. Sulfur based cathodes have a high theoretical storage capacity for application in lithium ion batteries, based on the conversion reaction of the cyclic S8 molecule with lithium to form smaller lithium polysulfides up to Li2S, and are also cheap and earth abundant. One of the major drawbacks of lithium sulfur cathode materials is the tendency of lithium polysulfides to be dissolved by the electrolyte, which causes the polysulfides to migrate away from the cathode, leading to an overall capacity loss. For application of porous silicon in a full cell lithium ion battery with sulfur it is important to understand the impact the presence of lithium polysulfides can have on the functionality of porous silicon as an anode. In this study porous silicon anodes with thicknesses of 6 µm and 12 µm were cycled in a half cell in the presence of varying concentrations of Li2S6 (0 M, 0.017 M and 0.083 M). For the electrolyte with 0.017 M Li2S6 the cycling behavior was comparable, or better, than the electrolyte with no polysulfides. The SEI layer formed on the surface of the porous silicon anodes was investigated ex situ with X-ray photoelectron spectroscopy, Raman spectroscopy and scanning electron microscopy after one, five and ten cycles. It was seen that in the first cycle lithium polysulfides are contained in the SEI and undergo an oxidation reaction to form sulfates over the following cycles. This leads to a more inorganic SEI layer in the presence of polysulfides, especially in the case of the 12 µm porous silicon, and long term cycling stability. The 12 µm porous silicon anode cycled in the presence of 0.083 M Li2S6 showed stable cycling behavior over one hundred cycles, with limited capacity loss and coulombic efficiencies of 96.2 % after one hundred cycles.

Facile hydrothermal construction of Nb2CTx/Nb2O5 as a hybrid anode material for high-performance Li-ion batteries

Herein, a simple yet efficient hydrothermal strategy is developed to in-situ convert multi-layered niobium-based MXene (Nb2CTx) to hierarchical Nb2CTx/Nb2O5 composite. In the hybrid, the Nb2O5 nanorods are well dispersed in and/or on the Nb2CTx. Thanks to the synergetic contributions from the high capacity of Nb2O5 and superb electrical conductivity of the two-dimensional Nb2CTx itself, the resultant Nb2CTx/Nb2O5 hybrid exhibits excellent rate behaviors and stable long-term cycling behaviors, when evaluated as anodes for Li-ion batteries.

3D Cube‐Maze‐Like Li‐Rich Layered Cathodes Assembled from 2D Porous Nanosheets for Enhanced Cycle Stability and Rate Capability of Lithium‐Ion Batteries

AbstractLi‐rich oxide is a promising candidate for the cathodes of next‐generation lithium‐ion batteries. However, its utilization is restricted by cycling instability and inferior rate capability. To tackle these issues, three‐dimensional (3D), hierarchical, cube‐maze‐like Li‐rich cathodes assembled from two‐dimensional (2D), thin nanosheets with exposed {010} active planes, are developed by a facile hydrothermal approach. Benefiting from their unique architecture, 3D cube‐maze‐like cathodes demonstrate a superior reversible capacity (285.3 mAh g−1 at 0.1 C, 133.4 mAh g−1 at 20.0 C) and a great cycle stability (capacity retention of 87.4% after 400 cycles at 2.0 C, 85.2% after 600 cycles and 75.0% after 1200 cycles at 20.0 C). When this material is matched with a graphite anode, the full cell achieves a remarkable discharge capacity (275.2 mAh g−1 at 0.1 C) and stable cycling behavior (capacity retention of 88.7% after 100 cycles at 5.0 C, capacity retention of 84.8% after 100 cycles at 20.0 C). The present work proposes an accessible way to construct 3D hierarchical architecture assembled from 2D nanosheets with exposed high‐energy active {010} planes and verifies its validity for advanced Li‐rich cathodes.

(Invited) “Decrepitation” and Mechanical Degradation: In Situ Investigation to Understand Chemo-Mechanical Stability in Batteries

Mechanical degradation and fracture have long been recognized as challenges that have impeded development of large-volume-change electrode materials that exhibit stable cycling behavior. Bob Huggins (along with Bill Nix) was among the first to quantify mechanical fracture and “decrepitation” or fracture processes in alloying anode materials, predicting that fracture during electrochemical reaction should be dependent on particle size, among other variables [1]. In recent years, our understanding of how reaction processes relate to mechanical degradation in battery materials has advanced significantly, and in situ/operando experimental techniques have been key for this progress. Here, I discuss my group’s recent efforts in understanding chemo-mechanical degradation in battery materials. First, in situ transmission electron microscopy (TEM) experiments are presented in which individual nanocrystal electrode materials are observed to react with various alkali ions (Li+, Na+, and K+). For FeS2 nanocrystals, the reaction with all three ions involves conversion to form a mixture of phases, along with volume expansion. Despite larger volume changes during reaction with Na+ and K+, only reaction with Li+ was observed to cause fracture. This surprising result was found to be due to the shape of the reaction front as it evolves during reaction, with sharp corners during lithiation resulting in stress concentration and fracture. In addition to this work, other in situ TEM investigations of reaction processes in metal alloying anode nanocrystals have revealed the importance of the mechanical properties of the native oxide in determining transformation pathways during electrochemical cycling. Finally, our research on chemo-mechanical degradation at interfaces within solid-state batteries will be briefly discussed. This work points to the necessity of understanding and controlling chemo-mechanical phenomena in high-capacity battery materials for developing next-generation battery materials. [1] R. A. Huggins, W. D. Nix “Decrepitation Model for Capacity Loss During Cycling of Alloys In Rechargeable Electrochemical Systems” Ionics, 2000, 6, 57.

Intensification of Pseudocapacitance by Nanopore Engineering on Waste-Bamboo-Derived Carbon as a Positive Electrode for Lithium-Ion Batteries.

Nanoporous carbon, including redox-active functional groups, can be a promising active electrode material (AEM) as a positive electrode for lithium-ion batteries owing to its high electrochemical performance originating from the host-free surface-driven charge storage process. This study examined the effects of the nanopore size on the pseudocapacitance of the nanoporous carbon materials using nanopore-engineered carbon-based AEMs (NE-C-AEMs). The pseudocapacitance of NE-C-AEMs was intensified, when the pore diameter was ≥2 nm in a voltage range of 1.0~4.8 V vs Li+/Li under the conventional carbonate-based electrolyte system, showing a high specific capacity of ~485 mA·h·g−1. In addition, the NE-C-AEMs exhibited high rate capabilities at current ranges from 0.2 to 4.0 A·g−1 as well as stable cycling behavior for more than 300 cycles. The high electrochemical performance of NE-C-AEMs was demonstrated by full-cell tests with a graphite nanosheet anode, where a high specific energy and power of ~345 Wh·kg−1 and ~6100 W·Kg−1, respectively, were achieved.

Metal multiple-sulfides with nitrogen doped carbon layer for high performance lithium-sulfur batteries

Lithium-sulfur battery has emerged as one of the greatest battery technologies because of its high energy density, however, the cycling performance is not satisfied mainly due to the dissolution of lithium polysulfides. To solve this problem, herein CoSx in a composite with nitrogen doped carbon and sulfur (CoSx-NC-S) synthesized from zeolitic imidazolate framework-67 (ZIF-67), was used to restrain shuttle-effect of polysulfides during cycling. The porous N-doped carbon polyhedra can not only improve the electronic conductivity, but also restrict the polysulfides and relieve the volume expansion of sulfur during cycling. Meanwhile, the CoSx nanoparticles embedded in the carbon polyhedra have powerful attraction with polysulfides, which is advantageous to the stable cycling behavior of electrodes. Applied in the lithium-sulfur battery as cathode, CoSx-NC-S electrode delivered a capacity of 952 mAh∙g−1 at 0.2 C after 150 cycles, and 570 mAh∙g−1 after 600 cycles even at the high rate of 2 C, which is significantly superior to the performance of NC-S electrodes and S-C electrodes.

Chemically-Engineered Host Materials Enabling Safe Sodium Metal Anodes

As an anode material, sodium (Na) metal is the most promising alternative for lithium for the next‐generation energy storage systems. Nevertheless, its practical implementation is impeded by the huge volume change and severe Na metal dendrite growth during electrochemical stripping/plating. Herein, the employment of chemically-engineered porous copper (Cu) and titanium carbide (Ti3C2) MXene as stable host for metallic Na anode is presented. By treating the commercial Cu foam through a facile and cost‐effective method, a composite matrix consists of cylindrical core–shell skeleton is achieved, facilitating uniform impregnation and confinement of Na within the matrix pores promoted by the chemical interaction between Na and the matrix. While by treating Ti3C2 via a facile cetyltrimethylammonium bromide prepillaring followed by subsequent Tin cation (Sn2+) pillaring, a Sn2+ pillared Ti3C2 MXene matrix is obtained, guiding the Na nucleation/growth within the matrix interlayer space and contributing to uniform Na deposition facilitated by the chemical interaction between Na and Sn-based nanocomplexes encapsulated within the MXene layers. The unique characteristic of the chemically-engineered host materials can well accommodate hostless Na+, suppressing the volume change and mossy/dendritic Na growth during cycling. A stable Na cycling behavior is demonstrated in carbonate electrolyte without any additives at a high capacity up to 3 mAh/cm2 with a current density up to 2 mA/cm2. While in ether electrolyte, a stable Na performance at a high capacity up to 5 mAh/cm2 along with a high current density up to 10 mA/cm2 is achieved. Furthermore, electrochemical measurements of a full cell made of the Na composite matrix anodes clearly reveal the superior performance over that using bare Na metal. We believe that our approach provides facile approaches to the fabrication of stable Na metal anodes for high‐energy Na‐based batteries, and could be a viable strategy for other metallic anode systems.[1,2] Reference： [1] C.Wang, H. Wang, E. Matios, X. Hu, W. Li, Adv. Funct. Mater, 2018, 28, 1802282. [2] J. Luo, † C. Wang, † H. Wang, X. Hu, E. Matios, X. Lu, W. Zhang, X. Tao, W. Li, Adv. Funct. Mater, 2018, 1805946. Figure 1

Lithium-Powder Based Electrodes Modified with ZnI2 for Enhanced Electrochemical Performance of Lithium-Metal Batteries

Lithium-powder electrodes, prepared via paste casting method using lithium powder and polyisobutylene (PIB) as a binder, were investigated for their electrochemical properties in lithium-metal cells. The electrode paste casting method allows preserving the spherical shape of lithium-powder particles during processing to electrodes. However, these lithium-powder based electrodes suffer from poor active material utilization, as electronic isolation of lithium particles during the lithium electrodissolution process was observed to occur. In order to improve the lithium inter-particle contact as well as the contact with the current collector, a simple and effective chemical modification of the lithium-powder based electrodes was considered. Using a cementation reaction with ZnI2, the growth of a Li-Zn intermetallic (“alloy”) between the lithium-powder particles and the surface of the lithium powder, lead to an increase of the active material utilization and overcame the side reactions due to lithium electrodissolution. Besides increasing the active material utilization, such simple chemical modification of the lithium-powder based electrodes improved the electrochemical performance resulting in more stable cycling behavior with low polarization and longer cycle life in both Li||Li-symmetric and Li||NMC 622 cells.

Yolk@Shell SiOx/C microspheres with semi-graphitic carbon coating on the exterior and interior surfaces for durable lithium storage

Silicon oxides (SiOx) represent an attractive high-capacity lithium-ion battery (LIB) anode material. However, the huge volume variation of SiOx causes rapid capacity fading and unstable solid electrolyte interface, seriously limiting the practical application. To address the inherent defects of SiOx, herein, we designed a yolk@shell structured SiOx/C anode with semi-graphitic carbon coatings on the exterior and interior surfaces (SiOx/C-CVD) through sol-gel process, selective etching, and chemical vapor deposition. The unique composite nanostructure endows the SiOx/C-CVD high electrical conductivity and excellent structural stability. The as-prepared SiOx/C-CVD composite demonstrates a high reversible capacity (1165 mA h g-1 at 100 mA g-1) as well as outstanding durability (972 mA h g-1 after 500 cycles at 500 mA g-1). Furthermore, the full cells of SiOx/C-CVD//LiCoO2 are also assembled, delivering a high energy density of ~428 W h kg-1 with a stable cycling behavior. The carbon coated yolk@shell design might be applied to optimize the lithium storage performances of other high-capacity anode materials suffering from poor electrical conductivity and large volume variations.

Stabilizing the Interface of NASICON Solid Electrolyte against Li Metal with Atomic Layer Deposition.

Solid-state batteries have been considered as one of the most promising next-generation energy storage systems because of their high safety and energy density. Solid-state electrolytes are the key component of the solid-state battery, which exhibit high ionic conductivity, good chemical stability, and wide electrochemical windows. LATP [Li1.3Al0.3Ti1.7 (PO4)3] solid electrolyte has been widely investigated for its high ionic conductivity. Nevertheless, the chemical instability of LATP against Li metal has hindered its application in solid-state batteries. Here, we propose that atomic layer deposition (ALD) coating on LATP surfaces is able to stabilize the LATP/Li interface by reducing the side reactions. In comparison with bare LATP, the Al2O3-coated LATP by ALD exhibits a stable cycling behavior with smaller voltage hysteresis for 600 h, as well as small resistance. More importantly, on the basis of advanced characterizations such as high-resolution transmission electron spectroscope-electron energy loss spectroscopy, the lithium penetration into the LATP bulk and Ti4+ reduction are significantly limited. The results suggest that ALD is very effective in improving solid-state electrolyte/electrode interface stability.

Constructing a Protective Pillaring Layer by Incorporating Gradient Mn4+ to Stabilize the Surface/Interfacial Structure of LiNi0.815Co0.15Al0.035O2 Cathode.

Nickel-rich layered oxides are regarded as very promising materials as cathodes for lithium-ion batteries because of their environmental benignancy, low cost, and high energy density. However, insufficient cycle performance and poor thermotic characteristics induced by structural degradation at high potentials and elevated temperatures pose challenging hurdles for nickel-rich cathodes. Here, a protective pillaring layer, in which partial Ni2+ ions occupy Li slabs induced by gradient Mn4+, is integrated into the primary particle of LiNi0.815Co0.15Al0.035O2 to stabilize the surface/interfacial structure. With the stable outer surface provided by the enriched Mn4+ gradient concentration and the pillar effect of the NiO-like phase, Mn-incorporated quaternary cathodes show enhanced structural stability and improved Li+ diffusion as well as lithium-storage properties. Compared with the severe capacity fade of a pure layered structure, the cathode with gradient Mn4+ exhibits more stable cycling behavior with a capacity retention of 80.0% after 500 cycles at 5.0 C.

A Chemically Engineered Porous Copper Matrix with Cylindrical Core–Shell Skeleton as a Stable Host for Metallic Sodium Anodes

AbstractSodium (Na) metal is the most promising alternative for lithium metal as anode for the next‐generation energy storage systems. However, its practical implementation is hindered by the huge volume change and severe Na metal dendrite growth during electrochemical stripping/plating. Herein, the use of a chemically engineered porous copper (Cu) matrix as a stable host for metallic Na anode is presented. By treating the commercial Cu foam through a facile and cost‐effective method, a composite matrix consists of cylindrical core–shell skeleton is achieved, facilitating uniform impregnation and confinement of Na within the matrix pores promoted by the chemical interaction between Na and the matrix. The unique matrix's surface characteristic can divert the Na deposition from the skeleton towards the Na reservoirs within the pores, suppressing the volume change and mossy/dendritic Na growth. A stable Na cycling behavior is demonstrated in carbonate electrolyte without any additives at a high capacity up to 3 mAh cm−2 with a current density up to 2 mA cm−2. Moreover, electrochemical measurements of a full cell made of the Na composite matrix anode clearly reveal the superior performance at high rate (5C) over that using bare Na metal.

Urea and Ethylene Glycol‐Assisted Solvothermal Synthesis of Spheroidal LiFePO4/C Nanoparticles as a Cathode Material for Lithium‐ion Batteries

AbstractSpheroidal LiFePO4/C nanoparticles were synthesized successfully via a urea and ethylene glycol‐assisted solvothermal synthetic route combined with high‐temperature calcinations under different solvothermal time and carbon coating amounts. The obtained samples were characterized with various techniques, including X‐ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electrochemical performance experiments. The test results showed that urea as an additive plays a critical role in controlling morphologies of the final products and ethylene glycol as a stabilizer avoids the agglomeration of particles in the process. As a promising cathode material of lithium ion batteries, the LiFePO4/C in this work could provide an initiate discharge capacity of 155 mAh⋅g–1 and maintain 91.6% of initial capacity after 100 cycles at 0.1 C. The discharge capacity is 78.8 mAh⋅g–1 when circulating at high rate up to 10 C, showing excellent discharge performance. Furthermore, the in‐situ generated carbon ensures the higher electrical conductivity and the nano‐sized spheroidal LiFePO4/C particles prolong the cycle life of batteries, thus exhibiting high charge‐discharge capability, excellent rate properties and stable cycling behavior.

Flame aerosol deposited Li4Ti5O12 layers for flexible, thin film all-solid-state Li-ion batteries

Flexible thin film all-solid-state Li-ion batteries are considered as promising candidates to power a multitude of flexible and miniaturized electronic devices. The production of crystalline battery active materials generally involves high process temperatures above 500 °C. One current challenge in mechanically flexible thin film electrode fabrication is the direct deposition of such crystalline active materials onto temperature sensitive substrates. In the current work we have made a paradigm shift depositing highly pure crystalline Li4Ti5O12 nanoparticles onto a flexible polyimide foil in a single step using flame spray pyrolysis technique. The Li4Ti5O12 films were mechanically compressed at room temperature to 0.55 µm thin layers, to enhance their adhesion to the substrates, i.e. to increase mechanical stability. The smooth Li4Ti5O12 electrodes were covered with a solid electrolyte and tested against lithium metal electrodes. Stable electrochemical cycling behavior of the battery cells demonstrated the feasibility of the proposed technique for LTO thin film electrode fabrication on temperature sensitive and mechanically flexible polyimide substrates. Fundamental data on possible electrode cyclability upon electrode bending was obtained by successful cycling of LTO flex-TFBs in statically bent condition. This study could initialize a new branch for facile manufacturing of flexible thin film battery cells.

An Electrospun Nanofiber Membrane as Gel‐Based Electrolyte for Room‐Temperature Sodium–Sulfur Batteries

AbstractWe report on the synthesis and characterization of an electrospun gel polymer electrolyte (GPE) membrane based on polyacrylonitrile nanofibers (PAN) swollen in a polyethylene glycol dimethyl ether/Na‐salt electrolyte solution, for application in room temperature sodium–sulfur (Na–S) batteries. The membranes show a high ionic conductivity, wide electrochemical stability window, and good thermal stability. We demonstrate the performance of the membrane in an Na–S cell using a sulfur–carbon nanotubes composite cathode and Na metal as anode. Our results show that the GPE membrane stabilizes the Na metal anode resulting in stable cycling behavior. The capacity of the Na–S cell, using the GPE membrane and operating at room temperature, is approximately 500 mAh g−1 over 40 cycles. The selected electrolyte configuration also provides improved safety by replacing the highly reactive sodium perchlorate (NaClO4) salt previously used in literature. All these benefits make the gel‐polymer electrolyte membrane a very promising system for application in room‐temperature sodium and sodium–sulfur batteries.