Li4Ti5O12 Electrode Research Articles

Investigation of structural, optical, and electrochemical properties of niobium-doped Li4Ti5O12 for high-performance aqueous capacitor electrode

In this study, nanocrystalline niobium-doped lithium titanate Li4Ti5O12 (LTO) was successfully synthesized with various stoichiometric ratios (x = 0, 0.025, 0.05, 0.075, 0.1) using a niobium ethoxide precursor via the solid-state synthesis method. X-ray diffraction spectroscopy results revealed that the synthesized samples possess a spinel structure without any impurities, and lattice constants expanded from 8.357 Å to 8.363 Å as the concentration of niobium ions increased. Scanning electron microscopy (SEM) analysis demonstrated that particle sizes ranged from 1.13 to 1.56 μm. The smallest particle size was observed in the LTO-Nb-0.075 sample. The maximum absorptions were detected in the ultraviolet region, and the band gaps of Nb-doped Li4Ti5-xNbxO12 (x = 0, 0.025, 0.05, 0.075, 0.1) were determined using Tauc plots. These results showed that the band gaps of Nb-doped LTO were lowered compared to pure LTO, suggesting enhanced electron conductivity. X-ray photoelectron spectroscopy (XPS) measurements confirmed that the band gaps of Nb-doped samples decreased as the formation of oxygen vacancies and Ti3+ ions increased due to Nb5+ substitution. All synthesized samples displayed well-defined redox peaks in pairs during the cyclic voltammetry (CV) measurement. The optimal stoichiometric ratio for doping lithium titanate was found to be x = 0.075, as it yielded the highest specific capacitance of 3.59 F/g and the lowered band gap value of 3.13 eV. Therefore, this study provides further encouragement for applying LTO electrodes in aqueous capacitors and electrical uses.

A Novel Graphene Based Bi-Function Humidity Tolerant Binder for Lithium-Ion Battery.

Binders play a critical role in rechargeable lithium-ion batteries (LIBs) by holding granular electrode materials, conductive carbons, and current collectors firmly together to form and maintain a continuous electron conduction phase with sufficient mechanical strength. In the commercial LIBs, the dominant binder is polyvinylidene fluoride for the cathode (LiCoO2 , LiFePO4 , LiNix Coty Mnz O2 , etc.) and carboxyl methylcellulose/styrene-butadiene rubber for the anode (graphite and Li4 Ti5 O12 ). However, these polymer binders have several drawbacks, particularly, a lack of electronic and lithium-ion conductivities. Here, a novel organic/inorganic hybrid conductive binder (LAP-rGO) for both the anode and cathode of LIBs is reported. The binder consists of 2D reduced graphene oxide sheets with anchored long alkane chains. Electrodes prepared using this binder exhibit sufficient high bond strength, fast electrolyte diffusion, high rate charge/discharge performance, and excellent cycling stability. Around 130 mAh g-1 capacity enhancement at 5C is demonstrated for LiFePO4 and Li4 Ti5 O12 electrodes owing to the combined improvement in electron and lithium ion transportation. LAP-rGO bond graphite anode shows specific capacity beyond its theoretical value. Electrode slurries prepared using this new binder have superior processing and coating properties that can be prepared under a high humidity and dried using less energy.

Cd-Doped Li4–xCdxTi5O12 (x = 0.20) as a High Rate Capable and Stable Anode Material for Lithium-Ion Batteries

Li4Ti5O12 (LTO), an excellent anode for lithium-ion batteries (LIBs), suffers from low electronic conductivity, limiting its high-power rate application. An aliovalent metal ion doping strategy that tunes the electronic/ionic conductivity can mitigate this issue. In this work, we investigated a series of Cd2+ dopings on the Li4–xCdxTi5O12 (x = 0, 0.05, 0.10, and 0.20) anode material by considering its effect on structural and electrochemical performance in Li- and Na-ion batteries. Combined Rietveld refinement and X-ray absorption spectroscopy (XAS) analysis explicitly identified Cd2+ doping into the Li(8a) tetrahedral site of the cubic spinel LTO structure. According to high-resolution powder diffraction (HRPD), scanning electron microscopy (SEM), 4-point probe, and X-ray photoelectron spectroscopy (XPS), an increase in Cd2+ doping from 5 to 20% at the Li (8a) site in the LTO results in a reduction in particle size, an expansion of lattice, an increase in conductivity, and an increase in Ti3+ content to Ti4+ ratio. High-resolution scanning transmission electron microscopy (HR-STEM) confirms that cadmium ions are interstitially doped in the LTO structure. Compared to the pristine LTO electrode in the Li half cell, the Li3.80Cd0.20Ti5O12 (Cd0.20-LTO) electrode showed a significant improvement in capacity at high rates and excellent cycling performance. The improvement in performance for Cd0.20-doped LTO is a consequence of the reduction in the diffusion path and the faster Li-ion kinetics. Therefore, this Cd-doped LTO series of electrodes demonstrates advantageous features for Li-ion battery systems.

Structure optimization of solvent-free Li4Ti5O12 electrodes by electrostatic spraying for lithium-ion capacitors

The manufacturing processes of electrodes have a prominent influence on the cost and performance of lithium-ion capacitors (LICs), which are limited by the conventional wet-coated method due to the usage of solvent. Herein, the solvent-free Li4Ti5O12 (LTO) electrodes are prepared with electrostatic spraying deposition using for LICs. Owing to the solvent being avoided during the manufacturing, the dry-sprayed electrode exhibits a higher porosity (∼40%) than that of the wet-coated electrode (∼30%), together with a larger electrochemically active surface area. The optimized microstructure improves electrolyte infiltration and offers effective Li-ion transport paths, which reduces the electrochemical polarization and boosts the specific capacity of the dry-sprayed electrode. When the current density increases from 0.5 C to 10 C, the reversible capacity retention of the dry-sprayed electrode is 74%, which is higher than that of the wet-coated electrode (56%). In addition, the powder resistivity of the dry-sprayed electrode decreases sharply by introducing two-dimension (2D) graphene nanoplate (GN) as the conductive agent, thus side effects have been effectively suppressed during the spraying process. As a result, the assembled LICs using the dry-sprayed LTO electrodes show superior energy density and excellent cycling performance, demonstrating this novel fabrication method has practical application prospects.

Smart Multi‐Layer Architecture Electrodes for High Energy Density Lithium‐Ion Capacitors

AbstractMulti‐layer architectures for use in both negative and positive electrodes are developed through a layer‐by‐layer spray printing approach using complementary material combinations, with the ultimate goal to realize an ideal concept of hybrid lithium‐ion capacitors more fully – delivering attractive energy densities of insertion‐type negative electrodes while preserving outstanding power performances of activated carbon positive electrodes. To sustain advantageous capacities of intercalation anodes even at ultra‐fast charging rates, a thin, discrete layer of high capacity Si was interleaved between high power Li4Ti5O12 electrodes. In a cathode electrode, a sequential layer of insertion‐type LiFePO4 was assembled with a conventional activated carbon layer into a single layer structure, aiming at boosting overall deliverable capacities. The lithium‐ion capacitor comprising the smart multi‐layer architectures of negative and positive electrodes then provided a remarkable energy density of ∼110 Wh/kg with an outstanding power performance of 15 kW/kg.

Free-Standing Li4Ti5O12/Carbon Nanotube Electrodes for Flexible Lithium-Ion Batteries

Lithium-ion batteries (LIBs) have been used in many fields, such as consumer electronics and automotive and grid storage, and its applications continue to expand. Several studies have attempted to improve the performance of LIBs. In particular, the use of high-capacity silicon and tin as anodes has been widely studied. Although anodes composed of silicone and tin have high theoretical capacities, poor electrical conductivity and considerable volume expansion of such anodes deteriorate the LIB performance. Thus, Li4Ti5O12 (LTO), a zero-strain material, has attracted much attention with high cycle stability and rate capability through improved electrical conductivity. However, LTO has the disadvantages of a low electrical conductivity (10−8 to 10−13 S cm−1) and moderate Li+ ion diffusion coefficient (10−9 to 10−16 cm2 s−1). In this study, the flexible and free-standing composite films were fabricated using only LTO and multi-walled carbon nanotube(CNT) with high electrical conductivity and ion diffusivity. The prepared LTO/CNT films showed a higher charge/discharge capacity than the theoretical capacity of the LTO electrode.

Hydrothermal synthesis of Co-free NMA cathodes for high performance Li-ion batteries

Scalable and sustainable production of high voltage cathodes is required to meet the increasing demands for Li-ion batteries. Additionally, the anticipated scarcity of critical materials like cobalt necessitates demonstration of Co-free alternatives that can match the performance metrics of conventional cathodes. Herein, a hydrothermal synthesis route for production of a new class of high-capacity, cobalt-free cathode material, LiNi0.9Mn0.05Al0.05O2 (NMA9055) for next-generation Li-ion batteries is reported. The synthesized cathode material shows high crystallinity and purity with monodispersed spherical morphology. Extensive electrochemical, structural, and post-mortem characterization of this novel NMA material is carried out. NMA-Li half cells show an initial discharge capacity of 200 mAh/g with a 96% capacity retention over 100 cycles when cycled between 3.0 and 4.4 V. On the other hand, NMA full cells with Li4Ti5O12 (LTO) electrodes as the anode, show an initial discharge capacity of 186 mAh/g with 81% capacity retention over 200 cycles. Post-mortem structural and morphological characterization show that the NMA morphology and crystal structure do not degrade significantly over 200 charge/discharge cycles. This new class of cobalt free cathode material containing nickel, manganese and aluminum synthesized by an ammonia-free synthesis route is expected to provide a facile solution towards sustainable cathode production.

Deciphering the Interplay between Binders and Electrolytes on the Performance of Li4Ti5O12 Electrodes for Li-Ion Batteries

Lithium titanium oxide (Li4Ti5O12, LTO) is an attractive negative electrode for the development of safe—next-generation—lithium-ion batteries (LIBs). LTO can find specific applications complementary to existing alternatives for LIBs thanks to its good rate capability at high C-rates, fast lithium intercalation, and high cycling stability. Furthermore, LIBs featuring LTO electrodes are inherently safer owing to the LTO’s operating potential of 1.55 V vs. Li+/Li where the commonly used organic-based electrolytes are thermodynamically stable. Herein, we report the combined use of water-soluble sodium alginate (SA) binder and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)-tetraglyme (1m-T) electrolyte and we demonstrate the improvement of the electrochemical performance of LTO-based electrodes with respect to those operating in conventional electrolyte 1M LiPF6-ethylene carbonate: dimethyl carbonate (LP30). We also tackle the analysis of the impact of combining the binder/electrolyte on the long-term cycling performance of LTO electrodes featuring SA or conventional polyvinylidene fluoride (PVdF) as binders. Therefore, to assess the impact of the combination of binder/electrolyte on performance, we performed post-mortem characterization by ex situ synchrotron diffraction experiments of LTO electrodes after cycling in LP30 and 1m-T electrolytes.

Three-dimensional printed lithium iron phosphate coated with magnesium oxide cathode with improved areal capacity and ultralong cycling stability for high performance lithium-ion batteries

Three-dimensional (3D) printing of Li-ion batteries with unconventional 3D electrodes has attracted considerable attention in recent years. However, fabricating 3D electrodes with high specific capacity, high areal capacity, ultralong cycling stability, and improved rate performance remains a challenge to date. Novel 3D grid-patterned LiFePO4@MgO composite electrodes with thicknesses of 143, 306, and 473 μm were fabricated via 3D printing. The electrochemical performance of half cells was evaluated. The 3D-printed LiFePO4@MgO (143 μm) electrodes exhibit stable specific capacities of 142.8 mAh g−1 @ 1.0 C and 90.3 mAh g−1 @ 10.0 C after 800 and 1700 cycles, respectively. In addition, the 473 μm-thick 3D grid-patterned LiFePO4@MgO achieves an areal capacity of 3.01 mAh cm−2 @ 0.1 C after 20 cycles. The full cells comprised 143 μm-thick 3D-printed LiFePO4@MgO, and 217 μm Li4Ti5O12 electrodes show a capacity of 139.0 mAh g−1 @ 1.0 C after 400 cycles. These results indicate that, this type of thick 3D-printed LiFePO4@MgO electrode achieves high capacity, high-rate capability, and ultralong cycle stability. The outstanding performance ascribes the fast electrolyte infusion of 3D-printed electrodes and the enhanced electronic/ionic transport.

Electrochemical Pretreatment of Solid–Electrolyte Interphase Formation for Enhanced Li 4 Ti 5 O 12 Anode Performance in a Molten Li–Ca Binary Salt Hydrate Electrolyte

“Significant improvement in the cycle performance of a Li4Ti5O12 electrode was achieved using a Li–Ca binary salt hydrate (LCH) electrolyte in combination with an optimized electrochemical pretreatment process. The LCH electrolyte provided less-water-soluble Ca-based SEI components, and careful pretreatment process enabled the formation of a thicker SEI layer on the Li4Ti5O12 electrode, leading to 95.5 % capacity retention over 50 cycles…“ Learn more about the story behind the research featured on the front cover in this issue's Cover Profile. Read the corresponding Research Article at 10.1002/celc.202200061.

Front Cover: Electrochemical Pretreatment of Solid‐Electrolyte Interphase Formation for Enhanced Li 4 Ti 5 O 12 Anode Performance in a Molten Li−Ca Binary Salt Hydrate Electrolyte (ChemElectroChem 11/2022)

The Front Cover illustrates that less-water-soluble Ca-based solid electrolyte interphase formed in a Li–Ca binary salt hydrate electrolyte effectively mitigates electrochemical reduction of water, leading to improvement in the cycle performance of a Li4Ti5O12 electrode. More information can be found in the Research Article by S. Kondou et al.

Electrochemical Pretreatment of Solid‐Electrolyte Interphase Formation for Enhanced Li4Ti5O12 Anode Performance in a Molten Li−Ca Binary Salt Hydrate Electrolyte

AbstractWater‐in‐salt electrolytes have been widely explored because of their expanded electrochemical stability (>3.0 V). However, the instability of solid‐electrolyte interphase (SEI) in aqueous electrolytes leads to their reductive decomposition on the negative electrodes of low‐potential anode materials. Here, we demonstrate significant improvement in the cycle performance of a Li4Ti5O12 electrode using a Li−Ca binary salt hydrate (LCH) electrolyte in combination with an optimized electrochemical pretreatment process. Compared with a hydrate‐melt electrolyte, the LCH electrolyte provided less water‐soluble Ca‐based SEI components, and careful pretreatment process enabled the formation of a thicker SEI layer on the Li4Ti5O12 electrode. Protected with the hardly soluble, thick SEI layer, the Li4Ti5O12 electrode effectively mitigated unfavorable side reactions and achieved 95.5 % capacity retention over 50 cycles. These results offer insight into a promising route for stable SEI layer formation for the practical use of low‐potential anode materials in aqueous rechargeable lithium‐ion batteries.

Synthesis, characterisation and electrochemical evaluation of lithium titanate anode for lithium ion cells

Lithium titanate, Li4Ti5O12 (LTO), a promising anode material for high power lithium ion (Li-ion) cells, was synthesised by sol-gel method using hydrated titania and lithium carbonate as precursors. The synthesised material was characterised by Fourier-transform infrared spectroscopy and X-ray diffraction methods. The morphology of the material was studied by scanning electron microscopy. The electrochemical evaluation of LTO electrode in Li-ion cells was carried out by assembling LTO electrode versus Li metal as counter electrode in half cell. The cell was subjected to initial charge-discharge cycles at C/10 rate and then tested at different rates viz. C/5, C/2, 1C, 2C, 5C, 10C and 20C. The specific capacity at these rates was 170, 167, 165, 164, 161, 160, 160 and 155 mAh/g, respectively. The columbic efficiency of the cell was close to 100% at these rates. Herein, we demonstrate that a pristine LTO formed by simple sol-gel method can retain more than 90% of the capacity at high current rate of 20C.

Enhancements of the structures and electrochemical performances of Li4Ti5O12 electrodes by doping with non-metallic elements

This paper systematically explores the non-metallic element (F, Cl, Br, I, C and N) doping modification of lithium titanate oxide(LTO) electrode materials. C, N, and Br play a significant role in improving the electrochemical performance of lithium titanate, and each of them had different modification advantages. In terms of the structure changes of LTO, it was found that the C dopant significantly reduced the particle size and agglomeration between LTO particles, the Br dopant performed best in increasing the unit cell volume of the LTO, and the N dopant could form oxygen vacancies and a small amount of metallic TiN structure. In terms of electrochemical performance change of the LTO, the C dopant could effectively reduce the charge transfer resistance, the Br dopant could significantly improve the capacity at low rates(174.5 mAh g−1 at 0.1 C; 172.3 mAh g−1 at 0.5 C), and the N dopant could greatly promote the high rate performance of LTO (compared with pure LTO, the capacity of N-LTO at 10 C and 20 C, increased by 13.5% and 4.1%, respectively). The three dopants could induce different numbers of Ti3+ active sites, narrow the bandgap, and thereby thus facilitate the electron transport in the lattice of the LTO. This study provides new insights into optimizing the electrochemical performance of Li4Ti5O12 by adjusting the morphology, crystal structure, and electronic structure of lithium titanate based on the characteristics of non-metallic materials.

Structure Optimization of Solvent-Free Li4ti5o12 Electrodes by Electrostatic Spraying for Lithium-Ion Capacitors

Structure Optimization of Solvent-Free Li4ti5o12 Electrodes by Electrostatic Spraying for Lithium-Ion Capacitors

Carbon additive effect on the electrochemical performances of inkjet printed thin-film Li4Ti5O12 electrodes

Conventional rigid batteries find limited applications in the wearable and flexible electronics field, as difficulties in device integration due to lack of shape conformability to unconventional substrates remain an obstacle. Accordingly, new fabrication techniques are under investigations and printing techniques have attracted great interest for their selectivity, low material waste and scalability. In this frame, inkjet printing (IJP) has emerged as a potential fabrication technique to obtain flexible patterned thin-film electrodes with high resolution. However, a more in-depth systematic study of how IJP can be applied to lithium-ion batteries fabrication is still missing. Herein, we propose a study that focuses on how different carbon-based additives (Nitta et al., 2015; Choi and Ahn, 2018 [1,2]), i.e. carbon black and multi-walled carbon nanotubes, affect the electrochemical performances of inkjet printed thin-films Li4Ti5O12 electrodes. A simple ink formulation is proposed, which is aqueous-based, non-toxic and safe to handle. The fabricated thin-film electrodes showed different specific capacity, the highest associated with the carbon nanotubes-based (CNTs) electrode, i.e. 150.3 mAh g−1 at 0.2 C, showing that CNTs improving electrochemical performances can be applied also to printed electrodes. The carbon nanotubes-based electrodes showed excellent cycle stability, with negligible capacity loss for over 100 cycles. The work highlights the importance of a valid material choice to reach the desired electrode performances and may inspire alternatives paths to deepen IJP of lithium-ion batteries fabrication.

Rivalry at the Interface: Ion Desolvation and Electrolyte Degradation in Model Ethylene Carbonate Complexes of Li+, Na+, and Mg2+ with PF6 - on the Li4Ti5O12 (111) Surface.

Spinel lithium titanate, Li4Ti5O12 (LTO), emerges as a “universal” electrode material for Li-ion batteries and hybrid Li/Na-, Li/Mg-, and Na/Mg-ion batteries functioning on the basis of intercalation. Given that LTO operates in a variety of electrolyte solutions, the main challenge is to understand the reactivity of the LTO surface toward single- and dual-cation electrolytes at the molecular level. This study first reports results on ion desolvation and electrolyte solvent/salt degradation on an LTO surface by means of periodic DFT calculations. The desolvation stages are modeled by the adsorption of mono- and binuclear complexes of Li+, Na+, and Mg2+ with a limited number of ethylene carbonate (EC) solvent molecules on the oxygen-terminated LTO (111) surface, taking into account the presence of a PF6– counterion. Alongside cation adsorption, several degradation reactions are discussed: surface-catalyzed dehydrogenation of EC molecules, simultaneous dehydrogenation and fluorination of EC, and Mg2+-induced decay of PF6– to PF5 and F–. Data analysis allows the rationalization of existing experimentally established phenomena such as gassing and fluoride deposition. Among the three investigated cations, Mg2+ is adsorbed most tightly and is predicted to form a thicker fluoride-containing film on the LTO surface. Gassing, characteristic for carbonate-based electrolytes with LTO electrodes, is foreseen to be suppressed in dual-cation batteries. The latter bears promise to outperform the single-ion ones in terms of durability and safety.

Towards High Energy Density Electrochemical Energy Storage Systems: Li- and Na-Ion-Based Ultrathick Electrodes with New Current Collector Architectures By Spark Plasma Sintering and Hard Templating Approach

High energy density electrodes are of great interest for the application in electrochemical energy storage systems as well as electric vehicles. While the vast majority of research is still focusing on crystallochemical search for the new high-voltage/high-capacity materials, the cell engineering approach goes relatively unnoticed. However, over the past couple of decades, more and more research activities are aimed at developing new battery configurations to further improve the energy density of Li- and Na-ion batteries without fundamentally changing the underlying chemistry. Some methods suggest the fabrication of (ultra)thick electrodes while others concentrate on the production of electrodes with a minimum amount of inactive materials (binder-free, conductive additive-free, integrated current collectors, etc). Owing to a rapid and highly efficient sintering process, Spark Plasma Sintering (SPS) offers the luxury of obtaining simultaneously binder-free and (ultra)thick electrodes which suffer no structural degradation.Combined with novel integrated current collector architectures, SPS-fabricated (ultra)thick electrodes could provide high active material accessibility while working at elevated current rates owing to the controlled pore network morphology and improved electronic conductivity. In 2018 Elango et. al reported a successful Spark Plasma Sintering of the LiFePO4 and Li4Ti5O12 electrodes with controlled porosity by hard templating method (NaCl leaching) [1]. Obtained by SPS and templating approach ultrathick electrodes (1 mm thick) showed remarkable electrochemical performance at C/20 against lithium metal delivering areal capacities 4 times higher than those of the conventional tape-casted electrodes. This study coming from our group demonstrated the proof-of-concept in the fabrication of Li-ion battery electrodes with an ultrathick design by means of SPS. A follow-up study on the correlation between the electrode’s architecture (porosity level and pore size) and its electrochemical performance has been conducted [6] showing that a moderate increase of porosity and decrease in pore size improves the rate capability of the (ultra)thick electrodes (1 mm thick) by reducing the pore tortuosity and promoting fuller electrolyte impregnation.Spark Plasma Sintering-based electrode fabrication technique is expected to be easily transferable to other battery types like Na-ion batteries. However, commonly used Na-ion battery materials are not as widely produced as their Li counterparts and still require long and tedious synthesis procedures. In our work, we have recently demonstrated that SPS could be used to synthesize a common Na-ion battery cathode material – Na3V2(PO4)2F3 – in under only 40 min [2] which resembles a phase-pure compound with a small particle size showing slightly enhanced electrochemical performance when compared to the solid-state synthesized NVPF. SPS-synthesized NVPF requires no further treatment and could be used directly as an active material component in the production of our thick binder-free electrodes.In this presentation, the detailed study on the correlation between the (ultra)thick electrode architecture (porosity, pore size/shape distribution, tortuosity, etc), synthesis/sintering parameters, nature of precursors, and the electrochemical performance will be discussed (both for Li- and Na-ion batteries). An insight into the fabrication of (ultra)thick electrodes with novel integrated current collector architectures and their impact on the structural integrity as well as the electrochemical performance of the electrode will be reported.[1] R. Elango et al., Advanced Energy Materials, Vol 8 Issue 15 (2018)[2] A. Nadeina et al., Energy Technol., 8: 1901304 (2020)[3] F. Lalère, et al, Journal of Power Sources, 247, 975-980 (2014)[4] G. Delaizir, et al., Adv. Funct. Mater., 22: 2140-2147 (2012)[5] A. Aboulaich, et al., Adv. Energy Mater., 1: 179-183 (2011)[6] R. Elango, A. Nadeina, et al., Journal of Power Sources, 488, 229402 (2021) Figure 1

Investigating Pore Microstructure Effects on Sintered Electrode Transport and Rate Capability

Lithium-ion (Li-ion) batteries have achieved significant commercial success and found widespread use in numerous applications. To further improve the energy density of Li-ion batteries, reducing the inert material and increasing the electrode thickness are two routes. Recently, electrodes that consist of active material only and fabricated via mild sintering treatment have been explored. These sintered electrodes have greater thickness and thus showed much higher areal capacity than composite electrodes. However, restricted Li+ transport in the electrolyte phase through the porous microstructure of thick electrodes limits the ability to achieve high current densities and rates of charge/discharge with these high energy cells.In this work, cells with sintered LiCoO2 (LCO) and Li4Ti5O12 (LTO) electrodes have been fabricated and tested. Processing routes to mitigate transport restrictions were pursued. For LTO electrodes, comparisons were done between using ice-templating to provide directional porosity and using sacrificial particles during processing to match the geometric pore/void density without pore alignment. The ice-templated electrodes retained much greater discharge capacity at higher rates of cycling, which was attributed to improved transport properties provided by the processing. The electrodes were further characterized using an electrochemical model of the cells and evaluated using neutron imaging. The results indicated that significant improvements can be made to electrochemical cell properties via templating the electrode microstructure for situations where the rate limiting step includes ion transport limitations in the cell.

Mechanical Stirring Synthesis of 1D Electrode Materials and Designing of Pyramid/Inverted Pyramid Interlocking for Highly Flexible and Foldable Li-Ion Batteries with High Mass Loading.

Flexible and foldable Li-ion batteries (LIBs) are presently attracting immense research interest for their potential use in wearable electronics but are still limited to electrodes with very small mass loading, low bending/folding endurance, and poor electrochemical stability during repeated bending and folding movements. Moreover, one-dimensional (1D) structured electrode materials have shown excellent electrochemical performance but are still restricted by the high cost and complicated fabrication process. Here, we present a very simple yet novel approach for fabricating extra-long Li4Ti5O12 (LTO) and LiCoO2 (LCO) nanofiber precursors by directly stirring the reagents in an atmospheric vessel. In addition, we present multilayer pyramid/inverted pyramid interlocking inside the LTO and LCO nanofiber films as well as between films and current collectors, which can create strengthened interfacial bonding like a zipper and tangentially disperse the strains generated during folding through the pyramidal planes and edges, leading to the realization of thick-film electrodes with outstanding electrochemical stability during folding movements. The foldable LIBs that are assembled with LTO and LCO nanofiber electrodes at a practical level of mass loading (14.9-19.4 mg cm-2) can maintain 102% of the initial capacity after 15 000 times of fully folding (180°) motions.