High Energy Density Li-ion Research Articles

Electrocatalysis driven high energy density Li-ion polysulfide battery

Though carbon-based porous materials have improved lithium-sulfur (Li-S) battery performance remarkably, the poor adsorption of polysulfides and their sluggish reaction kinetics limits them from practical application. On the other hand, the presence of lithium metal especially under the highly reactive polysulfide environment causes safety concerns. Herein, we use electrocatalytically active cathode and metallic lithium-free anode to construct Li-ion polysulfide battery with enhanced reversibility and safety. Stabilizing lithium polysulfides and enhancing the reaction kinetics with minimal polarization using platinum/graphene composite holds the key to obtaining better performance, which is realized against conventional metallic lithium as well as pre-lithiated porous silicon electrodes. The electrocatalyst containing cathode composites are comparable with graphene-based electrodes regarding enhanced specific capacity retention and better reversibility in charge/discharge behavior. Furthermore, metallic lithium-free polysulfide batteries displayed exceptional performance with an energy density of 450 Wh kg−1 considering the weight of both the electroactive materials and a capacity retention of about 70% for 240 charge-discharge cycles.

Material structure and chemical bond effect on the electrochemical performance of black phosphorus-graphite composite anodes

Black phosphorus (BP) is a little-studied but promising next-generation anode material for high-energy density Li-ion and Na-ion batteries. To understand the relationship between material property and electrochemical performance, black phosphorus-graphite (BP-G) composite materials are synthesized with two different BP-G molar ratios. This study demonstrates that the crystal structure and PC bond of BP-G composites are affected by the BP-G molar ratio, which are directly correlated to cycle stability and the lithiation/delithiation process. BP0.9G1 shows a medium-range ordered structure, retaining some features of BP and having fewer or weaker PC bonds. In contrast, BP0.3G1 has an amorphous-like structure with robust PC bonds, which is helpful in withstanding the large volume change upon lithiation or delithiation. As a result, fracture and pulverization of particles, which are clearly seen in BP0.9G1 electrode, are scarcely observed in the cycled BP0.3G1 electrode. The possibility of mechanical failure in the BP-based electrode induced by BP's hydrophilic nature and the formation of Cu3P is also discussed. This work not only contributes to improving the current understanding of phosphorus-based anodes, but also provides direct evidence of fracture and pulverization of BP particles during cycling.

Role of Polyacrylic Acid (PAA) Binder on the Solid Electrolyte Interphase in Silicon Anodes

To obtain high-energy density Li-ion batteries for the next-generation storage devices, silicon anodes provide a viable option because of their high theoretical capacity, low operating potential ve...

Double-helix-superstructure aqueous binder to boost excellent electrochemical performance in Li-rich layered oxide cathode

Li-rich layered oxides are highlighted as promising candidates for the next-generation cathode materials in Li-ion batteries, but suffer from poor cycling stability and voltage fading during the cycling process. Currently, less efforts are devoted to addressing these issues through exploring novel binders. In this work, we explore an aqueous binder of xanthan gum with double helix superstructure containing abundant charged functional groups. This unique structure is beneficial to the occurrence of significant mechanical interlocking effect and formation of chemical bond with particles’ surface, which can effectively suppress electrode exfoliation, particle pulverization and structural degradation during cycling. As a consequence, the electrode with xanthan gum still delivers the discharge capacity of 275.6 mAh g−1 with the retention of 98.4% after 200 cycles at 0.1C rate. Accordingly, the mid-point discharge voltage remains 87% (about 2.3 mV/per cycle drop). The current study provides a useful insight into how to design and develop superior binders based on charged double-helix superstructure for potential low-cost and environmentally friendly aqueous processing of high energy density Li-ion batteries.

Erratum to: Lithium-ion full cell with high energy density using nickel-rich LiNi0.8Co0.1Mn0.1O2 cathode and SiO-C composite anode

A high-energy-density Li-ion battery with excellent rate capability and long cycle life was fabricated with a Ni-rich layered LiNi0.8Mn0.1Co0.1O2 cathode and SiO−C composite anode. The LiNi0.8Mn0.1Co0.1O2 and SiO−C exhibited excellent electrochemical performance in both half and full cells. Specifically, when integrated into a full cell configuration, a high energy density (280 Wh·kg−1) with excellent rate capability and long cycle life was attained. At 0.5C, the full cell retained 80% of its initial capacity after 200 charge/discharge cycles, and 60% after 600 cycles, indicating robust structural tolerance for the repeated insertion/extraction of Li+ ions. The rate performance showed that, at high rate of 1C and 2C, 96.8% and 93% of the initial capacity were retained, respectively. The results demonstrate strong potential for the development of high energy density Li-ion batteries for practical applications.

Unveiling the Origin of Superior Electrochemical Performance in Polycrystalline Dense SnO2 Nanospheres as Anodes for Lithium-ion Batteries

Development of feasible electrode materials is significant to realize high energy density Li-ion batteries (LIBs). Tin(IV) oxide, in particular, has a number of merits including higher theoretical capacity compared with graphite (1493 mAh g–1), low cost, and environmental friendliness. Nevertheless, huge volume changes and subsequent pulverization usually resulted in poor capacity retention of SnO2, where various nanostructures have been adopted to overcome its intrinsic limitations. Here we introduce the new insights into employing polycrystalline dense SnO2 nanospheres (NSs), rather than its hollow structures, as high-performance electrode for LIBs. Contrary to the previous notions, polycrystalline dense SnO2 NSs can exhibit highly stable cycle retention characteristics (1009.9 mAh g–1 after 300 cycles at 0.5 A g–1) as well as considerable rate capabilities (349 mAh g–1 at 5.0 A g–1), even superior to those of polycrystalline hollow SnO2 NSs. Based on the in situ TEM analyses and electrochemical/postmor...

Problem and Simple Solutions of Layered Cathode Materials

Layered cathode materials, including Ni-rich and Li-rich lithium transition metal oxides, are one class of the most promising cathode materials for high energy density Li-ion batteries because of their high capacity and low cost. However, the Ni-rich and Li-rich cathode materials face two same problems of (1) oxygen evolution at high potentials, and (2) significant amount of Li residues in the forms of Li2O, LiOH, and Li2CO3 on the particle surface. Most of known concerns with these two types of cathode materials can be attributed to these two problems, such as irreversible phase transition from hexagonal to cubic phase, intergranular cracking with repeated cycling, transition metal ion dissolution, as well as electrolyte degradation that consequently results in impedance increase and volumetric swelling of the batteries. Since these two problems are the intrinsic properties of the layered lithium transition metal oxides, there are no perfect solutions that can completely solve these two problems. What one can do is to minimize the negative effects caused by these two problems. By selecting Ni-rich LiNi0.80Mn0.10Co0.10O2 (NMC811) as an example, in this presentation we demonstrate two simple strategies: (1) removing Li residues in the cathode slurry-coating step, and (2) in-situ eliminating the released active oxygen in the battery. Both strategies are simple without need of changing the existing procedures, and show different degree improvements on the cycling stability and rate capability of the Li/NMC811 cells. Our presented strategies are believed to be applicable to all other Ni-rich and Li-rich layered cathode materials.

In Situ Focused Ion Beam Scanning Electron Microscope Study of Microstructural Evolution of Single Tin Particle Anode for Li-Ion Batteries.

Tin (Sn) is a potential anode material for highenergydensity Li-ion batteries because of its high capacity, safety, abundance and low cost. However, Sn suffers from large volume change during cycling, leading to fast degradation of the electrode. For the first time, the microstructural evolution of micrometer-sized single Sn particle was monitored by focused-ion beam (FIB) polishing and scanning electron microscopy (SEM) imaging during electrochemical cycling by in situ FIB-SEM. Our results show the formation and evolution of cracks during lithiation, evolution of porous structure during delithiation and volume expansion/contraction during cycling. The electrochemical performance and the microstructural evolution of the Sn microparticle during cycling are directly correlated, which provides insights for understanding Sn-based electrode materials.

Requirements for Enabling Extreme Fast Charging of High Energy Density Li-Ion Cells while Avoiding Lithium Plating

To improve electric vehicle market acceptance, the charge time of their batteries should be reduced to 10–15 minutes. However, achieving 4C to 6C charge rates with today's batteries is only possible for cells with thin electrodes coming at the expense of low energy density and high battery manufacturing cost. An electrochemical model is validated versus high rate charge data for cells with several loadings. The model elucidates that the main limitations for high energy density cells are poor electrolyte transport resulting in salt depletion within the anode and Li plating at the graphite/separator interface. Next, the model is used to understand what future electrode and electrolyte properties can help enable 4C and 6C charging. Ideally, future electrolytes would be identified with 2X conductivity, 3–4X diffusivity, and transference number of 0.5–0.6. Alternatively charging at elevated temperatures enhances electrolyte transport by 1.5X conductivity and 2–3X diffusivity with a negligible effect on transference number. Another effective strategy to enable 4C and 6C charging is reducing electrode tortuosity. Conversely, increasing electrode porosity and negative/positive ratio are ineffective strategies to improve fast charge capability.

Weakened Capacity Fading of Li-Rich Cathode via Aqueous Binder for Advanced Lithium Ion Batteries

Poor capacity stability during long cycle and poor adhesion under high potential hinder the Lithium-manganese rich layered oxides cathode from applications, and necessary strategy for this is clearly needed. In this work, a novel aqueous binder (lithium poly (acrylic acid), Li-PAA) is introduced for stabilized cyclic performance of Li1.15Ni0.17Co0.11Mn0.57O2 materials. Contrasting with the commercial ones (polyvinylidene fluoride, PVDF), this binder is beneficial to enhance the connection between the electrode and current collector, which can improve cycle stability. In the meanwhile, optimization mechanisms are revealed via detailed measurements, which indicate the suppressed formation of spinel phase during cycling. As a result, the electrode with Li-PAA still delivers the specific capacity of 254.7 mAh g−1 with the retention of 90.77% after 200 cycles at 0.1C, higher than that of electrode with PVDF (223.6 mAh g−1,76.21%). The current subject study provides a conducive insight to develop an excellent binder based on Li-PAA for potential low-riced and environmentally friendly high energy density Li-ion batteries.

Concentrated Electrolytes for Enhanced Stability of Al-Alloy Negative Electrodes in Li-Ion Batteries

Replacing graphite with alloying Al negative electrodes would allow for the development of high energy density Li-ion batteries. However, large volume changes associated with the alloying/dealloying process often result in pulverization of the electrode and rapid capacity fade during cycling due to the continuous formation of solid electrolyte interphase (SEI) layers and loss of electronic contact. In this study, we report that increasing salt concentration in the electrolyte to > 5 mol dm−3 led to enhanced capacity retention during cycling of Li-Al half-cells, which was accompanied by nearly constant impedance for the Al electrode in lithium bis(fluorosulfonyl)imide (LiFSI)/dimethyl carbonate (DMC) 1:1.1 (mol/mol) superconcentrated electrolyte. X-ray photoelectron spectroscopy (XPS) revealed that a potential hold in the superconcentrated electrolyte formed an SEI layer with a greater LiF concentration than in standard 1 mol dm−3 solution. This was supported by Raman spectroscopy of LiFSI solutions in DMC, supplemented with density functional theory calculations, which showed an increased driving force for the reduction of FSI− anions to form LiF from Li+-coordinated DMC complexes with increasing salt concentration. Therefore, the enhanced capacity retention and stability can be attributed to the stability of LiF-rich SEI layers which limit carbonate reduction and charge transfer impedance growth.

Temperature dependent flux balance of the Li/Li7La3Zr2O12 interface

The potential for safe, high energy-density Li-ion batteries has motivated the development of the solid electrolyte Li7La3Zr2O12 (LLZO) to physically stabilize the Li-electrolyte interface. Although dense LLZO is a relatively hard ceramic, it has been observed that above a certain critical current density (CCD), Li metal can still propagate through both polycrystalline and single crystalline LLZO. However, reported values of CCD are still well below the current density regimes relevant to applications like electric vehicles (≥3 mA cm−2). The relationship between CCD and temperature was studied using recently developed methods for achieving consistently low interfacial impedances without interfacial coatings that can complicate the analysis of what controls interface stability. By analyzing the flux of Li+ ions at the Li-electrolyte interface, it is hypothesized here that solid-state diffusivity of Li in the Li electrode may be a governing mechanism that controls the CCD. These results demonstrate an improvement for dendrite-free cycling in LLZO up to ∼1 mA cm−2 at room temperature and ∼7 mA cm−2 at 100 °C without the need for coatings to achieve low interface resistances (∼10 Ω cm2). Furthermore, the presented analysis may provide additional insight on the role of Li diffusivity in Li propagation through ceramic electrolytes.

Non-flammable organic liquid electrolyte for high-safety and high-energy density Li-ion batteries

With increased energy density of rechargeable lithium-ion batteries for powering smart phones and electric vehicles and for their long range use, battery safety becomes more important than ever. This aspect motivated us to develop non-flammable liquid electrolyte that removes the risk of battery fire and explosion, which is urgently needed. Battery energy density and performance however should not be sacrificed to achieve just the safety. Here we report for the first time a rational design of non-flammable carbonate-based organic liquid electrolyte to satisfy safety, energy density and performance simultaneously. Our novel electrolyte, composed of 1 M lithium hexafluorophosphate salt and propylene carbonate and fluorinated linear carbonate co-solvents, at unmeasurable flash point does not fire representing non-flammable safe batteries but permits high-voltage stability to enable high-voltage charge of lithium-rich layered oxide cathode up to 5.0 V, high-energy density of 856 Wh per kg of cathode active mass and stable charge-discharge cycling performance of full-cell with graphite anode, in contrast to rapid performance fade of flammable conventional electrolyte system. The discovery of non-flammable carbonate-based organic liquid electrolyte opens up a new avenue to high-safety and high energy-density lithium-ion batteries for electric vehicles and advanced energy-storage applications.

Scale-up production of high-tap-density carbon/MnOx/carbon nanotube microcomposites for Li-ion batteries with ultrahigh volumetric capacity

Electrode materials with high tap density are important for their practical application to achieve high volumetric energy density Li-ion batteries. In this work, large-scale fabrication of microsized carbon/MnOx/carbon nanotube composites by a low-cost spray-drying method is reported. The carbon/MnOx/carbon nanotube is characteristic of microspherical morphology consisting of interconnected carbon nanotubes and nano-MnOx with an exterior carbon coating. The micropacking enables the composite to exhibit a tap density as high as 2.54 g cm−3. When evaluated as anode materials for Li-ion batteries, the high-tap-density carbon/MnOx/carbon nanotube electrode delivers a specific capacity of 927 mAh g−1 after 100 cycles, corresponding to an ultrahigh volumetric capacity of 2355 mAh cm−3. The carbon network also has dual-functions of excellent electrical conductivity and good mechanical elasticity for the MnOx to sustain superior rate and cycling properties. The scale-up production method provides a reliable practical avenue of fabricating high-tap-density metal-oxide materials for high-performance Li-ion batteries.

Hierarchical nanostructured silicon-based anodes for lithium-ion battery: Processing and performance

Silicon anodes are promising for high energy density Li-ion batteries but are prone to capacity fading with cycles due to volume change and stress buildup leading to failure of electrodes. This study presents an innovative approach for realizing a high capacity silicon anode based on easily available metallurgical low-grade polycrystalline silicon powder. A three-step technique comprising of etching to create silicon nanofibers on particles, rapidly freezing the homogeneous mixture of Si nanofibers and superconducting carbon black in furfuryl alcohol solution, and then converting the furfuryl alcohol to carbon is used to achieve hierarchical nanostructure and improved performance. This approach ensures that the porous structure is filled with and separated by superconducting carbon black and is covered with a conformal and uniform conducting carbon coating. This approach improves the conductivity of the electrode and offers the flexibility for managing the volume expansion during lithiation and delithiation. The resultant electrode shows a reversible specific capacity of ∼778 mA h g−1 even after 200 cycles and coulombic efficiency of 99.6%.

Non-Carbonate Based Electrolytes for High Energy Lithium-Rich Manganese-Based Positive Electrodes with Excellent Cyclability

The demand for high specific-capacity positive electrode materials has become a high priority for the integration for high-energy density rechargeable lithium-ion batteries (LIBs) in transportation and grid storage applications. With the advantages of high capacity of >280 mAh g-1, high operating voltage (>3.2 V vs. Li+/Li on average) and low cost, Li-rich Mn-based layered oxides xLi2MnO3-(1-x)•LiMO2 (M= Ni, Co, Mn) have emerged as a potential next-generation positive electrode materials for high-energy density Li-ion batteries. However, a poor cycling stability observed in Li-rich cathodes is regarded as a major obstacle to commercialization. It is now well recognized that the use of conventional carbonate-based electrolytes in current Li-rich positive electrodes, which can react with oxygen evolved from the lattice of Li-rich positive electrodes during cycling, is a major cause for theirs poor cycling stability. Therefore, here we select several non-carbonate based electrolyte solvents including ethers, crown ethers, fluorinated ethers (1, 1, 1, 3, 3, 3-hexafluoroisopropyl methyl ether, HFPM), sulfones and phosphates and prepare some electrolytes based these non-carbonated solvents. The results indicate that the Li-rich electrodes with non-carbonate electrolyte show good performance in galvanostatic cycling, confirming their potential as rich-Li positive materials with enhanced longevity and safety. Figure 1

Structural and mechanistic revelations on high capacity cation-disordered Li-rich oxides for rechargeable Li-ion batteries

High capacity cation-disordered Li-rich oxides not only enlarge the chemical design space of cathode materials, but also play an important role in promoting the development of high energy density Li-ion batteries. However, there are still some issues, such as capacity degradation, that impede their practical applications. In-depth understanding of the structure and mechanisms in cation-disordered Li-rich oxides is favorable for their further performance optimization. Herein, taking the new designed high capacity (~ 280 mA h/g) disordered Li1.2Ti0.35Ni0.35Nb0.1O1.8F0.2 as a model compound, we meticulously study its structure evolution and electrochemical reaction mechanisms upon cycling by combination of first principles calculation, synchrony X-ray diffraction (SXRD), X-ray pair distribution function (XPDF), X-ray absorption spectroscopy (XAS), in situ XRD, and Neutron powder diffraction (NPD) et al. The excellent structure stability and robust anions framework of cation-disordered Li-rich oxides are experimentally demonstrated. Meanwhile, the high capacity mechanisms rely on the simultaneous cations and anions redox reactions and the capacity degradation mechanism induced by oxygen loss upon cycling are also proposed. Based on these revelations, the optimization strategy and potential applications of cation-disordered Li-rich oxides are further proposed.

High-Performance LiNiO2 Cathodes with Practical Loading Cycled with Li metal Anodes in Fluoroethylene Carbonate-Based Electrolyte Solution

LiNiO2 is one of the most promising cathode materials for high energy density Li ion batteries because of its high theoretical capacity (275 mAh g–1) and reasonable cost. However, cathodes comprising pure LiNiO2 suffer from intrinsic instability problems, which lead to their capacity fading during cycling. We report herein on highly stable Li (metal)–LiNiO2 prototype cells with practical areal loading of the electrodes due to the quality of the cathode material and the use of a suitable electrolyte solution in which both the Li metal anodes and the LiNiO2 cathodes are stabilized. The electrolyte solution contains 1 M LiPF6 in 1:4 (by volume) mixture of fluoroethylene carbonate (FEC) and dimethyl carbonate (DMC)). The cells with practical cathode loading (4 mAh cm–2), low amount of the electrolyte solution (33 μL cm–2), and Li metal anodes were cycled at 0.8–1 mA cm–2 for more than 700 cycles with excellent capacity retention. We attribute these results to the combination of optimal structure and morpholog...

All electrochemical process for synthesis of Si coating on TiO2 nanotubes as durable negative electrode material for lithium ion batteries

The development of high energy density Li-ion batteries requires to look for electrode materials with high capacity while keeping their stability upon cycling. In this study, amorphous silicon (a-Si) thin film deposited on self-organized TiO2 nanotubes is investigated as negative electrode for Li-ion batteries. Nanostructured composite negative electrodes were fabricated by a two-step cost effective electrochemical process. Firstly, self-organized TiO2 nanotube arrays were synthesised by anodizing of Ti foil. Subsequently, thanks to the use of room temperature ionic liquid, conformal Si layer was electrodeposited on the TiO2 nanotubes to achieve the synthesis of nanostructured a-Si/TiO2 nanotube composite negative electrodes. The influence of the Si loading as well as the crystallinity of the TiO2 nanotubes have been studied in terms of capacity and cyclic stability. For an optimized a-Si loading, it is shown that the amorphous state for the TiO2 nanotubes enables to get stable lithiation and delithiation with a total areal charge capacity of about 0.32 mA h cm−2 with improved capacity retention of about 84% after 50 cycles, while a-Si on crystalline TiO2 nanotubes shows poor cyclic stability independently from the Si loading.

Fabrication of SU-8 Based Three-Dimensional Carbon Microelectrodes Array As Anode Material for Lithium Ion Batteries

Introduction The development of three-dimensional (3D) microelectrodes is essential not only to achieve high energy and power density Li-ion batteries but also to minimize the ohmic losses and therefore achieve better performance. In this work, we used SU-8, an epoxy based negative photoresist which yields hard carbon upon pyrolysis for fabricating 3D micro-post arrays as electrodes1. The SU-8 derived 3D carbon microelectrodes on Silicon (Si) wafer has been reported earlier in literature, however the capacity values were quite moderate2. This is due to the high resistance offered by Si wafer used as a collector. Our group reported recently that the gravimetric reversible capacity value may be almost doubled when SU-8 derived carbon film was prepared on stainless steel (SS) wafer as compared to Si wafer. This inspires us further to fabricate 3D carbon microelectrodes array on SS wafer and to test their electrochemical performance. Experimental SU-8 2100 was spin coated on cleaned SS wafer. Prebaking, UV exposure and post-exposure baking conditions were optimized to prepare SU-8 based 3D micropillars with an aspect ratio of 2 (50µm height and 25µm diameter), and 35µm spacing using photolithography. As-obtained micropillars were then pyrolysed under the controlled N2 atmosphere in a tubular furnace at 900ºC to obtain 3D carbon microelectrode arrays. As-fabricated, 3D carbon microelectrode array on SS wafer was used as working electrode while lithium foil as the counter electrode in Swagelok half-cell assembly to test their electrochemical performance using potentiostat/galvanostat. Results and discussions Figure 1a shows the optical profiler image of SU-8 derived 3D carbon microelectrode array. It was observed that the 3D cylindrical morphology was retained after carbonization however there was nearly 50% shrinkage. As-obtained 3D carbon microelectrode arrays were found to have 26µm height, 16µm diameter, and 40µm spacing. Galvanostatic charge-discharge experiments were carried out at 37.2 mA/g current density. These 3D carbon microelectrode arrays have shown a high discharge capacity (~600 mAh/g) even after 165 continuous charge/discharge cycles (Figure 1b). This is significantly higher than the reported values for 3D carbon micropillars on Si wafer2. A comparison of volumetric capacity was also made. Further detailed characterization of these carbon microelectrodes and their electrochemical performance with cyclic voltammetry results will be presented during the conference.