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Recharging battery‐powered electric vehicles (EVs) in a similar timeframe as those used for refueling gas‐powered internal combustion vehicles is highly desirable for rapid penetration of the EV market. It is well known that the electrolyte in a battery plays a critical role in fast‐charging capability of the battery because it determines the rate of ion transport together with its derived electrode/electrolyte interphases on both cathode and anode of the battery. In this study, the effects of contents of salt, coordinating solvent, and noncoordinating diluent on salt dissociation degree and electrolyte ionic conductivity are investigated, and a controlled solvation structure electrolyte is developed to improve the lithium ion mobility and conductivity in the electrolyte and to enhance the kinetics and stability of the electrode/electrolyte interphases in the battery. This electrolyte enables fast‐charging capability of high energy density lithium‐ion batteries (LIBs) at up to 5 C rate (12‐min charging), which significantly outperforms the state‐of‐the‐art electrolyte. The controlled solvation structure sheds light on the future electrolyte design for fast‐charging LIBs. [ABSTRACT FROM AUTHOR]

Localized high‐concentration electrolytes (LHCEs) based on five different types of solvents were systematically studied and compared in lithium (Li)‐ion batteries (LIBs). The unique solvation structure of LHCEs promotes the participation of Li salt in forming solid electrolyte interphase (SEI) on graphite (Gr) anode, which enables solvents previously considered incompatible with Gr to achieve reversible lithiation/delithiation. However, the long cyclability of LIBs is still subject to the intrinsic properties of the solvent species in LHCEs. Such issue can be readily resolved by introducing a small amount of additive into LHCEs. The synergetic decompositions of Li salt, solvating solvent and additive yield effective SEIs and cathode electrolyte interphases (CEIs) in most of the studied LHCEs. This study reveals that both the structure and the composition of solvation sheaths in LHCEs have significant effect on SEI and CEI, and consequently, the cycle life of energetically dense LIBs. [ABSTRACT FROM AUTHOR]

It has been widely assumed that the flammability of the liquid electrolyte is one of the most influential factors that determine the safety of lithium‐ion batteries (LIBs). Following this consideration, a completely nonflammable electrolyte is designed and adopted for graphite||LiFePO4 (Gr||LFP) batteries. Contrary to the conventional understanding, the completely nonflammable electrolyte with phosphorus‐containing solvents exhibits inferior safety performance in commercial Gr||LFP batteries, in comparison to the flammable conventional LiPF6‐organocarbonate electrolyte. Mechanistic studies identify the exothermic reactions between the electrolyte (especially the salt LiFSI) and the charged electrodes as the "culprit" behind this counterintuitive phenomenon. The discovery emphasizes the importance of reducing the electrolyte reactivity when designing safe electrolytes, as well as the necessity of evaluating safety performance of electrolytes on a battery level. [ABSTRACT FROM AUTHOR]

Despite being an effective flame retardant, trimethyl phosphate (TMPa) is generally considered as an unqualified solvent for fabricating electrolytes used in graphite (Gr)‐based lithium‐ion batteries as it readily leads to Gr exfoliation and cell failure. In this work, by adopting the unique solvation structure of localized high‐concentration electrolyte (LHCE) to TMPa and tuning the composition of the solvation sheaths via electrolyte additives, excellent electrochemical performance can be achieved with TMPa‐based electrolytes in Gr∥LiNi0.8Mn0.1Co0.1O2 cells. After 500 charge/discharge cycles within the voltage range of 2.5–4.4 V, the batteries containing the TMPa‐based LHCE with a proper additive can achieve a capacity retention of 85.4 %, being significantly higher than cells using a LiPF6‐organocarbonates baseline electrolyte (75.2 %). Meanwhile, due to the flame retarding effect of TMPa, TMPa‐based LHCEs exhibit significantly reduced flammability compared with the conventional LiPF6‐organocarbonates electrolyte. [ABSTRACT FROM AUTHOR]

LiNixMnyCo1−x−yO2 (NMC) cathode materials with Ni ≥ 0.8 have attracted great interest for high energy‐density lithium‐ion batteries (LIBs) but their practical applications under high charge voltages (e.g., 4.4 V and above) still face significant challenges due to severe capacity fading by the unstable cathode/electrolyte interface. Here, an advanced electrolyte is developed that has a high oxidation potential over 4.9 V and enables NMC811‐based LIBs to achieve excellent cycling stability in 2.5–4.4 V at room temperature and 60 °C, good rate capabilities under fast charging and discharging up to 3C rate (1C = 2.8 mA cm−2), and superior low‐temperature discharge performance down to −30 °C with a capacity retention of 85.6% at C/5 rate. It is also demonstrated that the electrode/electrolyte interfaces, not the electrolyte conductivity and viscosity, govern the LIB performance. This work sheds light on a very promising strategy to develop new electrolytes for fast‐charging high‐energy LIBs in a wide‐temperature range. [ABSTRACT FROM AUTHOR]

Abstract: Lithium (Li) metal is an ideal anode material for high energy density batteries. However, the low Coulombic efficiency (CE) and the formation of dendrites during repeated plating and stripping processes have hindered its applications in rechargeable Li metal batteries. The accurate measurement of Li CE is a critical factor to predict the cycle life of Li metal batteries, but the measurement of Li CE is affected by various factors that often lead to conflicting values reported in the literature. Here, several parameters that affect the measurement of Li CE are investigated and a more accurate method of determining Li CE is proposed. It is also found that the capacity used for cycling greatly affects the stabilization cycles and the average CE. A higher cycling capacity leads to faster stabilization of Li anode and a higher average CE. With a proper operating protocol, the average Li CE can be increased from 99.0% to 99.5% at a high capacity of 6 mA h cm−2 (which is suitable for practical applications) when a high‐concentration ether‐based electrolyte is used. [ABSTRACT FROM AUTHOR]

The stability of electrolytes against highly reactive, reduced oxygen species is crucial for the development of rechargeable Li-O2 batteries. In this work, the effect of lithium salt concentration in 1,2-dimethoxyethane (DME)-based electrolytes on the cycling stability of Li-O2 batteries is investigated systematically. Cells with highly concentrated electrolyte demonstrate greatly enhanced cycling stability under both full discharge/charge (2.0-4.5 V vs Li/Li+) and the capacity-limited (at 1000 mAh g−1) conditions. These cells also exhibit much less reaction residue on the charged air-electrode surface and much less corrosion of the Li-metal anode. Density functional theory calculations are used to calculate molecular orbital energies of the electrolyte components and Gibbs activation energy barriers for the superoxide radical anion in the DME solvent and Li+-(DME) n solvates. In a highly concentrated electrolyte, all DME molecules are coordinated with salt cations, and the C-H bond scission of the DME molecule becomes more difficult. Therefore, the decomposition of the highly concentrated electrolyte can be mitigated, and both air cathodes and Li-metal anodes exhibit much better reversibility, resulting in improved cyclability of Li-O2 batteries. [ABSTRACT FROM AUTHOR]

Dendrimer-encapsulated ruthenium oxide nanoparticles (DEN-RuO2) have been used as catalysts in lithium-oxygen (Li-O2) batteries for the first time. The results obtained from ultraviolet-visible spectroscopy, electron microscopy and X-ray photoelectron spectroscopy show that the nanoparticles synthesized by the dendrimer template method are ruthenium oxide, not metallic ruthenium as reported by other groups. The DEN-RuO2 significantly improves the cycling stability of Li-O2 batteries with carbon electrodes and decreases the charging potential even at ten times less catalyst loading than those reported previously. The monodispersity, porosity, and large number of surface functionalities of the dendrimer template prevent the aggregation of the RuO2 nanoparticles, making their entire surface area available for catalysis. The potential of using DEN-RuO2 as a standalone cathode material for Li-O2 batteries is also explored. [ABSTRACT FROM AUTHOR]

Fluoroethylene carbonate (FEC) is an effective electrolyte additive that can significantly improve the cycling ability of silicon and other anode materials. However, the fundamental mechanism of this improvement is still not well understood. Based on the results obtained from 6Li NMR and X-ray photoelectron spectroscopy studies, we propose a molecular-level mechanism for how FEC affects the formation of solid electrolyte interphase (SEI) film: 1) FEC is reduced through the opening of the five-membered ring leading to the formation of lithium poly(vinyl carbonate), LiF, and some dimers; 2) the FEC-derived lithium poly(vinyl carbonate) enhances the stability of the SEI film. The proposed reduction mechanism opens a new path to explore new electrolyte additives that can improve the cycling stability of silicon-based electrodes. [ABSTRACT FROM AUTHOR]

Abstract: The stability of various polymer binders was systematically investigated in the oxygen-rich environment required for the operation of Li–O2 batteries. Due to the coverage on air electrode surface by the discharge products and decomposition products of the electrolyte during the discharge process of Li–O2 batteries, the binder in the air electrode is hard to be detected making the evaluation of its stability problematic. Therefore, stability of the binder polymers against the reduced oxygen species generated during the discharge process was investigated by ball milling the polymers with KO2 and Li2O2, respectively. Most of the studied polymers are unstable under these conditions and their decomposition mechanisms are proposed according to the analyzed products. Polyethylene was found to exhibit excellent stability when exposed to superoxide and peroxide species and is suggested as a robust binder for air electrodes. In addition, the binding strength of the polymer significantly affects the discharge performance of Li–O2 batteries. [Copyright &y& Elsevier]

Abstract: The commercial Li4Ti5O12 (LTO) is successfully modified by AlF3 via a low temperature process. After being calcined at 400 °C for 5 h, AlF3 reacts with LTO to form a composite material which mainly consists of Al3+ and F− co-doped LTO with small amounts of anatase TiO2. Al3+ and F− co-doped LTO demonstrates ultrahigh rate capability comparing to the pristine LTO. Since the amount of the byproduct TiO2 is relatively small, the modified LTO electrodes retain the main voltage characteristics of LTO with a minor feature similar to those of anatase TiO2. The doped LTO anodes deliver slightly higher discharge capacity and maintain the excellent long-term cycling stability when compared to the pristine LTO anode. Therefore, Al3+ and F− co-doped LTO composite material synthesized at low temperature is an excellent anode for stable and ultra-high power lithium-ion batteries. [Copyright &y& Elsevier]

Abstract: The effects of six types of aprotic organic solvents on the discharge performance and discharge products in Li-O2 batteries are systematically investigated. A large amount of Li2O2 is identified in the air electrodes discharged in glyme-based electrolytes, while only a small amount of Li2O2 is detected in the air electrodes discharged in the electrolytes of nitrile, ionic liquid, phosphate, and sulfoxide. Li2CO3 and LiF are also found as byproducts whose compositions are related to the solvents. Li2CO3 is produced from oxidation and decomposition of the solvent, not from the oxidation of the carbon-based air electrode, as revealed by using a 13C-labeled carbon electrode and the solid-state 13C-magic angle spinning nuclear magnetic resonance technique. LiF in the discharge products can be attributed to the attack of superoxide radical anions to the Teflon binder and/or the F-containing imide salt. The formation of these byproducts will significantly reduce the Coulombic efficiency and cycle life of the Li-air batteries. Among the studied solvents, dibutyl diglyme is the suitable solvent for Li-O2 batteries based on its overall properties. However, better electrolytes that can ensure the formation of Li2O2 but minimize other reaction products need to be further investigated for long cycling rechargeable Li-air batteries. [Copyright &y& Elsevier]

Abstract: It is well known that LATP (Li1+x+y Al x Ti2−x Si y P3−y O12) glass is a good lithium (Li)-ion conductor. However, the interaction between LATP glass and H+ ions in aqueous electrolytes (including the diffusion and surface adsorption of H+ ions) needs to be well understood before the long-term application of LATP glass in an aqueous electrolyte can be realized. In this work, we investigate H+-ion diffusion in LATP glass and their interactions with the glass surface using both experimental and modeling approaches. Our results indicate that the apparent H+-related current observed in the initial cyclic voltammetry scan should be attributed to the adsorption of H+ ions on the LATP glass rather than the bulk diffusion of H+ ions. Furthermore, density functional theory calculations indicate that the H+-ion diffusion energy barrier (3.21 eV) is much higher than that for Li+ ions (0.79 eV) and Na+ ions (0.79 eV) in a NASICON-type LiTi2(PO4)3 material. As a result, H+-ion conductivity in LATP glass is negligible at room temperature. However, significant surface corrosion was found after the LATP glass in a strong alkaline electrolyte. Therefore, to prevent LATP glass from corrosion, appropriate electrolytes must be developed for long-term operation of LATP in aqueous Li–air batteries. [Copyright &y& Elsevier]

Abstract: The effects of different cell positive cans and separators on first-cycle Coulombic efficiency and long-term cycling stability of a high-voltage spinel cathode are investigated systematically. Compared to stainless steel (SS) positive cans, aluminum (Al)-clad SS-316 positive cans are much more resistant to oxidation at high voltages; therefore, the initial Coulombic efficiency of the batteries with Al-clad can is improved by more than 13%. Among the five separators studied in this work, the polyethylene (PE) separator exhibits the best electrochemical stability. The cells using LiCr0.05Ni0.45Mn1.5O4 as the cathode, an Al-clad positive can, and a PE separator exhibits a first-cycle Coulombic efficiency of about 90% and a capacity fading of only 0.01% per cycle. [Copyright &y& Elsevier]

Abstract: The charging voltage limits of mixed-carbonate solvents for Li-ion batteries were systematically investigated from 4.9 to 5.3 V in half-cells using Cr-doped spinel cathode material LiNi0.45Cr0.05Mn1.5O4. The stability of conventional carbonate electrolytes is strongly related to the stability and properties of the cathode materials in the de-lithiated state. This is the first time report that the conventional electrolytes based on mixtures of EC and linear carbonate (DMC, EMC and DEC) can be cycled up to 5.2 V on LiNi0.45Cr0.05Mn1.5O4 for long-term cycling, where their performances are similar. The discharge capacity increases with the charging cutoff voltage and reaches the highest discharge capacity at 5.2 V. The capacity retention is about 87% after 500 cycles at 1C rate for all three carbonate mixtures in half-cells when cycled between 3.0 V and 5.2 V. When cycled to 5.3 V, EC-DMC still shows good cycling performance but EC-EMC and EC-DEC show faster capacity fading. EC-DMC and EC-EMC have much better rate capability than EC-DEC. The first-cycle irreversible capacity loss increases with the cutoff voltage. The “inactive” conductive carbon is also partly associated with the low first-cycle Coulombic efficiency at high voltages due to electrolyte decomposition and possible PF6 - anion irreversible intercalation. [Copyright &y& Elsevier]

Abstract: In this work, nonaqueous electrolyte-based Li-air batteries with an O2-selective membrane have been developed for operation in ambient air of 20–30% relative humidity (RH). The O2 gas is continuously supplied through a membrane barrier layer at the interface of the cathode and ambient air. The membrane allows O2 to permeate through while blocking moisture. Such membranes can be prepared by loading O2-selective silicone oils into porous supports such as porous metal sheets and Teflon (PTFE) films. It was found that the silicone oil of high viscosity shows better performance. The immobilized silicone oil membrane in the porous PTFE film enabled the Li-air batteries with carbon black air electrodes to operate in ambient air (at 20% RH) for 16.3 days with a specific capacity of 789mAhg−1 carbon and a specific energy of 2182Whkg−1 carbon. Its performance is much better than a reference battery assembled with a commercial, porous PTFE diffusion membranes as the moisture barrier layer on the cathode, which only had a discharge time of 5.5 days corresponding to a specific capacity of 267mAhg−1 carbon and a specific energy of 704Whkg−1 carbon. The Li-air battery with the present selective membrane barrier layer even showed better performance in ambient air operation (20% RH) than the reference battery tested in the dry air box (<1% RH). [Copyright &y& Elsevier]

Abstract: A three-dimensional macroporous Cu/SnO2 composite anode sheet for lithium ion batteries was prepared via a novel method that is based on selective reduction of metal oxides at appropriate temperatures. SnO2 particles were imbedded on the Cu particles within the three-dimensionally interconnected Cu substrate, and the whole composite sheet was used directly as an electrode without adding extra conductive carbons and binders. Compared with the SnO2-based electrode prepared via the conventional tape-casting method on Cu foil, the porous Cu/SnO2 composite electrode shows significantly improved battery performance. This methodology produces limited wastes and is also adaptable to many other materials. It is a promising approach to make macroporous electrode for Li-ion batteries. [Copyright &y& Elsevier]

• The flame retardant effect of DMMP on electrolyte was evaluated quantitatively. • A numerical model was constructed to predict the flame extinction limit. • The mechanism of DMMP on reducing the flame extinction limit was analyzed. • The sensibilities of flammability of four solvents to DMMP were compared. An experimental and numerical study was conducted to quantify the flame retardant effects of different DMMP addition loadings on the flame extinction limits of four lithium-ion battery electrolyte solvents. The minimum extinguishing concentration (MEC) of CO 2 , which was measured using the cup-burner method, was applied to characterize the flame retardant effects of different DMMP loadings. Then, a model based on the perfectly stirred reactor concept was constructed to calculate the MEC and interpret the measurements established in the cup-burner test. A comparison was conducted between the measured and calculated MECs of N 2 and a satisfactory agreement was obtained. Further investigation found that DMMP could significantly improve the extinction temperature by clearing the H radical, suppressing the reaction temperature and increasing the sensitivity of temperature to reaction rate constants, which caused the decrease in the flame extinction limit of solvents. The experimental results showed that DMMP has a certain saturation effect on reducing the flame extinction limits of solvents. For the four solvents, the sensibilities of the flame extinction limits to the DMMP additions were different, which were ranked in the order of diethyl carbonate > ethyl methyl carbonate > dimethyl carbonate > ethyl acetate. [ABSTRACT FROM AUTHOR]

Electrolytes: Advanced Electrolytes for Fast-Charging High-Voltage Lithium-Ion Batteries in Wide-Temperature Range (Adv. Keywords: high-Ni layered cathodes; lithium ion batteries; localized high-concentration electrolytes EN high-Ni layered cathodes lithium ion batteries localized high-concentration electrolytes 1 1 1 06/11/20 20200609 NES 200609 In article number 2000368, Wu Xu and co-workers report the fabrication of an advanced localized high-concentration electrolyte with a high oxidation potential over 4.9 V. This electrolyte enables formation of ultrathin, uniform, robust and conductive electrode/electrolyte interphases on both graphite anodes and Ni-rich cathodes. High-Ni layered cathodes, lithium ion batteries, localized high-concentration electrolytes. [Extracted from the article]

Silicon anodes are regarded as one of the most promising alternatives to graphite for high energy‐density lithium‐ion batteries (LIBs), but their practical applications have been hindered by high volume change, limited cycle life, and safety concerns. In this work, nonflammable localized high‐concentration electrolytes (LHCEs) are developed for Si‐based anodes. The LHCEs enable the Si anodes with significantly enhanced electrochemical performances comparing to conventional carbonate electrolytes with a high content of fluoroethylene carbonate (FEC). The LHCE with only 1.2 wt% FEC can further improve the long‐term cycling stability of Si‐based anodes. When coupled with a LiNi0.3Mn0.3Co0.3O2 cathode, the full cells using this nonflammable LHCE can maintain >90% capacity after 600 cycles at C/2 rate, demonstrating excellent rate capability and cycling stability at elevated temperatures and high loadings. This work casts new insights in electrolyte development from the perspective of in situ Si/electrolyte interphase protection for high energy‐density LIBs with Si anodes. [ABSTRACT FROM AUTHOR]

Abstract: In this article, two-dimensional, Co3O4 hexagonal nanodiscs are prepared using a hydrothermal method without surfactants. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) have been employed to characterize the structural properties. As revealed by the SEM and TEM experiments, the thickness of our as-fabricated Co3O4 hexagonal nanodiscs is about 20 nm, and the pore diameters range from several nanometers to 30 nm. As an anode for lithium-ion batteries, porous Co3O4 nanodiscs exhibit an average discharge voltage of ∼1 V (vs. Li/Li+) and a high specific charge capacity of 1161 mAh g−1 after 100 cycles. They also demonstrate excellent rate performance and high Columbic efficiency at various rates. These results indicate that porous Co3O4 nanodiscs are good candidates as anode materials for lithium-ion batteries. [Copyright &y& Elsevier]

Abstract: The stabilities of different conductive carbon additives have been systematically investigated in high voltage lithium ion batteries. It is found that the higher surface area of conductive additives leads to more parasitic reactions initiating from different onset voltages. A closer inspection reveals that for the low surface area carbon such as Super P, anions reversibly intercalate into carbon structure at around 4.7 V. For high surface area carbons, in addition to the electrolyte decomposition, the oxidation of functional groups at high voltage further increases the irreversible capacity and Li+ ion consumption. Coulombic efficiency, irreversible capacity and cycling stability observed by using different carbon additives are correlated with their structure and surface chemistry, thus providing information for predictive selection of carbon additives in different energy storage systems. [Copyright &y& Elsevier]

Abstract: In this paper, we report the electrochemical characteristics of a novel cathode material, Li2CoPO4F, prepared by solid-state reactions. The solid-state reaction mechanism involved in synthesizing the Li2CoPO4F also is analyzed in this paper. When cycled between 2.0V and 5.0V during cyclic voltammetry measurements, the Li2CoPO4F samples present one, fully reversible anodic reaction at 4.81V. When cycled between 2.0V and 5.5V, peaks occurring at 4.81V and 5.12V in the first anodic scan evolved to one broad oxidative, mound-like pattern in subsequent cycles. Correspondingly, the X-ray diffraction (XRD) pattern of the Li2CoPO4F electrode discharged from 5.5V to 2.0V is slightly different from the patterns exhibited by a fresh sample and the sample discharged from 5.0V to 2.0V. This difference may correspond to a structural relaxation that appears above 5V. In the constant current cycling measurements, the Li2CoPO4F samples exhibited a capacity as high as 109mAhg−1 and maintained a good cyclability between 2.0V and 5.5V vs. Li/Li+. XRD measurements confirmed that the discharged state is Li2CoPO4F. Combining these XRD results and electrochemical data proved that up to 1mol Li+ is extractable when charged to 5.5V. [ABSTRACT FROM AUTHOR]

Abstract Irreversible parasitic reactions and the resulting accumulation of insulating side products are main barriers for practical application of rechargeable lithium–oxygen (Li O 2) batteries. Therefore, it is critical to develop multifunctional oxygen electrodes suitable for oxygen reduction reaction, oxygen evolution reaction, and decomposition of side reaction products. Here we report the application of ultrafine ruthenium on boron carbide (Ru/B 4 C) with highly efficient multifunctional activities as carbon-free oxygen electrodes for Li O 2 batteries. Li 2 CO 3 and LiOH can be completely decomposed by Ru/B 4 C at 4.0 V and 4.1 V, respectively, within the stability window of the electrolyte. A Li O 2 battery using the Ru/B 4 C oxygen electrode achieves low overpotentials for Li O 2 reactions, and excellent cycling performance under the capacities of 300 and 500 mAh g−1 Ru/B4C. In-situ gas chromatography analysis reveals that O 2 is the major gas product during charging. Only a negligible amount of CO 2 is observed in the first charging process. Therefore, Ru/B 4 C can be a very promising oxygen-electrode material for Li O 2 batteries and Li–air batteries operated in ambient air. Graphical abstract Image 1 Highlights • Non-carbon-based Ru/B 4 C oxygen electrode shows good activity for both ORR and OER. • Ru/B 4 C can completely decompose Li 2 CO 3 and LiOH below 4.1 V. • Ru/B 4 C is very stable against superoxide radical anion and Li 2 O 2. • Li O 2 batteries using Ru/B 4 C oxygen electrodes exhibit long cycling stability. • Side reaction during charge accounts for degradation of Ru/B 4 C oxygen electrode. [ABSTRACT FROM AUTHOR]

Silicon(Si)/graphene composite has been regarded as one of the most promising candidates for next generation anode materials with high power and energy density in lithium ion batteries. Introduction of graphene in Si anodes could improve the electronic conductivity, suppress the severe volume expansion of Si, and facilitate the formation of stable solid electrolyte interphase, etc. However, traditionally mechanical mixing of Si and graphene cannot realize uniform distribution of Si particles on the graphene sheets, which would largely weaken the effectiveness of the graphene in the composite. In this work, nano-Si/reduced graphene oxide porous composite (p Si/rGO) has been fabricated by a facile electrostatic self-assembly approach via using SiO 2 as the sacrificial template. Compared with the simply mechanically mixed nano-Si and rGO (Si/rGO), the nano-Si particles could be more uniformly dispersed among the rGO sheets in the p Si/rGO, which significantly increases its electronic conductivity. Moreover, the drastic volume expansion of nano-Si during repeated lithiation/delithiation cycles also has been effectively accommodated by the large number of pores left after removing the SiO 2 template in the composite. Thus, the p Si/rGO presented largely enhanced electrochemical performances, showing a high reversible capacity up to 1849 mA h g −1 at 0.2 A g −1 with good capacity retention, and high rate capability (535 mA h g −1 at 2 A g −1 ). [ABSTRACT FROM AUTHOR]

In this paper, we design a novel one dimensional and coaxial polyaniline@tin dioxide@multi-wall carbon nanotube (PANI@SnO 2 @MWCNT) composite as advanced conductive additive free anode material for the lithium ion battery. The SnO 2 nanoparticles (∼5 nm) are firstly fixed on the conductive MWCNT skeleton by self-assembling the nano-sized SnO 2 particles on the surface of MWCNT with the assist of surfactant P123 then followed by in-situ coating a flexible layer of PANI with excellent electron and lithium ion conductivity. The one dimensional and coaxial PANI@SnO 2 @MWCNT can effectively accommodate the volume expansion of SnO 2 nanoparticles during lithiating and delithiating via the wrapping of the flexible coating layer of PANI and the buffer of the one dimensional MWCNT. Moreover, the electronic and lithium ionic conductivities of the composite are also obviously improved by the synergistic action between the PANI and MWCNT. As a result, the PANI@SnO 2 @MWCNT composite exhibits an excellent rate capacity and stable cycling performance even without the adding of the conductive additive. [ABSTRACT FROM AUTHOR]

Significant progress has been made toward overcoming fundamental challenges in developing a silicon (Si) anode for lithium-ion batteries (LIBs). However, much less work has been reported on design and failure analysis of these batteries for practical applications. In this work, we analyzed the main factors that affect the performance of a Si anode and the energy density of pouch cells using micron-sized, nanoporous Si coated by pitch-derived carbon (p-Si/C). The volumetric energy density of the Si anode depends heavily on these factors, such as the loading of p-Si/C in the anode, the calendering density of the anode, the first-cycle coulombic efficiency, and the capacity density of the anode. The effects of other factors on the cycling performance were also revealed by postmortem analysis of cycled anodes. We found that a stable p-Si/C electrode structure is critical to avoid the disintegration of the anode structural integrity and lithium plating and enable long-term cycling. Moreover, prelithiation of Si anodes increases energy density, while the degree of prelithiation is another factor to balance with the cycle life of Si-based full cells. We propose pathways and strategies for adoption of micron-sized p-Si/C anodes in LIBs for their practical applications. • Factors affecting the performance of Si-based full cells have been investigated. • Corrosion of the Si surface largely contributes to capacity loss at early stage. • Destruction of Si anode is the main reason for the capacity loss at the late stages. • Prelithiation of Si anodes is found to worsen cycling stability if not optimized. • Pathways and strategies for adoption of Si anodes have been proposed. [ABSTRACT FROM AUTHOR]

Rechargeable lithium (Li) metal batteries with conventional LiPF 6 -carbonate electrolytes have been reported to fail quickly at charging current densities of about 1.0 mA cm −2 and above. In this work, we demonstrate the rapid charging capability of Li||LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) cells can be enabled by a dual-salt electrolyte of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(oxalato)borate (LiBOB) in a carbonate solvent mixture. The cells using the LiTFSI-LiBOB dual-salt electrolyte significantly outperform those using the LiPF 6 electrolyte at high charging current densities. At the charging current density of 1.50 mA cm −2 , the Li||NCA cells with the dual-salt electrolyte can still deliver a discharge capacity of 131 mAh g −1 and a capacity retention of 80% after 100 cycles. The Li||NCA cells with the LiPF 6 electrolyte start to show fast capacity fading after the 30th cycle and only exhibit a low capacity of 25 mAh g −1 and a low retention of 15% after 100 cycles. The reasons for the good chargeability and cycling stability of the cells using the LiTFSI-LiBOB dual-salt electrolyte can be attributed to the good film-formation ability of the electrolyte on the Li metal anode and the highly conductive nature of the sulfur-rich interphase layer. [ABSTRACT FROM AUTHOR]

The practical application of lithium (Li) metal anode in rechargeable Li batteries is hindered by both the growth of Li dendrites and the low Coulombic efficiency (CE) during repeated charge/discharge cycles. Recently, we have discovered that CsPF 6 as an electrolyte additive can significantly suppress Li dendrite growth and lead to highly compacted and well aligned Li nanorod structures during Li deposition on copper substrates. In this paper, the effect of CsPF 6 additive on the performance of rechargeable Li metal batteries with lithium iron phosphate (LFP) cathode is further studied. Li|LFP coin cells with CsPF 6 additive in electrolytes show well protected Li anode surface, decreased resistance, enhanced rate capability and extended cycling stability. In Li|LFP cells, the electrolyte with CsPF 6 additive shows excellent long-term cycling stability (at least 500 cycles) at a charge current density of 0.5 mA cm −2 without internal short circuit. At high charge current densities, the effect of CsPF 6 additive becomes less significant. Future work needs to be done to protect Li metal anode, especially at high charge current densities and for long cycle life. [ABSTRACT FROM AUTHOR]

In this work, localized high concentration electrolytes (LHCEs) based on tetramethylene sulfone (TMS) were designed. Similar to LHCEs based on other solvents, TMS-based LHCEs can achieve excellent compatibility with high energy density lithium-ion batteries (LIBs) when combined with a proper additive. The unique solvation structure of LHCEs facilitates the synergetic decomposition of anion, solvent and additive in the solid electrolyte interphase (SEI) formation. Proper combinations of the three constituents of the solvation sheaths in LHCEs can promote the formation of highly effective SEI on graphite negative electrode. The absence of LiPF 6 in LHCEs also suppresses the degradation of positive electrode materials in LIBs. The superior interphasial properties of LHCEs are the key to realizing the long lifespan of high energy density LIBs. • Tetramethylene sulfone (TMS) based LHCEs with different additives were studied. • Additive-free TMS-LHCE outperforms conventional electrolyte in Gr.||Ni-rich LIBs. • Proper additives in TMS-LHCE can further boost performance of Gr.||Ni-rich LIBs. • Electrolyte solvation structure/content govern interphase and battery performance. [ABSTRACT FROM AUTHOR]

Development of novel electrolyteswith increased electrochemicalstability is critical for the next generation battery technologies.In situ electrochemical fluid cells provide the ability to rapidlyand directly characterize electrode/electrolyte interfacial reactionsunder conditions directly relevant to the operation of practical batteries.In this paper, we have studied the breakdown of a range of inorganic/saltcomplexes relevant to state-of-the-art Li-ion battery systems by insitu (scanning) transmission electron microscopy ((S)TEM). In theseexperiments, the electron beam itself caused the localized electrochemicalreaction that allowed us to observe electrolyte breakdown in real-time.The results of the in situ (S)TEM experiments matches with previousstability tests performed during battery operation and the breakdownproducts and mechanisms are also consistent with known mechanisms.This analysis indicates that in situ liquid stage (S)TEM observationscould be used to directly test new electrolyte designs and identifya smaller library of candidate solutions deserving of more detailedcharacterization. A systematic study of electrolyte degradation isalso a necessary first step for any future controlled in operandoliquid (S)TEM experiments intent on visualizing working batteriesat the nanoscale. [ABSTRACT FROM AUTHOR]

A cost-effective and scalable method is developed toprepare acore–shell structured Si/B4C composite with graphitecoating with high efficiency, exceptional rate performance, and long-termstability. In this material, conductive B4C with a highMohs hardness serves not only as micro/nano-millers in the ball-millingprocess to break down micron-sized Si but also as the conductive rigidskeleton to support the in situ formed sub-10 nm Si particles to alleviatethe volume expansion during charge/discharge. The Si/B4C composite is coated with a few graphitic layers to further improvethe conductivity and stability of the composite. The Si/B4C/graphite (SBG) composite anode shows excellent cyclability witha specific capacity of ∼822 mAh·g–1(basedon the weight of the entire electrode, including binder and conductivecarbon) and ∼94% capacity retention over 100 cycles at 0.3C rate. This new structure has the potential to provide adequate storagecapacity and stability for practical applications and a good opportunityfor large-scale manufacturing using commercially available materialsand technologies. [ABSTRACT FROM AUTHOR]

It is well-known that upon lithiation, both crystallineand amorphousSi transform to an armorphous LixSi phase,which subsequently crystallizes to a (Li, Si) crystalline compound,either Li15Si4or Li22Si5. Presently, the detailed atomistic mechanism of this phase transformationand the degradation process in nanostructured Si are not fully understood.Here, we report the phase transformation characteristic and microstructuralevolution of a specially designed amorphous silicon (a-Si) coatedcarbon nanofiber (CNF) composite during the charge/discharge processusing in situ transmission electron microscopy and density functiontheory molecular dynamic calculation. We found the crystallizationof Li15Si4from amorphous LixSi is a spontaneous, congruent phase transition process withoutphase separation or large-scale atomic motion, which is drasticallydifferent from what is expected from a classic nucleation and growthprocess. The a-Si layer is strongly bonded to the CNF and no spallationor cracking is observed during the early stages of cyclic charge/discharge.Reversible volume expansion/contraction upon charge/discharge is fullyaccommodated along the radial direction. However, with progressivecycling, damage in the form of surface roughness was gradually accumulatedon the coating layer, which is believed to be the mechanism for theeventual capacity fade of the composite anode during long-term charge/dischargecycling. [ABSTRACT FROM AUTHOR]

Abstract: Nano-structured Li3V2(PO4)3/carbon composite (Li3V2(PO4)3/C) has been successfully prepared by incorporating the precursor solution into a highly mesoporous carbon with an expanded pore structure. X-ray diffraction analysis, scanning electron microscopy, and transmission electron microscopy were used to characterize the structure of the composites. Li3V2(PO4)3 had particle sizes of<50nm and was well dispersed in the carbon matrix. When cycled within a voltage range of 3 to 4.3V, a Li3V2(PO4)3/C composite delivered a reversible capacity of 122mAh g−1 at a 1C rate and maintained a specific discharge capacity of 83mAh g−1 at a 32C rate. These results demonstrate that cathodes made from a nano-structured Li3V2(PO4)3 and mesoporous carbon composite material have great potential for use in high-power Li-ion batteries. [ABSTRACT FROM AUTHOR]

Abstract: The entropy changes (ΔS) in various cathode and anode materials, as well as in complete Li-ion batteries, were measured using an electrochemical thermodynamic measurement system (ETMS). LiCoO2 has a much larger entropy change than electrodes based on LiNi x Co y Mn z O2 and LiFePO4, while lithium titanate based anodes have lower entropy change compared to graphite anodes. The reversible heat generation rate was found to be a significant portion of the total heat generation rate. The appropriate combinations of cathode and anode were investigated to minimize reversible heat generation rate across the 0–100% state of charge (SOC) range. In addition to screening for battery electrode materials with low reversible heat, the techniques described in this paper can be a useful engineering tool for battery thermal management in stationary and transportation applications. [Copyright &y& Elsevier]