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The reactivity of garnet solid electrolytes toward humid air hinders their practical application despite their attractive, superior properties such as high Li+ conductivity and wide electrochemical window. Sealing garnets with organic solvents can not only prevent them from reacting with humid air but also render them compatible with other processing technologies. Therefore, the chemical and structural stability of garnets in organic solvents must be studied. In this study, we selected several commonly used organic solvents with different representative functional groups to investigate their stability with garnets and reaction mechanisms. The experiments and theoretical calculations revealed that all of the solvents reacted with garnets through Li-H exchange, and solvent acidity determined the reaction strength. Furthermore, the solvent acidity was closely correlated to the functional groups connected to H atoms, which can affect charge distribution. Solvents or the tautomer of the solvents with hydroxyl groups such as alcohol, acetone, and N-methyl pyrrolidone, which are relatively more acidic, can lead to a violent reaction with changes in the lattice parameters of garnets. Ether compounds and saturated aliphatic hydrocarbons with relatively low acidity are highly stable against garnets. The proposed reaction mechanisms and rules may help in selecting appropriate solvents for different applications of garnets.

Anode-free lithium metal batteries can maximize the energy density at the cell level. However, without the Li compensation from the anode side, it faces much more challenging to achieve a long cycling life with a competitive energy density than Li metal-based batteries. Here, we prolong the lifespan of an anode-free Li metal battery by introducing Li-rich Li2 [Ni0.8 Co0.1 Mn0.1 ]O2 into the cathode as a Li-ions extender. The Li2 [Ni0.8 Co0.1 Mn0.1 ]O2 can release a large amount of Li-ions during the first charging process to supplement the Li loss in the anode, then convert into NCM811, thus extending the lifespan of the battery without the introduction of inactive elements. By the benefit of Li-rich cathode and high reversibility of Li metal on Cu foil, the anode-free pouch cells enable to achieve 447 Wh kg-1 energy density and 84 % capacity retention after 100 cycles in the condition of limited electrolyte addition (E/C ratio of 2 g Ah-1 ).

Anionic redox reaction (ARR) in lithium- and sodium-ion batteries is under hot discussion, mainly regarding how oxygen anion participates and to what extent oxygen can be reversibly oxidized and reduced. Here, a P3-type Na0.6[Li0.2Mn0.8]O2 with reversible capacity from pure ARR was studied. The interlayer O-O distance (peroxo-like O-O dimer, 2.506(3) Å), associated with oxidization of oxygen anions, was directly detected by using a neutron total scattering technique. Different from Li2RuO3 or Li2IrO3 with strong metal-oxygen (M-O) bonding, for P3-type Na0.6[Li0.2Mn0.8]O2 with relatively weak Mn-O covalent bonding, crystal structure factors might play an even more important role in stabilizing the oxidized species, as both Li and Mn ions are immobile in the structure and thus may inhibit the irreversible transformation of the oxidized species to O2 gas. Utilization of anionic redox reaction (ARR) on oxygen has been considered as an effective way to promote the charge-discharge capacity of the layered oxide cathodes for lithium- or sodium-ion batteries. The detailed mechanism of ARR, in particular how crystal structure affects and coordinates with the ARR, is not yet well understood. In the present work, a combination of X-ray and neutron total scattering measurements has been performed to study the structure of the prototype P3-type layered Na0.6[Li0.2Mn0.8]O2 with pure ARR. Unique structural characteristics, rather than prevailing knowledge of covalency of metal-oxygen, enable the stabilization of the crystal structure of Na0.6[Li0.2Mn0.8]O2 along with the ARR. This work suggests that reversible ARR can be manipulated by proper structure designs, thus to achieve high lithium or sodium storage in layered oxide cathodes. For P3-type Na0.6[Li0.2Mn0.8]O2 with relatively weak Mn-O covalent bonding, crystal structure factors play an important role in stabilizing the oxidized species, inhibiting the irreversible transformation of the oxidized species to O2 gas. The finding is important for better design of layered oxide positive materials with higher reversible capacity via the introduction of a reversible anionic redox reaction.

Organic materials, especially the carbonyl compounds, are promising anode materials for room temperature sodium-ion batteries owing to their high reversible capacity, structural diversity as well as eco-friendly synthesis from bio-mass. Herein, we report a novel anthraquinone derivative, C14H6O4Na2 composited with carbon nanotube (C14H6O4Na2-CNT), used as an anode material for sodium-ion batteries in ether-based electrolyte. The C14H6O4Na2-CNT electrode delivers a reversible capacity of 173 mAh g−1 and an ultra-high initial Coulombic efficiency of 98% at the rate of 0.1 C. The capacity retention is 82% after 50 cycles at 0.2 C and a good rate capability is displayed at 2 C. Furthermore, the average Na insertion voltage of 1.27 V vs. Na+/Na makes it a unique and safety battery material, which would avoid Na plating and formation of solid electrolyte interface. Our contribution provides new insights for designing developed organic anode materials with high initial Coulombic efficiency and improved safety capability for sodium-ion batteries.

Lithium-ion batteries with graphite as the anode consume ∼10% of the active lithium from the cathode to form a solid electrolyte interphase layer during the first cycle, resulting in a reduced reversible capacity. Here, we report using Li2S as a cathode pre-lithiation material to compensate for the loss of active lithium and, consequently, enhance the specific energy of lithium-ion batteries. A Li2S material with a core-shell structure is prepared by mixing Li2S, Ketjenblack (KB) and poly(vinylpyrrolidone) (PVP) in anhydrous ethanol, and the material shows a specific charge capacity of ∼1053 mAh g−1 (631 mAh g−1 based on the total weight of cathode pre-lithiation materials, binders and conductive additives). The ability of this material to compensate for active lithium is investigated by coating a typical cathode LiFePO4 as an example, with the core-shell Li2S/KB/PVP via a simple and non-toxic coating method. Our results show that the LiFePO4 (Li2S)/graphite full cell exhibits a specific discharge capacity of 146.7 mAh g−1 in the first cycle, which is the same as the specific discharge capacity of the LiFePO4 half cell. XPS analysis reveals Li2S decomposes into lithium ions and sulfur with release of electrons in the first charge. Such a successful extraction of the active lithium from Li2S results in excellent cycling performance with increased specific energy.

Batteries with lithium metal anodes are promising because of lithium’s high energy density. However, the growth of Li dendrites on the surface of the Li electrode in a liquid electrolyte during cycling reduces the safety and cycle performance of batteries, hindering their commercial application. In this work, we observe for the first time a smooth and dendrite-free Li deposition with a vertically grown, self-aligned, and highly compact columnar structure formed during cycling in a mixed carbonate–ether electrolyte. The stable microsized (∼10 μm in diameter and ∼20 μm in length) Li deposits are aligned in arrays on the surface of the Li electrode. The columnar Li deposits still exhibit a dendrite-free morphology and a compact structure after 200 cycles at a current density of 1 mA/cm2 and a 1.5 mAh/cm2 cycling capacity in a mixed carbonate–ether electrolyte. This work shows an optimiztic outlook for Li batteries with liquid electrolytes.

Detailed investigation of the influence of surface modification using a typical oxide (TiO2) on the electrochemical cycling performance of LiNi0.5Mn1.5O4 at room temperature (25 °C) and elevated temperature (55 °C) is reported. This spinel cathode material is commonly surface-modified with various metal oxides to improve its electrochemical cycling performance in lithium ion batteries. However, the underlying mechanisms of such a treatment, with respect to the surface crystal structure and chemistry evolution, have remained unclear. Bare-LiNi0.5Mn1.5O4 and TiO2-modified LiNi0.5Mn1.5O4 both show excellent cycling performance, i.e. almost no capacity retention and ∼99% coulombic efficiency for 150 cycles, at room temperature. However, at 55 °C the latter shows significantly better electrochemical cycling performance, with 93% capacity retention and ∼96% coulombic efficiency for 100 cycles, than the former with 70% capacity retention and ∼93% coulombic efficiency. Via advanced electron microscopy techniques, we observed that titanium ions migrated into the surface region of LiNi0.5Mn1.5O4 during the surface modification process at high temperature and reconstructed the (1–3 nm) surface spinel structure into a rocksalt-like structure and the subsurface (several nanometers) into a pseudo-rocksalt-like structure. The reconstruction of the surface and subsurface of the LiNi0.5Mn1.5O4 spinel cathode material mitigates not only the migration of Mn ions from the bulk into the electrolyte but also the formation of a solid state electrolyte interface, which plays a critical role in the improvement of electrochemical cycling performance at elevated temperatures.

To improve the safety of sodium (Na) batteries, we first report a new solid polymer electrolyte (SPE), composed of sodium (fluorosulfonyl)(n-nonafluorobutanesulfonyl)imide (Na[(FSO2)(n-C4F9SO2)N], NaFNFSI) and poly(ethylene oxide) (PEO), which is prepared by a facile solution-casting method. The NaFNFSI/PEO (EO/Na+ = 15) blended polymer electrolyte exhibits a relatively high ionic conductivity of 3.36 × 10−4 S cm−1 at 80 °C, sufficient thermal stability (>300 °C) and anodic electrochemical stability (≈4.87 V vs. Na+/Na) for application in solid-state Na batteries. Most importantly, the NaFNFSI-based SPE can not only deliver excellent chemical and electrochemical stability with Na metal, but can also display good cycling and current-rate performances for the Na|SPE|NaCu1/9Ni2/9Fe1/3Mn1/3O2 cell. All of these outstanding properties would make the NaFNFSI-based SPE promising as a candidate for application in solid-state Na batteries.

Solid polymer electrolytes (SPEs) would be promising candidates for application in high-energy rechargeable lithium (Li) batteries to replace the conventional organic liquid electrolytes, in terms of the enhanced safety and excellent design flexibility. Herein, we first report novel perfluorinated sulfonimide salt-based SPEs, composed of lithium (trifluoromethanesulfonyl)(n-nonafluorobutanesulfonyl)imide (Li[(CF3SO2)(n-C4F9SO2)N], LiTNFSI) and poly(ethylene oxide) (PEO), which exhibit relatively efficient ionic conductivity (e.g., 1.04 × 10–4 S cm–1 at 60 °C and 3.69 × 10–4 S cm–1 at 90 °C) and enough thermal stability (>350 °C), for rechargeable Li batteries. More importantly, the LiTNFSI-based SPEs could not only deliver the excellent interfacial compatibility with electrodes (e.g., Li-metal anode, LiFePO4 and sulfur composite cathodes), but also afford good cycling performances for the Li|LiFePO4 (>300 cycles at 1C) and Li–S cells (>500 cycles at 0.5C), in comparison with the conventional LiTFSI (Li[(C...

Sodium-ion batteries (SIBs), a promising substitute for lithium-ion batteries (LIBs), are considered to have potential to be employed in large-scale energy storage systems with lower cost and enhanced safety as primary concerns. Solid polymer electrolyte (SPE) based SIBs will better meet these demands because of their good flame-resistance and excellent flexibility, compared with conventional organic liquid electrolyte based SIBs. Here, we describe an SPE composed of sodium bis(fluorosulfonyl)imide (NaFSI) and poly(ethylene oxide) (PEO). The NaFSI/PEO (molar ratio of EO/Na+ = 20) blended polymer electrolyte exhibits a low glass transition temperature (i.e., 37.9 oC), relatively high ionic conductivity (i.e., ~4.1 × 104 S cm1 at 80 oC), and enough electrochemical and thermal stability for application in SIBs. Most importantly, the NaFSI/PEO blended polymer electrolyte displays excellent interfacial stability with Na metal in Na/Na cells and good cycling performance in prototype cells with Na0.67Ni0.33Mn0.67O2 (NNM) as cathode material. All these properties make NaFSI based solid polymer electrolytes promising candidates for use in SIBs.

Lithium (fluorosulfonyl)(n-nonafluorobutanesulfonyl)imide [Li[(FSO2)(n-C4F9SO2)N] (LiFNFSI)] is investigated as a conducting salt, which can form a relatively stable solid-electrolyte-interphase film in concentrated ether electrolyte to achieve favorable protection for lithium metal anodes. Li|Cu and Li|Li cells with concentrated LiFNFSI-based electrolyte have been demonstrated to display high average Coulombic efficiency (≈97%) and excellent cycling stability (over 1,000 h) of metallic lithium anodes, compared to concentrated lithium bis(trifluoromethanesulfonyl)imide [Li[N(SO2CF3)2] (LiTFSI)]-based electrolyte. The morphologies and compositions of the lithium–metal anode surface are also comparatively analyzed by scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. Moreover, superior electrochemical performance in the concentrated LiFNFSI-based electrolyte for Li|LiFePO4 cells is also presented herein. These results indicate that concentrated LiFNFSI-based electrolyte is a pr...

Spinel LiNi 0.5 Mn 1.5 O 4 (LNMO) exhibits two different Ni/Mn arrangements, i.e., the Ni/Mn ordered P4 3 32 phase and disordered Fd-3m phase. It has been found that the Ni/Mn disorder is correlated with the formation of oxygen vacancies, nevertheless the underlying mechanism remains unclear. Density functional theory (DFT) calculations show that formation of 1:3 ordered Ni 2+ and Mn 4+ ions is energetically favorable compared to the disordered Ni 3+ and Mn 3+ ions caused by Ni aggregation in the stoichiometric P4 3 32 phase. However, in oxygen deficient LiNi 0.5 Mn 1.5 O 4− δ , the oxygen vacancies tend to diminish the valence discrepancy between the Ni aggregated and the ordered P4 3 32 phases, making the former energetically competitive and consequently resulting in the disordered Ni/Mn distribution. Understanding the origin of Ni/Mn disorder also sheds light on the cation doping effect. Calculations show that Mg 2+ ion tends to replace Ni 2+ ion in ordered P4 3 32 phase, and maintaining the Ni/Mn order. By contrast, Al doping promotes the Ni/Mn disorder, as Al 3+ ion prefers to substitute for Ni 3+ and Mn 3+ ions emerged in Ni/Mn disordered structure. Our findings rationalize the experimental observations, and further reveal that Ni/Mn arrangement could be controlled by adjusting the electronic structure of spinel LNMO system.

Electrolytes compatible with lithium metal (Li) anode and cathode materials are regarded as one of the most crucial components toward the practical deployment of rechargeable lithium metal batteries (RLMBs). Herein, we report a highly salt-concentrated electrolyte (SCE) comprising lithium bis(fluorosulfonyl)imide (LiFSI) and 1,3-dioxolane (DOL)-based ether solvents for stable cycling of 4-V-class rechargeable Li cells. The selective addition of 1,8-diazabicyclo(5.4.0)undec‑7-ene (DBU) is capable of suppressing the ring-opening polymerization of DOL. The resulting LiFSI-DOL-based SCE shows excellent chemical stability (150 days), good anodic stability (ca. 5.0 V vs. Li/Li+), and decent ionic conductivity (1.3 mS cm−1) at room temperature. Using the LiFSI-DOL-based SCE, the Li || Cu cells exhibit dendrite-free Li deposition/dissolution processes with high Coulombic efficiencies (> 99%), and the Li || LiNi1/3Mn1/3Co1/3O2 cell shows good capacity retention (81% after 400 cycles). These results strongly suggest the feasibility of the LiFSI-DOL-based SCE as electrolyte for 4-V-class RLMBs.

Solid polymer electrolytes (SPEs), comprising lithium fluorinated sulfonimide including Li[(FSO2)(RFSO2)N] (RF = n-CmF2m+1, m = 0 (LiFSI), 1 (LiFTFSI), 2 (LiFPFSI), and 4 (LiFNFSI)) and Li[(CF3SO2)2N] (LiTFSI) as conducting salt and poly(ethylene oxide) (PEO) as polymer matrix, are utilized for investigating the impact of anionic structure of lithium salt on the performances of rechargeable lithium metal (Li) batteries (RLMBs), through comparing their fundamental physical properties, including ionic conductivity and anodic stability, and electrochemical performances for Li || Li and Li || LiFePO4 cells. It is found that the cycling stabilities of both the Li anode and LiFePO4 cathode are highly dependent on the structure of fluorinated imide anion. The cycling stabilities for both the Li || Li and Li || LiFePO4 cells with Li[(FSO2)(RFSO2)N] systematically outperfom those with LiTFSI at 0.2 mA cm−2 and 80 °C (i.e., being increased in the order of LiTFSI

A novel single lithium-ion (Li-ion) conducting polymer electrolyte composed of lithium poly[(4-styrenesulfonyl)(fluorosulfonyl)imide] (LiPSFSI) and poly(ethylene oxide) (PEO) exhibits a high Li-ion transference number (tLi+ = 0.90) and sufficient electrochemical stability for use in Li batteries. The ionic conductivities of the LiPSFSI/PEO blended polymer electrolytes are higher than those of the lithium poly(4-styrenesulfonate) (LiPSS)/PEO electrolyte and are comparable to those of the lithium poly[(4-styrenesulfonyl)(trifluoromethanesulfonyl)imide] (LiPSTFSI)/PEO electrolyte in the temperature range of 25–90 °C. More importantly, the complex of LiPSFSI/PEO exhibits excellent interfacial compatibility with the Li metal electrode compared to both those of the LiPSS/PEO and LiPSTFSI/PEO electrolytes.

Metallic tin (Sn) used as anode material for lithium ion batteries has long been proposed, but its low temperature electrochemical performance has been rarely concerned. Here, a Sn/C composite with nano-Sn embedded in expanded graphite (Sn/EG) is synthesized. The nano-Sn particles (∼30 nm) are uniformly distributed in the interlayers of expanded graphite forming a tightly stacked layered structure. The electrochemical performance of the Sn/EG, particularly at low temperature, is carefully investigated compared with graphite. At -20 °C, the Sn/EG shows capacities of 200 mAh g −1 at 0.1C and 130 mAh g −1 at 0.2C, which is much superior to graphite ( −1 ). EIS measurements suggest that the charge transfer impedance of the Sn/EG increases less rapidly than graphite with decreasing temperatures, which is responsible for the improved low temperature electrochemical performance. The Li-ion chemical diffusion coefficients of the Sn/EG obtained by GITT are an order of magnitude higher at room temperature than that at -20 °C. Furthermore, the Sn/EG exhibits faster Li-ion intercalation kinetics than graphite in the asymmetric charge/discharge measurements, which shows great promise for the application in electric vehicles charged at low temperature.

Due to the abundance of sodium in nature, sodium-ion batteries (SIBs) have attracted widespread attention. Numerous intercalated cathode materials have already been reported, but fewer intercalated anode materials are known. Among these materials, most anodes suffer from low coulombic efficiency and the dendritic growth of sodium due to the lower sodiated voltages (below 1.0 V). To improve the safety performance of batteries, exploring new anode materials which have higher sodiated voltage above 1.0 V is very important. Herein, a series of novel intercalated anode materials, ATiOPO4 (A = NH4, K, Na), is introduced for SIBs at the first time. Preparation of NaTiOPO4 by a traditional solid-state reaction is difficult. So we first synthesized NH4TiOPO4 (NTP) by a simple hydrothermal reaction, KTiOPO4 (KTP) and NaTiOPO4 (NaTP) were each prepared by ion exchange with the respective nitrate. These samples were investigated by electrochemical discharge/charge which showed average sodiated voltages of 1.45 V (NTP), 1.4 V (KTP) and 1.5 V (NaTP); respectively. In situ XRD results indicated that a two-phase reaction mechanism accompanies electrochemical Na insertion/extraction in NaTP. These anode materials are potential candidates for developing SEI-free and high safety SIBs.

Carbonaceous materials hold the most promising application among all anode materials for sodium-ion batteries (SIBs) because of the high storage capacity and good cycling stability. However, the high cost and the low initial Coulombic efficiency limit their further commercialization. Herein, an amorphous carbon material was fabricated through direct pyrolysis of low-cost pitch and phenolic resin at heat treatment temperatures between 1200 and 1600 °C. The electrochemical performances of the amorphous carbon were systematically investigated in SIBs with inexpensive Al foil as current collector and environmentally benign aqueous sodium alginate as binder. By optimizing the carbonization temperature and precursor, we achieved an initial Coulombic efficiency of 88% – the highest reported so far for carbon-based anodes in SIBs with a high reversible capacity of 284 mA h g − 1 and excellent cycling performance. It was found that both the carbonization temperature and the mass ratio of pitch to phenolic resin have significant impact on the local structure of amorphous carbon, which leads to various electrochemical behaviors. When coupled with an air-stable O3-Na 0.9 [Cu 0.22 Fe 0.30 Mn 0.48 ]O 2 cathode, the full cell shows excellent electrochemical performance with an initial Coulombic efficiency of 80%, a good cycling stability and an energy density of 195 Wh/kg. This contribution provides a new approach for the development of low-cost sodium-ion batteries.

Achieving high ionic conductivity in solid electrolytes and reducing the interfacial resistance between solid electrolytes and electrode materials are considered to be one of the biggest challenges in developing solid-state batteries. The integration of the high ionic conductivity of inorganic ceramics and the flexibility of organic polymers was attempted to yield a solvent-free ceramic/polymer composite solid electrolyte for Na batteries for the first time. The composite solid electrolytes exhibit a Na+ ion conductivity as high as 2.4 mS cm−1 at 80 °C. Meanwhile, this composite membrane is thermally stable up to 150 °C and maintains the flexibility of polymer electrolytes. The solid-state Na3V2(PO4)3/CPE/Na battery using this ceramic/polymer composite electrolyte exhibits an initial reversible capacity of 106.1 mA h g−1 and excellent cycle performance with negligible capacity loss over 120 cycles.

Lithium salt with a super-delocalized imide anion, namely (trifluoromethane( S -trifluoromethanesulfonylimino)sulfonyl) (trifluoromethanesulfonyl)imide ([CF 3 SO(=NSO 2 CF 3 ) 2 ] − ), [sTFSI] − ), has been prepared and studied as conducting salt for Li-ion cells. The fundamental physicochemical and electrochemical properties of neat Li[sTFSI] and its carbonate-based liquid electrolyte have been characterized with various chemical and electrochemical tools. Li[sTFSI] shows a low melting point at 118 °C, and is thermally stable up to 300 °C without decomposition on the spectra of differential scanning calorimetry-thermogravimetry-mass spectrometry (DSC-TG-MS). The electrolyte of 1.0 M (mol dm −3 ) Li[sTFSI] in ethylene carbonate (EC)/ethyl-methyl-carbonate (EMC) (3:7, v/v) containing 0.3% water does not show any hydrolytic decomposition on the spectra of 1 H and 19 F NMR, after storage at 85 °C for 10 days. The conductivities of 1.0 M Li[sTFSI]-EC/EMC (3:7, v/v) are slightly lower than those of Li[(CF 3 SO 2 ) 2 N] (LiTFSI), but higher than those of Li[(C 2 F 5 SO 2 ) 2 N] (LiBETI). The electrochemical behavior of Al foil in the Li[sTFSI]-based electrolyte has been investigated by using cyclic voltammetry and chronoamperometry, and scanning electron microscope (SEM). It is illustrated that Al metal does not corrode in the high potential region (3–5 V vs. Li/Li + ) in the Li[sTFSI]-based electrolyte. On Pt electrode, the Li[sTFSI]-based electrolyte is highly resistant to oxidation (ca. 5 V vs. Li/Li + ), and is also resistant to reduction to allow Li deposition and stripping. The applicability of Li[sTFSI] as conducting salt for Li-ion cells has been tested using graphite/LiCoO 2 cells. It shows that the cell with Li[sTFSI] displays better cycling performance than that with LiPF 6 .

A prototype rechargeable sodium-ion battery using an O3-Na0.90[Cu0.22 Fe0.30 Mn0.48]O2 cathode and a hard carbon anode is demonstrated to show an energy density of 210 W h kg(-1) , a round-trip energy efficiency of 90%, a high rate capability (up to 6C rate), and excellent cycling stability.

The alkali-ion storage in spinel lithium titanate (Li4Ti5O12) is comprehensively investigated in this work. In Li4Ti5O12, Na storage is more dependent on the particle size compared to Li storage. Electrochemical results show a Na-storage capacity from 150 to 16 mAh g−1, with increasing particle size from 50 to 500 nm, whereas the Li-storage capacity appears to be independent of particle size. The Na-storage rate capability in Li4Ti5O12 is much worse than that of Li, probably because of the sluggish Na+ diffusion in Li4Ti5O12. Ab initio molecular dynamics simulations also indicate that this can be attributed to the slow diffusion kinetics of Na+ in spinel Li4Ti5O12.

Cr-based cathode materials for Li-ion batteries have attracted significant attentions due to the feature of multiple electron transfer. The origin of the poor electrochemical inactivity of LiCrO2 has not been clarified for decades. Here an irreversible phase transformation from the layered to the rock-salt structure is observed at atomic scale in partially electrochemical delithiated LiCrO2: Cr ions migrate from Cr layers into Li layers in the surface regions. The Cr ions at Li layers in the surface regions could block extraction of lithium from the interior regions. Density functional theory (DFT) calculations confirm that Cr ions in Li layers can stabilize the structure in the Li-poor area, but the diffusion energy barrier of Li ions will be greatly increased. It is proposed accordingly that the surface phase transformation and the blocking of diffusion channel are the main origin for the poor electrochemical reactivity of LiCrO2. Such a surface blocking phenomenon may be a common origin for inactivity of some cathode materials, in which cation mixing become significant after initial delithiation. In addition, Cr ions in LiCrO2 are oxidized only from Cr3+ to Cr4+ during electrochemical delithiation, instead of Cr6+ as usually expected, based on synchrotron X-ray absorption spectra (XAS) studies.

Binary electrolytes, comprising of lithium bis(fluorosulfonyl) imide (LiFSI) and ionic liquids (ILs) of N -methyl- N -propylpiperidinium bis(fluorosulfonyl) imide (PI 13 FSI) with various concentrations of LiFSI (i.e., LiFSI/PI 13 FSI in 0.05:1, 0.1:1, 0.2:1, 0.5:1, 0.8:1 and 1:1, by mole) have been investigated as electrolyte for Li-ion cells, in terms of phase behavior, thermal stability, density, viscosity, ionic conductivity, lithium-ion transference number, and electrochemical behaviors on Al, Pt, Ni, and composite natural graphite electrodes, with particular attention to the effect of concentration of LiFSI in PI 13 FSI on these properties. The stability of Al in the high potential region (3.0–5.0 V vs. Li/Li + ) has been confirmed in these electrolytes using cyclic voltammetry, chronoamperometry and SEM morphology. The anodic stability of these electrolytes on Pt electrode has been little affected by addition of LiFSI. Li deposition/stripping on Ni electrode shows low columbic efficiencies ( − anions and PI 13 + cations. Reduction of FSI − anions for forming solid electrolyte interphase (SEI) films on the graphite is observed at ca. 2.0 V (vs. Li/Li + ), followed by intercalation of Li + ions and IL cations into graphite in these electrolytes at the first cathodic scan in CV measurements. The performances of SEI films formed on the graphite highly depend on the concentration of LiFSI, and a stable Li-ion conducting SEI film can only be formed in the electrolyte containing a high concentration of LiFSI. Li/natural graphite cell using LiFSI-PI 13 FSI (1:1, by mole) as electrolyte displays high specific capacities (> 360 mAh g −1 ) and columbic efficiencies (> 99%) after conditioning, except for a large irreversible capacity (139 mAh g −1 ) observed at the first cycle. Analyses of XPS and electrochemical impedance spectra reveal that a stable Li-ion conducting SEI film, mainly comprising reduction products of FSI − anions (e.g., LiF, LiOH, Li 2 SO 3 , and species containing NSO 2 -, FSO 2 -, and N − ), has been formed on the graphite.

The binary eutectic mixture of lithium bis(fluorosulfonyl)imide (LiFSI) and potassium bis(fluorosulfonyl)imide (KFSI) with a molar ratio of x(LiFSI): x(KFSI) = 0.41: 0.59 has been investigated as molten salt electrolyte for natural graphite/LiFePO4 lithium-ion cells at 80 degrees C. The electrochemical performances of the Li/natural graphite, Li/LiFePO4, and natural graphite/LiFePO4 cells using this molten salt electrolyte have been evaluated, in terms of cycling performances and electrochemical impedance spectra (EIS) at 80 degrees C. Both the Li/natural graphite and Li/LiFePO4 cells show good cycling performances. The initial specific capacities after conditioning for the natural graphite and LiFePO4 electrodes are 353 and 150 mAh g(-1), respectively, and the corresponding capacity retention rates are 98% and 97%, respectively, after 100 cycles at 80 degrees C, except for a large irreversible capacity (162 mAh g(-1)) observed for the natural graphite at the first cycle for forming solid electrolyte interface (SEI) film. The natural graphite/LiFePO4 lithium-ion cell using this molten salt electrolyte shows a low capacity in the range of 71-86 mAh g(-1), due to the large irreversible capacity (71 mAh g(-1)) at the first cycle, but it shows a good cycleability after the first cycle, and provides a specific capacity of 71 mAh g(-1) after 100 cycles at 80 degrees C. The variations of cycling performances of these cells can be well correlated with their impedance evolution with cycling. (C) 2014 Elsevier Ltd. All rights reserved.

New solid polymer electrolytes (SPEs) comprising of lithium bis(fluorosulfonyl)imide (LiFSI) and high molecular weight poly(ethylene oxide) (PEO, Mv = 5 × 106 g mol−1) have been prepared and characterized, and are comparatively studied with the representative SPEs, Li[N(SO2CF3)2] (LiTFSI)/PEO, at a molar ratio of EO/Li+ = 20. Their physicochemical properties have been investigated in terms of phase transition behavior, ionic conductivity, lithium-ion transference number (tLi+), electrochemical stability, and with particular attention to the interfacial behavior between lithium electrode and SPEs. It has been demonstrated that the ionic conductivities of LiFSI/PEO electrolyte are higher than those of LiTFSI/PEO one above 60 °C, and exceeds 10−3 S cm−1 at 80 °C. The interface resistances of Li symmetric cell (Li metal | polymer electrolytes | Li metal) using LiFSI/PEO electrolyte are much lower than those using LiTFSI/PEO. The Li/LiFePO4 cell using LiFSI/PEO electrolyte exhibits good cycling performance at 80 °C. These outstanding properties of the LiFSI/PEO electrolyte make it attractive as SPEs for Li battery.

Recently, lithium-sulfur batteries as high energy-density energy storage system have attracted more and more attention. In this article, we first introduce lithium-sulfur batteries and then review recent progress in carbon-sulfur cathodes and electrolytes for lithium-sulfur batteries. Furthermore, we analyze and summarize the reported strategies to inhibit lithium polysulfide dissolution. Particularly, we propose a new class of bi-functional Solvent-in-Salt (SIS) electrolyte with high lithium salt concentration for solving the problems resulting from both sulfur and lithium metal electrodes. Finally, we present the outlook for future lithium-sulfur batteries.

Molten salts have attracted wide attention as electrolyte for lithium battery due to their nonvolatile and nonflammable features. In this work, the phase diagram of high pure lithium bis(fluorosulfonyl)imide (LiFSI) and KFSI binary system has been measured. This system shows a high transfer number of lithium ion at 85 degrees C and its conductivity reaches to 10(-3)-10(-2)S cm(-1) from 40 degrees C to 150 degrees C. The electrochemical windows of this system have been measured using Pt, Al and Cu as working electrode, respectively. The reversibility of lithium deposition in eutectic mixture (LiFSI:KFSI = 0.4:0.6 by mole) were investigated on LiCoO2, artificial graphite and LiFePO4, respectively, by cyclic voltammetry using three-electrodes systems. It is found that the half cell with this eutectic system as electrolyte can charge and discharge reversibly for LiFePO4 cathode but fails for MCMB and Li4Ti5O12 anodes. This problem would be solved partially by forming a passivating layer in advance or coating a protection layer on anode. (C) 2013 Elsevier Ltd. All rights reserved.

Sixteen ionic liquids (ILs) based on two new asymmetric imide anions, (fluorosulfonyl) (polyfluorooxaalkanesulfonyl)imide {[(FSO2)(XCF2CF2OCF2CF2SO2)Nr](-) [5X3O-FOFSI](-), X= H and I), are synthesized and characterized by in combination with various oniums, including 1,3-dialkylimidazolium, quaternary alkyl (or ether-functionalized alkyl)ammonium, N-alkyl-N-methyl-pyrrolidinium and -piperidinium. Their physicochemical properties are investigated, in terms of phase transitions, thermal stability, density, viscosity, ionic conductivity, electrochemical stability, and the capability as electrolytes to allow Li deposition/stripping. The influences of the structural variations in both the cations and anions, particularly introduction of an ether group into the anion, on the above properties are systematically studied. All the ILs are liquids at room temperature and show low glass transition temperatures, suggesting the high flexibility of the ether-functionalized imide anion. It has been demonstrated that only having an ether group into the polyfluoroalkyl chain of the imide anion affect neither the cathodic nor anodic stability of the anion and their ILs. ThelLs based on the [5H30-FOFSI](-) anion have an enough electrochemical stability to allow Li deposition/striping, while those based on the [513O-FOFS](-)] - anion show relatively low cathodic stability due to the presence of a C I bond in the anion. (C) 2013 Elsevier Ltd. All rights reserved.

Employing density functional theory (DFT) calculations, we demonstrate that the stage-II configuration in delithiated LiFePO4 is a thermodynamically metastable but kinetically controlled state, distinct from the thermodynamically favorable stages in graphite intercalation compounds (GICs). Based on the computational results, we propose a dual-interface model to describe the delithiation mechanism of LiFePO4 upon charging. Accordingly, the experimentally observed LiFePO4/stage-II/FePO4 three-phase coexistence could be successfully reproduced. Formation of lithium-staging configuration is mainly attributed to the Fe center mediated interlayer Li-Li interactions, which is an essential indirect electrostatic force. The indirect interaction originates from the localized nature of Fe 3d electrons, for which the effective oxidation state of Fe redox is determined by the Li ion arrangement and, in turn, has an impact on the behavior of Li ion diffusion. Besides a better understanding of the microscopic lithium diffusion mechanism in LiFePO4, our results also shed light on the interactions between electron and ion and further emphasize the importance of studying the Li diffusion kinetics at phase boundary in phase separation materials.

Two types of NiO-Li2CO3 nanocomposite electrodes have been prepared for the electrochemical decomposition studies. The thin film electrode with a thickness of 225 nm and grain size around 5-8 nm is prepared by a pulsed laser deposition method. The powder sample is prepared by a solution evaporation and calcination method with primary particle size in the range of 20-50 nm. Using ex situ TEM, Raman and FTIR spectroscopy and synchrotron based in situ XRD, the electrochemical decomposition of Li2CO3 phase in both types of the NiO-Li2CO3 nanocomposite electrodes after charging up to about 4.1 V vs Li+/Li at room temperature is clearly confirmed, but not in the electrode containing only Li2CO3. The NiO phase does not change significantly after charging process and may act as catalyst for the Li2CO3 decomposition. The potential of using NiO-Li2CO3 nanocomposite material as additional lithium source in cathode additive in lithium ion batteries has been demonstrated, which could compensate the initial irreversible capacity loss at the anode side. (C) 2012 Elsevier B.V. All rights reserved.

Li(FSO2)(C4F9SO2)N (LiFNFSI) has been investigated as a single electrolyte salt to improve the stability of LiMn2O4 at 60 degrees C. The performances of LiFNFSI as an electrolyte salt have been comparatively studied with those of LiPF6 in a mixture of ethylene carbonate: dimethyl methyl carbonate (EC:DMC, v/v, 1: 1), in terms of separator wettability, battery cycling performance, dissolution of Mn2+ ions into the electrolytes, AC impedance and morphology evolution of electrodes. The wetting ability of the LiFNFSI based electrolyte with the battery materials is better, indicated by a smaller electrolyte/separator contact angle and lower AC impedances for LiMn2O4/Li and Li/Li cells. In addition, Mn2+ ions dissolution from LiMn2O4 cathode into the electrolytes at 60 degrees C is significantly suppressed. The LiMn2O4/Li cell with 1M LiFNFSI/EC:DMC (1:1, v/v) could be cycled over 400 times at 60 degrees C, while that with 1M LiPF6/EC: DMC (1: 1, v/v) failed rapidly after 38 cycles. These results suggest that LiFNFSI would be a highly potential contender to replace LiPF6 to extend the cycle life of LiMn2O4 battery at elevated temperatures. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.026208jes] All rights reserved.

A series of LiFe1−xMnxPO4/C materials with high Mn content (0.7 ≤ x ≤ 0.9) are synthesized by solid state reaction. The samples have mesoporous structure with an average pore size of 25 nm, particle size around 200–300 nm, crystalline size around 30 nm and specific areas around 50 m2 g−1. Their electrochemical performances are studied and the reversible capacity and rate performance decrease with the increase of Mn content. The redox potential of the Fe2+/Fe3+ and Mn2+/Mn3+ redox couple also shift accordingly. The overpotential value of the Mn2+/Mn3+ redox couple (80 mV) is close to that of the Fe2+/Fe3+ couple (60 mV) in all three compositions and shows a maximum (∼300 mV) in the regions of voltage transition.

LiNi0.5Mn1.5O4 is generally reported to crystallize in the spinel structure within two different space groups (Fd-3m and P4(3)32) depending on the oxygen stoichiometry/ordering of the Ni/Mn cations. This paper presents a contribution to the study of these two phases in order to have a better insight on how the preparation method influence their electrochemical properties. The phases were synthesized by a ceramic route and thoroughly characterized using X-ray diffraction (XRD). FTIR and Raman spectroscopy. This latter technique, together with the obtaining of the electrochemical signature, allows discriminating between the types of spinel phases. Based on thermal in situ XRD measurements, we further propose a peritectoid transformation as an explanation for the appearance of a nickel based rock salt phase during the preparation. Finally, we discuss on the electrochemical deinsertion mechanism. (C) 2011 Elsevier B.V. All rights reserved.

Lithium bis(fluorosulfonyl)imide (LiFSI) has been studied as conducting salt for lithium-ion batteries, in terms of the physicochemical and electrochemical properties of the neat LiFSI salt and its nonaqueous liquid electrolytes. Our pure LiFSI salt shows a melting point at 145 °C, and is thermally stable up to 200 °C. It exhibits far superior stability towards hydrolysis than LiPF 6 . Among the various lithium salts studied at the concentration of 1.0 M (= mol dm −3 ) in a mixture of ethylene carbonate (EC)/ethyl methyl carbonate (EMC) (3:7, v/v), LiFSI shows the highest conductivity in the order of LiFSI > LiPF 6 > Li[N(SO 2 CF 3 ) 2 ] (LiTFSI) > LiClO 4 > LiBF 4 . The stability of Al in the high potential region (3.0–5.0 V vs. Li + /Li) has been confirmed for high purity LiFSI-based electrolytes using cyclic voltammetry, SEM morphology, and chronoamperometry, whereas Al corrosion indeed occurs in the LiFSI-based electrolytes tainted with trace amounts of LiCl (50 ppm). With high purity, LiFSI outperforms LiPF 6 in both Li/LiCoO 2 and graphite/LiCoO 2 cells.

New hydrophobic ionic liquids based on (fluorosulfonyl)(pentafluoroethanesulfonyl)imide ([(FSO2)(C2F5SO2)N]−, FPFSI−) anion with various oniums, including imidazolium, tetraalkyl ammonium, pyrrolidinium, and piperidinium, were prepared and characterized. Their physicochemical and electrochemical properties, including phase transitions, thermal stability, viscosity, density, specific conductivity and electrochemical windows, were extensively characterized, and were comparatively studied with the corresponding ionic liquids containing the isomeric but symmetric TFSI− ([(CF3SO2)2N]−) anion. These new FPFSI−-based ionic liquids display low melting points, low viscosities, good thermal stability, and wide electrochemical windows allowing Li deposition/dissolution. All these desired properties suggest they are potential electrolyte materials for Li (or Li-ion) batteries.

New functionalized ionic liquids (ILs), comprised of multi-methoxyethyl substituted quaternary ammonium cations (i.e. [N(CH2CH2OCH3)4−n(R)n]+; n = 1, R = CH3OCH2CH2; n = 1, R = CH3, CH2CH3; n = 2, R = CH3CH2), and two representative perfluorinated sulfonimide anions (i.e. bis(fluorosulfonyl)imide (FSI−) and bis(trifluoromethanesulfonyl)imide (TFSI−)), were prepared. Their fundamental properties, including phase transition, thermal stability, viscosity, density, specific conductivity and electrochemical window, were extensively characterized. These multi-ether functionalized ionic liquids exhibit good capability of dissolving lithium salts. Their binary electrolytes containing high concentration of the corresponding lithium salt ([Li+] >1.6 mol kg−1) show Li+ ion transference number ( t L i + ) as high as 0.6–0.7. Their electrochemical stability allows Li deposition/stripping realized at room temperature. The desired properties of these multi-ether functionalized ionic liquids make them potential electrolytes for Li (or Li-ion) batteries.

The structural, electronic and Li diffusion properties of LiFeSO 4 F were analyzed by first-principles calculation under the DFT + U framework. The difference of the calculated lattice parameters and the reported data is within 3%. The redox potential of Fe 2+ /Fe 3+ versus Li metal is 3.7 V, and phase separation of LiFeSO 4 F and FeSO 4 F is expected during Li extraction. Pure LiFeSO 4 F is an insulator with a band gap of 3.6 eV, while the band gap in the partially delithiated form Li 1 − x FeSO 4 F is obviously smaller. A very low Li migration energy of 0.3 eV is required in the partially delithiated form Li 1 − x FeSO 4 F, and the diffusion coefficient is estimated to be about 1.6 ⁎ 10 − 7 cm 2 s − 1 .

Elastic band method has been used to calculate the activation energy for Li diffusion in the olivine structured LiFePO4 and FePO4. Screening from anions, the valence of the nearest neighbor transition metal, lattice parameters, are identified to be important factors to determine the activation energy for Li diffusion. The calculated activation energy in LiFePO4 and FePO4 are 0.5 eV and 0.27 eV, respectively. It is dependent on the concentration and configuration of lithium ions in the phase boundary regions and a kinetic model for Li extraction and insertion process is proposed. (C) 2010 Elsevier B.V. All rights reserved.

Monofluoropropylene carbonate (MFPC) and trifluoropropylene carbonate (TFPC) with a monofluoromethyl (or trifluoromethyl) replacing the methyl group in propylene carbonate (PC) as well as EC-CH2CH2Si(CH3)2OSi(CH3)3 (Si-A) and EC-CH2CH2Si(CH3)3 (Si-B) have been synthesized. The charge–discharge studies in a Li/MCMB (mesocarbon microbeads) cell using electrolyte containing these compounds show that the solid electrolyte interphase (SEI) formation capability of MFPC/DMC (dimethyl carbonate) and TFPC/DMC are about the same as ethylene carbonate (EC)/DMC, and TFPC/PC/DMC is better than that of EC/PC/DMC, while MFPC/PC/DMC is poorer than the EC/PC/DMC. The superior SEI formation capability of TFPC could be attributed to the strong electron withdrawing group of CF3, which promote the “ring-opening” reaction. In contrast, the electron donating group CH3 in the PC structure may demote the “ring opening” and cause the poor SEI formation. The results of MFPC with weaker electron withdrawing group give further support of this hypothesis. The bi-solvent electrolytes of Si-A/DMC and Si-B/DMC have comparable SEI formation capability as EC/DMC and TFPC/DMC, regardless of their bulky chains. This indicates that if proper chain structures are used, good SEI formation capability could be obtained for cyclic carbonate with bulky chains. These new solvents provide valuable information in studying the SEI formation mechanism and designing new electrolytes. Keywords: SEI film, Ring-opening reaction, Lithium-ion batteries, Electrolytes

A novel compound named pentafluorophenylboron oxalate (PFPBO) has been synthesized. PFPBO has a unique molecular structure containing a boron atom center with electron deficiency and an oxalate group. It is found that when PFPBO is used as additive, the solubility of lithium fluoride (LiF) or lithium oxide (Li2O, Li2O2) in propylene carbonate (PC) and dimethyl carbonate (DMC) solvents can be increased dramatically. The new electrolytes show high ionic conductivity, high lithium ion transference number and good compatibility with LiMn2O4 cathode and MCMB anode. PFPBO was synthesized with the designed structure to act as a bi-functional additive: boron-based anion receptor (BBAR) additive and stable solid electrolyte interphase (SEI) formation additive in PC-based electrolytes. The results show it does possess these two desired functionalities. Keywords: Pentafluorophenylboron oxalate, Boron-based anion receptors, Solid electrolyte interphase, Propylene carbonate, Lithium fluoride, Lithium oxide, Lithium peroxide, Non-aqueous electrolyte

The new electrolyte systems utilizing one type of Lewis acids, the boron based anion receptors (BBARs) with LiF, Li(2)O, or Li(2)O(2) in carbonate solutions have been developed and reported by us. These systems open up a new approach in developing non-aqueous electrolytes with higher operating voltage and less moisture sensitivity for lithium-ion batteries. However. the formation of a stable solid electrolyte interphase (SEI) layer on the graphitized anodes is a serious problem needs to be solved for these new electrolyte systems, especially when propylene carbonate (PC) is used as a co-solvent. Using lithium bis(oxalato)borate (LiBOB) as an additives, the SEI layer formation on mesophase carbon microbeads (MCMB) anode is significantly enhanced in these new electrolytes containing boron-based anion receptors. Such as tris(pentafluorophenyl) borane, and lithium salt such as LiF, or lithium oxides such as Li(2)O or Li(2)O(2) in PC and dimethyl carbonate (DMC) solvents. The cells using these electrolytes and MCMB anodes cycled very well and the PC co-intercalation was suppressed. Fourier transform infrared spectroscopy (FTIR) studies show that one of the electrochemical decomposition products of LiBOB, lithium carbonate (Li(2)CO(3)), plays a quite important role in the stablizing SEI layer formation. (c) 2008 Elsevier B.V. All rights reserved.

Olivine structured LiFe1/4Mn1/4Co1/4Ni1/4PO4 in pure solid solution single phase was obtained using solid-state reaction. For the carbon-coated material, in a voltage range of 3.0–5.1 V (vs. Li/Li+), three voltage plateaus were observed clearly in both galvanostatic discharging and galvanostatic intermittent titration technique (GITT) curves. These three plateaus are corresponding to Co3+/Co2+, Mn3+/Mn2+ and Fe3+/Fe2+ redox couples. No definite plateau can be assigned to Ni3+/Ni2+ redox couple in this voltage range. The overpotentials show the maximum when the redox reaction shifts from one redox couple to another couple. The apparent chemical diffusion coefficients of lithium (D˜Li) are in the same order of magnitude 10−15 cm2 s−1 for all transition reactions. Keywords: LiFe1/4Mn1/4Co1/4Ni1/4PO4, GITT, Voltage relaxation technique, Chemical diffusion coefficient, Lithium ion batteries

Aqueous sodium-ion batteries could be a potential solution for large-scale energy storage, but the conventional negative electrodes are not efficient. Here, the authors report a titanium-substituted tunnel-type Na0.44MnO2 material as a promising negative electrode for aqueous sodium-ion batteries.

Cr2O3 is a promising anode material for Li-ion batteries due to its relative low emf value, high Li-storage capacity and low cost. However, pristine Cr2O3 powder shows poor electrochemical performance due to its low electrical conductivity and large volume change during cycling. Several strategies are applied for its improvement, including constructing nanostructure, hetero-atom doping and preparing of carbon/Cr2O3 composite with different structures. Carbon coating is very effective for improving cyclic performance. The mechanism is discussed here.