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In this paper, we report a facile method for the in situ deposition of a thin solid electrolyte layer on the surface of anode materials, which can significantly improve the rate capability and reduce the time for reaching capacity maximum. The thin solid electrolyte layer (∼8 nm) is formed by adding a small amount of LiNO3 into the anode materials; the added LiNO3 decomposes irreversibly into Li3N and LiNxOy on the surface of the anode materials during the first cycle, facilitating fast diffusion of lithium ions and limiting the formation of the surface electrolyte interface films. This is verified by adding LiNO3 into graphite half-cells which shows a fast activation process at high current density: in particular, the charge capacity reaches its maximum after only ∼30 and ∼40 cycles at 170 and 340 mA g−1, respectively, compared to ∼50 and ∼80 cycles for the graphite half-cell. Furthermore, the LiNO3 additive results in high capacity retention at high C-rates, with a value of 82.4% at 680 mA g−1, compared with 22.4% for the graphite half-cell. The facile and low-cost method reported here is expected to be readily applicable to other electrode materials for high-performance lithium-ion batteries.

Solid electrolytes with high ionic conductivity and excellent electrochemical stability are of prime significance to enable the application of solid-state batteries in energy storage and conversion. In this study, solid composite polymer electrolytes (CPEs) based on sodium bis(trifluorosulfonyl) imide (NaTFSI) and poly (ethylene oxide) (PEO) incorporated with active ceramic filler (NASICON) are reported for the first time. With the addition of NASICON fillers, the thermal stability and electrochemical stability of the CPEs are improved. A high conductivity of 2.8 mS/cm (at 80 °C) is readily achieved when the content of the NASICON filler in the composite polymer reaches 50 wt%. Furthermore, Na 3 V 2 (PO 4 ) 3 /CPE/Na solid-state batteries using this composite electrolyte display good rate and excellent cycle performance.

The thermodynamic instability of the layered structure and severe side reactions with liquid carbonate electrolytes have been considered as the key obstacles for the practical application of LiCoO2 (LCO) at voltages of above 4.5 V (versus Li/Li+). Here, we have developed a facile wet-mixing synthetic method which can realize thin and uniform surface coating of aluminum doped zinc oxide (AZO) on LCO particles. The half-cells employing the AZO modified LCO display excellent 4.5 V cycle performance with the discharge capacity retention of 80% after 650 cycles and superior rate capability of 8C capacity of 100 mAh g−1. Combined with surface structure characterizations and bond valence calculations, it is revealed that the stabilized surface and superior kinetic properties contribute to the performance enhancement of AZO modified LCO at 4.5 V. This work demonstrates AZO a suitable coating material for surface protection of cathode materials for high-voltage applications. The preparation method developed in this work is also suitable for mass production and applicable to fabrication of other types of battery materials.

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 .

Si–Cu–Ti thin films with Cu 3 Si nanowires on the surface and voids in the Cu layer are fabricated for the first time by magnetron sputtering combined with atomic layer deposition (ALD) of alumina. The formation of the surface Cu 3 Si nanowires is strongly dependent on the thickness of the coated alumina and cooling rate of the thin films during annealing. The maximum coverage of the surface Cu 3 Si nanowires is obtained with an alumina thickness of 2 nm and a cooling rate of 1 °C min −1 . The electrode based on this thin film shows an excellent capacity retention of more than 900 mAh g −1 and a high columbic efficiency of more than 99% after 100 cycles. The improvement of the electrochemical performance of Si–Cu–Ti thin film electrode is attributed to the surface Cu 3 Si nanowires which reduce the polarization and inhomogeneous lithiation by formation of a surface conductive network, in addition to the alleviation of volume expansion of Si by voids in the Cu layer during cycling.

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.

Monoclinic phase LiFeSO4F has a triplite like structure in which Li+/Fe2+ is fully mixing. Not 100% Li can be extracted from the lattice easily even at a rate of C/20, and the valence of Fe changes between ca +2 and +2.5 observed by XANES for a Li/LiFeSO4F cell cycled between 2.2 and 4.6 V. Two-phase reaction mechanism is verified by GITT due to the appearance of a flat plateau, and large polarization appears after more than 50% Li extracted from triplite-LiFeSO4F. A core–shell model has been mentioned to explain its extreme polarization. In the fully mixing structure, there is no intact long-range pathway for Li+, so leading to sluggish kinetics effect and “inert” Li+ in the lattice.

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.

Silicon is the most promising high capacity anode material to replace graphite for developing next generation high energy density Li-ion batteries. In this approach, patterned amorphous and microcrystalline Si thin film electrodes (a-Si and μc-Si) have been prepared by rf-sputtering and etched further by a reactive ion etching (RIE) system to form square-shape microcolumn electrodes with controllable size (5 × 5 μm width, 500 nm height, aspect ratio of width/height is 10:1) and array distance (5 μm). It has been found that the volume expansion and contraction of a-Si and μc-Si are anisotropic, about 180% along vertical direction and 40% along lateral direction. The total volume variation changes linearly with the increase of lithium insertion content up to ∼310% for a-Si and ∼300% for μc-Si. It occurs nearly reversibly. In addition, it is observed that the original square-shape Si column transforms into the dome-like appearance after lithium insertion and changes into bowl shape after lithium extraction gradually. Radial-like curved cracks are formed after 5−10 cycles and the neighboring Si columns tend to merge together when the distance of the columns is less than 1 μm.

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.

MnO microspheres with and without carbon coating are prepared as anode materials for lithium ion batteries. The MnO microsphere material shows a reversible capacity of 800 mAh g(-1) and an initial efficiency of 71%. It can deliver 600 mAh g(-1) at a rate of 400 mA g(-1). Results of Mn K-edge X-ray absorption near-edge structure (XANES) spectra and extended X-ray absorption fine structure (EXAFS) confirm further the conversion reaction mechanism, indicate that pristine MnO is reduced to Mn after discharging to 0 V and part of reduced Mn(0) is not oxidized to Mn(2+) after charging to 3 V. This explains the origin of the initial irreversible capacity loss partially. The quasi open circuit voltage and the relationship between the current density and the overpotential are investigated. Both indicate that there is a significant voltage difference between the charging and discharging profiles even when the current density decreases to zero. (C) 2010 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.

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.

In order to study the electronic structure changes of the electrochemically delithiated Li 1− x Fe 0.5 Co 0.5 PO 4 system, in situ Fe and Co K-edge XAS and ex situ P K-edge XAS have been carried out during the first charging process. The Fe and Co K-edge XAS results showed that the major charge compensation at the metal sites during charge is achieved by the oxidation of Fe 2+ ions at lower potential plateau (∼3.6 V) and the oxidation of Co 2+ ions at higher potential plateau (∼5.0 V). The gradual shift of main edge features in P K-edge XANES spectra showed that P O bonds become less covalent during delithiation, due to the increased covalency of Fe 3+ O bonds via the inductive effect. From the observation of pre-edge peaks, it is concluded that the electrochemical delithiation of Li 1− x FePO 4 result in the hybridization of P 3p states with the metal 3d states.

A series of carbon-coated layered structured Li[Cr x Li (1/3− x /3) Ti (2/3−2 x /3) ]O 2 samples (0.3 ≤ x ≤ 0.45) were prepared. Among them, the sample of x = 0.4 shows the highest initial reversible capacity of 207 mAh g −1 at 30 mA g −1 in 2.5–4.4 V. The reversible Li-storage capacities for the samples with high x values ( x = 0.4, 0.45) faded slightly while the samples with low Cr content ( x = 0.3 and 0.35) showed a capacity increase upon cycling. It was found that the relative intensity ratio of (0 0 3) peak to (1 0 4) peak ( R (0 0 3) = I (0 0 3) / I (1 0 4) ) is influenced strongly by x value in as-prepared samples. The samples of x = 0.35 and 0.4 turn to a similar structure with low R (0 0 3) value during cycling. These phenomena indicate that the cation mixing of Cr 3+ in the lithium layer occurs in as-prepared samples and became more significant upon delithiation and lithiation. This is supposed being a necessary process for Cr-based layered structure materials possessing electrochemical reactivates. The occurrence of the cation mixing is beneficial from the local lattice distortion caused by the short-range ordering between Ti and Li. This is supposed to be helpful for the migration of Cr 6+ and Cr 3+ at tetrahedral and octahedral sites. Different from the case of LiNiO 2 , the cation mixing is essential for the transport and storage of lithium in the carbon-coated Li–Cr–Ti–O layered compounds.

LiFe(1-x)CoxPO(4) (0

A new compound Li–Ni–Ti oxide-based material (LiNi0.5Ti0.5O2) with cubic structure was prepared by solid state reaction at 900 °C. Powder X-ray diffraction (XRD) was used to determine the phase purity and structure of the material. The Bragg peaks of LiNi0.5Ti0.5O2 can be indexed based on a cubic unit with dimension a = 4.142 A, belonging to space group Fd3m (SG number 225). X-ray photoelectron spectroscopy (XPS) study showed that the chemical valences of Ni and Ti were +2 and +4, respectively. The electrochemical testing indicated that the Li+ ions in LiNi0.5Ti0.5O2 cannot be extracted until 4.8 V. However, two initial Li ions per LiNi0.5Ti0.5O2 can be intercalated into LiNi0.5Ti0.5O2 and one Li+ ion can be extracted reversibly.

Several 18650 lithium-ion batteries using LiCoO2, LiMn2O4, and LiFePO4 as cathode materials were assembled separately. Gas species of these batteries under normal cycling and overcharging to 4.5 and 5.0 V conditions were examined by means of GC–MS method. Under the normal charge and discharge voltage range, it is found that gas components are independent to the cathode materials. C2H5F gas was detected in all cases. A formation mechanism is proposed. Under overcharging condition, it is found that the gas components are different and there is a correlation between the C2H2 product and the oxidation ability of various delithiated cathode materials.

Fourier-transform infrared (FTIR) spectra of nanometer SnO anodes at different charge/discharge states in lithium rechargeable batteries were recorded. Solvent decomposition reaction that generally presents on the surface of carbon or alkali metal is also presented on SnO anode. The surface film is composed of Li2CO3 and ROCO2Li. In addition, FTIR data indicates that absorption bands of ROCO2Li are changed below 0.7 V, which is believed to be related to the change of the surface layer of SnO anode around 0.7 V versus Li/Li+ during the first discharge process. (C) 2002 Published by Elsevier Science B.V.

The surface enhanced Raman scattering (SERS) spectrum of the solid electrolyte interphase (SEI) film on the Ag electrode discharged to 0.0 V in lithium battery was measured by normal Raman spectrometer at different excited wavelength. Compared with the Raman spectra of pure LiOH.H2O and Li2CO3 reagents, all the SERS bands of the SEI film formed on the surface of the Ag electrode can be assigned to Li2CO3 and LiOH.H2O. which are the main stable components of the SEI film in the presence of trace water. LiF may be another possible stable component, however, it cannot be detected due to its inactivity in Raman spectrum. (C) 2002 Elsevier Science B.V. All rights reserved.

Fine powders of tin oxide doped with traces of silicon in combination with highly dispersed amorphous silicon oxide have been synthesized by an advanced ultrasonic spray method. The mixtures have been analyzed by XRD and IR. The electrochemical results showed that addition of silicon decreases the tin oxidation state, and, hence, reduces the irreversible capacity during the first discharge/charge cycle. SiO2 and Li2SiO3 appeared during the first discharging as confirmed by IR spectroscopy. Furthermore, a reversible capacity of 900 mA h/g to 950 mA h/'g for these composites has been found, which is even higher than the theoretical value (783 mA h/g according to the Li4.4Sn). The chemical diffusion coefficients of lithium in the Li-Sn alloy phases formed (Li0.4Sn, LiSn, Li3Sn7, Li3.5Sn and Li4.4Sn) have been measured by galvanostatic intermittent titration technique (GITT). Below a Li content corresponding to Li3Sn7, a reduced voltage polarization as well as an increased lithium chemical diffusion coefficient were observed. This improved performance is due to an enhanced interfacial diffusion, caused by highly dispersed inert second phases, i.e., SiO2 and LiSi2O3. (C) 1999 Elsevier Science S.A. All rights reserved.

The mechanisms for the high capacity of lithium insertion in low-temperature pyrolytic carbons are not fully understood though several models have been proposed. None of the existing models considers the reversible crystalline structural changes within a graphene layer in the discharge–charge processes. In this report, low-temperature pyrolytic phenolic resin and lithium ion cells made of it are characterized by Raman spectroscopy, XRD and elemental analysis as well as discharge/charge measurements. The linear relation is confirmed between the specific capacity of the low-temperature pyrolytic carbon and its H/C atomic ratio after eliminating the influence of the crystallite size to the capacity. It is found that the evolution of the Raman spectrum of the pyrolytic carbon electrode upon discharge and charge is quite different from that of the other forms of carbonaceous electrodes. Based on the characteristic Raman spectra and the discharge–charge curves of the carbon electrode, a breaking-recovery model of the weak C⋯H bond is suggested for the lithium insertion/extraction processes in the low-temperature pyrolytic carbon electrodes.

A series of composite SnO materials were prepared by mixing SnO powder with reducing agents and heating at different temperatures for different periods under argon atmosphere. It was found that alpha-SnO with its tetragonal structure could transform into the beta-Sn phase or orthorhombic SnO depending on treatment conditions. The electrochemical behaviors of these materials used as an anode active material in lithium rechargeable batteries was investigated. It was found that excessive amounts of reducing agents, especially in the case of carbon black, may provide a good dispersion environment for SnO which is similar to the case of amorphous tin composite oxides (TCO). The presence of beta-Sn or orthorhombic SnO is not beneficial to the cycling performance, although a large ratio of beta-sn in the starting anode material can decrease the capacity loss during the first cycle. Superfine SnO material was also prepared by decomposing SnC2O4 which was synthesized by a sol-gel method. Its cyclic performance was improved significantly. (C) 1999 Elsevier Science S.A. All rights reserved.

Nano-SnO and normal SnO anodes for lithium rechargeable batteries have been investigated by electrochemical impedance spectroscopy (EIS). Three types of equivalent circuits have been used to fit the spectra at different discharge states. The variations of impedance spectra, charge-transfer resistance and double layer capacitance have been discussed. The electrochemical reaction mechanism of SnO anode for lithium ion batteries can be deduced as follows: a passivating film forms on the surface of SnO particles firstly, then Li+ ions pass through the surface film and react with SnO to produce amorphous Li2O and to form fine grains of Li–Sn alloys in the core region underneath the passivating film.

The stability of polytetrafluorethylene (PTFE) and polyvinylidene fluoride (PVDF) used as the anode binders in lithium-ion batteries was studied by electrochemical and X-ray photospectroscopy (XPS) measurements. The characteristic discharge/charge curves for PTFE and PVDF were obtained. It is shown that the behavior of PTFE and PVDF exhibits much discrepancy when they are attacked by high active lithium ion in electrochemical cells. PTFE reacts with lithium easily and decomposes during the first discharge process, which is indicated by a long plateau appearing around 1.2 V in the first discharge curve of Li/Ni(PTFE) cell. XPS results show that PTFE decomposes after one discharge/charge cycle. PVDF is rather stable due to a possible surface passivation process.

All-solid-state lithium microbatteries were fabricated using the ceramic superconductor YBa 2 Cu 3 O 7−δ as cathode, and a PAN-based polymer as electrolyte. The employed cathode films had a thickness of about 10μm. The charge and discharge current can reach values up to 100 μA/cm 2 at room temperature. The performance of the microbatteries was evaluated by cyclic voltammetry and a.c. impedance spectroscopy measurements. The batteries exhibit a good cycle life, capacity and efficiency.

LiCoO2 is synthesized by microwave heating. It has high capacity and good cycleability. The advantages of microwave synthesis are: (i) the calcination process is very fast; (ii) the synthesized powders have small and uniform grains; (iv) the synthesis temperature can be lower, and (iv) the lithium oxide loss is smaller. (C) 1997 Elsevier Science S.A.