Li-ion Source Research Articles

Lithium Salt Combining Fluoroethylene Carbonate Initiates Methyl Methacrylate Polymerization Enabling Dendrite‐Free Solid‐State Lithium Metal Battery

This work demonstrates a novel polymerization‐derived polymer electrolyte consisting of methyl methacrylate, lithium bis(trifluoromethanesulfonyl)imide and fluoroethylene carbonate. The polymerization of MMA was initiated by the amino compounds following an anionic catalytic mechanism. LiTFSI plays both roles including the initiator and Li ion source in the polymer electrolyte. Normally, lithium bis(trifluoromethanesulfonyl)imide has difficulty in initiating the polymerization reaction of methyl methacrylate monomer, a very high concentration of lithium bis(trifluoromethanesulfonyl)imide is needed for initiating the polymerization. However, the fluoroethylene carbonate additive can work as a supporter to facilitate the degree of dissociation of lithium bis(trifluoromethanesulfonyl)imide and increase its initiator capacity due to the high dielectric constant. The as‐prepared poly‐methyl methacrylate‐based polymer electrolyte has a high ionic conductivity (1.19 × 10−3 S cm−1), a wide electrochemical stability window (5 V vs Li+/Li), and a high Li ion transference number () of 0.74 at room temperature (RT). Moreover, this polymerization‐derived polymer electrolyte can effectively work as an artificial protective layer on Li metal anode, which enabled the Li symmetric cell to achieve a long‐term cycling performance at 0.2 mAh cm−2 for 2800 h. The LiFePO4 battery with polymerization‐derived polymer electrolyte‐modified Li metal anode shows a capacity retention of 91.17% after 800 cycles at 0.5 C. This work provides a facile and accessible approach to manufacturing poly‐methyl methacrylate‐based polymerization‐derived polymer electrolyte and shows great potential as an interphase in Li metal batteries.

Improved Lewis Acidity Using Ionic Liquid-Grafted Bimetallic Zr/Ti Uio-66 Fillers for Composite Solid Electrolytes

In recent years, solid-state lithium batteries have gained significant attention due to their high energy density and stability. However, challenges such as low ionic conductivity, non-homogeneous Li ion flux, and low interfacial compatibility of solid electrolytes still remain. Composite solid electrolytes (CSEs) have emerged as a potential solution to these issues, by combining an inorganic filler with a polymer matrix. To develop high-performance CSEs, extensive research has been conducted on inorganic active fillers with an abundance of Lewis acidic sites. The acidic sites of the filler can induce Lewis acid-base interactions, which can decrease the crystallinity of fillers by weakening the attraction between polymer segments and increasing chain mobility. Additionally, they increase the degree of dissociation of lithium salt, resulting in an increase in ionic conductivity. In terms of the concentration gradient of Li-ions, the free anion of lithium salt can be trapped by an acidic filler, thereby reducing the mobility and concentration of the anion. Finally, the acidic filler prevents the oxidation of ether oxygen groups in PEO, thus, improves its electrochemical stability. Furthermore, for increasing the ionic conductivity, inorganic filler should be an active filler capable of serving as Li-ion sources to the interfacial region between polymeric matrix and inorganic fillers, thereby facilitating Li-ion transport. Consequently, Li-ions can hop along the surface of active fillers. Therefore, in order to achieve high-performance CSEs with a polymer matrix, inorganic active fillers with an abundance of acidic sites have emerged as one of the most effective strategies for designing high performance fillers with good compatibility with the matrix. To address this technological need, in this work, we present a novel CSE based on a polyethylene oxide (PEO) matrix with a bimetallic (Zr/Ti) UiO-66-ionic liquid grafted filler (BUIL) that simultaneously modified the metal and ligand sites of UiO-66 MOF particles. The bimetallic structure of BUIL was prepared by replacing the metal sites of UiO-66 with Ti metal ions using the metal exchange method, resulting in the formation of more structural defects and an increase in the number of Lewis acid sites of filler. In addition, the pre-synthesized ionic liquids containing a -OH functional group (IL-OH), N-hydroxyhexyl-N’-methyl imidazolium bis(trifluoromethylsulfonyl)imide, were grafted when synthesizing UiO-66 with a ligand containing a -Br functional group. The BUIL filler functions as a high Lewis acid filler owing to its bimetallic structure and grafted ionic liquid. Also, to utilize BUIL as an active filler, lithium bis(trifluoromethanesulfonyl)imide/1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (IL, LiTFSI/EMIM-TFSI) was loaded into BUIL (IL@BUIL). In order to confirm the effect of Lewis acid filler interaction on PEO polymer matrix and lithium salt, various spectroscopic characterization methods were employed. As a result, CSEs containing IL@BUIL filler and PEO matrix exhibited markedly improved ionic conductivity, lithium-ion transference number, electrochemical stability, and long-cycle stability of Li metal electrode. After optimization, the ionic conductivity of CSEs at 30°C was enhanced to 0.458 mS cm-1, the lithium-ion transference number was raised to 0.668, and the electrochemical stability window was widened to 4.5 V. In addition, during a continuous plating/stripping test, the lithium metal symmetric cell of CSEs stably cycled for 500 h at a current density of 0.2 mA cm-2. Finally, LiFePO4/IL@BUIL/Li cell shows a capacity of 148 mA h g-1 at 1C.The present strategy of simultaneously modifying the metal and the ligand sites of MOF to improve the properties of CSEs can be used as a general platform for the design of a MOF filler in CSEs system, as well as a guideline for the next generation CSEs.

Beam optics simulation of the ion injector for sodium Beam Emission Spectroscopy (Na-BES) on EAST

To upgrade the Li-BES to Na-BES on Experimental Advanced Superconducting Tokamak (EAST), a high-brightness and stable sodium (Na) ion source is developed, and the performance of Na ion beam optics is simulated by the COMSOL Multiphysics. The porous tungsten disk with 70% porosity and filled with albite Na2O·Al2O3·6SiO2 is successfully developed as the Na ion source. The extracted current density of the Na-beam increases with the extraction voltage, and its maximum current can reach 9 mA with the ion source diameter of 20 mm. The lifetime of the Na ion source is evaluated to be 63 mAh, which is much longer than that of the Li ion source. The simulation shows that the preferable distances among the ion source (or anode electrode), extractor and puller to get the well-focused beam are x puller - x extractor ∼ 0.06 m and x extractor - x ion source ∼ 0.02 m. Further simulation with these optimized distances determines the extraction voltage and ion source size for good beam performance. In addition, the simulation shows the beam divergence angle decreases by more than 40% by optimizing the Einzel voltage to 5 kV, suggesting an excellent focusing property of the Einzel lens. These works provide the basis and the design references for the Na-BES development on EAST.

All-thin-film inorganic complementary electrochromic devices with the novel self-aligned lithium-rich ion conductor

An all-thin-film inorganic complementary electrochromic device (ECD) with the novel self-aligned lithium-rich ion conductor has demonstrated. The 80nm-thick self-aligned lithium-rich ion conductor has formed between the WO3 electrochromic layer and Li:Ta2O5 ion conductor during the device activation process and confirmed with the transmission electron microscope image. Furthermore, the energy-dispersive X-ray spectroscopy element map also provides the ECD composition distribution analyses. Although the ion mobility extracted with the activated ECD has showed a decrease from 4.47 × 10−9 cm2/Vs to 1.86 × 10−10 cm2/Vs, the ion conductivity has increased from 9.12 × 10−9 S/cm to 2.95 × 10−8 S/cm due to the increase of ion concentration. The increase of the ion concentration could be related to the presence of the lithium-rich ion conductor. As a result, the fast colored switching time of the ECD in this study is mainly due to the self-aligned lithium-rich ion conductor, which has directly provided the nearest Li-ion source for the WO3 layer.

Synthesis and Comparative Electrochemical Studies of Bottlebrush Solid Polymer Electrolytes (SPEs) for Li-Ion Transport

Solid polymer electrolytes in solvent-free lithium batteries may overcome some of the disadvantages of liquid electrolytes such as flammability and instability.1 Thereby, the polymer electrolyte acts as both ion transport medium and electrical separator between the electrodes. Compared to rigid separators (e.g. fiber glass) a higher shape flexibility is a further advantage, as these SPEs can compensate volume changes of the electrodes by elastic and plastic deformation.2 Poly(ethylene glycol) (PEG) possesses one of the highest ionic conductivities among solvent-free SPEs but suffers from a conductivity drop below its melting temperature about 50-60°C due to high crystallinity depending on the molecular weight.1 In addition to linear PEG polymers, ion-conducting bottlebrush graft copolymers can be obtained by attaching PEG side chains to a polymer backbone in order to reduce the crystallinity maintaining very high molecular weight.In this work we synthesized five new bottlebrush polymers using free radical polymerization as well as ring-opening metathesis polymerization (ROMP). These brush polymers contain different lengths of PEG side chains (1 kg mol-1 and 2 kg mol-1) and two different backbones, poly(methacrylate) and poly(norbornene). We present the influence of the polymer architecture on mechanical stability, ionic conductivity, Li-ion transport number and electrochemical stability of a series of SPEs obtained thereof by mixing with different amounts of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). We also compare the results to the respective linear PEG counterparts. The differences in ionic conductivity were analyzed and correlated with respect to thermal properties such as T g and ΔH melt in order to understand the fundamental factors which influence the properties of solvent-free PEG-containing bottlebrush SPEs.We also examined the implications of changing a linear polymer system to a brush architecture for potential applications in batteries and correlate the occurring processes in the cell with the distribution of relaxation times (DRT). Detailed comparative measurements under similar cell configurations for diverse O/Li ratios in a temperature range of 25 to 80 °C for different SPEs were carried out to elucidate structure-property relationships. The interesting findings are that by applying a brush architecture, we suppress the crystallinity of PEG and improve the mechanical strength without losing ionic conductivity. We obtained conductivities in the range of 10-3 to 10-4 S cm-1 for solvent-free SPEs. Furthermore, the best ionic conductivities for any system correlate strongly with their respective T g.3 Nevertheless, there are still several unresolved questions regarding these bottlebrushes compared to linear PEG in terms of interfacial as well as bulk processes in both blocking steel (ionic conductivity) and lithium (lithium plating/stripping, interfacial resistance) electrode setups. In addition to the polymer component, the lithium salt has a major effect on the properties of the electrolyte. LiTFSI is probably the most common Li-ion source in SPEs.4 Besides that, lithium borate salts have gained high interest due to their high thermal stability, cost-effectiveness, favorable solid electrolyte interface (SEI) formation and ionic conductivities in the same range as LiTFSI.5 For example, Lithium bis(oxalate)borate (LiBOB) and its asymmetric counterpart Lithium difluoro(oxalate) borate (LiDFOB) are stable in organic solvents and the electrochemical stability is higher than 4.5 V vs. Li/Li+.6 Different salts in an electrolyte can influence the Li-ion transport as well as the processes at the interfaces or the formation of the SEI. This again requires a detailed comparative analysis.For this, we prepared promising bottlebrush polymer electrolytes (1 kg mol-1 PEG sidechain) containing LiBOB and LiDFOB and subsequently analyzed them electrochemically by impedance spectroscopy. The measurement data was finally interpreted by the extended Distribution of Relaxation Times (eDRT). Both SPEs showed similarities in the lithium-ion conducting process in possessing one major, resistive-capacitive bulk conductivity mechanism. The resulting, temperature-dependent conductivities were evaluated and are in the range of 10-4 to 10-5 S cm-1.During cycling, the SPEs showed increased interface resistances over time, which are higher than respective bulk resistances. By applying eDRT, the time-dependent formation of an interphase layer in the SPEs is identified, separated from the slower charge transfer process and quantified. Thus, the electrolytes cannot be considered electrochemically stable against metallic Li, which is similar for liquid electrolytes.7 References (1) Scrosati, B.; Energy Environ. Sci. 2011, 4, 3287.(2) Janek, J.; Nat. Energy 2016, 1, 16141.(3) Rosenbach, D.; ACS Appl. Energy Mater. 2019, 2, 3373–3388.(4) Etacheri, V.; Energy and Environmental Science 2011, pp 3243–3262.(5) Xu, K. Chem. Rev. 2014, 114, 11503–11618.(6) Liu, Z.; Coord. Chem. Rev. 2015, 292, 56–73.(7) Hahn, M.; Electrochim. Acta 2020, 344, 136060. Figure 1

Fabrication of the Sulfur Lithium Ion Secondary Battery with Different Li Ion Source

Introduction Sulfur, with the theoretical specific capacity of 1672mAhg-1 undergoing the rocking chair reaction (S8+16Li++16e-↔8Li2S), is the most promising cathode material candidates for future Li ion batteries excepting two main drawbacks hindered its application.1 On the one hand, during cycling, the Li deposited on Li foil is readily to form Li dendrite, resulting in the internal short-circuit of the battery.2 On the other hand, the dissolution of polysulfide species in electrolyte will lead to fast capacity fading. However, most papers reported are focused on the S cathode problems, less researchers paid attention to the drawbacks caused by the Li metal. In order to resolve the safety issue, a surface contact pre-lithiation method was used to introduce the Li ion in the S electrode.3 In this way, the Li metal can be replaced by other anode forming Li metal free full cell. Experimental The sulfur/ Ketjen Black (S/KB) composite was mixed in a weight ratio of 1:1 after a heating process at 155 ℃. The S cathode was prepared by mixing S/KB composite:PVdF= 90:10 wt%. The KB can provide conductivity and physical confinement for the sulfur species, alleviating the dissolution of polysulfides. Moreover, the ionic liquid electrolyte, triglyme (G3) was used in the full cell which showed good polysulfide suppression ability.4 Because of the compatibility of the G3 electrolyte for the graphite anode, the graphite electrode (made in graphite:AB:PVdF=90:5:5 wt%) with an areal capacity of 0.9 mAh cm-2 (~300 mAhg-1) was used to pair with the pre-lithiated S/KB cathode (Li2S/KB). The graphite anode was pre-lithiated at the same condition to fabricate LixC anode. The graphite electrode with a solid electrolyte interphase layer (CSEI) anode was fabricated by disassembling the C-Li cell after 5 cycles. All the electrodes used were cut into 1 cm2size. Results and Discussion The cycling performance of the difference cells were tested at 0.1 C-rate (based on the weight of sulfur), showed in Fig. 1. Firstly, it is observed that the S-Li cell showed fast capacity fading using G3 electrolyte. It has been proved that the increased internal resistance give rise to the fast capacity decay in the S-Li half cell. In the initial cycle, the S-Li cell showed high specific capacity higher than 1600 mAhg-1 (0.8 mAh cm-2) due to the abundant Li ion source from Li metal. The S-Li cell turned to internal short in 80 cycle due to the formation of Li dendrite, indicating the safety issue of the Li metal containing sulfur battery.Secondly, Li2S-C cell showed over half amount of capacity (about 53.3%) decay in the first cycle, leading to only 673 mAhg-1 discharge capacity. In order to study to reason caused the irreversible capacity lost in the first cycle, the Li2S-CSEI was assembled showing higher reversible capacity in the first cycle than that of the Li2S-C cell, indicating the irreversible capacity lost in the first cycle was mainly caused by the formation of the SEI layer on the graphite anode. Under this context, the surface contact pre-lithaition method was applied to graphite anode to introduce Li ion. The SEI layer was expected to be formed on the graphite surface at the same time. As a result, the S-LixC full cell showed increased capacity retention than the Li2S-C cell in Fig. 1. In conclusion, it is convictive to say that the lithium metal free S-LixC cell showed high irreversible capacity and better safety. We believe that this work will make contribution to future sulfur lithium ion secondary battery. Fig. 1 Cycling performance of different sulfur lithium secondary batteries at 0.1 C-rate. Acknowledgement This work is supported by Advanced Low Carbon Technology Research and Development Program (JST-ALCA) Special Priority Research Area "Next-generation Rechargeable Battery”, and JSPS KAKENHI Grant Numbers JP17J09973.

A cost-effective approach for practically viable Li-ion capacitors by using Li2S as an in situ Li-ion source material

With the aid of surface oxygen functionalities, Li2S enables in situ lithiation of negative electrode for simplified preparation of Li-ion capacitors.

Au-coated carbon electrodes for aprotic Li–O2 batteries with extended cycle life: The key issue of the Li-ion source

Despite having the capability of achieving high energy densities, Li–O2 batteries still suffer from many inherent disadvantages such as electrolyte stability, sluggish kinetics of the oxygen reduction/evolution reactions in the aprotic environment and electrodes stability.Our research demonstrates by combining electrochemical and analytical techniques that the performances of Li–O2 batteries based on LiTFSI-Tetraglyme electrolyte and Au-coated carbon electrodes are manly hindered by the instability of the lithium metal anode in the oxygen-saturated environment. Although the Au-coated carbon electrodes are able to minimize side reactions arising from electrolyte decomposition, oxygen crossover on the lithium metal results in the formation of decomposition products (LiOH, Li2CO3) that are clearly detrimental for the battery performance. Finally it is demonstrated that the Au-coated carbon electrodes in combination with the LiTFSI-Tetraglyme electrolyte can sustain extended cycling (100 cycles) when a more stable source of Li-ion, namely lithium iron phosphate (LFP), is used.

Using waste Li ion batteries as cathodes in rechargeable Li–liquid batteries

The rechargeable Li-liquid battery was developed using waste Li ion battery materials immersed in water and used as the liquid cathode. Either the Li metal or Li ions (by the formation LixC6 or Li(4+x)Ti5O12) was harvested from waste Li ion source materials such as a waste anode (LixC6), cathode (LixFePO4), and electrolyte (LiPF6 in EC:DEC) by charging the cell, which then discharged with the waste products in the liquid cathode solution to produce electric energy. When the Li4Ti5O12 was used as the anode with the waste products as the cathode in the proposed battery system, a good cycle-life with high coulombic efficiency was observed.

Lithium–liquid battery: harvesting lithium from waste Li-ion batteries and discharging with water

This study demonstrates the feasibility of using water and the contents of waste Li-ion batteries for the electrodes in a Li–liquid battery system. Li metal was collected electrochemically from a waste Li-ion battery containing Li-ion source materials from the battery's anode, cathode, and electrolyte, thereby recycling the Li contained in the waste battery at room temperature. The harvested Li metal in the battery system was discharged to produce electricity by using water as the cathode. The discharge voltage of the water showed 2.7 V at 0.1 mA cm−2versus Li metal harvested from waste Li-ion batteries, compared to 2.8 V versus fresh Li metal at the same current rate. Since the electrodes for this proposed battery system are water and the contents of waste Li-ion batteries, the cost of the battery decreases, which is an attractive strategy for a large size energy storage application.

One-step hydrothermal routine for pure-phased orthorhombic LiMnO 2 for Li ion battery application

This paper reports a simple one-step hydrothermal routine to prepare orthorhombic LiMnO 2 powder for Li ion battery application. Employing Mn 2O 3 and LiOH as the starting materials, hydrothermal reaction operated under 160 °C for 12 h generated pure-phased o-LiMnO 2 powder. The morphological change and reduction in grain size between the reagent and the resultant were revealed by SEM observation, which indicated that LiOH played two important roles in the process, one as the Li ion source to form orthorhombic LiMnO 2 by intercalation and the other as the corrosive medium to control the morphology and reduce the particle size. Detailed investigation showed that the LiOH concentration and the hydrothermal temperature were two key factors influencing phase purity of the final product. Pure-phased o-LiMnO 2 prepared under optimized hydrothermal conditions showed higher capacity and better cyclical performance than the commonly prepared o-LiMnO 2 powder, and therefore promised potential application for lithium ion secondary batteries.

Preparation and ion-conducting behaviors of poly(ethylene oxide)-composite electrolytes containing lithium montmorillonite

Filler effects of layer-structured lithium montmorillonite (Li-MMT) clays on the structure and ion conductivity of poly(ethylene oxide) (PEO)-based electrolytes were investigated. Sodium cations in MMT were exchanged by Li cations for a usage as Li ion sources in Li batteries. With the increase of filler content to 20%, melting temperature and crystallinity of polymer composite electrolytes (PCEs) had been gradually decreased. Accordingly, the PCEs containing 20% Li-MMT showed the highest conductivity of 5.3 × 10 − 6 (S/cm) and the highest lithium transference number of 0.55. These enhanced conducting behaviors were probably attributed to the decreased crystallinity of PEO, resulting from the structural and morphological changes by addition of Li-MMT. The change of conductivity with temperature was found to be related to the polymer segmental motion by an Arrhenius plot analysis.

Phase conversion and morphology evolution during hydrothermal preparation of orthorhombic LiMnO 2 nanorods for lithium ion battery application

This paper reports a hydrothermal conversion of MnOOH needles into orthorhombic LiMnO 2 nanorods for lithium ion battery application. XRD investigation indicated phase conversion during the Li ion incorporation, and several intermediate phases were formed during the hydrothermal reaction. SEM observation of the sample powder revealed morphological changes during the process, showing that LiOH, not only worked as the Li ion source during the incorporation, but also served as the corrosive media to create nanorod like shape. TEM observation revealed the single crystalline nature of the nanorods and a preferred growth direction along b axis direction was also determined. o-LiMnO 2 nanorods prepared by such hydrothermal routine showed high electric capacity and stable cyclability at current density of 1/10 C, indicating potential application in the lithium ion battery field.

Proposal for an Intense Polarized Li-Ion Source

We propose to use optical pumping with a high-power dye laser to produce the polarized Li atoms necessary for a polarized Li ion source. It should be possible to produce very intense beams of highly polarized Li ions.

Two lithium ion sources for accelerators

Two types of Li ion sources developed for the investigation of charge-exchange and nuclear reactions by accelerated Li ions, are described and preliminary results concerning their performance are given.