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Battery safety is an ever-increasing significance to guarantee consumer's safety. Reducing or preventing the risk of battery fire and explosion is a must for battery manufacturers. Major reason for the occurrence of fire in commercial lithium-ion batteries is the flammability of conventional organic liquid electrolyte, which is typically composed of 1 M LiPF6 salt and ethylene carbonate (EC)-based organic solvents. Herein, we report the designed 1 M LiPF6 and EC-based nonflammable electrolyte including methyl(2,2,2-trifluoroethyl)carbonate, which breaks the conventional perception that EC-based liquid electrolyte is always flammable. The designed electrolyte also provides high anodic stability beyond the conventional charge cut-off voltage of 4.2 V. A graphite∥LiNi0.6Co0.2Mn0.2O2 lithium-ion full cell with our designed EC-based nonflammable electrolyte with a small fraction of vinylene carbonate additive under an aggressive condition of 4.5 V charge cut-off voltage, 0.5C rate, and 45 °C exhibits increased capacity, reduced interfacial resistance, and improved performance and rate capability. A basic understanding of how a high-voltage cathode-electrolyte interface and anode-electrolyte interface are stabilized and how failure modes are mitigated by fire-preventing electrolyte is discussed.

The formation of a robust solid electrolyte interphase (SEI) layer at the surface of graphite anode via electrolyte control is a key technology for high performance of lithium-ion batteries. Despite propylene carbonate (PC) offers like lower melting point over ethylene carbonate, its combination with graphite anode without additive is the worst choice, due to co-intercalation of PC and Li + ion into graphite, exfoliation of graphene sheets and death of a battery. Herein, we report for the first time unprecedented high initial coulombic efficiency of 94% and closely theoretical capacity of graphite anode, and excellent capacity retention 99% after 100 cycles in PC-based electrolyte system even under unusually high rate of 0.2C, which is generally attainable only at a very low rate below 0.05C in commercial electrolyte. The SEI stabilization approach on graphite anode in PC-based electrolyte system provides a new avenue for high-energy and high-performance batteries in widened working temperatures. The strong correlation between anode-electrolyte interfacial stabilization and highly reversible cycling performance is clearly demonstrated.

Beyond current lithium-ion technologies, magnesium–sulfur (Mg–S) batteries represent one of the most attractive battery chemistries that utilize low cost, sustainable, and high capacity materials. In addition to high gravimetric and volumetric energy densities, Mg–S batteries also enable safer operation due to the lower propensity for magnesium dendrite growth compared to lithium. However, the development of practical Mg–S batteries remains challenging. Major problems such as self-discharge, rapid capacity loss, magnesium anode passivation, and low sulfur cathode utilization still plague these batteries, necessitating advanced material design strategies for the cathode, anode, and electrolyte. This review critically appraises the latest research and design principles to address specific issues in state-of-the-art Mg–S batteries. In the process, we point out current limitations and open-ended questions, and propose future research directions for practical realization of Mg–S batteries and beyond.

Driven by a high demand for safe lithium-ion batteries (LIBs) with no risk of fire, we develop a nonflammable organic liquid electrolyte, which is composed of 1 M lithium hexafluorophosphate salt a...

Demands of increased energy density and high-safety of lithium-ion and lithium metal batteries are growing for advanced electronics, electric vehicles and energy storage systems. Nickel-rich layered oxides such as LiNi0.8Co0.1Mn0.1O2 (NCM811) are appealing as promising high-capacity cathode materials. Their reversible capacity increases further by charging to higher voltages than conventional 4.2 V, which is however difficult to make because of unstable cathode-electrolyte interface and structural degradation. Herein, we report the combination of NCM811 cathode active material with non-aqueous functional polyimide binder to imparts enhanced thermal stability and highly stable interface originating from in situ building-up of surface protective polyimide layer at cathode through monodentate metal-carboxylate chemical bonds during slurry preparation, which permits to charge to 4.4 V despite in commercial electrolyte without any additive. This unique active material-binder combination not only suppresses metal-dissolution and cathode degradation and produces increased reversible capacity higher than 200 mAh g−1 but also provides unprecedented non-flammable characteristics contrary to the case of conventional binder, enabling a stable operation of higher energy and safer batteries.

The structural design and synthesis of sulfur-carbon composite materials with high performance is still a major challenge for rechargeable lithium-sulfur batteries. Interconnected three-dimensional frameworks comprising multi-walled carbon nanotubes, graphene, or carbon particles offer a combination of constituent advantages and can thus be used to achieve superior energy conversion and storage properties. Herein, we designed and prepared free-standing three-dimensional sulfur papers containing interconnected highly conductive carbon materials, which enable to be flexible binder-free cathodes for Li-S batteries. The resultant sulfur-carbon composite paper cathode exhibited high reversible specific capacity of 1386 mAhg−1, good rate capability up to 5C, and excellent cycling performance (a capacity retention 68% after 400 cycles), all of which are significantly improved from those of bare sulfur cathode or sulfur-GO composite only. Rational design of cathode composition, structure, and a simple fabrication process can give insight into the development of various advanced cathode materials for high-performance Li-S batteries.

Uniform distribution of siloxane-grafted SiO 0.26 hydrophobic nanoparticles in porous micron hard-carbon matrix was in situ made by a simple mixing in the organic medium of N-methylpyrrolidinone during the slurry preparation of composite anode for a fast-charge of lithium-ion batteries, whose characteristics are advantageous for a good electronic conductivity and the accommodation of volume change of silicon during charge-discharge cycling. The composite anode enables fast charge in 6 min at the rate of 10 C and high cycling stability, delivering the discharge capacities of 648–538 mAh g −1 , coulombic efficiencies of 99%, and high capacity retention of 98% at the 100th cycle. Surface and structural analysis results reveal that the formation of relatively thinner solid electrolyte interphase (SEI) layer at 10 C and higher structural maintenance than at low rate (0.2 C) are correlated to lowered interfacial resistances at 10 C and a good high-rate cycling stability. The data give an insight into material design principles and the SEI property of anode for high-rate lithium-ion batteries.

Fabrication and high-rate performance of a safe lithium ion-sulfur battery (LISB) with sulfur-copolymer [poly(S-co-divinylbenzene (DVB)] cathode having a sulfur content higher than 90 wt %, a carbon-fiber interlayer, and a prelithiated hard-carbon (Li-HC) anode are reported, which mitigates problems of lithium-sulfur cells such as performance fade and safety issues due to dissolution of polysulfides and lithium-dendrite growth. The poly(S-co-DVB) cathode offers scalability owing to the abundance and low cost of DVB. The Li-HC anode, the surface of which is passivated by a solid electrolyte interphase, inhibits the deposition of polysulfides. As a result, the LISB exhibits reversible and stable cycling performance at high rates up to 3 C, which enables quick charging within 20 min, and delivers a reversible capacity of approximately 400 mAh g-1 at 3 C for 500 cycles. The results give insight into the design principle of promising, quickly charged, and safe LISBs.

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

Rechargeable lithium–sulfur (Li–S) batteries have drawn significant attention as next-generation energy storage systems. Sulfur-copolymers are promising alternative cathode materials to elemental sulfur in Li–S batteries as they provide high reversible capacity. However, the redox mechanisms of these materials are not well understood owing to the difficulty in characterizing amorphous structures and identifying individual ionic species. Here, we use solid-state NMR techniques together with electrochemistry experiments and quantum calculations to investigate the structural evolution of the prototype S-copolymer cathodes, sulfur–diisopropenylbenzene copolymers (poly(S-co-DIB)), during cycling. We demonstrate that polysulfides with different chain lengths can be distinguished by 13C and 7Li NMR spectroscopy, revealing that the structure of the copolymers can be tuned in terms of polysulfide chain lengths and resulting reaction pathways during electrochemical cycling. Our results show that the improved cyclab...

Driven by the limited global resources of lithium, magnesium metal batteries are considered as potential energy storage systems. The battery chemistry of magnesium metal anode, however, limits the selection of electrolytes, cathode materials and working temperature, making the realization of magnesium metal batteries complicated. Herein, we report the development of a new magnesium-insertion anode, magnesium stannide (Mg2Sn), and demonstrate reversible electrochemical Mg2+-extraction and insertion of Mg2Sn anode at 0.2 V versus Mg, delivering discharge capacity of 270 mAhg−1 in a half-cell with the electrolyte of PhMgCl/THF and enabling of room temperature magnesium-ion batteries with Mg2Sn anode combined with Mg-free oxide cathode and conventional-type electrolyte of Mg(TFSI)2/diglyme. The combination of Mg2Sn anode with various cathodes and electrolytes holds great promise for enabling room temperature magnesium-ion batteries.

All-solid-state lithium batteries offer notable advantages over conventional Li–ion batteries with liquid electrolytes in terms of energy density, stability, and safety. To realize this technology, it is critical to develop highly reliable solid-state inorganic electrolytes with high ionic conductivities and adequate processability. Li1+xAlxTi2−x(PO4)3 (LATP) with a NASICON (Na superionic conductor)-like structure is regarded as a potential solid electrolyte, owing to its high “bulk” conductivity (ca. 10−3 S cm−1) and excellent stability against air and moisture. However, the solid LATP electrolyte still suffers from a low “total” conductivity, mainly owing to the blocking effect of grain boundaries to Li+ conduction. In this study, an LATP–Bi2O3 composite solid electrolyte shows very high total conductivity (9.4×10−4 S cm−1) at room temperature. Bi2O3 acts as a microstructural modifier to effectively reduce the fabrication temperature of the electrolyte and to enhance its ionic conductivity. Bi2O3 promotes the densification of the LATP electrolyte, thereby improving its structural integrity, and at the same time, it facilitates Li+ conduction, leading to reduced grain-boundary resistance. The feasibility of the LATP–Bi2O3 composite electrolyte in all-solid-state Li batteries is also examined in this study.

We report a promising approach to achieve the maximum capacity (>230 mA h g−1) and high capacity retention (95% during 100 cycles) of a nickel-rich cathode of LiNi0.8Co0.1Mn0.1O2 (NCM811) by charging to 4.5 V in a non-flammable electrolyte of propylene carbonate and fluorinated linear carbonates. Our electrolyte permits the stabilization of the cathode–electrolyte interface and cathode structure at high-voltage, enabling stable and safe operation of the Ni-rich cathode for high-energy density and high-safety lithium-ion and lithium metal batteries.

Lithium-ion batteries (LIBs) are ubiquitous power sources and demand for higher energy and higher performance LIBs than state-of-the-art ones continues to increase for longer range use of electric mobility and energy-storage systems. Performance of conventional LIBs is often limited or failed in tough working environments, particularly, subzero-temperatures because of reduced ionic conductivity of electrolyte and diffusion kinetics of both anode and cathode, causing lithium metal plating and dendrite growth and finally safety issue and death of LIBs. Herein, for the first time we report a lithium metal plating-free and unprecedented high-performance graphite∥LiNi0.8Co0.1Mn0.1O2 (NCM811) full-cell under subzero-temperature of −10 °C and high-voltage of 4.45 V through the construction of robust solid electrolyte interphase (SEI) layers at both anode and cathode and their structural stabilization in 1 M LiPF6 and nonflammable electrolyte. Subzero-temperature operation of commercial electrolyte-based full-cell however results in a drastic performance failure in early cycles and shows distinguishing marks such as lithium metal plating at graphite anode and irreversible phase transformation of NCM811 to disordered H3 phase with a large volume contraction. The strong correlation between anode-electrolyte and cathode-electrolyte interfacial stabilization, bulk structural stabilization of both anode and cathode, and highly reversible cycling performance under subzero-temperature is clearly demonstrated.

The demand for eco-friendly and renewable resources has dramatically increased in scientific and technological areas including energy storage systems and production of new functional materials. Sulfur copolymers with high sulfur contents of up to 90 wt% were prepared via inverse vulcanization from environment-friendly, sustainable raw materials: cost-effective waste-product elemental sulfur and eugenol allyl ether (EAE), which is obtained from clove oil. The thermal properties and electrochemical activities of the resulting poly(S-co-EAE) materials can be tuned by controlling the EAE : S feed ratio. Employed as a cathode material in Li–S batteries, the copolymer with 90 wt% sulfur content provides good cycling stability at a capacity of ∼650 mA h g−1 and high Coulombic efficiencies (>99%) over 100 cycles.

Rapidly growing interest and demand for wearable electronics require the development of flexible and lightweight all-solid-state batteries as power sources that guarantee high performance and safety with the absence of the risk of fire or explosion that can occur with traditional liquid electrolyte systems. Herein, we successfully fabricate new flexible all-solid-state microbatteries integrating a solid electrolyte film of lithium boron oxynitride (LiBON) on a flexible substrate using sophisticated thin-film fabrication technology. The new microbattery of Li/LiBON/LiCoO 2 exhibits excellent mechanical integrity even under severe bending and twisting test conditions, enabling the realization of flexible microbatteries. The microbatteries demonstrate superior electrochemical cycling stability relative to conventional batteries, delivering an outstanding capacity retention of 90% on the 1000 th cycle. Furthermore, operation at various temperatures from −10 °C to +60 °C and fast charging within 3–6 min are achieved. With various types of flexible substrates, the microbatteries can provide diverse opportunities for flexible and wearable electronics.

Electrochemical cycling performance of microsize bulk and thin film Sn electrodes up to 50 cycles in Mg half-cell configuration, as well as Mg diffusivity and interfacial reaction behavior in a phenylmagnesium chloride (PhMgCl)/THF electrolyte are studied. The bulk Sn electrode delivers capacities of 321–289 mAh g−1 with capacity retention of 90 % and coulombic efficiencies higher than 99 % over 30 cycles, and thus demonstrates the potential of Sn anodes. The Sn film electrode shows good cycling ability. Surface analysis by XPS reveals that the surface of cycled electrodes is composed of a mixture of various inorganic salts of Sn and Mg formed by interfacial reactions between Sn and PhMgCl, and organic functionality produced by decomposition of THF, indicating surface film formation. The Mg2+ diffusivity of Sn is on the order of 10−11 cm2 s−1, which is four orders of magnitude lower than the Li+ diffusivity of Sn in Li-ion batteries. Advanced material design for enhanced electronic conductivity and control of the interfacial chemistry for formation of a surface protective film are believed to be the keys to overcome such sluggish kinetics, increase the capacity, and improve the cycling performance.

Research progress of high-energy performance and interfacial phenomena of Li 1.13 Mn 0.463 Ni 0.203 Co 0.203 O 2 cathode and graphite anode in a 55 °C full-cell under an aggressive charge cut-off voltage to 4.7 V (4.75 V vs. Li/Li + ) is reported. Although anodic instability of conventional electrolyte is the critical issue on high-voltage and high-temperature cell operation, interfacial phenomena and the solution to performance improvement have not been reported. Surface spectroscopic evidence revealed that structural degradation of both cathode and anode materials, instability of surface film at cathode, and metal-dissolution from cathode and -deposition at anode, and a rise of interfacial resistance with high-voltage cycling in 55 °C conventional electrolyte are resolved by the formation of a stable surface film with organic/inorganic mixtures at cathode and solid electrolyte interphase (SEI) at anode using blended additives of fluorinated linear carbonate and vinylene carbonate. As a result, significantly improved cycling stability of 77% capacity retention delivering 227−174 mAhg −1 after 50 cycles is obtained, corresponding to 819−609 Wh per kg of cathode active material. Interfacial stabilization approach would pave the way of controlling the performance and safety, and widening the practical application of Li-rich layered oxide cathode materials and high-voltage electrolyte materials in various high-energy density Li-ion batteries.

Capacity of layered lithium nickel-cobalt-manganese oxide () cathode material can increase by raising the charge cut-off voltage above 4.3 V vs. , but it is limited due to anodic instability of conventional electrolyte. We have been screening and evaluating various sulfone-based compounds of dimethyl sulfone (DMS), diethyl sulfone (DES), ethyl methyl sulfone (EMS) as electrolyte additives for high-voltage applications. Here we report improved cycling performance of cathode by the use of dimethyl sulfone (DMS) additive under an aggressive charge condition of 4.6 V, compared to that in conventional electrolyte, and cathode-electrolyte interfacial reaction behavior. The cathode with DMS delivered discharge capacities of over 50 cycles and capacity retention of 84%. Surface analysis results indicate that DMS induces to form a surface protective film at the cathode and inhibit metal-dissolution, which is correlated to improved high-voltage cycling performance.

High loading level of micron cathode active material is essential for high energy density Li-ion batteries. High loading level and thick cathode however limit not only rate capability but also cycle life, which is mainly caused by inhomogeneous current distribution from bottom (current collector side) to the top (interface side to electrolyte) of the cathode. Here we report a significant improvement of rate performance of micron LiNi0.6Co0.2Mn0.2O2 cathode material with high loading level of more than 10 mgcm−2, through simple and homogeneous dispersion and interweaving of bulk carbon fibers (CF) to active material. This microstructure permits the building-up of 3D electrical conduction network over the thick cathode. While the interwoven carbon fiber network guarantees fast electron transfer, porous characteristic of a thick cathode leads to a rapid access of Li+-ion through a good electrolyte wetting, and favorable rate capability and cycling stability. The resulting highly loaded CF-interwoven cathode achieves rate capability upto 5 C, high capacity of 163 mAhg−1 at 1 C and stable 1 C cycling performance even under an aggressive test condition between 3.0 and 4.6 V utilizing high-voltage electrolyte additive.

Elevating the charge cut-off voltage of lithium-ion battery above 4.2 V vs. Li/Li+ can increase the capacity of cathode and energy density of the battery but requires higher anodic stability of electrolyte and higher interface stability between charged cathode and electrolyte than those of the state-of-the-art commercial electrolyte. Utilization of a small fraction of high-voltage electrolyte additive is a promising and economic approach to mitigate the high-voltage stability issue. Fluorinated ethyl phosphate (FEP) is known as a flame-retardant but we examine it as a high-voltage additive of a commercial electrolyte with 1 M LiPF6 in EC:EMC (3:7 vol ratio). Herein, we report FEP-assisted performance improvement of a lithium-ion cell under high charge cut-off voltage of 4.6 V vs. Li/Li+, with reduced impedance rise. Our surface analysis results reveal that FEP additive in a graphite‖LiNi0.5Co0.2Mn0.3O2 full-cell is effective preferably on cathode over anode by forming a surface-passivating organics-rich and fluorine-rich solid electrolyte interphase (SEI) layer. We propose that the anodic reaction of FEP begins by a single electron transfer from the O atom of P − O − C to the cathode surface and forms FEP-derived SEI species. The SEI layer enables the inhibition of metal-dissolution phenomena from the cathode, evidenced by elemental analysis results on the metal species at graphite anode, leading to superior cycling performance to the full-cell with commercial electrolyte only. A basic understanding of interface stabilization pathway of the cathode via FEP additive in the lithium-ion full-cell is clearly demonstrated.

As mobile electronics and electric vehicles become essential in our lives, the specific energy density of a lithium-ion battery is one of the criteria that determines the quality of a battery and customers’ use range. Cathode is the one that primarily determines the capacity and energy density of the battery, and consists of active material, binder and carbon black. Nickel-rich layered oxides such as LiNi0.8Co0.1Mn0.1O2 (NCM811) are promising high-capacity cathode active materials, and its reversible capacity increases more by charging to higher cut-off voltages than the conventional 4.2 V. We observed that NCM811 cathode fabricated with commercial polyvinylidene fluoride binder has an unstable interface to electrolyte under high cut-off charge voltages and undergoes drastic structural changes during cycling in particular at elevated temperature, leading to capacity fade and reduced lifespan of the battery. In order to acquire a high reversible capacity and enhanced cycling performance with NCM811 cathode by mitigating the problems, we have designed an unique and functional high-voltage binder and make the combination with NCM811. In the meeting, we are going to report improved thermal stability and cycling performance of the designed binder-assisted cathode. Acknowledgement This research was supported by the Ministry of SMEs and Startups (S2788978) of Korea, National Research Foundation grant funded by the Korean Ministry of Science and ICT (No. 2019R1A2C1084024) and Creative Human Resource Development Consortium for Fusion Technology of Functional Chemical/Bio Materials of BK Plus program by Ministry of Education of Korea.

As the lithium-ion battery (LIB) market for electric vehicles and grid-based energy storage systems is rapidly growing, the upcoming urgent challenge is to charge faster the LIB than ever. Thus, battery chemistry and reaction kinetics are being evolved toward the development of quickly charged LIBs in minutes scale, not in hours scale. In the LIB electrolyte perspective, commercial carbonate-based liquid electrolyte has multiple limitations in attaining high rate performance, due to the limited ionic conductivity and viscosity, sluggish de-solvation kinetics on graphite anode, low thermal stability, etc. To overcome those limitations, extensive research on new electrolyte systems (e.g., highly concentrated salt, aqueous system, etc.) have been reported. Herein, we present the improved rate capability and cycling performance of nickel-rich layered oxide-based lithium cell with our newly designed electrolytes. We are going to discuss electrode-electrolyte interface chemistry and its correlation to performance in this meeting. Acknowledgements This research was supported by the National Research Foundation grant funded by the Ministry of Science and ICT (No. 2019R1A2C1084024) and Creative Human Resource Development Consortium for Fusion Technology of Functional Chemical/Bio Materials of BK Plus program by Ministry of Education of Korea.

Lithium-rich layered oxide, xLi2MnO3·(1-x)LiMO2 (M = Mn/Ni/Co), is a promising high-capacity cathode active material for high-energy density rechargeable lithium batteries. While the capacity of lithium-rich layered oxide cathode can increase by increasing the charge cut-off voltage toward 5 V, it t relies on the anodic stability of electrolyte and the interface stability of charged cathode. We have been developing and suggesting fluorinated carbonates as effective high-voltage additives and solvents of new designed electrolytes, which provide a significant improvement in the stability of cathode-electrolyte interface, solid electrolyte interphase (SEI) layer and cycling performance, and longer life span of various high-capacity cathodes, with respect to commercial electrolyte system. Herein, we present our recent progress on the exploration of the limit of anodic stability of fluorinated carbonate-assisted electrolyte toward 5 V level and the capacity of a Li-rich cathode based full-cell, and the enhancement of battery safety. The mechanistic studies utilizing systematic spectroscopic analyses on the correlation among interfacial processes, the SEI formation and stabilization, and performance improvement would be discussed in the meeting. Acknowledgements This research was supported by the Ministry of Trade, Industry and Energy (A0022-00725) and the National Research Foundation grant (2019R1A2C1084024) funded by the Ministry of Science and ICT of Korea.

The effects of lithium bis(fluorosulfonyl)imide, Li[N(SO2F)2] (LiFSI), as an additive on the low-temperature performance of graphite‖LiCoO2 pouch cells are investigated. The cell, which includes 0.2M LiFSI salt additive in the 1M lithium hexafluorophosphate (LiPF6)-based conventional electrolyte, outperforms the one without additive under -20 °C and high charge cutoff voltage of 4.3 V, delivering higher discharge capacity and promoted rate performance and cycling stability with the reduced change in interfacial resistance. Surface analysis results on the cycled LiCoO2 cathodes and cycled graphite anodes extracted from the cells provide evidence that a LiFSI-induced improvement of high-voltage cycling stability at low temperature originates from the formation of a less resistive solid electrolyte interphase layer, which contains plenty of LiFSI-derived organic compounds mixed with inorganics that passivate and protect the surface of the cathode and anode from further electrolyte decomposition and promotes Li+ ion-transport kinetics despite the low temperature, inhibiting Li metal-plating at the anode. The results demonstrate the beneficial effects of the LiFSI additive on the performance of a lithium-ion battery for use in battery-powered electric vehicles and energy storage systems in cold climates and regions.

Lithium diffusivity of fluorine-free and -doped tin-nickel (Sn-Ni) film model electrodes with improved interfacial (solidelectrolyte interphase (SEI)) stability has been determined, utilizing variable rate cyclic voltammetry (CV). The methodfor interfacial stabilization comprises fluorine-doping on the electrode together with the use of electrolyte including flu-orinated ethylene carbonate (FEC) solvent and trimethyl phosphite additive. It is found that lithium diffusivity of Sn islargely dependent on the fluorine-doping on the Sn-Ni electrode and interfacial stability. Lithium diffusivity of fluorine-doped electrode is one order higher than that of fluorine-free electrode, which is ascribed to the enhanced electrical con-ductivity and interfacial stabilization effect.Keywords: Lithium-ion batteries, Lithium diffusivity T, in-nickel anode, Film model electrode, Fluorine-doping In, terfacials tability Received July 13, 2015 : Accepted November 2, 2015 1. Introduction Tin (Sn)-based materials have been recognized asone of the attractive anode materials, which can replacethe commercialized graphite, primarily because of thelarger theoretical capacity (~994 mAhg

Advanced SiO2–carbon composite anode active material for lithium-ion battery has been synthesized through a simple chelation of silicon cation with citrate in a glyme-based solvent. The resultant composite material demonstrates a homogeneous distribution of constituents over the submicron particles and a unique hollow spherical microstructure, which provides an enhanced electrical conductivity and better accommodation of volume change of silicon during electrochemical charge–discharge cycling, respectively. As a result, the composite electrode exhibits a high cycling stability delivering the capacity retention of 91% at the 100th cycle and discharge capacities of 662–602 mAh/g and coulombic efficiencies of 99.8%. This material synthesis is scalable and cost-effective in preparing various submicron or micron composite electrode materials.

The interfacial origin of performance improvement and fade of high-voltage cathodes of LiNi0.5Co0.2Mn0.3O2 for high-energy lithium-ion batteries has been investigated. Performance improvement was achieved through interfacial stabilization using 5 wt % methyl (2,2,2-trifluoroethyl) carbonate (FEMC) of fluorinated linear carbonate as a new electrolyte additive. Cycling with the FEMC additive at 3.0–4.6 V versus Li/Li+ results in the formation of a stable solid electrolyte interface (SEI) layer and effective passivation of cathode surface, leading to improved cycling performance delivering enhanced discharge capacities to 205–182 mAhg–1 and capacity retention of 84% over 50 cycles. The SEI layer notably includes plenty of metal fluorides and −CF-containing species formed by additive decomposition. On the contrary, the origin of performance fade in electrolyte only was ineffective surface passivation and dissolution of metal elements, which leads to oxygen loss, surface structural degradation and crack format...

Recently, researchers are devoted to develop all-solid-state batteries based on solid electrolytes such as polymers, sulfides, oxide ceramics that can provide improved thermal stability and safety than conventional lithium-ion batteries based flammable organic liquid electrolyte. However, solid electrolytes faces to challenge lower ionic conductivity and interfacial contact problem between cathode and electrolyte, which causes large interfacial resistance. In this presentation, we report the fabrication of polymer-based all-solid-state batteries with high-nickel LiNi0.8Co0.1Mn0.1O2 cathode, attainment of high areal capacity ~1.5 mAhcm-2 and improvement of cycling performance using additive combination. Studies of the changes in the structure and morphology of cathode and surface composition and their correlation to the performance would be discussed in the meeting. Acknowledgements This research was supported by the Korean Ministry of Trade, Industry & Energy (10080025), and Creative Human Resource Development Consortium for Fusion Technology of Functional Chemical/Bio Materials of BK Plus program by Ministry of Education of Korea.

High-capacity Li-rich layered composite oxide, xLi2MnO3(1-x)LiMO2 (M = Mn, Ni, Co), is a promising candidate cathode material for high-energy electrochemical energy storage. Enabling the high-performance of high-voltage cathode relies on an electrolyte breakthrough and the solid electrolyte interface (SEI) stabilization. In this study, the 0.6Li2MnO30.4LiNi0.45Co0.25Mn0.3O2 (Li1.2Mn0.525Ni0.175Co0.1O2, LMNC) cathode is operated at 2.5–4.8 V with 5 wt% fluorinated linear carbonate, di-(2,2,2 trifluoroethyl)carbonate (DFDEC), as a high-voltage electrolyte additive, for the first time and applied to a high-energy lithium-ion battery. The cathode with DFDEC outperforms that in electrolyte only, delivering a high capacity of 250 mAhg−1 with an excellent charge-discharge cycling stability at the rate of 0.2C. Upon the use of DFDEC, the cathode surface is effectively passivated by a stable SEI composed of DFDEC decomposition products, which inhibit a detrimental metal dissolution and structural cathode degradation. A full-cell based on the SEI-stabilized LMNC cathode and graphite anode successfully demonstrates doubled energy density (~278 Whkg−1) compared to ~136 Whkg−1 of a commercialized cell of graphite//LiCoO2 and an excellent cycling stability.

We present the first report on carbon fiber-interwoven amorphous nano-SiOx/graphene prepared by a simple and facile room temperature synthesis of amorphous SiOx nanoparticles using silica, followed by their homogeneous dispersion with graphene nanosheets and carbon fibers in room temperature aqueous solution. Transmission and scanning electron microscopic imaging reveal that amorphous SiOx primary nanoparticles are 20-30 nm in diameter and carbon fibers are interwoven throughout the secondary particles of 200-300 nm, connecting SiOx nanoparticles and graphene nanosheets. Carbon fiber-interwoven nano-SiO0.37/graphene electrode exhibits impressive cycling performance and rate-capability up to 5C when evaluated as a rechargeable lithium battery anode, delivering discharge capacities of 1579-1263 mAhg(-1) at the C/5 rate with capacity retention of 80% and Coulombic efficiencies of 99% over 50 cycles, and nearly sustained microstructure. The cycling performance is attributed to synergetic effects of amorphous nano-SiOx, strain-tolerant robust microstructure with maintained particle connectivity and enhanced electrical conductivity.

Lithium diffusivity of the silicon (Si)-based materials of Si-Cu and SiO x (x = 0.4, 0.85) withimproved interfacial stability to electrolyte have been determined, using variable rate cyclic vol-tammetry with film model electrodes. Lithium diffusivity is found to depend on the intrinsic prop-erties of anode material and electrolyte; the fraction of oxygen for SiO x (x = 0.4, 0.85), which isdirectly related to electrical conductivity, and the electrolyte type with different ionic conductivityand viscosity, carbonate-based liquid electrolyte or ionic liquid-based electrolyte, affect the lithiumdiffusivity. Keywords : Rechargeable lithium batteries, Si-based anode, Lithium diffusivity, Film model electrode ( Received September 23, 2013 : Accepted October 7, 2013) 1. Introduction There is an increasing need of high-energyrechargeable lithium batteries for their applications toelectric vehicles and stationary energy storage gridsystems. This represents the development need ofhigher capacity anode materials, and higher capacityand higher voltage cathode materials with a stablecycling ability and safer characteristics than the con-ventional ones.

Present affiliation: Iljin Electric Co, Ltd.Received January 9, 2013, Accepted January 31, 2013Key Words : Lithium-ion battery, Anode materials, Silicon, Silicon-graphite composite, SEI layerSilicon (Si)-based materials are considered as potentialalternative anode materials to graphite for a use in thelithium-ion batteries for electric vehicles and energy storagesystems because of superior theoretical capacity of 3759mAhg

Film model electrodes of silicon oxide (SiOx) with various oxygen content (x = 0.4, 0.85, 1.0 and 1.3) have been studied for the effects of oxygen content and interfacial reaction behavior on cycling ability. IR and XPS analyses on the origin of initial charge plateau in 1M LiPF6/EC:DEC indicate that the contribution of electrolyte reduction to the plateau is far larger than the formation of lithium silicates, lithium oxide and silicon. Higher oxygen content of SiOx induces to decrease initial electrolyte reduction, whereas larger fraction of oxides is subjected to dissolution by acid (e.g., HF)-etching. Cycling ability at higher oxygen content however is remarkably improved when constructing a surface protective siloxane network at the electrodes using silane electrolyte additive. The SiO1.0 electrode exhibits superior capacity retention of 84% at the 200th cycle delivering discharge capacity of 1206–1017 mAh/g. The SEI layer formed over surface siloxane network consists of a plenty of organic compounds and lithium carbonate, in contrast to mainly inorganic salts and organic phosphorus fluoride compounds upon cycling without silane adidtive. A better protection and passivation of electrode surface should be of the effects of siloxane network, and in that fashion cycling ability is greatly stabilized.

The cycling behavior of Li 4 Ti 5 O 12 /LiCoO 2 cells in the ionic liquid electrolytes based on 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (BMP-TFSI) with different additives, such as vinylene carbonate (VC), 1,3-propane sultone (PS) and their mixture is investigated. The cell assembled with BMP-TFSI containing 10 wt% VC/PS (1:1 by weight) exhibits reversible cycling behavior with good capacity retention. FTIR studies reveal that the electrochemically stable solid electrolyte interphase forms on Li 4 Ti 5 O 12 electrode in the presence of a mixture of VC and PS during cycling. The additives hardly affect the composition, thickness and stability of the surface film formed on the LiCoO 2 cathode.

Structural volume change occurring on the Si-based anode battery materials during alloying/dealloying with lithium is noticed to be a major drawback responsible for a limited cycle life. Silicon monoxide has been reported to show relatively improved cycling performance compared to Si-containing materials for rechargeable lithium batteries, due to the structural buff- ering role of in-situ formed Li2O and lithium silicate during the reaction of silicon monoxide and lithium. Here we report improved cycling ability of interfacially stabilized Si-SiO2-graphite composite anode using silane-based electrolyte additive for rechargeable lithium batteries, which includes low cost silicon dioxide for structural stabilization and graphite for enhanced conduc- tivity.

A FeSi 2.7 thin film is deposited on a copper substrate by RF magnetron sputtering of a Fe–Si alloy target. The electrochemical behavior of the FeSi 2.7 electrode in ionic liquid electrolyte based on 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide is investigated and compared with that of a FeSi 2.7 electrode in conventional liquid electrolyte. The FeSi 2.7 electrode in the ionic liquid electrolyte delivers an initial discharge capacity of 756 mAh g −1 at room temperature, and its discharge capacity is maintained to be 92% of the initial discharge capacity after the 100th cycle. AC impedance and FTIR analysis reveal that the formation of a stable solid electrolyte interphase (SEI) layer on the FeSi 2.7 electrode in the ionic liquid electrolyte leads to a good capacity retention. This study demonstrates that the FeSi 2.7 electrode exhibits stable cycling behavior and good interfacial characteristics in the ionic liquid electrolyte without any solvents and additives.

Mesoporous TiO2 anatase microspheres consisting of self-assembled nanocrystals have been synthesized by a one-step hydrothermal method at 120 oC using titanium-peroxo complex, without a post-calcination process. Transmission and scanning electron microscopic imaging reveal that diamond-shaped nanocrystals as primary particles, which are 20 nm in average width and 50 nm in length and oriented with (101) plane of anatase phase, are aggregated to form a secondary microsphere particle with 0.5–1 μm in diameter. BET analysis data show that the TiO2 anatase particles possess significantly large surface area of 254 m2 g–1 with the pore size of ∼14 nm. Mesoporous TiO2 anatase anode shows an enhanced lithium storage performance in pyrrolidinium-based ionic liquid electrolyte diluted with ethyl methyl carbonate, delivering 195 - 150 mAhg-1 at the C/2 rate with 77 % capacity retention and 98–99 % Coulombic efficiencies over 50 cycles despite the absence of surface carbon-coating. AC impedance analysis results reveal...

An investigation is made of the high-rate capability (up to 10 C) of all-solid-state thin-film lithium batteries that comprise of Li/LiPON/LiCoO 2 on a flexible substrate, as well as of the effect of high-rate cycling on the structure of these batteries. Raman spectroscopic analysis results reveal that an increase in the rate promotes film orientation of the LiCoO 2 cathode with (1 0 1)/(1 0 4) planes and limited lithium intercalation and deintercalation within the layered hexagonal structure without a phase transition to monoclinic. Although with high-rate cycling the LiCoO 2 columnar grains tend to aggregate and lose grain orientation, as observed by scanning electron microscopic imaging, the film morphology is efficiently preserved when there is exterior multilayered encapsulation on thin-film batteries. Encapsulated thin-film batteries at 10 C show excellent capacity retention of 95% over 800 cycles, delivering > 22 μAh cm −2 μm −1 . The data contribute to a basic understanding of the structure–rate performance relationship of all-solid-state battery systems.

Titanium oxide nanotube and graphite composites are prepared by adding graphite before and after a hydrothermal reaction to enhance the cyclic performance and high-rate capability of lithium-ion batteries. The composite powders, their anode electrodes, and lithium half-cells containing the anodes are characterized by means of morphological and crystalline analysis, Raman spectroscopy, cyclic voltammetry, impedance spectroscopy, and repeated discharge–charge cycling at low and high C-rates. Notably, the composite anode (R5G5-T) that concurrently uses natural graphite and rutile particles before the hydrothermal reaction shows superior high-rate capability and achieves a discharge capacity of ca. 70 mAh g −1 after 100 cycles at 50 C-rate. This may be due to the high-rate supercapacitive reactions of the TiO 2 nanotube on the graphite surface caused by a diffusion-controlled or a charge-transfer process.

Gel polymer electrolytes containing a mixture of organic solvent and ionic liquid were prepared and their electrochemical properties were investigated. The gel polymer electrolytes exhibited good electrochemical stability and stable interfacial properties toward lithium metal. Using these gel polymer electrolytes, lithium metal polymer cells composed of a lithium anode and a LiFePO4 cathode were assembled, and their cycling performances were evaluated. The cells showed good cycling performance comparable to that of a cell assembled with gel polymer electrolyte containing only organic liquid electrolyte. The Li/LiFePO4 cells assembled with a gel polymer electrolyte containing ionic liquid are expected to be one of the promising candidates for high energy density lithium batteries with improved safety.

From mixed (anatase and rutile) bulk particles, anatase TiO2 nanotubes are synthesized in this study by an alkaline hydrothermal reaction and a consequent annealing at 300–400 °C. The physical and electrochemical properties of the TiO2 nanotube are investigated for use as an anode active material for lithium-ion batteries. Upon the first discharge–charge sweep and simultaneous impedance measurements at local potentials, this study shows that interfacial resistance decreases significantly when passing lithium ions through a solid electrolyte interface layer at the lithium insertion/deinsertion plateaus of 1.75/2.0 V, corresponding to the redox potentials of anatase TiO2 nanotubes. For an anatase TiO2 nanotube containing minor TiO2(B) phase obtained after annealing at 300 °C, the high-rate capability can be strongly enhanced by an isotropic dispersion of TiO2 nanotubes to yield a discharge capacity higher than 150 mAh g−1, even upon 100 cycles of 10 C-rate discharge–charge operations. This is suitable for use as a high-power anode material for lithium-ion batteries.

Thin film electrodes of Sn in various film thckness of 58 -200 nm have been prepared on stainless steel with a pulsed laser deposition technique. The 58 nm thick film electrode showed a stable cycling at the limited voltage window of 0.1-1.0 V, delivering capacity ~265 mAh/g for 50 cycles. The superior performance, when compared to porous electrode of this metal, is due to the shorter lithium diffusion path and enhanced conductivity from the substrate. The SEI layer formed on Sn electrode after cycled at 0.1-1.0 V was characterized using FTIR spectroscopy; the layer is composed of a mixture of inorganics and organics. The continuous formation of the SEI layer contributes to a continuous irreversible capacity loss on the extended cycles.

Crystalline films of WO3 were directly fabricated on alumina and zirconia ceramic substrates via a facile hydrothermal fabrication process using an aqueous peroxy-tungstate solution. The process utilized kinetically controlled decomposition reaction of the peroxy-tungstate solution to tungsten oxide following supersaturation and heterogeneous nucleation at the surface of the substrates. The films possessed remarkably different microstructures depending on the reaction conditions, but all particles were oriented normal to the substrates. X-ray diffraction, transmission electron microscopic and Raman spectroscopic data indicated that the WO3 film had a hexagonal structure and film orientation. The WO3 films showed a rapid gas response to NO2 of ppm level. The data contribute to the development of film fabrication methods of a variety of oxide gas sensing elements.

Palladium-coated magnesium–manganese–nickel films behave as gasochromic switchable mirrors, becoming transparent on exposure to dilute hydrogen, and reverting to a mirror state on exposure to air. The cycling stability of the optical switching depends upon preservation of the integrity of the Pd catalyst overlayer. Alloying between Mg and Pd causes interdiffusion of the two elements, and leads to degradation in switching speed and eventual deactivation. Incorporation of a thin niobium oxide barrier layer between the active magnesium alloy film and the Pd layer substantially improves the cycling stability of the mirror.

LiMO2 (M=Ni and Co) films were directly fabricated in a concentrated LiOH solution at fixed temperatures, between 100 and 200 °C, using Soft Solution Processing. Film formation mechanism studies elucidate the key role of hydroxyl group in obtaining the LiCoO2 films and of electrochemical anodic process in obtaining the LiNiO2 films. It is also found that the formation of the LiMO2 (M=Ni and Co) is fully based on dissolution–precipitation model. Successful preparation of LiMO2 (M=Ni and Co) films using the newly designed experimental conditions based on the elucidation of the microstructuring mechanism shows a good example of how to introduce more economical, energy and material efficient, and environment-friendly synthetic route.

An increase in the energy density of lithium-ion batteries has long been a competitive advantage for advanced wireless devices and long-driving electric vehicles. Li-rich layered oxide, xLi2MnO3∙(1−x)LiMn1−y−zNiyCozO2, is a promising high-capacity cathode material for high-energy batteries, whose capacity increases by increasing charge voltage to above 4.6 V versus Li. Li-rich layered oxide cathode however suffers from a rapid capacity fade during the high-voltage cycling because of instable cathode–electrolyte interface, and the occurrence of metal dissolution, particle cracking, and structural degradation, particularly, at elevated temperatures. Herein, this study reports the development of fluorinated polyimide as a novel high-voltage binder, which mitigates the cathode degradation problems through superior binding ability to conventional polyvinylidenefluoride binder and the formation of robust surface structure at the cathode. A full-cell consisting of fluorinated polyimide binder-assisted Li-rich layered oxide cathode and conventional electrolyte without any electrolyte additive exhibits significantly improved capacity retention to 89% at the 100th cycle and discharge capacity to 223–198 mA h g−1 even under the harsh condition of 55 °C and high charge voltage of 4.7 V, in contrast to a rapid performance fade of the cathode coated with polyvinylidenefluoride binder.

Increasing the capacity of Li-rich layered oxide (LMNC) cathode material for high-energy density lithium-ion batteries relies on the increase of charge cut-off voltage toward 5 V, under the utilization of anodically stable electrolyte component. The utilization of di-(2,2,2 trifluoroethyl)carbonate (DFDEC)-containing electrolyte permits significant improvement of anodic stability, cathode–electrolyte interface, and cycling stability of LMNC cathode, with respect to conventional electrolyte. In the present study, the limit of anodic stability of DFDEC under charging to 5.5 V versus Li is explored, and the interfacial processes of DFDEC-derived surface protection mechanism are investigated, utilizing charge cut-off voltage-dependent surface and structural analyses. The oxidative decomposition of DFDEC is found to begin at 4.7 V, producing metal fluorides and CF-containing organic compounds as the earliest surface species, passivating the cathode surface and reducing metal dissolution, structural transformation, and cathode degradation. The tolerable limit of charge cut-off voltage of a model electrolyte of 0.1 m LiPF6/DFDEC is determined to be 5.0 V, to which the cathode outperforms conventional electrolyte, delivering discharge capacities of 261–225 mAhg−1 with the capacity retention of 86% at the 50th cycle. The data give an insight into the principles of electrolyte design and high-voltage cathode–electrolyte interfacial stabilization toward advanced 5 V lithium-ion batteries.