Design of Non-Incendive High-Voltage Liquid Electrolyte Formulation for Safe Lithium-Ion Batteries.

Battery safety has an ever-increasing significance and is required for consumer's safety. The high flammability of traditional organic liquid electrolyte, which consists of ethylene carbonate and highly flammable linear carbonate, is one of the major reasons for thermal runaway and battery fire events. Replacement of flammable liquid electrolyte with non-incendive one is urgently needed for safe lithium-ion batteries. A fluorinated linear sulfate paired with 1 m LiPF6 was developed and evaluated as a solvent of non-incendive liquid electrolyte for a use in high-voltage (4.4 V) and high-temperature (45 °C) LiNi0.82 Mn0.07 Co0.11 O2 (NCM811) chemistry-based lithium-ion batteries. Non-incendive liquid electrolyte containing sulfate with two trifluoroethyl groups exhibited superior anodic and thermal stability and promoted cathode-electrolyte and anode-electrolyte interfacial stability, compared to flammable traditional electrolyte. Non-incendive electrolyte showed markedly improved 300 cycle performance of an industrial graphite‖NCM811 lithium-ion pouch cell with a nominal capacity of 730 mAh under harsh conditions, and high safety of 10 V overcharge abuse tolerance, from which safe and high-performing high-energy lithium-ion batteries and battery-powered electric vehicles and energy storage system are anticipated.

Material design strategies to improve the performance of rechargeable magnesium-sulfur batteries.

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.

Fire-Preventing LiPF6 and Ethylene Carbonate-Based Organic Liquid Electrolyte System for Safer and Outperforming Lithium-Ion Batteries.

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.

Robust Solid-Electrolyte Interphase Enables Near-Theoretical Capacity of Graphite Battery Anode at 0.2†C in Propylene Carbonate-Based Electrolyte.

The formation of a robust solid-electrolyte interphase (SEI) layer at the surface of a graphite anode by electrolyte control is a key technology for high-performance lithium-ion batteries. Although propylene carbonate (PC) offers a lower melting point than ethylene carbonate, its combination with the graphite anode without additive is a worse choice, owing to co-intercalation of PC and Li+ ion into graphite, exfoliation of graphene sheets, and death of the battery. This study reports a graphite anode with an unprecedentedly high initial coulombic efficiency of 94 %, close to theoretical capacity, and excellent capacity retention of 99 % after 100 cycles in a PC-based electrolyte system, even at an unusually high rate of 0.2 C, which is generally attainable only at a very low rate of below 0.05 C in commercial electrolyte. The SEI stabilization for a graphite anode in PC-based electrolyte provides a new avenue for high-energy and high-performance batteries in widened range of working temperatures. A strong correlation between anode-electrolyte interfacial stabilization and highly reversible cycling performance is clearly demonstrated.

Interface stabilization via lithium bis(fluorosulfonyl)imide additive as a key for promoted performance of graphite‖LiCoO2 pouch cell under -20 ○C.

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.

Approaching the maximum capacity of nickel-rich LiNi0.8Co0.1Mn0.1O2 cathodes by charging to high-voltage in a non-flammable electrolyte of propylene carbonate and fluorinated linear carbonates.

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.

Enabling High-Rate and Safe Lithium Ion-Sulfur Batteries by Effective Combination of Sulfur-Copolymer Cathode and Hard-Carbon Anode.

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.

Composite Electrolyte for All-Solid-State Lithium Batteries: Low-Temperature Fabrication and Conductivity Enhancement.

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+x Alx Ti2-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-Bi2 O3 composite solid electrolyte shows very high total conductivity (9.4×10-4  S cm-1 ) at room temperature. Bi2 O3 acts as a microstructural modifier to effectively reduce the fabrication temperature of the electrolyte and to enhance its ionic conductivity. Bi2 O3 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-Bi2 O3 composite electrolyte in all-solid-state Li batteries is also examined in this study.

Facile synthesis and high anode performance of carbon fiber-interwoven amorphous nano-SiOx/graphene for rechargeable lithium batteries.

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.

One-step hydrothermal synthesis of mesoporous anatase TiO2 microsphere and interfacial control for enhanced lithium storage performance.

Mesoporous TiO(2) anatase microspheres consisting of self-assembled nanocrystals have been synthesized by a one-step hydrothermal method at 120 (o)C 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 TiO(2) anatase particles possess significantly large surface area of 254 m(2) g(-1) with the pore size of ∼14 nm. Mesoporous TiO(2) 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 that the formation of a stable solid electrolyte interphase (SEI) layer in diluted ionic liquid electrolyte induces the enhanced cycling performance. Control of electrode-electrolyte interfacial compatibility enables the enhancement of cycling performance and the preservation of microstructure. The data contribute to provide cost-efficient synthetic method for the TiO(2) and the interfacial control aspect of performance control for safer batteries.

Strontium magnesium phosphate, Sr(2+x)Mg(3-x)P4O15 (x ~ 0.36), from laboratory X-ray powder data.

The previously unknown crystal structure of strontium magnesium phosphate, Sr(2+x)Mg(3-x)P(4)O(15) (x ~ 0.36), determined and refined from laboratory powder X-ray diffraction data, represents a new structure type. The title compound was synthesized by high-temperature solid-state reaction and it crystallizes in the orthorhombic space group Cmcm. It was earlier thought to be stoichiometric Sr(2)Mg(3)P(4)O(15), but our structural study indicates the nonstoichiometric composition. The asymmetric unit contains one Sr (site symmetry ..m on special position 8g), one M (= Mg 64%/Sr 36%; site symmetry 2/m.. on special position 4b), one Mg (site symmetry 2.. on special position 8e), two P (site symmetry m.. on special position 8f and site symmetry ..m on special position 8g), and six O sites [two on general positions 16h, two on 8g, one on 8f and one on special position 4c (site symmetry m2m)]. The nonstoichiometry is due to the mixing of magnesium and strontium ions on the M site. The structure consists of three-dimensional networks of MgO(4) and PO(4) tetrahedra, and MO(6) octahedra with the other strontium ions occupying the larger cavities surrounded by ten O atoms. All the polyhedra are connected by corner-sharing except the edge-sharing MO(6) octahedra forming one-dimensional arrangements along [001].