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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.

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.

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.

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.

Understanding the chemical processes that occur at the electrode/electrolyte interface in a battery is crucial, as the interactions between anode/cathode and electrolyte and between cathode and anode of a full-cell determine the final battery performance. We have investigated the correlation among cycling performance, interfacial reaction behavior and the solid electrolyte interphase (SEI) stability of a LiNi 0.5 Co 0.2 Mn 0.3 O 2 //Si-graphite full-cell under an aggressive test condition between 3.0 and 4.55 V using fluoroethylene carbonate (FEC)-based electrolyte, and blended additives of methyl (2,2,2-trifluoroethyl)carbonate (FEMC) and vinylene carbonate (VC). Through the formation of a stable SEI at both high-voltage cathode and anode, metal dissolution from the cathode is inhibited and full-cell achieves enhanced cycling performance. Interfacially stabilized full-cell delivers a high energy of 622 Wh per kg of active material and improved capacity retention, whereas the cell in conventional electrolyte shows a rapid performance fade.

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.

Interfacial reactions of Sn during initial cycling in 1 M LiPF6/EC:DMC (1:1) were studied by characterizing the surface species formed on thin film electrodes of Sn, prepared with a pulsed laser deposition, using ex-situ ATR FTIR spectroscopy and microscopy. FTIR analyses indicated that at high voltage region above 1.0 V vs. Li/Li+ the surface of Sn electrode was covered by PF-containing inorganic species probably by the interfacial reactions between Sn and PF6− anions. With charging to 0.63 V low amounted organic species with carboxylate metal salt and alkyl functionalities appeared, due to the reductive decomposition of organic solvents. The organic surface species however were destroyed upon a deep charge to 0.1 V and reproduced on the subsequent discharge process, whereas P–F containing inorganic species remained preserved. No sustainment of organic surface species but the stable passivation of Sn surface by PF-containing species during initial cycling are believed to cause unstable interfacial structure and the possibility of reduced utilization of active Sn, respectively, resulting in the large initial irreversible capacity loss.

We report for the first time new Li + ion conducting thin film solid electrolytes based on Li-B-O-N system. Substitution of oxygen in xLi 2 O-B 2 O 3 (x = 1,3,5) by nitrogen was successfully achieved by reactive sputtering under nitrogen plasma. FTIR and XPS analyses indicated that N atom was incorporated in the Li―B―O matrix film, and an increase in the composition of Li 2 O together with N-substitution caused the structural conversion from ring-type borate to open structured one, where more free space and ionic bonding characteristic are offered for higher mobility of Li + ions. A high ionic conductivity of ca. 2.3 x 10 ―6 S cm ―1 at room temperature was obtained from the thin film electrolyte of Li 3.09 BO 2.53 N 0.52 glass that was prepared using 3Li 2 O-B 2 O 3 target. Electrochemical analyses suggest the high Li + ion conductivity is induced by the reduced activation energy through the control of the composition and the structure.

Mg{sub 2}Si films, prepared by pulsed laser deposition (PLD), were amorphous, as prepared, and nanocrystalline following annealing. Their micro-structure and electrochemical characteristics were studied by high resolution transmission electron microscopy (HRTEM) and electrochemical cycling against lithium. HRTEM analysis revealed that some excess Si was present in the films. The more amorphous thinner film exhibited excellent cyclability. However, when the film becomes crystalline, the irreversible capacity loss was more significant during the initial cycling and after *50 cycles. Interpretations of the superior stability of the amorphous films are examined.