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Graphene oxide, an oxidized derivative of graphene, has many intriguing properties, such as amphiphilicity, negative charge, and easy mass production. However, due to the electronic insulation, graphene oxide cannot be directly used as a conductive agent for lithium batteries before reduction. Here we have demonstrated the enhanced rate and cycle capability of LiMn0.7Fe0.3PO4 with in situ electrochemically reduced graphene oxide by starting from discharge to 1.5 V vs. Li+/Li. For example, LiMn0.7Fe0.3PO4 with 2 wt% electrochemically reduced graphene oxide can obtain a high discharge capacity of ∼83 mAh g−1 at 30C and capacity retention of ∼90% at 1C after 200 cycles, much higher performance than that without graphene oxide (∼10 mAh g−1 and ∼56%, respectively). Moreover, the cathode with in situ electrochemically reduced graphene oxide also shows better performances than that with the externally reduced graphene oxide. The boosted performance is attributed to the effective conductive network formed by the well-dispersed graphene oxide.

The ambient temperature application of PEO-based polymer electrolytes has been restrained by their poor ionic conductivity. Herein, we report a super-concentrated polymer in “solvated ionic liquid” which is composed of polyethylene oxide (PEO), LiN(SO2CF3)2 (LiTFSI), and solvent with low viscosity. It is found that the maximum coordination during Li, polymer, and the solvent can be formed by the molar ratio of PEO/Li = 1:1 with 25 wt% of solvent, left no free solvent exits in the mixture. The electrochemical performance of the designed electrolyte was evaluated by using a LiFePO4/Li cell. Comparing to the conventional carbonate liquid electrolyte, the designed electrolyte achieves comparable rate performance (155.4 and 157.8 mAh g−1 discharge at 1 C for the designed and carbonate electrolyte, respectively) and higher cycle performance (capacity retention of 95.5% and 75.5% after 100 cycles for the designed and carbonate electrolyte, respectively). It has been further proven that incombustibility can be obtained by only adding ~15 wt% fire-retardant. We believe that the developed electrolyte is promising and practical for being applied in the polymer lithium-ion battery.

The requirements for volume and weight performance are becoming more and more urgent for the application of lithium-ion batteries in consumer electronics and electric vehicles. Herein, we demonstrate a facial and cost-effective synthesis approach of lithium-ion conducting glass ceramic (LICGC)/reduced graphene oxide (rGO) composite, in which the LICGC particles anchor on the rGO sheets densely and homogenously, forming a sandwich-like structure. The unique feature offers ultrafast Li-ion and electron pathways through the LICGC network and rGO sheets, resulting in the enhancement of the rate and cycle performances for the electrodes. For example, the results show that for LiFePO4 cathode with the polymer electrolyte, the addition of 10 wt% of LICGC/rGO composite achieved the higher rate capability (~122 mAh g−1, discharge at 3 C) and cyclability (~98.2% after 180 cycles at 1 C), compared to add LICGC only (~115 mAh g−1 and ~93.4%, respectively).

Highly concentrated solutions composed of lithium bis(fluorosulfonyl)imide (LiFSI) and sulfolane (SL) are promising liquid electrolytes for lithium metal batteries because of their high anodic stability, low flammability, and high compatibility with lithium metal anodes. However, it is still challenging to obtain the stable lithium metal anodes in the concentrated electrolytes due to their poor wettability to the conventional polyolefin separators. Here, we report that the highly concentrated 1:2.5 LiFSI/SL electrolyte coupled with a three-dimensionally ordered macroporous polyimide (3DOM PI) separator enables the stable lithium plating/stripping cycling with an average Coulombic efficiency of ca. 98% for over 400 cycles at 1.0 mA cm-2. The 3DOM PI separator shows good electrolyte wettability and large electrolyte uptake due to its high porosity and polar constituent of the imide structure, allowing superior cycling performance in the highly concentrated solution, compared with the polyolefin separators. Electrochemical and spectroscopic analyses reveal that the superior cycling stability in the concentrated electrolyte is attributed to the formation of highly stable and Li+ ion conductive solid electrolyte interphase (SEI) layer derived from FSI- anions, which reduces the side reactions of SL with lithium metal, prevents the growth of lithium dendrites, and suppresses the increase in cell impedance over long-term cycling. Our findings demonstrate that polar and porous separators could effectively improve the affinity to the concentrated electrolytes and allow the formation of the anion-derived SEI layer by increasing the salt concentration of the electrolytes, achieving the long-term stable lithium metal anode.

A high-capacity thick cathode has been studied as one of ways to improve the energy density of lithium secondary batteries. In this study, the LiFePO 4 cathode with a capacity per unit area of 8.4 m Ah cm −2 corresponding to four times the capacity of conventional cathodes has been developed using a three-dimensional porous aluminum current collector called “FUSPOROUS”. This unique current collector enables the smooth transfer of electrons and Li + -ions through the thick cathode, resulting in a good rate capability (discharge capacity ratio of 1.0 C/0.2 C = 0.980) and a high charge-discharge cycle performance (80% of the initial capacity at 2000th cycle) even though the electrode thickness is 400 μm. To take practical advantage of the developed thick cathode, conceptual designs for a 10-Ah class cell were also carried out using graphite and lithium-metal anodes.

Li metal battery with garnet-type Li7La3Zr2O12 (LLZ) as a solid electrolyte has attracted attentions as a promising candidate for high-energy batteries. However, the interfacial resistance between LLZ and Li is huge due to a point-point contact, leading to poor battery performances such as rate capability and cycleability. Here, we have studied the hybrid-electrolyte structure using the liquid electrolyte interlayer containing LiBH4 between LLZ and Li at high operating temperature of 120 °C. This hybrid-electrolyte structure offers high current density usage and a long-term cycleability. The Li|LLZ|Li symmetric cell shows high critical current density of 13 mA cm−2 and a long term cycle. The liquid electrolyte interlayer containing LiBH4 provides an improved coulombic efficiency of Li striping/plating due to an excellent reductive stability. Our findings suggest that the interfacial conditions on LLZ|Li could be effectively improved by using the modified liquid electrolyte interlayer.

Li metal battery with garnet-type Li7La3Zr2O12 (LLZ) as a solid electrolyte has attracted attentions as a promising candidate for high-energy batteries. However, the interfacial resistance between LLZ and Li is huge due to a point-point contact, leading to poor battery performances such as rate capability and cycleability. Here, we have studied the hybrid-electrolyte structure using the liquid electrolyte interlayer containing LiBH4 between LLZ and Li at high operating temperature of 120 °C. This hybrid-electrolyte structure offers high current density usage and a long-term cycleability. The Li|LLZ|Li symmetric cell shows high critical current density of 13 mA cm-2 and a long term cycle. The liquid electrolyte interlayer containing LiBH4 provides an improved coulombic efficiency of Li striping / plating due to an excellent reductive stability. Our findings suggest that the interfacial conditions on LLZ|Li could be effectively improved by using the modified liquid electrolyte interlayer.

Graphene has attracted considerable attention as the conductive agent for lithium batteries by providing a superior interfacial contact. However, the wrapping of active materials by the large area of graphene sheets may hinder the transportation of Li+ between active particles and electrolyte, especially at a high charge/discharge rates. Herein, holey graphene oxide (h-GO), which is made by a green wet ball-milling of GO in one step without using any catalysts or chemicals, is combined with carbon nanotubes (CNTs) and LiMn0.7Fe0.3PO4 (LMFP) to make a composite cathode for lithium batteries. Results show that after the electrochemical reduction, the LMFP cathode with h-GO/CNT shows remarkedly improved electrochemical performances due to the facilitated Li+ transport pathway, compared to that with conventional GO/CNT. For example, LMFP/h-GO/CNT composite cathode can achieve a discharge capacity of 112 mAh g−1 when discharged at 20 C, while LMFP electrode with conventional GO/CNT only shows a discharge capacity of 35 mAh g−1. This study provides a new approach for fabricating holey graphene and can open up new possibilities for applications on power sources.

Introduction Olivine-type LiMnPO4 which is a cathode material for lithium ion batteries exhibits a higher operating potential (4.1 V vs. Li+/Li) than LiFePO4 thus has gathered more attention in recent years. However, due to the low electron conductivity of LiMnPO4 and the Jahn-Teller effect of Mn3+, it is difficult to achieve satisfied cycle performance. Fe doping of 10-30 mol% is promising as a solution to this problem [1]. Graphene is a single atomic monolayer of graphite and has been found a variety of applications in energy conversion and storage devices, due to the excellent properties such as high carrier mobility (~10,000 cm2 V−1 s−1 at room temperature), structural flexibility, chemical and thermal stability, mechanical strength and ultrahigh theoretical specific surface area (2630 m2g−1) [2]. Previous studies have reported the improved performance of LiMPO4 (M = Fe, Mn and Co by combining with graphene. In particular, it is attractive that the active material is supported on both sides of graphene to form a sandwich structure. One is that active material particles can be highly loaded and interconnected by the highly conductive matrix formed by graphene. The other one is that the sandwich structure can be beneficial for suppressing the graphene restacking and active material particles agglomeration. It is reported that such a graphene-metal oxide nanoparticle composite material can greatly improve the performances of the anode. However, there is still lack of a facial way to obtain ideally sandwich-structured composite material for cathode [3]. We will introduce a facial and high efficient way to synthesize carbon-coated LiMn0.7Fe0.3PO4 (LMFP)/reduced graphene oxide (rGO) sandwich-structured composite for high power lithium ion batteries [4]. Results and discussion The synthesis of sheet-like carbon-coated LMFP/rGO composite material is shown in Fig. 1. First, 0.3 g of LMFP powder (without carbon coating, average particle size 200 nm), 3 mL of oxidized graphite suspension and 0.04 g of sucrose are dispersed in 100 mL of water. Thereafter, by ultrasonic treatment for 2.5 hours, the oxidized graphite gradually peels off to form graphene oxide, and at the same time, the LMFP nanoparticles are supported on the surface of the GO by interaction with the GO functional group. The dissolved sucrose is coated with GO and LMFP particles to form a polymeric coating. After lyophilization, carbon coated LMFP/rGO composite material (LMFP/rGO@C) having a sandwich structure was obtained by heat treatment at 700 degrees under a reducing atmosphere. LMFP/rGO@C, acetylene black and binder were mixed at a mass ratio of 8:1:1 and coated onto Al foil to obtain a cathode electrode. Electrochemical characteristics were evaluated by preparing a 2032 type coin cell using Li foil as the counter electrode. The electrolyte was 1 mol dm-3 LiPF6/EC-DEC (1: 2). SEM image of the synthesized LMFP/rGO@C composite material is shown in Fig. 2. It is clearly observed that all the LMFP particles are uniformly dispersed on the rGO surface at high density (50 to 100 particles mm-2), forming a sandwich structure. The total content of rGO and carbon coating is estimated to be about 7 wt% from TG. Figure 3 shows the discharge rate performance of LMFP/rGO@C and carbon coated only LMFP (LMFP@C). It was confirmed that the discharge capacity of LMFP/rGO@C is greatly improved compared with LMFP@C. This should be due to the formation of a good three-dimensional conductive network by graphene. Acknowledgement We thank Taiheiyo Cement Co., Ltd for the providing of LiMn0.7Fe0.3PO4 powders and NIMS for the TEM measurement. Reference 1) Gong, et.al., Energy Environ. Sci. 4, 3223 (2011). 2) S. Han, et.al., Small. 9 1173–1187 (2013). 3) Z.-S. Wu, et.al. Nano Energy. 1 (2012). 4) D. Ding, et.al., submitted. Figure 1

The picosecond spectroscopy with the time delayed double excitation technique has revealed that the F - H center pair ([ F - H ]) is converted from the self-trapped exciton ( S T E L ) at the a 1 g state within 20 ps in KCl, NaCl and RbCl at 14 K. Conversion efficiencies from the S T E L to the [ F - H ] and to unknown X states were estimated by assuming two possible candidates of the hole π g state or the higher electronic state in the STE as the precursor for [ F - H ] formation. Percentages of branching from the precursor to the [ F - H ] were 49, 86 and 20% in KCl, NaCl and RbCl, respectively. Rest of the STE were converted to unknown X states. By making use of these results, we criticized the state acceptable as the precursor, i.e., the hole π g state or the electronic states.

The relation between the transition temperature of typical nematic liquid crystal mixtures and the dynamic properties of twisted nematic (TN) cells are presented. The extrapolated response time at ...