To enhance the long stability of sulfur cathode for a high energy lithium-sulfur battery system, a sulfur-carbon sphere composite was prepared by encapsulating sulfur into micropores of carbon spheres by thermal treatment of a mixture of sublimed sulfur and carbon spheres. The elemental sulfur exists as a highly dispersed state inside the micropores of carbon spheres with a large surface area and a narrow pore distribution, based on the analyses of the X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), thermogravimetry (TG) and local element line-scanning. It is demonstrated from galvanostatic discharge-charge process, cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) that the sulfur-carbon sphere composite has a large reversible capacity and an excellent high rate discharge capability as cathode materials. In particular, the sulfur-carbon sphere composite with 42 wt% sulfur presents a long electrochemical stability up to 500 cycles, based on the constrained electrochemical reaction inside the narrow micropores of carbon spheres due to strong adsorption. Therefore, the electrochemical reaction constrained inside the micropores proposed here would be the dominant factor for the enhanced long stability of the sulfur cathode. The knowledge acquired in this study is important not only for the design of efficient new electrode materials, but also for understanding the effect of the micropores on the electrochemical cycle stability.

The Mn-based oxides including MnO, Mn3O4, Mn2O3, MnO2, CoMn2O4, ZnMn2O4and their carbonaceous composite/oxide supports with different morphologies and compositions as anode materials are reviewed.

There is a great interest in the utilization of silicon-based anodes for lithium-ion batteries. However, its poor cycling stability, which is caused by a dramatic volume change during lithium-ion intercalation, and intrinsic low electric conductivity hamper its industrial applications. A facile strategy is reported here to fabricate graphene oxide-immobilized NH2-terminated silicon nanoparticles (NPs) negative electrode (Si@NH2/GO) directed by hydrogen bonding and cross-linked interactions to enhance the capacity retention of the anode. The NH2-modified Si NPs first form strong hydrogen bonds and covalent bonds with GO. The Si@NH2/GO composite further forms hydrogen bonds and covalent bonds with sodium alginate, which acts as a binder, to yield a stable composite negative electrode. These two chemical cross-linked/hydrogen bonding interactions-one between NH2-modified Si NPs and GO, and another between the GO and sodium alginate-along with highly mechanically flexible graphene oxide, produced a robust network in the negative electrode system to stabilize the electrode during discharge and charge cycles. The as-prepared Si@NH2/GO electrode exhibits an outstanding capacity retention capability and good rate performance, delivering a reversible capacity of 1000 mAh g(-1) after 400 cycles at a current of 420 mA g(-1) with almost 100% capacity retention. The results indicated the importance of system-level strategy for fabricating stable electrodes with improved electrochemical performance.

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The rate performance of LiMnPO 4 -based materials is further improved via synergistic strategies including a surfactant-assisted solid state method, Fe-substitution and carbon-coating. The surfactant-assisted solid state strategy effectively decreases the primary particle size of the cathode material, which can greatly shorten the diffusion distance of lithium ions. The Fe-substitution improves the effectiveness of Li + insertion/extraction reactions in the solid phase. The uniform carbon coating layer and the conductive networks provided by the carbon between the nanoparticles ensure the continuous conductivity by the nanoparticles. As a consequence of the synergistic effects, the as prepared LiFe 0.5 Mn 0.5 PO 4 sample with 6.10 wt% carbon exhibits high specific capacities and superior rate performance with discharge capacities of 155.0, 140.9 and 121 mA h g À1 at 0.1, 1 and 5 C (1 C ¼ 170 mA g À1 ), respectively.Meanwhile, it shows stable cycling stability at both room temperature (25 C, 94.8% and 90.8% capacity retention after 500 cycles at 1 and 5 C rates, respectively) and elevated temperature (55 C, 89.2% capacity retention after 300 cycles at 5 C rate). This material may have great potential application in advanced Li-ion batteries.

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LiMnPO 4 (LMP) is one of the most potential candidates for high energy density (≈700 W h kg -1 ) lithium ion batteries (LIBs). However, the intrinsically low electronic conductivity and lithium ion diffusion coefficient of LMP result in its low performance. To overcome these challenges, it is an effective approach to prepare nanometer-sized Fe-doping LMP (LFMP) materials through optimization of the preparation routes. Moreover, surface coating can improve the ionic and electronic conductivity, and decrease the interfacial side reactions between the nanometer particles and electrolyte. Thus, a uniform surface coating will lead to a significant enhancement of the electrochemical performance of LFMP. Currently, considerable efforts have been devoted to improving the electrochemical performance of LiFe 1-y Mn y PO 4 (0.5 ≤ y < 1.0) and some important progresses have been achieved. Here, a general overview of the structural features, typical electrochemical behavior, delithiation/ lithiation mechanisms, and thermodynamic properties of LiFe 1-y Mn y PO 4based materials is presented. The recent developments achieved in improvement of the electrochemical performances of LiFe 1-y Mn y PO 4 -based materials are summarized, including selecting the synthetic methods, nanostructuring, surface coating, optimizing Fe/Mn ratios and particle morphologies, cation/ anion doping, and rational designing of LFMP-based full cells. Finally, the critical issues at present and future development of LiFe 1-y Mn y PO 4 -based materials are discussed.of LIBs. [3,4] Investigation on the design and preparation of high performance cathode materials has received extensive attention from academic and industrial research worldwide. The first successful example of LiCoO 2 discovered by Goodenough and his co-workers in 1980 is a dominating cathode material in commercial portable electronic devices. [5] It displays medium specific capacity and high compaction density when it is employed as a cathode material in the fabrication of electrode, resulting in its high energy density. In order to improve the safety of LIBs, decrease the cost and to enhance specific capacity, researchers have been trying to find other efficient materials. Many oxide-based positive insertion materials, such as LiMn 2 O 4 , [6] LiMn 1.5 Ni 0.5 O 4 , [7] LiNi 0.8 Co 0.15 Al 0.05 O 2 [8]and LiMn 0.33 Co 0.33 Ni 0.33 O 2[9] were proposed as possible alternatives to the existing layered LiCoO 2 cathodes because of its own shortcomings, such as the toxicity and high cost of cobalt as well as its poor thermal stability. [10] Figure 1 illustrates crystal structures and discharge curves for some typical cathode materials, including layered LiCoO , spinel LiNi 0.5 Mn 1.5 O 4 and olivine LiFePO 4 , in which spinel and olivine materials show flat potential plateaus, while layered materials display sloping potential profiles. [11] Besides the transition metal oxides-based cathode materials, phospho-olivines introduced firstly by Goodenough and co-workers in 1997 as cathode materials for L...

A novel composite of sulfur immobilized into porous N-doped carbon microspheres (NCMSs-S) was synthesized. This composite cathode for lithium-sulfur batteries delivers a high specific capacity and superior rate capability and cycle stability, with a reversible capacity of ~605 mA h g(-1) at 2 C and 85% capacity retention after 500 cycles.