•Li2S-rich composite Li2S–FePS3 was prepared by the combination process of thermal heating and mechanical milling.•The Li2S–FePS3 composite consisted of mainly Fe- and P-containing low-crystalline Li2S.•The Li2S–FePS3 composite cells showed relatively high discharge capacity without any pre-cycling treatments.•The improved performance was attributed mainly to the formation of some PS4-like component.For an attempt to incorporate phosphorous ions into the Fe-containing Li2S, we have prepared Li2S–FePS3 composite positive electrode materials using the combination process of the thermal heating and the mechanical milling. The XRD results showed that the Li2S–FePS3 composite samples consisted of low-crystalline Li2S and small amounts of FeP as impurity. The electrochemical tests demonstrated that the Li2S-rich composite sample cells (Li2S:FePS3 = 4:1 mol) showed relatively high initial discharge capacity (ca. 780 mAh·g− 1) without any pre-cycling treatments. This makes a clear contrast to the Fe-containing Li2S (Li2S–FeSx composite) sample cells, which showed the initial discharge capacity of ca. 330 mAh·g− 1 and it was enlarged to ca. 730 mAh·g− 1 after the stepwise pre-cycling treatment. Ex-situ XRD and XAFS measurements showed the reversible changes of the peaks ascribed to Li2S and the local structures around S atoms during cycling. The incorporation of phosphorous ions into the Fe-containing Li2S was effective for improving the structural reversibility against Li extraction/insertion reactions, resulting in the improved electrochemical performance of the cells.

•Cross section of electrode layer of all-solid-state batteries was observed.•Homogeneous electrode layer was designed by using smaller-sized electrolyte particles.•Well-dispersed solid electrolyte suppressed the cracks of LiNi1/3Co1/3Mn1/3O2.•Capacity at high-rate operation is improved by designing homogeneous electrode.The effect of the particle sizes of LiNi1/3Co1/3Mn1/3O2 and Li2S–P2S5 solid electrolytes (SEs) on the electrode morphology was investigated. Smaller-sized SE particles were advantageous in fabricating dense and homogeneous electrode layers with an effective lithium-ion conduction pathway and a large electrode–electrolyte interfacial contact area because of the unique mechanical properties of sulfide-based SEs. The homogeneous distribution of the SE is also effective in the suppression of cracking and fracturing of LiNi1/3Co1/3Mn1/3O2 because of the favorable mechanical properties of the sulfide-based SEs. The capacity of the all-solid-state cells under high-rate operation was thus remarkably improved.

•Composite electrodes “a-TiSx/TiS2” were designed for all-solid-state batteries.•Conductivity of a-TiSx/TiS2 was higher than that of the a-TiS4.•Capacity of a-TiSx/TiS2 was higher than that of a-TiS4.Composite electrodes composed of amorphous titanium polysulfide (a-TiSx) and titanium disulfide (TiS2) were designed for application in all-solid-state batteries. The conductivity of the a-TiSx/TiS2-based working electrode was higher than that of the amorphous TiS4 (a-TiS4); the reversible capacity of the cell using a-TiSx/TiS2 electrode was higher than that of the cell using a-TiS4. Designing nanocomposite materials such as the a-TiSx/TiS2 described in this paper is an effective way to improve the performance of all-solid-state batteries.

•Graphite–solid electrolyte composite anode was prepared by spark-plasma-sintering.•The graphite–SE/Li2S cells showed higher energy density than In/Li2S cells.•The graphite–SE sample cells showed an improved rate capability.•The improved performance was attributed mainly to the reduced interfacial resistance.Graphite–solid electrolyte (SE) composite anode, prepared by spark-plasma-sintering (SPS) process, was applied to all-solid-state lithium secondary batteries with lithium sulfide (Li2S) positive electrode. The electrochemical tests demonstrated that the graphite–SE/Li2S cells showed the discharge capacity of ca. 750 mAh·g− 1-Li2S with the average voltage of ca. 1.98 V. Although the discharge capacity was lower than that of the In/Li2S cells (ca. 920 mAh·g− 1-Li2S), the estimated energy density was higher than that (ca. 1490 and 1220 mWh·g− 1-Li2S for graphite–SE/Li2S and In/Li2S cells, respectively), due mainly to its higher average voltage. The graphite–SE/Li2S cells showed improved rate capability as compared with the cells with the graphite + SE blended powder, which was attributable mainly to the reduced interfacial resistance between the graphite and SE particles caused by the SPS process.

Electrochemically active lithium sulfide–carbon (Li2S–C) composite positive electrodes, applicable for rechargeable lithium-ion batteries, were prepared using spark-plasma-sintering (SPS) process. The electrochemical tests demonstrated that the SPS-treated Li2S–C composites showed the initial charge and discharge capacities of ca. 1200 and 200 mAh g−1, respectively, though Li2S has been reported to show no significant charge capacities when conventionally mixed with carbon powder. Such activation of Li2S was attributed principally to strong bindings between Li2S and carbon powders, formed by the SPS treatment. The ex situ XRD measurements showed that some amounts of Li2S were still remained unchanged and any elemental sulfur was not detected even at fully charged state, which was similar to Li/S cells.