Sulfide electrolytes show great potential as solid electrolytes
for all-solid-state batteries due to their high ionic conductivity
and low interfacial resistance toward electrode materials. The structure
of the P–S framework in the composition of sulfides plays a
crucial role in the conductivity. Introducing LiI in the Li3PS4 structure can tailor the P–S frameworks and
thus achieve high ionic conductivities. Herein, the dopant of LiI
is optimized by high-rotation milling, followed by a sintering route
to achieve the highest Li-ion conductivity of 2.3 mS cm–1 for the Li3PS4-50% LiI electrolyte (also denoted
as Li7P2S8I) among different compositions.
The phase variations and structure evolution of the P–S frameworks
in the LiI-doped Li3PS4 electrolytes are carefully
investigated in a combination of X-ray diffraction and Raman spectra.
All-solid-state Li–S batteries using the prepared Li7P2S8I electrolyte combined with a nano Li2S cathode and a Li–In anode deliver a high initial
discharge capacity of 739.7 mA h g–1 and sustain
a discharge capacity of 517.7 mA h g–1 after 60
cycles with a capacity retention of 70.0% at 0.13 mA cm–2 at room temperature. When the operating temperature rises to 60
°C, it shows a higher discharge capacity of 862.8 mA h g–1 with fast capacity decay. However, it exhibits stable
capacities and superior cycling performance under 0 °C over 70
cycles. Electrochemical impedance spectroscopy and in situ stack-pressure
results find that the electrochemical performance differences of the
assembled battery at different operating temperatures are associated
with the interfacial resistance caused by volume changes. This work
provides the strategy to obtain highly conductive sulfide electrolytes
for SSBs and unravels the temperature effects on the electrochemical
performance of all-solid-state Li–S batteries.