A Separator with Double Coatings of Li4Ti5O12 and Conductive Carbon for Li‐S Battery of Good Electrochemical Performance

Abstract The market demand for energy pushes researchers to pay a lot of attention to Li‐S batteries. However, the ‘shuttle effect’, the corrosion of lithium anodes, and the formation of lithium dendrites make the poor cycling performances (especially under high current densities and high sulfur loading) of Li‐S batteries, which limit their commercial applications. Here, a separator is prepared and modified with Super P and LTO (abbreviation SPLTOPD) through a simple coating method. The LTO can improve the transport ability of Li+ cations, and the Super P can reduce the charge transfer resistance. The prepared SPLTOPD can effectively barrier the pass‐through of polysulfides, catalyze the reactions of polysulfides into S2−, and increase the ionic conductivity of the Li‐S batteries. The SPLTOPD can also prevent the aggregation of insulating sulfur species on the surface of the cathode. The assembled Li‐S batteries with the SPLTOPD can cycle 870 cycles at 5 C with the capacity attenuation of 0.066% per cycle. When the sulfur loading is up to 7.6 mg cm−2, the specific discharge capacity at 0.2 C can reach 839 mAh g−1, and the surface of lithium anode after 100 cycles does not show the existence lithium dendrites or a corrosion layer. This work provides an effective way for the preparation of commercial separators for Li‐S batteries.

same way for comparison. All prepared pieces were cut into 15 mm round pieces before use.

Preparation of Li 2 S 8 electrolyte
The preparation of Li 2 S 8 electrolyte was similar to that reported previously. [2] A blank electrolyte was prepared by dissolving 1 M LITFSI in DOL and DME (volume ratio was 1:1).
According to the following reaction equation (2): The sublimated sulfur (448 mg) and Li 2 S (92 mg) were placed in the prepared blank electrolyte (10 mL) and stirred overnight at 50 ℃ to obtain the Li 2 S 8 electrolyte (0.2 M).
The above polysulfides electrolytes were only used in some specific tests (catalytic performance tests, and Li 2 S nucleation and dissolution tests), and the commercial electrolytes (LS-009) were used in other electrochemical tests.

Li 2 S nucleation and dissolution test
According to our previous report, [2] the carbon papers were cut into small discs as fluid collectors, and the modified material was evenly coated on the carbon papers, S-4 the area load on the discs was about 3.0 mg cm -2 , and the cathodes were obtained after drying. The separator was DKJ-14, and the anode was a lithium foil, the Li 2 S 8 electrolyte (25 μL) and corresponding blank electrolyte (25 μL) were added on both sides of the separator respectively, and the cell was obtained by pressing them into the CR 2032 battery shell in the glove box filled with argon.
The Li 2 S nucleation test was completed by discharging the above cell with a current of 0.134 mA to 2.09 V and keeping the voltage at 2.08 V.
The Li 2 S dissolution test was completed by discharging the above cell at a current of 0.134 mA to 1.8 V, then converting Li 2 S into soluble lithium polysulfides (LiPSs) at 2.4 V. [3] Calculation According to equation (3), the ionic conductivity of different separators at different temperatures can be calculated from the EIS.
The symbols in the equation are ionic conductivity (σ), the thickness of separators (L), bulk resistance (R b ), and the contact area between the stainless steel sheet and the separator (A).
The activation energy of different separators can be calculated according to the Arrhenius equation (4).
The symbols in the equation are the pre-exponential factor (A), activation energy S-5 (E a ), and the perfect gas constant (R).
The Li + transference number is calculated by equation (5).
In the equation, I 0 and I P are the initial current and steady-state current in the current curve respectively, V 1 is the transition potential (10 mV), R 0 and R S are the AC impedance of the cell before and after polarization, respectively.