Supporting Information

Curbing polysulfide shuttling by synergistic engineering layer composed of supported Sn4P3 nanodots

electrocatalyst in lithium-sulfur batteries

Zhengqing Yea, Ying Jianga, Tao Fenga, Ziheng Wanga, Li Lia,b, Feng Wua,b, and Renjie Chena,b,*

aBeijing Key Laboratory of Environmental Science and Engineering, School of Material Science and

Engineering, Beijing Institute of Technology, Beijing 100081, China.

bCollaborative Innovation Center of Electric Vehicles in Beijing, Beijing 100081, China.

E-mail: chenrj@bit.edu.cn

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Experimental Method

Preparation of AS PC

Natural acorn shells were rinsed with distilled water several times to remove some contaminants and

dried in a vacuum oven at 80 °C for 24 h. The dried acorn shells were carbonized at 1000 °C for 2 h with

a ramp rate of 5 °C min-1 under pure Ar (99.999%) flow. The obtained acorn shell derived carbon (AS

C) was mixed with 6 M potassium hydroxide (KOH) aqueous solution at a weight ratio of 1:5. After

drying at 120 °C, the products were activated 800 °C for 2 h with a heating rate of 5 °C min -1 at

continuous Ar atmosphere. The AS PC was rinsed through 0.5 M HCl and deionized water until it was

neutral, then kept in oven at 80 °C for 12 h.

Synthesis of AS PC-Sn4P3

200 mg AS PC was dispersed in 10 mL ethanol and water (1:1 in volume) by sonication for 20 min.

Subsequently, 300 mg SnCl4⋅5H2O was added into above solution and magnetic stirring for 30 min.

Then the mixture was sealed and heated at 80 °C in an oven for 12 h. After that, the solution was dried

in a vacuum oven at 60 °C for 24 h. The precipitate was further annealed in a tube furnace at 400 °C

with a heating/cooling rate of 5 °C min-1, and maintained for 2 h under Ar to yield AS PC-SnO2. The AS

PC-SnO2 (50 mg) and 1 g of sodium hypophosphite (NaH2PO2) were uniformly mixed and put in an

alumina crucible. Then, the alumina crucible was placed into a tube furnace and heated to 300 °C for 2

h at a ramp rate of 1 °C min−1 in Ar atmosphere. The reaction products were washed using 0.5 M HCl

solution and deionized water via centrifugation to yield AS PC-Sn4P3. G- Sn4P3 was prepared by the

same procedure, except G was used as the substrate material instead of AS PC.

Fabrication of functional separators

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Typically, the obtained AS PC, AS PC-Sn4P3, or G-Sn4P3, conductive acetylene black (AB) and

poly(vinylidenefluoride) binder (7:2:1 by mass) were dispersed in N-methyl-2-pyrrolidone (NMP) to

prepare a homogeneous slurry. The slurry was further coated onto a separator (Celgard 2325) and then

dried at 45 °C under vacuum for 12 h. The functional separator was punched into a disk before using.

Bare celgard separator was prepared in the same conditions.

Adsorption tests of polysulfides

The Li2S4, Li2S6, and Li2S8 with a concentration of 5 mmol L-1 were prepared by mixing S powders and

Li2S at molar ratio of 3:1, 5:1, and 7:1 in 1,2-dimethoxyethane (DME) solution under magnetic stirring

for 48 h at 50 °C. 10 mg of AS PC and AS PC-Sn4P3 was introduced into the Li2S4, Li2S6, and Li2S8

solution (2 mL), respectively, followed by magnetic stirring for 2 h and aging for 6 h or 12 h.

Fabrication of Li2S6 symmetric cells and measurements

Functional materials (AS PC or AS PC-Sn4P3) and PVDF binder with a weight ratio of 9:1 were

uniformly mixed into the NMP and then coated onto the aluminum foil. After dried at 60 °C for 12 h

and punched into disks with a diameter of 11.0 mm, the areal loading of the obtained electrode was

about 1 mg cm−2. Then, the identical working and counter electrodes of AS PC, AS PC-Sn 4P3 with a

Celgard 2325 separator, and 40 μL electrolyte containing 0.5 M Li2S6 and 1 M LiTFSI in a mixed

solvent dimethoxyethane (DME) and 1,3-dioxolane (DOL) (v/v=1:1) were fabricated into the

symmetric cells. EIS and CV tests were carried out with a CHI660E electrochemical working station

(CHI Instruments, Inc). EIS measurement was carried out with an amplitude of 5 mV in the frequency

range of 105 Hz to 0.01 Hz. The CV curves were recorded at a scan rate of 10 mV s -1 with in the voltage

range of -1 V to 1 V.

Exchange current measurement

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The linear sweep voltammetry (LSV) technique was performed on the CHI 604D electrochemical

workstation using CR2025-type coin cells. The preparation of AS PC or AS PC-Sn4P3 electrode was

identical to that of the symmetric cells. A Li2S6 (0.2 M) solution with LiTFSI (1 M) in DME and DOL

(v/v=1:1) (40 μL) was used as the electrolyte. LSV curves were recorded at 0.2 mV s-1 with the voltage

window limited to ±100 mV from open-circuit potential. The Tafel curves composed of LSV were fitted

to calculate the exchange current density the cell with different electrodes according to the Bulter-

Volmer equation.

Nucleation of Li2S test

A 0.2 M Li2S6/DME and DOL (v/v=1:1) solution with 1.0 M LiTFSI was used as the catholyte. The

aforementioned AS PC-Sn4P3 and AS PC were used as work electrode and lithium metal as the counter

electrode. A 20 μL amount of Li2S6 catholyte was dropped onto the side of AS PC-Sn4P3 or AS PC

working electrode, while 20 μL without Li2S6 were added to the counter electrode side. The assembled

cells were discharged galvanostatically at 112 µA to 2.10 V and then discharged potentiostatically at

2.05 V to make Li2S nucleation/growth.

Assembly of Lithium–Sulfur batteries and their electrochemical measurements

Carbon/sulfur cathode was prepared via mixing sublimed sulfur and MWCNT with a weight ratio of

7:3. Subsequently, the uniformly mixed powder was heated at 155 °C for 12 h in Ar-filled autoclave.

The obtained MWCNT/S composite with a sulfur content of 70% (MWCNT/S70), AB, and

poly(vinylidenefluoride) binder in a weight ratio of 8:1:1 were mixed in NMP to form a homogeneous

slurry. The slurry was coated onto aluminum foil, followed by drying at 60 °C for 12 h in a vacuum

oven and punched into discs with a diameter of 11 mm. The areal sulfur loading is about 1-1.2 mg cm−2.

To explore the potential of AC-Sn4P3 for practical applications, the MWCNT/S70 or MWCNT/S80 (90

wt%) and poly(vinylidenefluoride) binder (10 wt%) were used to prepare Li-S cathode by the similar

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processes. The sulfur cathodes with high sulfur loading is around 5.1 and 7.1 mg cm−2, respectively.

After that, standard coin cell (CR2025) with MWCNT/S cathode, Li anode, and functional separator

was assembled in Ar-filled glove box with oxygen and water contents below 0.1 ppm. The electrolyte

was consisted of 1.0 mol L−1 of bis(triuoromethane) sulfonimide lithium (LiTFSI) and 0.2 mol L−1

lithium nitrate (LiNO3) dissolved in DOL/DME (v/v = 1/1). The electrolyte/sulfur ratios are around 40

uL mg−1 for the cathodes with 1-1.2 mg cm−2 sulfur loading. The cells were discharged and charged at

various current densities on an LAND CT2001A electrochemical station. The cells were activated at a

0.05 C rate with 3 cycles for cycling stability of high rate. The specific capacity was determined by the

mass of sulfur in the active material. EIS measurements were recorded in the frequency range between

10 mHz and 105 Hz under a AC amplitude of 5 mV.

Characterization

XRD was carried out with a Rigaku X-ray power diffractometer (Ultima IV-185, Japan) at 40.0 kV and

40.0 mA with Cu Kα radiation. FESEM (HITACHI S-4800, Japan) and HR-TEM (JEOL, JEM–1200

EX, Japan). were used to acquire SEM and HR-TEM images. The specific surface area and pore size

distribution of all samples were recorded by Brunauer−Emmett−Teller (BET) and Density Functional

Theory (DFT) models at -196°C on an adsorption instrument (Micromeritics, ASAP 2460). Raman

spectra measurement was performed on a spectrometer (Renishaw inVia, UK) with 532 nm laser

excitation. XPS (Thermo escalab 250XI, USA) were determined by a monochromatized Al Kα X-ray

source (hv = 1486.6 eV). TGA was conducted on a thermal analyzer (NETZSCH STA 449 F3,

Germany) with a heating rate of 10 °C min−1. All the chemicals and samples were weighted by a

METTLER TOLEDO XS105DU balance.

DFT Calculations

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Density functional theory (DFT) calculations was employed with the CASTEP of Material Studio

software. PerdewBurke-Ernzerhof (PBE) of generalized-gradient approximation (GGA) functions and

ultrasoft pseudopotentials were used to describe exchange-correlation energy and the electron-ion

interaction. Self-consistent field calculations (SCF) were performed until the SCF tolerance was below

1×10-6. In geometry optimizations, the energy and maximum force convergence criteria were set to be

10−5 eV per atom and 0.03 eV/Å. The energy cut-off was set to 400 eV, whereas a 4×4×1 k-point mesh

is used. Adsorption energy Eads of typical polysulfides (Li2S2, Li2S4, Li2S6, and Li2S8) with (015) and

(107) crystal planes of Sn4P3 is formulated from Eads = Eps+sub - Eps – Esub, where Eps+sub, Eps, and Esub are

the energy of the polysulfides-Sn4P3, polysulfides, and Sn4P3, respectively. According to this definition,

the much lower (more negative) Eads represents stronger interactions.

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Fig. S1 (a,b) Acorn forest in the mountain, photographed near the Qinglong Gorge of Beijing, China.

(c) Optical image of the acorn shells. (d) Optical images of AS C synthesis process.

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.

Fig. S2 The particle size distribution of Sn4P3 in the AS PC.

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Fig. S3 SEM images of SnO2.

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Fig. S4 SEM images of AS PC-SnO2 particles.

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Fig. S5 HR-TEM image of the AS PC-Sn4P3 composite.

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Fig. S6 (a) SEM and (b)HAADF-STEM image of the AS PC-Sn4P3 and corresponding EDS elemental maps.

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Fig. S7 TGA curve of the AS PC-Sn4P3 composite in air.

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Fig. S8 XRD pattern of AC-SnO2.

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Fig. S9 N2 absorption-desorption isotherm curves of AS C, AS PC, and AS PC-Sn4P3.

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Fig. S10 Results of (a) Li2S4, (b) Li2S6, and (c) Li2S8 adsorption experiments with AS C, AS PC and AS

PC-Sn4P3.

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Fig. S11 EIS of symmetric cells of AS PC and AS PC-Sn4P3 electrodes (Inset in (i): the full view of

EIS).

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Fig. S12 TGA curve of the MWCNT/S material.

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Fig. S13 SEM image of the MWCNT/S70 material.

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Fig. S14 The contact angles of different modified separators after immersion in the electrolyte.

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Fig. S15 CV profiles of AS PC-Sn4P3 configuration at a sweep rate of 0.1 mV s-1.

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Fig. S16 Galvanostatic discharge/charge profiles of (a) celgard, (b) AS PC, and (c) AS PC-Sn4P3

celgard at different current rates.

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Fig. S17. Electrochemical performance of AS PC-Sn4P3 electrode was measured

within the operating potential range of 1.7 to 2.8 V at the current density of 167.5

mA g-1 (equivalent to 0.1 C for sulfur).

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Fig. S18 The capacity decay rate of Li–S batteries with different confgurations at a current rate of 0.2 C.

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Fig. S19 Discharge/charge profiles of Li–S batteries with (a) celgard, (b) AS PC, and (c) AS PC-Sn4P3

configurations at a current rate of 1 C.

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Fig S20 (a) SEM image and (b) XRD pattern of G-SnO2.

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Fig. S21 (a) SEM image and (b) XRD pattern of G-Sn4P3.

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Fig. S22 (a) SEM image of G-Sn4P3 coating separator surface.

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Fig. S23 Long cycle life at 1 C of the Li–S batteries with AS PC-Sn4P3 and G-Sn4P3 configurations.

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Fig. S24 Long cycle life at 2 C of the Li–S batteries with AS PC-Sn4P3 and G-Sn4P3 configurations.

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Fig. S25 Cycling capabilities of AS PC-Sn4P3 layer at 0.1 C after 0.01 C activation process.

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Fig. S26 Relationship between Z´ and ω-1/2 in the middle -frequency region (a-c) before cycling and (d-

f) after 200 cycles.

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Fig. S27 SEM image of Li metal anode after cycling with (a) celgard and (b) AS PC-Sn4P3

configurations.

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Fig. S28 The adsorption energy (Eads) of Li2S2, Li2S4, Li2S6, and Li2S8 on the (001) surface of graphene,

respectively.

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Table S1 Pore volume and surface area of AS C, AS PC, and AS PC-Sn4P3.

Sample SBET (m2 g-1)

[a]

Smi (m2 g-1)[b] Micropore volume Total pore volume (cm3 g-1)[c]

AS C 41 38 0.015 0.015

AS PC 729 487 0.24 0.49

AS PC-Sn4P3 288 199 0.1 0.18

[a] SBET surface area were calculated from Brunauer-Emmett-Teller (BET) model. [b] Smi, the data of

surface area and micropore volume were obtained by t-plot method. [d] Total pore volume, measured at

P/P0 =0.99.

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Table S2 The comparisons of electrochemical performance of present work with the reported novel

functional interlayers for Li-S batteries.

Separator materials

Mass loading

oflayer(mg

cm−2)

S content (wt.

%)

Rate (C)

Reversible capacity

(mAh g-1)/Cycle number

Decay rate

(%per cycle)

Rate properties

(mAh g-1/C)

acidized CNT[S1]

- 70 1 454/400 0.1 660/2

Co9S8 hollow nanowall arrays[S2]

0.16 70 1 530/1000 0.039 428/2

N-Doped Graphene[S3] 0.1 76.5 1 -/250 0.15 987/2

Mesoporous TiN

microspheres[S4]

(a thickness

of 10 mm)

70 1 560/400 0.091 672/3

V2O5

Nanowire/Graphene

[S5]

0.642 70 1 300/1000 0.061 648/3

CoP nanospher

e[S6]

0.2 70 1 550/500 0.078 725/5

VS4/Graphene[S7]

- 74.5 0.5 -500 0.06 800/2

Graphene Aerogel-Carbon

Nanofibers-Ni[S8]

0.4-0.6

- 1.25 620/500 0.056 620/2.5

carbon nanofiber/CoS

/Ketjen black[S9]

0.36 70 1 -/760 0.076 464/2

N,S-doped carbon[S10]

(a thickness

of 42 mm)

- 0.5 609/300 0.06 515/1

AS PC-Sn4P3

(This work) 0.17 70 1 461.5/900 0.046 667.8/3

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