In Situ Formed Amorphous Bismuth Sulfide Cathodes with a Self‐Controlled Conversion Storage Mechanism for High Performance Hybrid Ion Batteries

Abstract Conversion‐type electrodes offer a promising multielectron transfer alternative to intercalation hosts with potentially high‐capacity release in batteries. However, the poor cycle stability severely hinders their application, especially in aqueous multivalence‐ion systems, which can fundamentally impute to anisotropic ion diffusion channel collapse in pristine crystals and irreversible bond fracture during repeated conversion. Here, an amorphous bismuth sulfide (a‐BS) formed in situ with unprecedentedly self‐controlled moderate conversion Cu2+ storage is proposed to comprehensively regulate the isotropic ion diffusion channels and highly reversible bond evolution. Operando synchrotron X‐ray diffraction and substantive verification tests reveal that the total destruction of the Bi─S bond and unsustainable deep alloying are fully restrained. The amorphous structure with robust ion diffusion channels, unique self‐controlled moderate conversion, and high electrical conductivity discharge products synergistically boosts the capacity (326.7 mAh g−1 at 1 A g−1), rate performance (194.5 mAh g−1 at 10 A g−1), and long‐lifespan stability (over 8000 cycles with a decay rate of only 0.02 ‰ per cycle). Moreover, the a‐BS Cu2+‖Zn2+ hybrid ion battery can well supply a stable energy density of 238.6 Wh kg−1 at 9760 W kg−1. The intrinsically high‐stability conversion mechanism explored on amorphous electrodes provides a new opportunity for advanced aqueous storage.


Experimental Section Materials Synthesis
Bi 2 S 3 nanosheets were prepared by a hydrothermal method.The necessary chemicals were Bi(NO 3 ) 3 •5H 2 O (99.0%), HCl, and thioacetamide (TAA), which were purchased from Sinopharm Chemical Reagent Co., Ltd.First, 1.87 g Bi(NO 3 ) 3 •5H 2 O, 0.96 ml HCl, and 1.31 g TAA were added sequentially in 250 ml of deionized water (DI) and then dissolved uniformly with a magnetic stirrer for 1 h.Subsequently, the solution was transferred to the oven and reacted for 72 h at 60 °C.After that, black viscous deposition was obtained and washed five times in turn with alcohol and DI water.The acquired Bi 2 S 3 nanosheet was dried at room temperature and then ground to powder in an agate mortar for approximately 10 minutes.

Material Characterization
The synthesized Bi 2 S 3 was characterized by a Bruker D8 Advance X-ray diffractometer using Cu-Kα radiation (λ = 1.54178Å).Raman spectral tests were performed on a spectrometer (RENISHAW inVia Basis; 532 nm).Transmission electron microscopy (TEM, JEM-2100) was performed to obtain TEM and HRTEM images of the pristine Bi 2 S 3 electrode.Ex situ X-ray photoelectron spectroscopy (XPS) spectra were obtained on a Kratos Analytical Axis UltraDLD instrument (Calibrated to reference C 1s peak (284.8 eV)).SXRD experiments were conducted on beamline BL02U2 (X-ray wavelength of 0.6887 Å after adoption of the NIST LaB 6 standard (660b)) at the Shanghai Synchrotron Radiation Facility (SSRF), and the size of the beam was confined to 0.3×0.3mm 2 .The SXRD signal is obtained through the Pilatus 2 M detector and converted into a two-dimensional SXRD signal using Fit2D software integration.Moreover, the custom-built CR2032-coin cell was designed with two 4 mm diameter transparent visual windows in the centre of each positive and negative shell, sealing them with polyimide tape.

Electrochemical Evaluation
To prepare the Bi 2 S 3 electrode, Bi 2 S 3 powder, acetylene black, and polyvinylidene fluoride (PVDF) (weight ratio of 7:2:1) were mixed in 1-methyl-2-pyrrolidinone solvent with magnet stirring to form a homogeneous slurry for 12 h and then coated on carbon paper and dried in a vacuum drying oven at 60°for 12 h to obtain a load of approximately 1.7 mg cm -2 .An electrochemical activation process was designed for the transformation of c-BS to a-BS state (the c-BS used as working electrode, copper foil as the counter/reference electrode, and 1M CuSO 4 aqueous solution as electrolyte).
The amorphous activation was conducted at a current density of 200 mA g −1 (calculation based on the mass of c-BS), and the fully amorphization of BS can be obtained after one activation cycle.A CR2025 coin battery with a Bi 2 S 3 electrode as the cathode, a high-purity Cu foil as the anode, a Whatman glass fibre membrane as the separator and aqueous 1 M CuSO 4 as the electrolyte (200 μL) was assembled.
Galvanostatic charge and discharge (GCD) measurements were tested on a battery testing system (Neware) with a voltage range of 0-0.5 V vs. Cu/Cu 2+ and 1.1-1.6V vs.
Zn/Zn 2+ .Galvanostatic intermittent titration technique (GITT) measurements were tested on a LAND CT2001A battery test system.Cyclic voltammetry measurements were performed on an electrochemical workstation (CHI 760E) at various scan rates.facilitates the amorphous transformation of c-BS (Figure S6a, b).The Cu 2+ electrochemical activation process under high current density (10 A g −1 ), where the amount of Cu 2+ interaction with BS is decreased in a non-thermodynamically stable manner, demonstrates the obviously amorphous transition tendency of BS even a small amount of Cu 2+ reaction with BS (Figure S6c).The lattice spacing of 0.324 nm is distinctly observable at D 0.49 V, which corresponds to the crystalline plane (021) of c-BS, indicating its high degree of crystallinity.In the complete discharge state (D 0.34 V), the lattice stripe has become blurred, indicating that the crystallinity is deteriorating, and the subsequent copper ion extraction processes further evolve towards amorphization.As a control, we proposed a Bi-loaded CuS composite cathode (Bi@CuS, with a molar ratio of 2:3, the same atomic ration as Bi 2 S 3 ) to explore a deep conversion process based on the presumptive discharge/charge products.If the BS involved in a deep conversion, the discharge products will be Bi and copper sulfide.The deep conversion reaction of CuS with Cu 2+ has been demonstrated in the literature [1] .
Despite the conductive Bi promotes the conversion reaction, Bi@CuS cathodes manifest a poor rate performance, low Coulomb efficiency at 1 A g −1 , and a longer activation process (1600 cycles) at 10 A g −1 .When compared with the a-BS, the capacity (Bi@CuS cathodes) rapidly degrades after activation owing to the deactivation of the cathode material induced by the deep conversion reaction.We further analyze the EIS data, and the Bi@CuS appears in a higher charge transfer resistance than the a-BS cathode.These results all demonstrate the advantages of amorphous structures and self-controlled moderate conversion in a-BS.
Electrochemical impedance spectroscopy (EIS) was carried out on an electrochemical workstation (AUTOLAB) at frequencies of 100 kHz ~ 0.01 Hz and an AC voltage of 5 mV.The a-BS Cu 2+ ‖Zn 2+ hybrid ion battery with 1 M CuSO 4 electrolyte on the a-BS side and 1 M ZnSO 4 electrolyte on the zinc foil side was separated by an anion exchange membrane (AEM) (fumasepFAB-PK-130).

Figure S1 .
Figure S1.Schematic diagram of the detailed synthetic process of c-BS.

Figure S3 .
Figure S3.SEM image and corresponding elemental mapping of c-BS.

Figure S4 .
Figure S4.EDS spectra of the as-prepared c-BS.

Figure S5
Figure S5 HRTEM image of c-BS.

Figure
Figure S6.a) The XRD of Bi 2 S 3 electrode under electrochemical activation at 200 mA g −1 using Mg 2+ carriers.b) The XRD of Bi 2 S 3 electrode under electrochemical activation at 200 mA g −1 using Zn 2+ carriers.c) The XRD of Bi 2 S 3 under electrochemical activation at 10 A g −1 using Cu 2+ carriers.Following a complete electrochemical activation, neither Mg 2+ nor Zn 2+

Figure S7 .
Figure S7.The SAED of Bi 2 S 3 electrode at various electrochemical activation states: a) D 0.49 V (vs.SHE, discharge to 0.49 V), b) D 0.34 V (discharge to 0.34 V), c) C 0.59V (charge to 0.59 V), d) C 0.84 V (charge to 0.84 V).The HRTEM of Bi 2 S 3 electrode at various electrochemical activation states: e) D 0.49 V, f) D 0.34 V, g) C 0.59 V, h) C 0.84 V.

Figure S9 .
Figure S9.Contrast in the polarization voltage in different metal-ion batteries at the same current density.

Figure S10
Figure S10The capacity of a-BS electrode with different mass loadings at 1 A g −1 (200 μL electrolyte per cell).

Figure S11 .
Figure S11.The discharge capacity of a-BS at varied electrolyte quantity from 10 to 200 μL (mass loading 1.8 mg cm -2 ).

Figure S12 .
Figure S12.EIS of c-BS‖Cu and a-BS‖Cu battery.

Figure S13 .
Figure S13.XRD pattern of electrode in different charge-discharge states.

Figure
Figure S14.a) Rate performance of the Bi@CuS cathode.b) Cycling performance of the Bi@CuS cathode at 1 A g −1 .c) Cycling performance of the Bi@CuS cathode at 10 A g −1 .e) Capacity and corresponding Coulombic Efficiency of Bi@CuS‖Cu and a-BS‖Cu battery at various current densities.f) EIS of Bi@CuS‖Cu and a-BS‖Cu battery.

Figure S15 .
Figure S15.Ex situ XPS spectrum of Cu 2p of a-BS cathodes at the various discharging-charging states.

Figure
Figure S16.a) HRTEM image of a-BS cathodes at the fully discharged state after 50 cycles (200 mA g −1 ).b) EDS of a-BS cathodes at the fully discharged state after 50 cycles (200 mA g −1 ).

Figure S17 .
Figure S17.HRTEM image of a-BS cathodes at full charging state.

Figure S18 .
Figure S18.SAED image of a-BS cathodes at full charging state.

Figure
Figure S19.a) Schematic of the a-BS Cu 2+ ‖Zn 2+ hybrid ions battery.b) Photograph of the a-BS Cu 2+ ‖Zn 2+ hybrid ions battery.

Table S1 .
Comparsion of this work with reported Bi 2 S 3 -based secondary ion batteries Bi 2 S 3 /Bi 2 Se 3 vdW