Lino3

Zirconium oxynitrate hydrate (ZrO(NO₃)₂·xH₂O), In(NO₃)₃·xH₂O, and LiNO₃ (all purchased from Aldrich) were employed as dielectric, MOS, and dopant precursors, respectively, while 2-methoxyethanol (2MeEtOH, Aldrich) was utilized as a solvent. A 100-nm-thick SiO₂ layer on a highly doped p-type Si substrate was used to fabricate a coplanar bottom gate. A 0.1 M ZrO₂ precursor solution was first prepared by dissolving ZrO(NO₃)(NO₃)₂·xH₂O in 2MeEtOH with stirring at room temperature for 12 h. Next, 0.3 M MOS precursor solutions were made by dissolving In(NO₃)₃·xH₂O in 2MeEtOH with stirring at 40 °C for 4 h. Different amounts of LiNO₃ as an additive were then introduced to the In₂O₃ precursor solutions with stirring at 40 °C for 2 h; the Li fraction was varied from 0 to 30 mol% (stoichiometry in solution). All solutions were filtered through a 0.2 μm membrane-syringe filter prior to solution casting.

All the samples in the present work were prepared by conventional solid‐state reaction (SSR). Nb₂O₅ (99.99%), Ba(NO₃)₂ (≥99%), Sr(NO₃)₂ (≥99%), Co(NO₃)₂·6H₂O (≥98%), KNO₃ (≥99%), LiNO₃ (99.99%), and Fe₂O₃ (99.995%) were purchased from Aldrich Ltd. and used as starting materials. For the preparation of the SBN, SBNC30, SBNC45, and SBNC60 samples, the corresponding chemicals were mixed homogeneously in stoichiometric ratios according to the formula Sr_0.5Ba_0.5Nb_2‐xCo_xO_6‐δ (x = 0, 0.3, 0.45, 0.6). The mixed powders were first pressed into pellets under axial pressure (8 MPa) and calcinated at 700 °C for 2 h in air. After cooling down, these pellets were reground into fine powders and repressed into pellets under axial pressure (12 MPa). After sintering at 1150 °C for 12 h in air atmosphere, all the pellets were ground for 2 h before characterizations and electrochemistry tests. Sr_0.5Ba_0.5Fe_0.45Nb_1.55O₆ denoted as SBNF45 and Sr_0.4Ba_0.4Co_0.2Nb₂CoO₆ denoted as (SBC)N were also prepared under the same conditions. KNb_0.775Co_0.225O₃ (KNC), LiNb_0.925Co_0.075O₃ (LNC075), and LiNb_0.775Co_0.225O₃ (LNC225) were prepared by following the same procedure except for their relatively lower final sintering temperature (1000 °C). Commercial IrO₂ (99.9%) with a Brunauer–Emmett–Teller (BET) surface area of ≈32.5 m² g⁻¹ was also purchased from Aldrich Ltd. and tested after grinding.

The blank electrolyte was 1 M lithium bis(trifluoromethanesulfonyl) imide (LiTFSI, 99.95% trace metal basis from Sigma-Aldrich, Saint Louis, MO, USA) dissolved in 1,3-dioxolane (DOL, 99.8% from Sigma-Aldrich) and 1,2-dimethoxyethane (DME, 99.5% from Sigma-Aldrich) (1:1 volume ratio). Lithium nitrate (LiNO₃, 99.99% from Aldrich, 1 wt. %) was added to develop a stable solid-electrolyte-interphase (SEI) on the surface of the Li metal anode during cycling. The catholyte (1 M Li₂S₆) was prepared by dissolving stoichiometric amount of Li₂S (99.9% from Alfa-Aesar, Haverhill, MA, USA) and sulfur (≥99.5% from Sigma-Aldrich) in the blank electrolyte.

LiPS (Li₂S₈ based) solutions of 0.2 M were prepared by heating and stirring stoichiometric amounts of lithium sulfide (Li₂S) and sulfur (S₈) (both from Sigma-Aldrich) in DOL:DME (Sigma-Aldrich) (1:1 in volume). The catholytes were mixed at 60 °C for 12 h, along with 0.2 M lithium nitrate (LiNO₃, Sigma-Aldrich) additive and one of the following lithium salts: 1 M lithium bis(trifluromethanesulfonyl)imide (LiTFSI, 3 M), lithium trifluoromethanesulfonate (LiTf, Sigma-Aldrich), or LiBr (Sigma-Aldrich).

Lithium bis(trifluorosulfonyl)imide (LiTFSI), LiPF₆, LiBF₄, 1,2-dimethoxyethane (DME), 1,3-dioxolane (DOL), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), vinylene carbonate (VC) and fluoroethylene carbonate (FEC) were purchased from KISIDA Chemical. LiAsF₆, LiClO₄, Li₃PO₄, LiNO₃, LiBr, LiCl, LiF and lithium bis(oxalate)borate (LiBOB) were purchased from Sigma Aldrich and used after drying at 100 °C for 15 h under vacuum.

The prepared cathodes were used for the assembly of Li–S pouch cells. The cathodes were prepared with different sulfur loadings (2.0, 4.0, and 5.3 mg_s cm⁻²) and different theoretical capacities (3.3, 6.6, and 8.9 mAh cm⁻², respectively), derived from the theoretical capacity of elemental sulfur (1,672 mAh g⁻¹).
One layer of a commercial polyolefin separator, Celgard 2,500 was used. The electrolyte was based on 0.38 M LiTFSI (Sigma Aldrich) and 0.32 M LiNO₃ (Sigma Aldrich) as an additive in a 3/1 (v/v) mixture of DME and DOL (both purchased from BASF). Lithium foils with a thickness of 50, 75, 100, and 125 µm purchased from Rockwood Lithium were used as the anode.
Vacuum drying of electrodes and cell assembly was conducted in a dry room with a dew point below −50°C. Thereafter, the assembled pouch cells were cycled in a BaSyTec Cell Test System (Germany) at 25 ± 1°C controlled by air conditioning.
The electrochemical behavior of the assembled pouch cell was evaluated at different discharge C-rates (C/20, C/10, C/5, C/2.5, and 1C), considering the theoretical capacity of elemental sulfur (C = 1,672 mAh g⁻¹). The cycle life of the pouch cells was investigated within a 1.9–2.5 V cycling interval at C/10 charge-discharge current C-rate.