Anode and electrolyte materials

Anode and electrolyte materials on one page: hard carbon pyrolysed from biomass or resin and how it stores sodium, silicon nanoparticles held in yolk–shell and pomegranate carbon, a LiPF₆ carbonate electrolyte made in a glovebox, the HF that trace water makes from it, and the argyrodite solid electrolyte Li₆PS₅Cl. Every step and number is quoted from the cited papers.

1. Making hard carbon: Hard carbon, so far the only commercially viable sodium-ion anode, is made by pyrolysing organic precursors, usually at 1000–1500 °C; in one reviewed example olive shells were pre-carbonised at 300 °C, then treated at high temperature under argon (Geng 2026). Industrially feasible precursors include resins, biomass and needle coke (Yang 2026). 2. Where the sodium goes: Randomly oriented, curved graphitic domains ("house of cards") with a (002) spacing over 0.37 nm, against 0.335 nm in graphite, and many nanopores and defects. In the widely accepted three-stage model Na is adsorbed on surfaces and defects in the high-potential sloping region, fills closed nanopores as quasi-metallic sodium in the low-voltage plateau, and deposits on the surface at ultra-low potential, with a risk of dendrites (Geng 2026). Closed-pore engineering targets the low initial Coulombic efficiency and the limited plateau capacity (Wu 2026). 3. Silicon held in carbon: Silicon has ten times the theoretical capacity of carbon anodes, but its volume change (~300%) degrades its structure and destabilises the SEI (Liu 2014). Yolk–shell: commercial Si nanoparticles sealed in thin carbon shells with designed void space, made mostly at room temperature; ~2800 mAh/g at C/10, 74% retention after 1000 cycles, Coulombic efficiency 99.84% (Liu 2012). Pomegranate: clusters of such particles sealed in micrometre-size carbon pouches: 97% retention after 1,000 cycles and 1,270 mAh/cm³ (Liu 2014). 4. LiPF₆ in carbonates: 1 M LiPF₆ in ethylene carbonate/dimethyl carbonate (50/50, v/v), cells assembled in an argon-filled glovebox (Mou 2022); or 1 M LiPF₆ in EC : DEC (1 : 1) in a glovebox with < 0.1 ppm water and oxygen (Ahangari 2024). VC and FEC stabilise the SEI, improving its structure, density and mechanical strength (Zhang 2020), and are considered the most effective additives for Si-containing anodes (Stehle 2023). 5. Trace water makes HF: Trace water, inevitably introduced in manufacturing, hydrolyses LiPF₆ to HF, which degrades the SEI and corrodes electrode materials (Peng 2026); PF₅ and HF from the decomposition and hydrolysis of LiPF₆ attack both the SEI on the anode and the CEI on the cathode (Han 2020). 6. A sulfide solid electrolyte: Li₂S, P₂S₅ and LiCl sealed in a WC-coated jar under argon (H₂O, O₂ < 0.3 ppm), mixed at 110 rpm for 1 h instead of high-energy milling, and annealed for 10 h in sealed quartz tubes: pure cubic Li₆PS₅Cl at 500–550 °C, best at 550 °C with 4.96 mS/cm at 26.2 °C (Yu 2018). With moisture, argyrodites give off toxic H₂S and lose their high conductivity (Lee 2025). Garnet LLZO is the oxide alternative: hot-pressed Ga-LLZO reached 2.8 mS/cm in the bulk (Vema 2023).

Starting materials: Biomass or resin precursors; Si nanoparticles and a carbon source; LiPF₆ in ethylene carbonate with dimethyl or diethyl carbonate; Li₂S, P₂S₅ and LiCl. Product: Hard carbon, yolk–shell and pomegranate Si–C anodes, a 1 M LiPF₆ carbonate electrolyte and argyrodite Li₆PS₅Cl.

Geng et al., “Beyond Isolated Optimization: A Holistic Review Across the Pre-Mid Post-Treatment Chain for Hard Carbon in Sodium-Ion Battery”, Nano-Micro Lett. 2026 (doi:10.1007/s40820-026-02248-y); Wu et al., “Unlocking High-Energy Sodium-Ion Batteries via Chemically Engineered Closed Pores in Hard Carbon”, Small 2026 (doi:10.1002/smll.76093); Yang et al., “Hard Carbon Anodes for Sodium-Ion Batteries: Industrial Precursors, Structural Regulation, and Future Prospects”, Small 2026 (doi:10.1002/smll.74334); Liu et al., “A yolk-shell design for stabilized and scalable Li-ion battery alloy anodes”, Nano Lett. 2012 (doi:10.1021/nl3014814); Liu et al., “A pomegranate-inspired nanoscale design for large-volume-change lithium battery anodes”, Nat. Nanotechnol. 2014 (doi:10.1038/nnano.2014.6); Mou et al., “Scalable Advanced Li(Ni₀.₈Co₀.₁Mn₀.₁)O₂ Cathode Materials from a Slug Flow Continuous Process”, ACS Omega 2022 (doi:10.1021/acsomega.2c05521); Ahangari et al., “Advancing Lithium-Ion Batteries’ Electrochemical Performance: Ultrathin Alumina Coating on Li(Ni₀.₈Co₀.₁Mn₀.₁)O₂ Cathode Materials”, Micromachines 2024 (doi:10.3390/mi15070894); Zhang et al., “Operando Electrochemical Atomic Force Microscopy of Solid-Electrolyte Interphase Formation on Graphite Anodes: The Evolution of SEI Morphology and Mechanical Properties”, ACS Appl. Mater. Interfaces 2020 (doi:10.1021/acsami.0c11190); Stehle et al., “The Optimal Amount of Lithium Difluorophosphate as an Additive for Si-Dominant Anodes in an Application-Oriented Setup”, ChemSusChem 2023 (doi:10.1002/cssc.202301153); Peng et al., “Water-Scavenging Suspended Mediator in Electrolytes for Silicon-Based Lithium-Ion Batteries with High-Nickel Cathode”, Molecules 2026 (doi:10.3390/molecules31050863); Han et al., “Dual-Functional Electrolyte Additives toward Long-Cycling Lithium-Ion Batteries: Ecofriendly Designed Carbonate Derivatives”, ACS Appl. Mater. Interfaces 2020 (doi:10.1021/acsami.0c04372); Yu et al., “Facile Synthesis toward the Optimal Structure-Conductivity Characteristics of the Argyrodite Li₆PS₅Cl Solid-State Electrolyte”, ACS Appl. Mater. Interfaces 2018 (doi:10.1021/acsami.8b07476); Lee et al., “Fluoride-rich Sulfide Solid Electrolyte With Ultrahigh Air Stability for All-Solid-State Batteries”, Small 2025 (doi:10.1002/smll.202411349); Vema et al., “Clarifying the Dopant Local Structure and Effect on Ionic Conductivity in Garnet Solid-State Electrolytes for Lithium-Ion Batteries”, Chem. Mater. 2023 (doi:10.1021/acs.chemmater.3c01831); Lyu, He & Liu, “PEO-LITFSI-SiO₂-SN System Promotes the Application of Polymer Electrolytes in All-Solid-State Lithium-ion Batteries”, ChemistryOpen 2020 (doi:10.1002/open.202000107).

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