Triweekly Patent Update – Free Version

A solid electrolyte membrane for sulfide-based solid-state batteries incorporates a low-water-absorption cycloolefin/alkene copolymer binder to suppress H₂S gas produced by sulfide electrolyte hydrolysis in humid environments.

The first electrolyte layer comprises Li₆PS₅Cl argyrodite, an ethylene-norbornene copolymer (cycloolefin/alkene copolymer, water absorption ≈0.01%, Mw ≈37.5 kDa) as the low-absorption first binder, and nitrile butadiene rubber (NBR, water absorption 0.5%) as a co-binder (NBR : copolymer = 40 : 60). The saturated carbon backbone, free of polar functional groups, together with the ordered chain packing imposed by the ring structures retained within the backbone, restricts water ingress. A slurry of Li₆PS₅Cl, binder, and para-xylene (98 : 2 : 50 by mass) was blade-coated onto aluminium foil and dried (110°C) to a ≈60 μm membrane.

The membrane exhibits an ionic conductivity of 1.92 × 10^-3 S/cm, compared to 1.56 × 10^-3 S/cm for a membrane using NBR as the sole binder. H₂S release in a 70% relative humidity environment is 20.5 cm³/g, versus 75.8 cm³/g for the NBR-only membrane. All-solid-state cells with a LiNi_0.83Co_0.12Mn_0.05O₂ composite positive electrode, a pressed Li₆PS₅Cl second electrolyte layer, and a silicon-carbon negative electrode deliver a 200-cycle capacity retention of 91.2% (0.33C, 2.0–4.3 V), compared to 82.2% for cells with the NBR-only membrane.

Quasi-spherical silicon-carbon composite particles were developed, distinguished by planar silicon-carbon faces joined to adjacent transitional arc surfaces — a geometry intermediate between fully spherical particles (point contact only) and angular bulk particles (sharp edges). To quantify this morphology, the patent defines a polyhedron degree Q (0–1; values nearer 1 are more ideally polyhedral). The composite is produced by silane (SiH₄) chemical vapor deposition (CVD) of silicon onto porous carbon derived from phenolic resin.

Monodisperse B-stage phenolic resin microspheres (D₅₀ ≈ 11 μm) were hot-pressed (200°C, 20 MPa) and deagglomerated, the mutual compression creating planar faces bridged by transitional arc surfaces. Carbonization (900°C, 2 h, N₂) and water activation (800°C, 4 h) yielded porous carbon retaining this faceted morphology. Silicon was then deposited by CVD under 20.0 vol% SiH₄ in N₂ at 500°C for 8 h (heated at 2°C/min), followed by a carbon coating from 10.0 vol% acetylene (C₂H₂) in N₂ at 600°C for 1 h.

The polyhedron degree Q is computed per particle from the planar-face area fraction k, the number of planar faces N, and the relative standard deviation S of face areas, approaching 1 as k ≈ 0.9, N ≈ 12, and S → 0. The material exhibits a polyhedron degree Q of 0.97, a silicon content of 52.3 mass%, and a BET (Brunauer–Emmett–Teller) specific surface area of 1.5 m²/g.

In half-cells, the material exhibits a delithiation capacity of 1,804.3 mAh/g, a first-cycle efficiency of 84.70% (0.8 V cutoff), and a 1C/0.1C rate capability of 85.8%, and in LiCoO₂ full cells a capacity retention of 99% after 100 cycles (1 C, 25°C). At comparable silicon content (≈52–53 mass%) and capacity, a quasi-spherical comparative (Q ≈ 0.35, point contact only) exhibits a rate capability of 34.2% and a retention of 98.3%, and an angular polyhedral comparative with planar faces but no arc surfaces (Q ≈ 0.94, k = 1) exhibits 65.6% and 94.5%.

Figure: SEM (scanning electron microscopy) image of the quasi-spherical silicon-carbon composite (Example 1), showing micron-scale particles with broad planar faces meeting at rounded transitional arc surfaces rather than sharp edges (scale bar: 5 μm).

An aqueous solution of nickel, cobalt, and manganese nitrates (Ni : Co : Mn = 90 : 5 : 5; metal concentration 2 M) was ultrasonically sprayed (50 ml/min) into a heated quartz tube under an argon carrier gas (6 L/min), with a 1000°C particle-formation zone. Rapid evaporation at the droplet surface raises the surface metal concentration, drawing the core solution outward by osmosis to form hollow metal oxide precursor particles (average diameter 30 μm, shell thickness 3 μm) consisting of an empty core enclosed by a shell.

The hollow precursor was ball-milled to an average diameter of 3.5 μm, mixed with LiOH (Li/metal molar ratio 1.03), and sintered (850°C, 10 h) to yield single-particle LiNi_0.90Co_0.05Mn_0.05O₂.

In coin half-cells (4.3–3.0 V vs. Li⁺/Li), the material exhibits a 0.1 C discharge capacity of 218.1 mAh/g, a first-cycle coulombic efficiency of 93.7%, and a capacity retention of 89% after 100 cycles, as compared to 190.8 mAh/g, 82.9%, and 75% for a precursor with a 19 μm average diameter (below the 20 μm lower limit, formed at 700°C), and 219.5 mAh/g, 94.2%, and 68% for a precursor with a 45 μm average diameter (above the 40 μm upper limit, formed at 1200°C).

A proton conductor for solid polymer fuel cell (SPEFC) electrolyte membranes was developed combining fine fibrous cellulose (component A, fiber width ≤1,000 nm) bearing cellulose-esterified phosphate groups with a polymer compound bearing phosphooxoacid groups (component B), targeting high proton conductivity at temperatures above 100°C without humidification.

In Example 1, fine fibrous cellulose was prepared from bleached needle-leaf kraft pulp by phosphorylation with diammonium hydrogen phosphate (45 mass parts per 100 mass parts pulp), urea (120 mass parts), and water (150 mass parts), heated at 165°C for 250 seconds, followed by washing, alkaline neutralization, and wet fibrillation at 200 MPa to yield cellulose with average fiber width of 3.5 nm, degree of polymerization (DP) of 485, and phosphate group loading of 1.45 mmol/g (first dissociation acid amount by NaOH titration). The cellulose was combined with vinylphosphonic acid monomer in dimethylformamide and polymerized via RAFT at 75°C for 24 h to produce a proton conductor with component B / component A mass ratio of 50 / 50 (poly(vinylphosphonic acid) / phosphorylated fine fibrous cellulose). This was blended with polybenzimidazole (PBI) membrane-forming polymer (component C) at (A+B) / C = 50 / 50, cast at 80°C, and immersed in 85 mass% phosphoric acid solution at 80°C for 24 h to obtain a phosphoric acid-doped membrane.

Proton conductivity of phosphoric acid-doped membranes was measured under anhydrous conditions at 100–160°C by AC impedance spectroscopy. Example 3 ((A+B) / C = 10 / 90; phosphoric acid uptake 350 mass%) achieves 7.7–7.9 × 10^-2 S/cm at 140–160°C versus 2.7–2.8 × 10^-2 S/cm for comparative example 1 (PBI only, no proton conductor; phosphoric acid uptake 232 mass%) at the same temperatures. Proton conductivity retention after 24 h at 150°C reaches 84.6% for Example 3 versus 38.3% for comparative example 1. The improved retention is proposed to result from interaction between the phosphooxoacid groups on component B and the phosphoric acid dopant, suppressing acid leaching from the membrane at high temperature.