Triweekly Patent Update – Free Version

Sulfide solid electrolyte particles in solid-state cathodes conduct only through point contacts, which the applicant links to typical 20–30 mass% loadings. The claimed cathode layer adds cellulose fibers along which the sulfide particles line up in a bead-on-string arrangement, with the fibers also contacting the active material. The method claims require negatively charged cellulose in the premix, cited as the basis for this alignment.

Sulfonated ethyl cellulose (8 μm diameter, 1 mm length) and Li₆PS₅Cl (LPSC, 4 μm) were homogenized in butyl butyrate (40 MPa, 1 h) and spray-dried, then mixed with NCM811, VGCF and PVDF and coated onto aluminum foil (80 μm), giving 0.5 mass% cellulose and 14.5 mass% LPSC in the layer. Cells used a 50 μm LPSC separator and a 25 μm lithium foil negative electrode, with no operating stack pressure stated.

The cathode exhibits an ionic conductivity of 4.3 × 10^-4 S/cm (EIS), compared to 2.5 × 10^-4 S/cm with unsulfonated ethyl cellulose, 3.4 × 10^-4 S/cm without cellulose, and 3.0 × 10^-4 S/cm for an undried cellulose–LPSC premix. Full cells deliver 179 mAh/g initial discharge capacity, 85.3% initial coulombic efficiency and 88.9% retention after 200 cycles (0.1 C, 2.5–4.25 V, 25°C), against 170 mAh/g, 82.2% and 85.1% without cellulose. Substituting 2.8 μm LPSC raises capacity to 181 mAh/g at 87.3% efficiency.

A: sulfide solid electrolyte particles (Li₆PS₅Cl or Li₃PS₄)
B: sulfonated cellulose fiber (ethyl, methyl or cyano cellulose)
C: positive electrode active material (NCM811)

Figure: Cathode layer in which sulfide solid electrolyte particles (A) line up along sulfonated cellulose fibers (B) in a bead-on-string arrangement, with the fibers also contacting the positive electrode active material (C).

A porous carbon scaffold (BET specific surface area: 2,050 m²/g, pore volume: 1.03 cm³/g) was prepared by carbonizing phenolic resin (10 μm) at 600°C for 1 h and activating it with CO₂ at 850°C and 500 kPa gauge pressure for 3 h. Dried only partially at 100°C under nitrogen, it retains COOH, OH and C_xH_y groups that release CO and CO₂.

Monosilane (SiH₄) was fed continuously at 370°C and 25–190 kPa gauge pressure with an equal hydrogen flow, depositing silicon oxide with dangling bonds inside the pores, presumably via gas-phase decomposition through silylene. Nitrogen-diluted oxygen was admitted under reduced pressure at ≤50°C, forming low-valent surface oxides (total oxygen: 1 mass%).

Acetylene was decomposed at 600°C and 8 kPa for 12 h, forming a carbon film and Si–C bonds, partly as dimethylsiloxane, concentrated in the surface layer (≤50 nm). The silicon is essentially amorphous (Scherrer grain size: 0.8 nm), and the ²⁹Si MAS NMR peak ratio A/B of Si–C to amorphous Si is 0.46.

In half-cells against lithium metal, electrodes contained 9.3 mass% active material and 83.7 mass% graphite. With the graphite contribution calculated out, the active material exhibits a reversible capacity of 2,160 mAh/g (1.0 V cutoff), and the blended electrode a first-cycle efficiency of 90%. Full cells exhibit capacity retentions of 85% after 1,000 cycles (0.7 C charge / 0.5 C discharge) and 85% after 500 cycles at 4 C charge, as compared to 2,120 mAh/g / 87% / 70% / 57% for the same scaffold with acetylene pre-infiltrated at 30 kPa, extending Si–C formation into the bulk.

Li₂CO₃, MnO₂, Mn₂O₃, and TiO₂ were mixed in stoichiometric ratios, ball-milled with zirconia balls (350 rpm, 12 × 1 h, Ar), and heat-treated under Ar (5°C/min, 600°C for 3 h, then 900°C for 12 h).

The resulting Li-excess oxyfluoride Li_1.5(Mn²⁺)_0.284(Mn³⁺)_0.448(Ti⁴⁺)_0.264O₂F_0.468 is a lithium manganese titanium oxide with cation-disordered rock-salt (DRX) structure, containing only Mn²⁺, Mn³⁺, and Ti⁴⁺ as transition-metal ions (nominally 28.51, 44.98, and 26.51 mol% of total transition metals).

In half-cells (0.1 C, 1.5–4.8 V vs. Li⁺/Li, 25°C), the material exhibits a first-cycle discharge capacity of 260 mAh/g, as compared to 239 mAh/g for Mn²⁺-rich comparative material without Li excess (72–74 mol% Mn²⁺, Li/transition-metal ratio ≈0.7) and 247 mAh/g for comparative material with a similar Mn²⁺/Mn³⁺ balance but added Nb⁵⁺ (11.11 mol%). At 45°C (0.1 C, 2.0–4.65 V vs. Li⁺/Li), a Mn³⁺-richer variant (17.36 mol% Mn²⁺, 59.67 mol% Mn³⁺) reaches 257 mAh/g, as compared to 247 mAh/g for the Nb⁵⁺-containing material.

A PEMFC (proton exchange membrane fuel cell) cathode catalyst was developed in which an inert-gas anneal relocates part of the Pt on a solid (non-hollow) carbon black support from the outer surface into shallow pores. On solid carbon, nearly all Pt otherwise contacts the ionomer, whose sulfonic acid groups poison it, most severely at low humidity.

Commercial 40 mass% Pt on Vulcan carbon black was annealed under Ar at 700°C for 2 h (Example 1) and compared with the untreated catalyst (Comparative Example 1) in 0.168 mg-Pt/cm² cathodes tested at 80°C under H₂/air.

STEM (scanning transmission electron microscopy) tomography shows 10–14 nm pores rising from 13% to 17% of total pore volume, and the share of near-surface Pt particles lying 2–10 nm inside the aggregate rather than at its surface rising from 38% to 52%. Surface oxygen on the carbon and the Pt is thought to widen pores just enough to admit Pt but not ionomer. The Ar-annealed catalyst reaches a 0.86 V mass activity of 175.3 A/g-Pt at 30% RH against 134.9 A/g-Pt untreated, with a smaller gain at 80% RH (top Figure). Sulfonic acid coverage of the Pt, measured by CO displacement, falls from 17.5–17.9% to 15.8–16.1% (bottom Figure), attributed by the inventors to reduced Pt–ionomer contact. No polarization curves, durability data or other annealing temperatures are disclosed.

実施例 1: Example 1, Pt/Vulcan annealed under Ar at 700°C
比較例 1: Comparative Example 1, untreated Pt/Vulcan
80%RH / 30%RH: relative humidity of the 80°C cell test
Top Figure y-axis: Mass activity at 0.86 V [A/g-Pt]
Bottom Figure y-axis: Fraction of Pt surface with adsorbed sulfonic acid groups [%], by CO displacement

Top Figure: Mass activity at 0.86 V for Example 1 and Comparative Example 1 at 80% and 30% RH
Bottom Figure: Fraction of the Pt surface with adsorbed sulfonic acid groups, by CO displacement, for Example 1 and Comparative Example 1