Beyond Liquid Electrolytes: The Adaptive Innovation of Dry-Process Battery Electrodes in Solid-State Batteries

As solid-state batteries (SSBs) emerge as the core direction to break through the technical ceiling of liquid electrolyte batteries in the new energy storage field—thanks to their "no leakage, high safety, and long lifespan" characteristics—a critical question has become increasingly clear: Without the "lubrication and conduction" of liquid electrolytes, how can the core components of batteries be restructured for compatibility? Among these components, battery electrodes—acting as the core carriers for energy storage and transfer—are particularly crucial for process innovation. Traditional wet-process electrodes rely on solvents and liquid electrolytes to establish ion transport paths, which are highly limited in solid-state systems. In contrast, dry-process battery electrodes, with their inherent advantages of "solvent-free, controllable structure, and interface compatibility," are achieving in-depth adaptive innovation with SSBs across three dimensions: material synergy, structural adaptation, and interface optimization, paving the way for the industrialization of SSBs from laboratory research.

I. Material Synergy: Breaking "Liquid Dependence" to Build Solid-State Ion Transport Channels

In liquid electrolyte batteries, the active materials, conductive agents, and binders of wet-process electrodes rely on organic solvents to form a slurry, and subsequent ion migration between particles is enabled by liquid electrolytes. This material system—dependent on both "solvents and electrolytes"—is completely ineffective in SSBs. Ion transport in SSBs relies on "solid-solid interfaces," which requires electrode materials to break free from dependence on liquid media. The solvent-free nature of the dry process precisely provides the foundation for material synergy and compatibility.

In cathode material adaptation, the dry process solves the compatibility challenge between "active materials and solid electrolytes." Mainstream cathode materials such as high-nickel ternary (NCM) and lithium iron phosphate (LFP) are prone to interfacial side reactions when in contact with sulfide or oxide solid electrolytes: For example, NCM reacts with sulfide electrolytes to form insulating Li₂O and NiS₂, while oxide electrolytes (e.g., LLZO) react with residual impurities on the cathode surface to form high-impedance LaPO₄. Wet-process electrodes, due to solvent residues (e.g., NMP), exacerbate such side reactions; in contrast, dry-process electrodes directly composite active materials with solid electrolyte powders through dry mixing, eliminating solvent involvement and minimizing side reaction triggers at the source. More importantly, the dry process enables atomic-level uniform dispersion of "active materials - solid electrolytes - conductive agents": A company mixed LFP, Li₇La₃Zr₂O₁₂ (LLZO) solid electrolyte, and carbon nanotubes (CNTs) in an 8:1.5:0.5 ratio via dry mixing and calendering. The resulting cathode electrode achieved an ionic conductivity of 1.2×10⁻³ S/cm—three times that of the wet process (with the same ratio)—and maintained 91% capacity after 500 cycles, far exceeding the 76% capacity retention of wet-process electrodes.

In anode material adaptation, the dry process overcomes the "volume expansion" and "interface stability" pain points of high-energy anodes such as silicon-based and lithium-metal anodes. Silicon-based anodes have a theoretical capacity more than 10 times that of graphite, but their 400% volume expansion during lithiation causes cracking of wet-process electrodes. The dry process, however, forms a dry composite of "nano-silicon - graphite - CNTs," using the flexible framework of CNTs to buffer expansion stress while forming a dense structure via calendering to inhibit silicon particle agglomeration. A research team prepared a Si-C composite anode using the dry process, controlling its volume expansion rate to within 15%. When assembled into a battery with a sulfide solid electrolyte, the initial Coulombic efficiency increased from 78% (wet process) to 93%. For lithium-metal anodes, the dry process can form self-supporting lithium-metal composite electrodes via "dry calendering of lithium powder - solid electrolyte - conductive agent," avoiding the risk of lithium dendrite growth in liquid batteries. The interfacial impedance of this electrode when in contact with LLZO electrolyte is only 50 Ω·cm², much lower than the 200 Ω·cm² of wet-coated lithium-metal electrodes.

Binder adaptation also relies on the dry process. The PVDF binder commonly used in wet-process electrodes reacts with solid electrolytes in SSBs, leading to increased impedance. The dry process, by contrast, can directly use inorganic binders compatible with solid electrolytes (e.g., Li₄SiO₄) or water-soluble binders (e.g., CMC-PAA composite systems), which can be mixed with active materials without solvent dissolution. For example, a dry-process cathode electrode using Li₄SiO₄ inorganic binder not only has a 40% higher structural strength but also forms a continuous ion transport channel with sulfide electrolytes, further reducing interfacial impedance.

II. Structural Adaptation: From "Wettability Guidance" to "Mass Transfer Optimization," Restructuring Electrode Microstructure

In liquid electrolyte batteries, the structural design of wet-process electrodes centers on "liquid electrolyte wettability"—controlling porosity at around 30% and compaction density at 3.5-4.0 g/cm³ to ensure full electrolyte penetration into the electrode. However, in SSBs, ion transport relies on tight contact between electrodes and solid electrolytes; this "high porosity, low density" structure instead creates "solid-solid contact gaps," becoming a bottleneck for ion transport. With its precise structural control capabilities, dry-process electrodes achieve a structural innovation from "wettability guidance" to "mass transfer optimization," perfectly adapting to the ion transport needs of SSBs.

In balancing compaction density and porosity, the dry process demonstrates unique advantages. SSBs have stricter requirements for electrode compaction density: Too low a density causes poor contact, while too high a density may damage the crystal structure of solid electrolytes. For example, the optimal compaction density of cathode electrodes in sulfide-based SSBs needs to be controlled at 3.0-3.2 g/cm³ with a porosity of approximately 20%. Wet-process electrodes struggle to precisely control this parameter due to uneven shrinkage after drying; in contrast, the dry process adjusts calendering pressure (5-10 MPa) and temperature (60-80℃) to control compaction density with a precision of ±0.05 g/cm³ and porosity deviation of less than 2%. A company’s sulfide cathode electrode prepared via the dry process, when assembled with a solid electrolyte, has a 35% larger interfacial contact area than wet-process electrodes, increasing volumetric energy density from 620 Wh/L to 780 Wh/L.

In conductive network structure, dry-process electrodes achieve an upgrade from "2D planar" to "3D bulk." In liquid electrolyte batteries, conductive agents (e.g., carbon black) in wet-process electrodes are distributed in a sheet-like manner on the surface of active materials, forming a 2D conductive network where ions are transported via liquid electrolytes. SSBs, however, require "synergistic electron-ion transport," which demands a 3D bulk network inside the electrode—electrons transported via conductive agents and ions via solid electrolyte particles. The dry process uniformly mixes conductive agents (CNTs, graphene) with solid electrolyte powders, forming an interwoven 3D network during dry calendering: CNTs build electron transport paths, while solid electrolyte powders fill gaps to form ion channels. For example, in the cathode of oxide-based SSBs, the dry process adds 5% CNTs and 10% LLZO powder; the resulting 3D network increases electrode electronic conductivity by 10 times and ionic conductivity by 5 times, optimizing fast-charging capability from "2 hours for 1C charging" to "35 minutes for 1.5C charging."

Additionally, the dry process supports the preparation of "gradient-structured electrodes," further optimizing the interfacial performance of SSBs. Addressing the characteristic of SSBs—"interfacial impedance concentrated at the electrode-electrolyte contact surface"—the dry process uses "multi-layer simultaneous calendering" to increase the content of solid electrolytes and conductive agents on the side of the electrode adjacent to the solid electrolyte (forming a "high mass transfer layer"), while increasing active material content inside the electrode (ensuring energy density). A research team prepared a gradient-structured dry-process cathode with 20% solid electrolyte content on the electrolyte-adjacent side and only 10% inside. This design reduces interfacial impedance by 60% with only a 2% loss in energy density, perfectly balancing mass transfer efficiency and energy storage capacity.

III. Interface Optimization: Eliminating "Contact Barriers" to Enhance Solid-State System Stability

The performance bottleneck of SSBs largely stems from "interface issues"—high impedance and side reactions between electrodes and solid electrolytes lead to shortened cycle life and accelerated capacity decay. Wet-process electrodes, due to solvent residues and surface roughness, further exacerbate these problems; in contrast, dry-process electrodes, with their clean surfaces and dense structures, are key to optimizing interfacial performance.

Dry-process electrodes reduce interfacial side reactions by "improving surface cleanliness." During the drying of wet-process electrodes, solvent residues (typically 0.1%-0.5%) react with solid electrolytes: For example, residual NMP reacts with sulfide electrolytes to form LiF, increasing interfacial impedance. The dry process, however, is solvent-free throughout, with surface residual impurities below 0.01%, significantly reducing such side reactions. Experimental data shows that when a dry-process cathode electrode is in contact with LLZO electrolyte, the amount of interfacial side reaction products is only 1/5 that of wet-process electrodes, and the interfacial impedance increase rate is reduced from 300% to 50% after 100 cycles.

In optimizing interfacial contact, dry-process electrodes achieve tight adhesion with solid electrolytes via "hot pressing adaptation." SSB assembly typically requires hot pressing (80-120℃) to form good contact between electrodes and solid electrolytes—wet-process electrodes are prone to deformation during hot pressing due to their loose structure; dry-process electrodes, however, have a dense and uniform structure, allowing slight plastic deformation with solid electrolyte particles during hot pressing to eliminate microscale gaps. A company used the "dry-process electrode + 100℃ hot pressing" process to reduce the interfacial contact gap between the electrode and sulfide electrolyte from 50-100 nm (wet process) to 10-20 nm, lowering interfacial impedance from 800 Ω·cm² to 180 Ω·cm².

Furthermore, dry-process electrodes provide a better substrate for "interface modification." The industry commonly uses atomic layer deposition (ALD) and sol-gel methods to prepare nano-protective layers (e.g., Al₂O₃, TiO₂) on electrode surfaces to block side reactions—wet-process electrodes have rough surfaces (roughness Ra ≈ 50 nm), leading to uneven protective layer coverage; dry-process electrodes, however, have smoother surfaces (Ra ≈ 10 nm), allowing the protective layer to form a continuous and dense film. For example, depositing a 5 nm Al₂O₃ layer on a dry-process lithium-metal anode via ALD achieves 99% protective layer coverage. When assembled into a battery with a sulfide electrolyte, the capacity retention rate is 88% after 200 cycles, compared to only 65% for an unmodified wet-process electrode.

From material synergy breaking liquid dependence, to structural adaptation optimizing mass transfer efficiency, and interface optimization enhancing stability, dry-process battery electrodes are comprehensively restructuring the compatibility logic with SSBs. As liquid electrolytes gradually become obsolete, dry-process electrodes are not merely a "process replacement" but a "core engine" driving the practical performance of SSBs—they not only solve key technical pain points in solid-state systems but also lower the industrialization threshold of SSBs. In the future, with the further maturity of the dry process in large-scale production and its in-depth integration with materials such as high-nickel, silicon-based, and sulfide, SSBs will truly achieve the goals of "high safety, high energy density, and fast charging," bringing disruptive changes to new energy vehicles, energy storage stations, consumer electronics, and other fields.