From Materials to Structure: How Battery Electrodes Reshape Solid-State Battery Performance?

In the race to upgrade power battery technology toward "higher safety, higher energy density, and longer lifespan," solid-state batteries (SSBs) are regarded as the core direction to break through the performance ceiling of traditional liquid electrolyte batteries. Unlike conventional liquid batteries, SSBs replace liquid electrolytes and separators with solid electrolytes, fundamentally eliminating safety hazards such as leakage and combustion. However, what often goes unnoticed is that battery electrodes—acting as the "core carrier for energy storage and transfer"—are becoming a critical variable determining the practical performance of SSBs, thanks to their material selection, structural design, and manufacturing processes (especially the dry process). From optimizing the adaptability of active materials to reconstructing conductive networks and fine-tuning interface structures, every innovation in electrodes (including the application of dry-process technology) is reshaping the energy density, fast-charging capability, and cycle stability of SSBs.

I. Material Adaptation: "Solid-State Modification" of Electrode Active Materials and the Compatibility Advantages of Dry-Process Technology

The ion transport mechanism of SSB electrolyte systems (e.g., sulfides, oxides, polymers) differs drastically from that of traditional liquid electrolytes. This requires electrode active materials to break free from "liquid-centric thinking" and undergo targeted "solid-state modification." The dry-process technology, with its "solvent-free residue" characteristic, demonstrates inherent advantages in adapting to these modified materials and reducing interfacial side reactions.

For cathode materials: In traditional liquid batteries, ion conduction between cathode particles relies on liquid electrolytes. In SSBs, however, ions must migrate between cathode particles through solid electrolytes—this demands that cathode active materials not only have high specific capacity but also form good "solid-solid contact" with solid electrolytes. For instance, in sulfide-based SSBs, the surface of high-nickel ternary materials (NCM811) reacts with sulfide electrolytes to form an insulating oxide layer, blocking ion transport. To address this, the industry optimizes cathode materials through "coating modification": inorganic coating layers such as LiPO₃ and Li₂SiO₃ are applied to form a dense protective film on NCM particles, which not only inhibits side reactions but also enhances ion conduction efficiency. When manufacturing such coated NCM811 cathodes, the dry process avoids organic solvents, preventing solvent-induced erosion or dissolution of the coating layer and fully preserving its protective function. Experimental data shows that coated NCM811 cathodes prepared via the dry process, when paired with sulfide solid electrolytes, exhibit a 1.5-order-of-magnitude increase in room-temperature ionic conductivity compared to wet-process counterparts, with capacity retention rate rising from 65% to 90% after 500 cycles.

For anode materials: "Solid-state adaptation" focuses on solving "volume expansion" and "interfacial impedance" issues. Silicon-based anodes, with a theoretical capacity (4200 mAh/g) far exceeding that of graphite (372 mAh/g), are key to boosting SSB energy density. However, silicon undergoes 400% volume expansion during lithiation—this causes electrode cracking in liquid batteries, and in SSBs, such expansion damages the interfacial contact between the anode and solid electrolyte, leading to a surge in impedance. To tackle this, anode materials adopt a "nanonization + composite" strategy: silicon is fabricated into nanoparticles (50-100 nm) and then compounded with graphite and carbon nanotubes (CNTs) to form a "rigid framework + flexible buffer" composite structure. In manufacturing such composite anodes, the dry process uses dry powder mixing and precision calendering to better control the dispersion uniformity of silicon nanoparticles, avoiding particle agglomeration caused by solvent evaporation in the wet process. Meanwhile, the dense structure formed by dry calendering buffers silicon’s volume expansion, reducing the risk of electrode cracking. For example, a Si-C composite anode prepared via the dry process by a company exhibits a volume expansion rate of less than 12% in oxide-based SSBs, with initial Coulombic efficiency increasing from 75% to 94% and capacity decay rate remaining only 8% after 1000 cycles.

Additionally, electrode binders need to "keep pace with the times." The PVDF binder commonly used in traditional liquid batteries has poor compatibility with solid electrolytes in SSBs, leading to increased interfacial impedance. The industry now prefers water-soluble binders (e.g., CMC, PAA) or solid-electrolyte-compatible binders (e.g., Li₄SiO₄-based inorganic binders). The dry process eliminates the need to dissolve binders in solvents; instead, it directly mixes dry binders with active materials and conductive agents, avoiding structural defects that may occur during the dissolution and re-solidification of binders in solvents and further enhancing electrode structural stability.

II. Structural Reconstruction: "Mass Transfer Efficiency Revolution" of Electrode Microstructure and the Precision Control Capability of Dry-Process Technology

In liquid batteries, the design of electrode microstructure focuses more on "liquid electrolyte wettability." In SSBs, however, since ions are primarily transported through "solid-solid interfaces," the porosity, particle packing mode, and conductive network distribution of electrodes directly determine the efficiency of ion and electron transport. This requires electrodes to undergo a "macro-to-micro" structural reconstruction to create efficient "ion-electron dual transport channels." The dry process, with its ability to precisely control electrode structure (e.g., controllable compaction density and porosity), serves as a crucial means to achieve this reconstruction.

At the macro level: A precise balance between electrode "compaction density" and "porosity" is essential. In traditional liquid batteries, the compaction density of cathodes is typically 3.5-4.0 g/cm³ with a porosity of ~30% to ensure sufficient liquid electrolyte wettability. In SSBs, electrodes need tight contact with solid electrolytes—too low a compaction density increases "solid-solid contact gaps," hindering ion transport; too high a density damages the crystal structure of solid electrolytes, reducing conductivity. By adjusting calendering pressure and temperature, the dry process enables fine control of compaction density (with a precision of ±0.05 g/cm³), far exceeding that of the wet process (±0.1 g/cm³). For example, the optimal compaction density of cathodes in sulfide-based SSBs is usually 3.0-3.2 g/cm³ with a porosity of ~20%—the dry process can achieve this parameter in a single calendering step, avoiding structural damage caused by secondary calendering after drying in the wet process. A research team used the dry process to adjust cathode compaction density, increasing the volumetric energy density of sulfide-based SSBs from 600 Wh/L to 780 Wh/L while reducing interfacial impedance by 45%.

At the micro level: The electrode’s "conductive network" is upgraded from a "2D planar" to a "3D bulk" structure. In traditional liquid batteries, conductive agents (e.g., carbon black) are usually distributed in a "sheet-like" manner on the surface of active material particles, forming a 2D conductive network where ions are transported between particles via liquid electrolytes. In SSBs, however, electrons and ions need to be transported simultaneously inside the electrode, requiring a 3D network for "synergistic ion-electron transport." In preparing such 3D networks, the dry process mixes "conductive agents (carbon black, CNTs) and solid electrolyte powders" via dry high-shear mixing to form a uniform "composite conductive phase"—CNTs build electron transport channels, while solid electrolyte powders provide ion transport paths. These components interweave and wrap around active material particles. Compared to the wet process (where solvents may cause conductive agent agglomeration and solid electrolyte powder dissolution), the dry process better preserves the dispersion and integrity of the composite conductive phase. For example, in the cathode of oxide-based SSBs, adding 5% CNTs and 10% Li₇La₃Zr₂O₁₂ (LLZO) solid electrolyte via the dry process creates a 3D network that increases electrode electronic conductivity by 12 times and ionic conductivity by 6 times. This optimizes fast-charging capability from "2 hours for 1C charging" to "35 minutes for 1.5C charging."

Furthermore, the "layered structure" of electrodes is evolving into a "gradient structure." Traditional electrodes adopt a "uniformly mixed" single-layer structure, but in SSBs—where interfacial impedance is concentrated at the "electrode-solid electrolyte interface"—the industry is experimenting with "gradient electrode" designs: the side of the electrode adjacent to the solid electrolyte has a higher content of solid electrolyte and conductive agent, forming a "high ion-electron conduction layer" to reduce interfacial impedance; the inner part of the electrode has a higher content of active material to ensure energy density. Using "multi-layer simultaneous calendering" technology, the dry process can fabricate gradient-structured electrodes in one step, eliminating the need for multiple coating and drying steps in the wet process. This not only simplifies the process but also avoids solvent residue issues at interlayer interfaces. For example, a company developed a gradient-structured cathode using dry multi-layer calendering: the solid electrolyte content on the electrolyte-adjacent side is 20%, while the inner part is only 10%. This design reduces the interfacial impedance between the electrode and solid electrolyte by 60% with only a 2% loss in energy density, achieving a "win-win" for efficiency and capacity.

III. Interface Regulation: "Stability Guarantee" for Electrode-Electrolyte Interfaces and the Supporting Role of Dry-Process Technology

The performance bottleneck of SSBs largely stems from "interface issues"—excessively high "interfacial impedance" and frequent "interfacial side reactions" between electrodes and solid electrolytes lead to shortened cycle life and accelerated capacity decay. As the component in direct contact with solid electrolytes, the surface treatment and interface modification of electrodes are the "final mile" to solving SSB interface problems. Although the dry process does not directly participate in interface modification, it provides a better foundation for interface regulation by optimizing electrode surface flatness and cleanliness.

On one hand: "Surface coating" of electrodes builds an "interface protection layer." Both cathode and anode active materials may undergo side reactions when in contact with solid electrolytes—for example, transition metal ions (Ni³⁺, Co³⁺) in cathodes diffuse into solid electrolytes, damaging the electrolyte structure; Li metal in anodes reacts with solid electrolytes to form insulating products such as Li₂O and LiF. Nanoscale protection layers (e.g., Al₂O₃, TiO₂) formed via "atomic layer deposition (ALD)" or "sol-gel coating" on electrode surfaces can effectively block these side reactions. Electrodes prepared via the dry process have a flatter surface (without surface wrinkles caused by wet-process drying), allowing the coating layer to cover the electrode surface more uniformly and avoiding coating gaps caused by surface unevenness. For example, depositing a 5 nm Al₂O₃ layer on Li metal anodes via ALD: when the anode is prepared via the dry process, interfacial side reaction products are reduced by 75% compared to wet-process anodes, with interfacial impedance increasing by only 12% after 100 cycles (vs. a 200% increase in uncoated wet-process batteries).

On the other hand: "Interface wetting" of electrodes optimizes "solid-solid contact." Even with tight compaction between electrodes and solid electrolytes, microscale "contact gaps" still exist, forming "ion transport dead zones." The industry uses two methods for optimization: first, adding "interface modifiers" (e.g., Li₂CO₃, Li₃PO₄) at the electrode-solid electrolyte interface—these substances decompose during the first charge of the battery, forming a high-ionic-conductivity interface phase to fill contact gaps; second, adopting a "hot pressing" process—at a specific temperature (e.g., ~100°C for sulfide-based SSBs), electrodes and solid electrolyte particles undergo slight "plastic deformation" to eliminate microscale gaps. Electrodes prepared via the dry process have a denser structure and no solvent residue, enabling better adhesion to solid electrolytes during hot pressing. The contact area is increased by over 30% compared to wet-process electrodes, further reducing contact gaps. A company used a combined scheme of "dry-process electrodes + hot pressing + interface modifiers," reducing the interfacial impedance of SSBs from 1000 Ω·cm² to 180 Ω·cm² and increasing room-temperature discharge capacity by 35%.

From the "solid-state adaptation" of materials (dry process enhances compatibility) to the "mass transfer efficiency revolution" of structures (dry process enables precision control), and to the "stability guarantee" of interfaces (dry process optimizes foundational conditions), battery electrodes are shifting from "passive adaptation" to "active shaping" of SSB performance—and dry-process technology serves as a critical technical enabler in this transition. As solid electrolyte technology matures, electrode innovations (including the in-depth application of dry-process technology) will become the key variable determining whether SSBs "move from the laboratory to mass production." Electrodes are not only carriers of energy storage but also core links connecting materials to systems and balancing performance with cost. In the future, with continuous optimization of electrode materials and structures, and further breakthroughs in the large-scale production of dry-process technology, SSBs will truly achieve the unification of "high safety and high energy density," driving disruptive changes in new energy vehicles, energy storage stations, and other fields.