1. Introduction

In recent years, the development of advanced energy storage systems has become increasingly important to meet the growing demand of electric vehicles, portable electronics, and grid-scale applications. Among various options, lithium-ion batteries (LIBs) have dominated the market due to their relatively high energy density and long cycle life. However, LIBs face certain limitations, particularly related to safety concerns and energy density ceilings. These issues stem primarily from the use of flammable liquid electrolytes and graphite anodes, which limit the maximum achievable capacity and pose risks of leakage, thermal runaway, and fire hazards. Solid-state batteries (SSBs) have been proposed as a promising alternative to liquid-based batteries, offering several advantages such as enhanced safety, higher energy density, and the potential for better performance at extreme temperatures. SSBs use a solid electrolyte to replace the liquid electrolyte, which not only eliminates the risks associated with leakage and flammability but also enables the use of more energy-dense anode materials, such as lithium metal. The solid electrolyte also provides a safer interface between the anode and cathode, reducing the risks of short circuits caused by dendrite growth.

This paper provides an overview of recent advances in solid-state battery technology, with a particular focus on solid electrolytes, interface engineering, dendrite suppression mechanisms, and manufacturing challenges. It also highlights the current research gaps and challenges, as well as the future directions required to make solid-state batteries commercially viable.

2. Types of solid electrolytes 

Solid electrolytes are crucial components of solid-state batteries, as they serve as the medium for ion conduction between the anode and cathode. The performance of solid-state batteries is largely determined by the ionic conductivity, stability, and mechanical properties of the solid electrolyte. Several types of solid electrolytes have been explored for SSBs, each with its own advantages and limitations. These include sulfide-based electrolytes, oxide-based electrolytes, and polymer-based electrolytes.

Sulfide-based electrolytes, such as lithium thiophosphate (Li3PS4), are among the most widely studied solid electrolytes due to their high ionic conductivity, which can exceed that of conventional liquid electrolytes. These electrolytes are also relatively easy to process, and they have a wide electrochemical stability window. However, sulfide electrolytes are highly sensitive to moisture and require strict handling conditions. Additionally, the high reactivity with air and moisture poses challenges in large-scale manufacturing and commercialization.

Oxide-based electrolytes, such as lithium lanthanum zirconate (LLZO), have garnered significant attention due to their excellent chemical stability and wide electrochemical window. They are less sensitive to moisture compared to sulfide-based electrolytes and are considered more suitable for practical applications. However, oxide electrolytes generally have lower ionic conductivity than sulfide-based electrolytes, which limits their performance in SSBs. Researchers are actively exploring ways to improve the ionic conductivity of oxide electrolytes through doping and composite materials.

Polymer-based electrolytes, such as polyethylene oxide (PEO)-based electrolytes, offer flexibility and ease of processing. These materials can be used to form thin, lightweight solid electrolyte films, which are advantageous for battery designs that require high flexibility or thin form factors. However, polymer electrolytes generally exhibit lower ionic conductivity compared to inorganic electrolytes, especially at room temperature. To address this limitation, researchers are working on developing composite electrolytes that combine polymers with inorganic materials to enhance conductivity and stability.

3. Interface engineering in SSBs

Interface engineering is a cornerstone in the performance, safety, and stability of SSBs. The interface contact between the solid electrolyte and the electrode materials significantly influences ironic transport, cycle life, and overall electrochemical efficiency. Inadequate interfacial compatibility oftens lead to high interfacial resistance, limited ion mobility, dendrite formation, and in severe cases, internal short circuits. Addressing these interfacial issues is thus central to advancing practical SSB technology.

To improve interficial stability and conductivity, various engineering strategies have been developed. One common approach is surface modification. The surface of solid electrolytes can be modified to improve their wettability and adhesion to the electrode materials. This can be achieved through chemical treatments or the deposition of thin functional coatings that enhance the interaction between the solid electrolyte and electrodes. For example, thin layers of lithium phosphorous oxynitride (LiPON) have been used to enhance the interface between the solid electrolyte and lithium metal anodes [1].

Another effective strategy involves creating interfacial layers or buffer zones between the solid electrolyte and the electrode materials that helps mitigate stress and prevent unwanted reactions at the interface. These layers, which can be composed of materials such as ceramics or polymers, can also act as ionic conductors and improve the overall ionic conductivity across the interface. For instance, the use of a thin layer of sulfide-based electrolytes at the interface with a lithium anode has shown to reduce dendrite formation [2].

Mechanical contact optimization is also crucial. A good mechanical contact between the solid electrolyte and electrode materials is essential for minimizing interfacial resistance and improving ion transport. This can be achieved by optimizing the pressing conditions during the fabrication of the battery, such as applying high pressure during assembly or employing techniques such as cold sintering or hot-pressing. Additionally, the use of binder-free electrodes can reduce interfacial resistance and improve contact quality [3]. The addition of conductive materials, such as carbon or metal nanoparticles, to the interface can further enhance ionic and electronic conductivity. These additives can help in reducing resistance at the interface and facilitate better charge transport during cycling. Researchers have investigated the use of carbon nanotubes and graphene as conductive additives to enhance the interface between the solid electrolyte and electrodes [4]. Moreover, incorporating soft or elastic interlayers at the interface can help accommodate volume changes during charge/discharge cycles. This is particularly important for preventing cracks and void formation at the interface, which can lead to performance degradation. For example, polymer-based interlayers that are flexible and able to deform with the electrode materials during cycling have been shown to improve cycle stability and prevent interfacial degradation [5].

In summary, effective interface engineering is crucial for improving the performance and longevity of solid-state batteries. Continued research in developing new materials, surface treatments, and interfacial strategies will be essential for overcoming the current limitations of SSBs and realizing their full potential in commercial applications.

4. Dendrite suppression mechanisms

One of the key obstacles to the practical application of solid-state batteries is the formation and growth of lithium dendrites. These needle-like structures can pierce through the solid electrolyte, leading to internal short circuits, capacity loss, and severe safety hazards. Although solid electrolytes were initially expected to act as a physical barrier against dendrites, it has been observed that dendrite growth can still occur, especially at grain boundaries or under non-uniform current densities. Several mechanisms and strategies have been proposed to suppress dendrite formation:

High Mechanical Modulus Electrolytes: According to the Monroe–Newman criterion, solid electrolytes with shear moduli greater than twice that of lithium metal (~4.2 GPa) can theoretically suppress dendrite penetration. Oxide-based electrolytes like LLZO meet this criterion, although practical success also depends on interface quality [6].

Interface Engineering: Enhancing the electrode–electrolyte contact and eliminating voids can reduce local current hotspots that initiate dendrite growth. Conformal coatings and soft interlayers help distribute current more uniformly [2] (Han et al., 2021).

Gradient Structures and 3D Architectures: Designing spatially graded electrolyte structures or 3D porous current collectors can help redirect lithium deposition and minimize dendritic protrusions.

Electrochemical Conditioning and Cycling Protocols: Controlled formation cycling and pulse charging have shown promise in altering lithium plating behavior, promoting uniform deposition, and healing nascent dendrites during early growth stages.

Self-Healing Materials: Emerging studies suggest that incorporating self-healing polymers or dynamic bonds within electrolytes could help repair microcracks or disruptions caused by dendritic intrusion [5] (Zheng et al., 2022).

Continued research into the thermodynamics and kinetics of lithium dendrite formation in solid-state systems will enable more reliable battery designs. Multi-physics modeling combined with real-time imaging techniques such as in situ electron microscopy and operando synchrotron X-ray tomography are critical for visualizing dendrite evolution and validating suppression methods.

5. Manufacturing and scalability

The commercialization of solid-state batteries (SSBs) is highly dependent on the development of scalable, cost-effective manufacturing processes. Unlike conventional lithium-ion batteries, the fabrication of SSBs involves unique challenges related to solid–solid interfaces, dense electrolyte processing, and integration with high-capacity electrodes. Key challenges in manufacturing include:

High-temperature sintering and densification: Many inorganic solid electrolytes, such as oxide ceramics (e.g., LLZO), require high-temperature sintering (>1000°C) to achieve sufficient density and ionic conductivity. This process is energy-intensive and incompatible with standard battery manufacturing lines [7] (Xu et al., 2020).

Air/moisture sensitivity: Sulfide-based electrolytes offer excellent ionic conductivity but are highly sensitive to moisture and oxygen, necessitating inert-atmosphere processing and specialized equipment [8] (Fang et al., 2022).

Interface assembly: Achieving intimate and stable contact between solid electrolyte layers and electrode materials is difficult, especially over large areas. Techniques like cold pressing, hot isostatic pressing, and tape casting are being investigated to improve interfacial bonding [9] (Kim et al., 2021).

Scalable coating methods: Developing scalable coating techniques such as atomic layer deposition (ALD), sputtering, or slurry casting to produce uniform solid electrolyte layers is a major research focus. Binder-free or roll-to-roll processes are considered for industrial relevance.

Emerging scalable strategies include:

Hybrid solid-state configurations: Semi-solid or gel-based electrolytes offer more processing flexibility while retaining many of the safety benefits of solid-state designs.

Co-extrusion and co-sintering: These techniques aim to fabricate multi-layer battery structures in a single step, reducing processing complexity and misalignment.

Additive manufacturing: 3D printing is being explored for producing intricate cell geometries and graded architectures that enhance performance while simplifying integration [10].

Overall, the transition from laboratory-scale prototypes to large-scale SSB production will depend on the parallel development of robust processing techniques, compatible materials, and streamlined supply chains. Collaboration between materials scientists, battery engineers, and manufacturers will be essential to scale up these technologies.

6. Current challenges and future directions

Despite notable progress in the development of SSBs, several significant challenges must be overcome before they can achieve large-scale commercialization and compete effectively with conventional lithium-ion batteries in terms of performance, cost, and manufacturability. Key challenges include:

Ionic Conductivity and Electrolyte Stability: Many solid electrolytes still struggle to match the ionic conductivity and stability of liquid electrolytes. While sulfide-based electrolytes exhibit high ionic conductivity, they suffer from poor stability and sensitivity to moisture. Oxide-based electrolytes, while more stable, often have lower ionic conductivity [11].

Dendrite Growth and Electrochemical Stability: Dendrite formation, as discussed in previous sections, continues to be a primary concern in SSB development. Even with strategies to suppress dendrite formation, achieving long-term cycling stability remains a major hurdle.

Interfacial Compatibility: The compatibility between solid electrolytes and electrodes is still suboptimal. Issues such as poor adhesion, interfacial resistance, and the formation of voids at the interfaces can significantly affect the performance and safety of SSBs [12].

Manufacturing Scalability: As discussed in the previous section, the scaling up of solid-state battery manufacturing presents significant challenges, particularly in terms of processing techniques, materials availability, and cost-effectiveness.

Future research should focus on developing novel solid electrolytes with both high ionic conductivity and long-term stability. New material systems, such as halide-based electrolytes, lithium phosphorus oxynitride (LiPON), and other composite systems, hold promise for overcoming current limitations [13]. The development of advanced coatings and interlayers to improve interfacial compatibility will be essential for achieving high performance and durability. Coatings that can self-heal or repair damage caused by dendrites could prove particularly beneficial [14]. To overcome manufacturing challenges, innovative techniques such as roll-to-roll processing, laser sintering, and scalable electrode coatings will be crucial. These techniques will help reduce production costs and improve the scalability of SSBs. As the electric vehicle (EV) market grows, solid-state batteries are expected to play a key role in powering next-generation EVs. Integration with technologies such as fast charging, energy harvesting, and high-efficiency power management will be critical for the success of SSBs in real-world applications.

Overall, the successful commercialization of solid-state batteries will depend on continued innovation in materials, manufacturing techniques, and system integration. Collaboration between academia, industry, and government will be essential to overcome the remaining technical and economic barriers.

7. Conclusion

Solid-state battery (SSB) technology represents a transformative advancement in energy storage, offering significant improvements in safety, energy density, and electrochemical performance over conventional lithium-ion batteries. While recent years have seen meaningful progress in the design of high-conductivity solid electrolytes and novel interface engineering approaches, several technical and economic challenges continue to impede commercial viability. Chief among these are dendrite penetration, low room-temperature ionic conductivity, interfacial instability, and the difficulty of scalable, cost-effective manufacturing.

To address these issues, ongoing research is focused on the discovery of new electrolyte materials—such as halide-based and hybrid organic–inorganic systems—that combine high conductivity with environmental and mechanical stability. Additionally, innovative interface engineering methods, including self-healing coatings and flexible interlayers, have shown promise in improving cycle stability and mitigating degradation mechanisms. On the manufacturing front, scalable techniques like roll-to-roll processing, cold sintering, and additive manufacturing are being actively explored to transition lab-scale breakthroughs into industrial practice.

Looking ahead, the integration of SSBs with fast-charging infrastructure, high-energy-density cathodes, and smart battery management systems will be critical for meeting the growing demand in electric vehicles and renewable energy storage. Strong collaboration across academia, industry, and government institutions will be essential to overcoming remaining barriers and accelerating the deployment of SSBs. With sustained innovation, solid-state batteries are well-positioned to become a cornerstone of the next-generation clean energy ecosystem.