All-solid-state batteries (ASSBs) are the most promising next-generation energy storage systems due to their high theoretical energy density and intrinsic safety. However, the limitation of the “solid-solid” contact between the electrodes and the solid electrolyte severely hinders the interfacial charge transfer. It has been shown that the introduction of external pressure can effectively reduce the “solid-solid” contact resistance and extend the cycle life of the battery. The performance of solid-state batteries can be optimized by appropriately adjusting the external pressure. However, the effects of external pressure on solid-state batteries are multifaceted, mainly involving the solid-state electrolyte (SSE), the electrodes, and the interface between them (Figure 1). The following is a detailed analysis of these effects:

1. Interfacial Contact Performance

Improvement of interfacial contact performance: External pressure can deform the solid components, thus improving the contact state between the components inside the solid state battery. When the external pressure is applied uniformly, it can ensure that the contact between the various interfaces inside the battery (e.g., the electrode-electrolyte interface) is closer, reducing poor contact and porosity, and improving the transfer efficiency of ions and electrons.

Reduced interfacial resistance: Uniform external pressure helps to reduce interfacial resistance because tight contact reduces the obstruction of electrons and ions in the transmission process, thus improving the overall performance of the battery. Uneven stresses are shown in Figure 2.

Figure.1.Solid-state Battery Composition[1][3]

2. Cycle stability and safety

Preventing lithium dendrite growth: Lithium dendrites are one of the common problems in solid-state batteries, where they can penetrate the electrolyte and cause short circuits. Uniform external pressure can inhibit the growth of lithium dendrites because the pressure can be evenly distributed throughout the cell, preventing localized stress concentrations and preferential growth of lithium dendrites (Figure 3).

Improved cycle life: Uniform external pressure helps maintain the stability of the cell during cycling, reducing performance degradation due to poor contact and stress concentrations. This significantly improves the cycle life of the cell, making it more suitable for applications that require long periods of operation. Enhanced

Safety: The safety of solid-state batteries is a major advantage over liquid batteries. Uniform external pressure can further enhance this safety, reducing the probability of safety incidents such as thermal runaway and explosions by minimizing potential risks such as short circuits and leakage.

Figure 3. states at different pressures [2][4]

3. Energy Density and Power Density

Increased Energy Density: Uniform external pressure helps optimize the internal structure of the battery, reducing ineffective spaces and pores, thus increasing the energy density of the battery. This means that solid-state batteries can store more energy for the same volume or weight.

Improved Power Density: The power density of solid-state batteries may also be improved due to the uniform external pressure improving the efficiency of ion and electron transport. This allows the battery to charge and discharge faster for high power applications.

IEST Solid State Battery Condition Analyzer can apply uniform external pressure to solid state batteries, and can perform tests at different temperatures (-20℃~80℃) with different pressures and different conditions, with an upper pressure limit of up to 10T, and a thickness testing accuracy of 1μm, which can help in the pre-production mapping of external pressure for solid state batteries.

Figure 4. IEST Solid State Battery Condition Analyzer SSB2D00

Figure 5. Application case test data

4. Summarize

In summary, the influence of external pressure on solid-state batteries are multifaceted, including both the direct effect on SSE, electrodes and the interface between them, and the indirect effect on the overall performance of the battery. When designing and manufacturing solid-state batteries, the role of external pressure needs to be fully considered to optimize the performance of the battery by reasonably designing the pressure parameters. At the same time, attention also needs to be paid to controlling the uniformity and stability of the pressure to avoid performance degradation or safety problems caused by uneven pressure.

5. Reference