Ion transport mechanism, lithium dendrite growth mechanism, and solid-solid interface problem are the three major problems faced by solid-state batteries
However, the high energy barrier of the solid-solid interface in the solid-state battery still leads to the low transmission rate of lithium ions, the growth of lithium dendrites, the interface reaction, and the physical contact between lithium metal and the solid electrolyte (SE), resulting in the poor charging and discharging speed of the finished solid-state battery, and the cycle life is lower than that of the traditional liquid battery.
Solid-Solid Interface Issues: Critical Challenges for Solid-State Battery Performance and Safety
The solid-solid interface problem directly affects the performance of solid-state batteries, such as cycle life: In most cases, the solid-solid interface contact of solid-state batteries is point contact, and the contact area is small. In some battery systems, the interface may initially be in surface contact, but with the cycle of the battery, the volume expansion of the electrode material inevitably occurs, which deteriorates the original good contact, thereby increasing the interface impedance and deteriorating the battery performance. At the same time, continuous stress accumulation may also lead to micron-scale cracks in the cathode and solid electrolyte layers, and the contact between the cathode and the electrolyte will deteriorate, which will exacerbate the degradation of battery performance.
The contact interface between the solid electrolyte and lithium metal is usually fragile, and the contact resistance may be relatively large, and if the interface is unstable, it may trigger a violent interface reaction, resulting in rapid degradation of interface performance.
In the liquid electrolyte system, dynamic SEI will be formed on the surface of lithium metal, and the SEI layer can alleviate the side reaction between the electrolyte and lithium metal to a certain extent, while maintaining the conductivity of lithium ions. In addition, the liquid electrolyte has good contact and wettability, and can self-repair or re-form the SEI layer to a certain extent, thereby adapting to the changes in surface morphology during lithium metal deposition and making the formation and growth of lithium dendrites more controllable, because lithium can be deposited more evenly under the action of the liquid electrolyte.
Solid-state is more susceptible to thermal runaway due to interface problems than liquid: once a solid-state electrolyte forms cracks or has poor contact with lithium metal, it is not as capable of forming an SEI film and self-healing as a liquid electrolyte, which is more likely to lead to the breakage of lithium-ion transmission channels and the formation of lithium dendrites, which may penetrate the electrolyte and cause a large amount of heat production and temperature increase in the battery short circuit. The high temperature may cause the cathode to decompose, and the high specific volume ternary cathode material may produce oxygen during thermal decomposition, which reacts with the lithium metal anode and triggers an exothermic reaction, resulting in a further increase in battery temperature and thermal runaway.
Interface engineering and modification effectively solve the solid-solid interface problem: In view of the solid-solid interface problem existing in solid-state batteries, the current mainstream is improved through interface engineering and modification, and the improvement is achieved through two dimensions: materials and processes. 1) Material dimension: Choose the Li metal anode and the coated composite cathode with less volume change. 2) Process dimension: macroscopic interface problem, by increasing the pressure in the preparation process, in order to eliminate porosity and enhance interface contact.
Article source: battery technology TOP+
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