Solid‐state batteries (SSBs) are attracting growing interest as long‐lasting, thermally resilient, and high‐safe energy storage systems. As an emerging area of battery chemistry, there are many issues with SSBs, including strongly reductive lithium anodes, oxidized cathodes (state of charge), the thermodynamic stability limits of solid‐state electrolytes (SSEs), and the ubiquitous and critical interfaces. In this Review, we provided an overview of the main obstacles in the development of SSBs, such as the lithium anode|SSEs interface, the cathode|SSEs interface, lithium‐ion transport in the SSEs, and the root origin of lithium intrusions, as well as the safety issues caused by the dendrites. Understanding and overcoming these obstacles are crucial but also extremely challenging as the localized and buried nature of the intimate contact between electrode and SSEs makes direct detection difficult. We reviewed advanced characterization techniques and discussed the complex ion/electron‐transport mechanism that have been plaguing electrochemists. Finally, we focused on studying and revealing the coupled electro‐chemo‐mechanical behavior occurring in the lithium anode, cathode, SSEs, and beyond.

The crystal structure and magnetic property of the single crystalline hexagonal rare-earth indium oxides ${\mathrm{GdInO}}_3$ have been studied by combing experiments and model calculations. The two inequivalent ${\mathrm{Gd}}^{3+}$ ions form the centered honeycomb lattice, which consists of honeycomb and triangular sublattices. The dc magnetic susceptibility and specific heat measurements suggest two antiferromagnetic phase transitions at $T_{\text{N1}}=2.3\mathrm{K}$ and $T_{\text{N2}}=1.02\mathrm{K}$. An inflection point is observed in the isothermal magnetization curve, which can be an indication of an up-up-down phase with a 1/3 magnetization plateau, further supported by our theoretical calculation. We also observe a large magnetic entropy change originated from the magnetic frustration in ${\mathrm{GdInO}}_3$. By considering a classical spin Hamiltonian, we establish the ground state phase diagram, which suggests that ${\mathrm{GdInO}}_3$ has a weak easy-axis anisotropy and is close to the equilateral triangular-lattice system. The theoretical ground-state phase diagram may be used as a reference in NMR, ESR, or $\mu \mathrm{SR}$ experiments in future.