Cost Thin-film solid-state batteries are expensive to make and employ manufacturing processes thought to be difficult to scale, requiring expensive
vacuum deposition equipment. Solid-state batteries with ceramic separators may break from mechanical stress. In June 2023, Japanese research group of the Graduate School of Engineering at
Osaka Metropolitan University announced that they have succeeded in stabilizing the high-temperature phase of {{chem2|Li_{3}PS_{4} }} (α-{{chem2|Li_{3}PS_{4} }}) at room temperature. This was accomplished via rapid heating to crystallize the {{chem2|Li_{3}PS_{4} }} glass.
Interfacial resistance High interfacial resistance between a cathode and solid electrolyte has been a long-standing problem for all-solid-state batteries. Traditional densification techniques used in
Li-ion battery production—such as
hot-rolling and uniaxial pressing—produce a non-uniform
pressure field and therefore non-uniform closure of
porosity in the
solid electrolyte. In contrast, modern equipment designed specifically for
solid-state batteries, such as
warm isostatic pressing, applies a nearly uniform pressure throughout the
solid electrolyte, leading to more
homogeneous densification and, as a consequence, reduced
bulk and
grain boundary resistivity. To better understand degradation mechanisms at the interfaces and within materials, advanced nanoscale imaging techniques are often employed.
Atomic force microscopy (AFM) enables topographical mapping of solid-state battery materials at the nanometer scale, revealing microstructural features such as cracks, dendrite initiation sites, or interphase evolution.
Kelvin probe force microscopy (KPFM) extends this capability by mapping surface potential distributions, making it particularly useful for visualizing local charge accumulation and interfacial instabilities. Additionally,
Conductive AFM (C-AFM) is used to map nanoscale electrical conductivity across electrodes and solid electrolytes, helping to identify failure zones and to evaluate the uniformity of ionic pathways.
Interfacial instability The interfacial instability of the electrode-electrolyte has always been a serious problem in solid-state batteries. After solid-state electrolyte contacts with the electrode, the chemical and/or electrochemical side reactions at the interface usually produce a passivated interface, which impedes the diffusion of Li+ across the electrode-SSE interface. Upon high-voltage cycling, some SSEs may undergo oxidative degradation.
Dendrites Solid
lithium (Li) metal anodes in solid-state batteries are replacement candidates in
lithium-ion batteries for higher
energy densities, safety, and faster recharging times. Such anodes tend to suffer from the formation and the growth of Li
dendrites, non-uniform metal growths which penetrate the electrolyte leading to electrical
short circuits. This shorting leads to energy discharge,
overheating, and sometimes fires or
explosions due to
thermal runaway. Li dendrites reduce
coulombic efficiency. The exact mechanisms of dendrite growth remain a subject of research. Studies of metal dendrite growth in solid electrolytes began with research of molten sodium / sodium - β - alumina / sulfur cells at elevated temperature. In these systems, dendrites sometimes grow as a result of micro-crack extension due to the presence of plating-induced pressure at the sodium / solid electrolyte interface. However, dendrite growth may also occur due to chemical degradation of the solid electrolyte. The uneven
densification of
hot-rolling of the solid electrode, due to the non-uniform applied pressure, results in
crack-initiation points for dendrite formation. In Li-ion solid electrolytes apparently stable to Li metal, as visualized and measured using photoelasticity experiments, dendrites propagate primarily due to pressure build up at the electrode / solid electrolyte interface, leading to crack extension. Meanwhile, for solid electrolytes which are chemically unstable against their respective metal, interphase growth and eventual cracking often prevents dendrites from forming. Dendrite growth in solid-state Li-ion cells can be mitigated by operating the cells at elevated temperature thereby deflecting dendrites and delaying dendrite induced short-circuiting. Aluminum-containing electronic rectifying interphases between the solid-state electrolyte and the lithium metal anode have also been shown to be effective in preventing dendrite growth.
Mechanical failure A common failure mechanism in solid-state batteries is
mechanical failure through volume changes in the anode and cathode during
charge and discharge due to the addition and removal of
Li-ions from the host structures.
Cathode Cathodes will typically consist of active cathode particles mixed with SSE particles to assist with
ion conduction. As the battery charges/discharges, the cathode particles change in volume typically on the order of a few percent. This volume change leads to the formation of interparticle
voids which worsens
contact between the cathode and SSE particles, resulting in a significant loss of
capacity due to the restriction in ion transport. One proposed solution to this issue is to take advantage of the
anisotropy of volume change in the cathode particles. As many cathode materials experience volume changes only along certain
crystallographic directions, if the secondary cathode particles are grown along a crystallographic direction which does not expand greatly with charge/discharge, then the change in volume of the particles can be minimized. Another proposed solution is to mix different cathode materials which have opposite expansion trends in the proper ratio such that the net volume change of the cathode is zero. Lithium metal has a relatively low
melting point of 453K and a low
activation energy for
self-diffusion of 50 kJ/mol, indicating its high propensity to significantly creep at room temperature. It has been shown that at room temperature lithium undergoes power-law creep where the temperature is high enough relative to the melting point that
dislocations in the metal can climb out of their
glide plane to avoid obstacles. The creep stress under power-law creep is given by: \sigma_{creep} = \left(\frac{\dot{\varepsilon}}{A_c}\right)^{1/m}\exp{\left(\frac{Q_c}{mRT}\right)} Where R is the
gas constant, T is temperature, \dot{\varepsilon} is the uniaxial
strain rate, \sigma_{creep} is the creep
stress, and for lithium metal m = 6.6, Q_c = 37\,\mathrm{kJ} \cdot \mathrm{mol}^{-1}, A_c^{-1/m}=3\times 10^5\,\mathrm{Pa} \cdot \mathrm{s}^{-1} . The normal operating cell pressure for lithium metal anode is anywhere from 1-7 MPa. Some possible strategies to minimize stress on the lithium metal are to use cells with springs of a chosen
spring constant or controlled pressurization of the entire cell. While these alloys do expand quite a bit when lithiated, often to a greater degree than lithium metal, they also possess improved mechanical properties allowing them to operate at pressures around 50 MPa. This higher cell pressure also has the added benefit of possibly mitigating void formation in the cathode. == Advantages ==