Ceramic batteries equipped with Li-metal anodes are expected to double the energy density of conventional Li-ion batteries. Besides high energy densities, also high power is needed when batteries have to be developed for electric vehicles. Practically speaking, so-called critical current densities (CCD) higher than 3 mA cm À2 are needed to realize such systems. As yet, this value has, however, not been achieved for garnet-type Li 7 La 3 Zr 2 O 12 (LLZO) being one of the most promising ceramic electrolytes.Most likely, CCD values are influenced by the area specific resistance (ASR) governing ionic transport across the Li|electrolyte interface. Here, single crystals of LLZO with adjusted ASR are used to quantify this relationship in a systematic manner. It turned out that CCD values exponentially decrease with increasing ASR. The highest obtained CCD value was as high as 280 mA cm À2 . This value should be regarded as the room-temperature limit for LLZO when no external pressure is applied. Concluding, for polycrystalline samples either stack pressure or a significant increase of the interfacial area is needed to reach current densities equal or higher than the above-mentioned target value.

Understanding the cause of lithium dendrites formation and propagation is essential for developing practical all-solid-state batteries. Li dendrites are associated with mechanical stress accumulation and can cause cell failure at current densities below the threshold suggested by industry research (i.e., >5 mA/cm2). Here, we apply a MHz-pulse-current protocol to circumvent low-current cell failure for developing all-solid-state Li metal cells operating up to a current density of 6.5 mA/cm2. Additionally, we propose a mechanistic analysis of the experimental results to prove that lithium activity near solid-state electrolyte defect tips is critical for reliable cell cycling. It is demonstrated that when lithium is geometrically constrained and local current plating rates exceed the exchange current density, the electrolyte region close to the defect releases the accumulated elastic energy favouring fracturing. As the build-up of this critical activity requires a certain period, applying current pulses of shorter duration can thus improve the cycling performance of all-solid-solid-state lithium batteries.

Lithium dendrites are amongst the key challenges hindering Solid-State Li Batteries (SSLB) from reaching their full potential in terms of energy and power density. The formation and growth of these dendrites cause an inevitable failure at charge rates far below the threshold set by industry (>5 mA/cm2) and are supposedly caused by stress accumulation stemming from the deposited lithium itself. Herein, we demonstrate that MHz pulsed currents can be used to increase the current density by a factor of six, reaching values as high as 6.6 mA/cm2 without forming Li dendrites. To understand the origin of this improvement we propose an extension of previous mechanisms by considering the Li activity as a critical factor. The Li activity becomes relevant when Li is geometrically constrained, and the local plating rate exceeds the exchange current density. Over a critical Li activity, the solid-state electrolyte close to the tip of the dendrite fractures and releases the accumulated elastic energy. These events deteriorate the functional and mechanical performance of the SSLB. Since the buildup of a critical Li activity requires a certain time, the application of current pulses at shorter time scales can be used to significantly improve the rate-performance of SSLB, representing a potential step towards the practical realization of electric vehicles and other emerging applications.

Lithium dendrites belong to the key challenges of solid-state battery research. They are unavoidable due to the imperfect nature of surfaces containing defects of a critical size that can be filled by lithium until fracturing the solid electrolyte. The penetration of Li metal occurs along the propagating crack until a short circuit takes place. We hypothesise that ion implantation can be used to introduce stress states into Li6.4La3Zr1.4Ta0.6O12 which enable an effective deflection and arrest of dendrites. The compositional and microstructural changes are studied via atom probe tomography, FIB-SEM with correlative TOF-SIMS, STEM and nano XRD indicating that Ag-ions can be implanted up to 1 µm deep and amorphization takes place down to 650-700 nm, in good agreement with kinetic Monte Carlo simulations. Based on nano XRD results pronounced stress states up to -700 MPa are generated in the near-surface region. Such a stress zone and the associated microstructural alterations exhibit the ability to not only deflect mechanically introduced cracks but also dendrites, as demonstrated by nano-indentation and galvanostatic cycling experiments with subsequent FIB-SEM observations. These results demonstrate ion implantation as a viable technique to design “dendrite-free” solid-state electrolytes for high-power and energy-dense solid-state batteries.