All-solid-state batteries promise to enable lithium metal anodes and outperform state-of-the-art lithium-ion battery technology. To achieve high battery capacity, utilization of the active material in the cathode must be maximized. Carbon-based conductive additives are known to improve the capacity and rate performance of electrode composites. However, their influence on cathode composites in all-solid-state batteries is yet not fully understood. Here, we study the influence of several carbon additives with different morphologies and surface areas on the performance of an all-solid-state battery cell Li|β-Li 3 PS 4 | Li(Ni 0.6 Co 0.2 Mn 0.2 )O 2 /β-Li 3 PS 4 /carbon. Cycling tests and microstructure-resolved simulations show that higher utilization of the cathode active material can be achieved using fiber-shaped vapor-grown carbon additives, whereas particle-shaped carbons show a minor influence. Unfortunately, carbon additives generally lead to an accelerated capacity loss during cycling and an enhanced formation of solid electrolyte decomposition products. The latter was studied in more detail using cyclic voltammetry, X-ray photoelectron spectroscopy, and cycling experiments. The results show that carbon additives with a small surface area and a fiber-like morphology result in the lowest degree of decomposition. To completely overcome electrolyte degradation caused by the use of carbon additives, a protection concept is developed. A thin alumina coating with a few nanometers thickness was deposited on the carbon fibers by atomic layer deposition, which successfully prevents decomposition reactions, reduces long-term capacity fading, and leads to an enhanced overall all-solid-state battery performance.

Ni-rich Li­[Ni x Co y Mn1–x–y ]­O2 (NCM) cathode materials have attracted great research interest owing to their high energy density and relatively low cost. However, capacity fading because of parasitic side reactions, mainly occurring at the interface with the electrolyte, still hinders widespread application in advanced Li-ion batteries (LIBs). Surface modification via coating is a feasible approach to tackle this issue. Nevertheless, achieving uniform coatings is challenging, especially when using wet chemistry methods. In this work, a protective alumina shell on NCM701515 (70% Ni) was prepared through the reaction of surface-active −OH groups with trimethylaluminum as the precursor. The coated NCM701515 shows significantly improved capacity retention over uncoated (pristine) NCM701515. Part of the reason is the lower impedance buildup during cycling due to the effective suppression of adverse side reactions and secondary particle fracture. Taken together, the solution-based coating strategy described herein offers an easy way to apply surface treatment to stabilize Ni-rich NCM cathode materials in next-generation LIBs.

Ni-rich Li­(Ni1–x–y Co x Mn y )­O2-based cathodes still suffer from low cycling stability, which arises from capacity fading and impedance rise due to parasitic side reactions at the interface. Surface coatings have shown promising results in stabilizing the cathode surface and improving the cycling stability. However, a comprehensive understanding on the beneficial effect of the coating is still missing. In this paper, we used a solution-based technique to coat Ni-rich Li­(Ni0.70Co0.15Mn0.15)­O2 with a thin Al2O3 layer followed by post-annealing at 600 °C. Electrochemical characterization shows a drastic improvement of the cathode’s cycling stability due to the coating. After post-annealing, the cycling stability is even further improved, accompanied with its C-rate performance. Structural characterization confirms that annealing results in the formation of an amorphous Al2O3/LiAlO2 coating layer, which exhibits increased lithium-ion conductivity compared to the Al2O3 coating. More importantly, temperature-dependent impedance measurements reveal that the coatings do not affect the activation energy of the charge transport, which guarantees a sufficient electronic conductivity between the secondary NCM particles in the cathode. Thus, the Al2O3/LiAlO2 layer not only inhibits direct contact between electrode and electrolyte, preventing side reactions and stabilizes the performance, but also facilitates conductive pathways for lithium ions while preserving the electronic connectivity between cathode’s particles, leading to a low interfacial resistance and excellent rate capability. The results show the importance of providing a sufficiently high electrical conductivity accompanied with low activation energies in coating layers for both ions and electrons, which needs to be considered in design strategies for next-generation lithium-ion batteries.

Considering the high theoretical energy density and improved safety, thiophosphate-based all-solid-state batteries (ASSBs) have become one of the most promising candidates for next-generation energy storage systems. However, the intrinsic electrochemical instability of thiophosphate-based solid electrolytes in contact with oxide-based cathodes results in rapid capacity fading and has driven the need of protective cathode coatings. In this work, for the first time, a fumed lithium titanate (LTO) powder-based coating has been applied to Ni-rich oxide-based cathode active material (CAM) using a newly developed dry-coating process. The LTO cathode coating has been tested in thiophosphate-based ASSBs. It exhibits a significantly improved C-rate performance along with superior long-term cycling stability. The improved electrochemical performance is attributed to a reduced interfacial resistance between coated cathode and solid electrolyte as deduced from in-depth electrochemical impedance spectroscopy analysis. These results open up a new, facile dry-coating route to fabricate effective protective CAM coatings to enable long-life ASSBs. This nondestructive coating process with no post-heat-treatment approach is expected to simplify the coating process for a wide range of coatings and cathode materials, resulting in much improved cathode/electrolyte interfacial stability and electrochemical performance of ASSBs.

Porous yttria-stabilized zirconia (YSZ) thin films were prepared by pulsed laser deposition to investigate the influence of specific surface area on the electrical and protonic transport properties.