Solid-state batteries (SSB) have received increasing attention as a next-generation energy storage technology due to their potential in delivering superior energy density, power density and safety compared to commercial Li-ion batteries. One of the main challenges limiting their practical implementation is the rapid capacity decay caused by the loss of contact between cathode active material and solid electrolyte upon cycling. Here we use the promising high voltage, low-cost spinel LiNi0.5Mn1.5O4 (LNMO) as a model system to demonstrate the importance of the cathode microstructure in SSBs. We design Al2O3-coated LNMO particles with a hollow microstructure aimed at suppressing electrolyte decomposition, minimise volume change during cycling and shorten the Li-diffusion pathway to achieve maximum cathode utilisation and improve areal capacity. When cycled with a Li6PS5Cl solid electrolyte and a Li-In anode, we demonstrate capacity retention above 70% after 100 cycles with an active material loading of 27 mg/cm2 (2.2 mAh/cm2) at a current density of 0.8 mA/ cm2.