Grain-boundary-rich cathode enabling fast ion diffusion kinetics for low-temperature and high-rate lithium-ion batteries

Lithium-ion batteries (LIBs) suffer from severe capacity degradation and shortened cycle life at low operating temperatures due to sluggish Li⁺ diffusion kinetics within the bulk phase of large-sized electrode materials, limiting their applicability in extreme environments. However, practical strategies to address these challenges are scarce, and a systematic understanding of low-temperature Li⁺ storage remains limited. In this work, we construct a grain-boundary-rich crystal structure in vanadium oxide cathode through a solid-state phase transition strategy, and reveal that both the grain boundary density and the amorphous region ratio are closely linked to low-temperature capacity retention. Unlike conventional nanoparticle agglomeration or assembly, this structure features large grains segmented into numerous nanocrystallites by amorphous regions, while preserving overall structural integrity. The loose atomic packing at the grain boundaries reduces topological constraints and introduces significant free volume within the bulk phase, thereby enhancing Li⁺ transport kinetics under low-temperature conditions. Additionally, lattice strain fluctuations, induced by abundant defects, effectively mitigate the volume changes during lithiation and delithiation processes by releasing local stress at the grain boundaries. As a result, the developed vanadium oxide cathode exhibits unprecedented high-rate capacity (152 mA h g⁻¹ at 1.0C and 105 mA h g⁻¹ at 3.3C), excellent capacity retention (72.5%), and long-term cycling stability (5000 cycles) at −40 °C, alongside superior performance even at lower temperatures.