  The biggest challenge for the commercialization of layered structured nickel
rich lithium transition metal oxide cathode is the capacity and voltage fading.
Resolving this problem over the years follows an incremental progress. In this
work, we report our finding of totally a new approach to revolutionize the
cycle stability of aggregated cathode particles for lithium ion battery at both
room and elevated temperatures. We discover that infusion of a solid
electrolyte into the grain boundaries of the cathode secondary particles can
dramatically enhance the capacity retention and voltage stability of the
battery. We find that the solid electrolyte infused in the boundaries not only
acts as a fast channel for Li ion transport, but also most importantly prevents
penetration of the liquid electrolyte into the boundaries, consequently
eliminating the detrimental factors that include solid-liquid interfacial
reaction, intergranular cracking, and layer to spinel phase transformation. The
present work, for the first time, reveals unprecedented insight as how the
cathode behaves in the case of not contacting with the liquid electrolyte,
ultimately points toward a general new route, via grain boundary engineering,
for designing of better batteries of both solid-liquid and solid state systems.
