Polycrystalline metal oxides with enriched grain boundaries

An electrochemical cell, comprising:

• an anode,
• an electrolyte, and
• a cathode, the cathode comprising an electrochemically active cathode active material comprising a plurality of particles, said plurality of particles comprising a plurality of crystallites each comprising a first composition comprising lithium, nickel, and oxygen;
• a grain boundary between adjacent crystallites of the plurality of crystallites and comprising a second composition having a layered α-NaFeO2-type structure, a cubic structure, a spinel structure, or a combination thereof;
• wherein the electrochemically active cathode active material has an initial discharge capacity of 180 mAh/g or greater;
• and
• wherein the electrochemical cell has an impedance growth at 4.2V less than 50% for greater than 100 cycles at 45° C.