Copper Phosphate as a Cathode Material for Rechargeable
Li Batteries and Its Electrochemical Reaction Mechanism
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Abstract
In the search for new cathode materials
for rechargeable lithium
batteries, conversion-type materials have great potential because
of their ability to achieve high specific capacities via the full
utilization of transition metal oxidation states. Here, we report
for the first time that copper phosphate can be used as a novel high-capacity
cathode for rechargeable Li batteries, capable of delivering a reversible
capacity of 360 mAh/g with two discharge plateaus of 2.7 and 2.1 V
at 400 mA/g. The underlying reaction involves the formation as well
as the oxidation of metallic Cu. The solid-state NMR, <i>in situ</i> XAFS, HR-TEM, and XRD results clearly indicate that Cu can react
with Li<sub>3</sub>PO<sub>4</sub> to form copper phosphate and Li<sub><i>x</i></sub>Cu<sub><i>y</i></sub>PO<sub>4</sub> during the charging process, largely determining the reversibility
of Cu<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>. This new reaction scheme
provides a new venue to explore polyanion-type compounds as high-capacity
cathode materials with conversion reaction processes
