The degradation of charging/discharging capacities in the rate-performance test of lithium iron phosphate (LFP) cathodes with different loading amounts of an active material on both sides of a current collector (i.e., "unbalanced" LFP/LFP cathodes) in a laminated cell (typically composed of anode/separator/unbalanced cathodes/separator/ anode) was not observed actually at low Crates (e.g., 0.1 C). However, the rate-performance data obtained at high Crates (e.g., >5 C) indicated that the imbalance of the loading amounts of an active cathode material on both sides of an Al current collector causes a significant capacity degradation. We have found that it is possible to prevent the capacity degradation observed at high Crates by holing the unbalanced LFP/LFP cathodes in a micrometer-sized grid-patterned way (the percentages of the holed area are typically several %) using a pico-second pulsed laser: The non-holed unbalanced LFP/LFP cathodes exhibited a considerable capacity degradation at Crates which are, for example, larger than 5 C, while the holed ones showed no degradation in capacity even at high Crates (e.g., 5-20 C). Forming micrometer-sized grid-patterned holes in the LFP/LFP cathodes leads to an improved capacity and high-rate performance of their charging/discharging processes.

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