Advanced Cu-free Bipolar Solid-state Lithium-ion Battery Promoted by Li+ Conductive Matrix Enabled Excellent Iron Oxide Anode

Abstract Bipolar lithium-ion batteries (b-LIBs) with internal series configuration possess great advantages in conversion rate from theoretical energy density to practical values when compared with classic ones. Herein, advanced Cu-free b-LIBs with further simplified structure can be achieved by utilizing an amorphous Li+ conductive Li-Fe-BO2 matrix enabled iron oxide anode (FeOx-LFBO) with intermediate cutoff voltage (≥0.5 V) beyond lithiation potential of Al foil. The rational designed LFBO matrix can serve as a Li+ conductor/reservoir to enable fast Li+ diffusion, a heterogeneous nano-reactor to interdict aggregation of Fe + Li2O precipitates, a binder to aggregate particles, and a soft buffer to remit volume change. The FeOx-LFBO has a high tap density of 1.6 g/cm3, good electronic conductivity, and high Li+ conductivity. As an anode the intermediate cutoff voltage of 0.5 V, it harvests the admirable capacity of 710 mA h/g at 0.5 A/g, excellent cycling stability (95% after 1000 cycles), and capacitive rate capability (192 mA h/g at 50 A/g). Such an excellent anode is assembled into a novel Cu-free LIB, delivering an ultra-high energy density of 350 Wh/kg, outstanding power density of 6700 W/kg, and long-term cycling stability (75% after 2000 cycles), much better than state-of¬-the-art Li4Ti5O12 battery (≤100 Wh/kg, ≤5000 W/kg). Moreover, a Cu-free solid-state bipolar pouch cell is also fabricated sucessfully with high volatge of 7.6 V, great cycling stability, and safety. This study may set off an upsurge in studying intermediate cut-off voltage anodes and novel b-LIBs in the future.