A Fast Charge/Discharge and Wide-Temperature Battery with a Germanium Oxide Layer on a Ti₃C₂ MXene Matrix as Anode

A rapid charge/discharge secondary battery is critical in portable electronic devices and electric vehicles. Germanium, due to the metallic property and facile alloying reaction with lithium, displays great potential in fast charge/discharge batteries in contrast to other intercalation batteries. In order to accommodate the over 300% volume change, a 2D hybrid composite electrode consisting of a homogeneous, amorphous GeO_x(x=1.57) layer bonded on Ti₃C₂ MXenes was successfully developed via an industry available method. The expanded interlayer space inside the MXene matrix accommodates the restricted isotropic expansion from the stress-released, ultrathin GeO_x layer. Owing to the improved e^–/Li⁺ conductivity from both metallic reduced Ge and MXene, the battery showed an excellent charge/discharge performance as fast as 3 min (20.0 C). A high-capacity retention of ∼1048.1 mAh/g along with a Coulombic efficiency (CE) of 99.8% at 0.5 C after 500 cycles was achieved. Under 1.0 C, the capacity was still up to 929.6 mAh/g with a CE of 99.6% (<0.02% capacity decay per cycle) after ultralong (1000) cycling. An almost doubled capacity of 671.6 mAh/g compared to graphite (372 mAh/g at 0.1 C) under 5.0 C and a capacity of 300.5 mAh/g under 10.0 C after 1000 cycles were respectively received. Under cold conditions, due to the low interface energy barrier, an efficient alloying reaction happens which prevents the Li plating on the electrode surface. High capacities of 631.6, 333.9, and 841.7 mAh/g under −20, −40, and 60 °C after 100 cycles demonstrate a wide temperature tolerance of the battery. In addition, a full-cell battery paired with LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) displayed a high capacity of 536.8 mAh/g after 200 cycles. A high capacity retention of a full pouch cell after 50 cycles was also obtained. The superhigh rate capability along with long cycling, wide temperature range, scalable production, and relatively low cost of this hybrid composite display promising potential in specific energy storage applications.