A high-performance sodium-ion battery enhanced by macadamia shell derived hard carbon anode

Hard carbon anode materials for sodium-ion batteries (SIB) have usually been tested in half-cells by cycling between 0-2 V, and is believed to exhibit low rate capability. However, we find that the specific capacity, the rate performance, and the cycling performance may all be severely underestimated with the traditional half-cell cycling evaluation method, due to premature truncation of part II of the capacity (part I is sloping, part II is plateauing, while part III is Na metal deposition). Here we introduce a sodium-matched SIB full-cell architecture, with newly developed hard carbon derived from macadamia shell (MHC) as anode and Na[Cu1/9Ni2/9Fe1/3Mn1/3]O-2 (NCNFM) as the cathode material, with anode/cathode areal capacity ratio of 1.02-1.04. Our carefully balanced full-cells exhibit a cell-level theoretical specific energy of 215 Wh kg(-1) at C/10 and 186 Wh kg(-1) at 1C based on cathode-active and anode-active material weights, and an outstanding capacity retention of 70% after 1300 cycles (similar to 2000 h). Traditional half-cell test (THT) of MHC using superabundant Na metal counter electrode shows only 51.7 mAh g(-1) capacity at 1C, and appears to die in no more than 100 h due to low open-circuit voltage slope and large polarization. A revised half-cell test (RHT) which shows much better agreements with full-cell test results, delivers a specific capacity of 314 mAh g(-1), with an initial Coulombic efficiency of similar to 91.4%, which is comparable to that of graphite anode in lithium-ion batteries.