In the presentation, some new research progress of stabilizing high-voltage layered oxide cathode materials for Li/Na ion batteries in this group will be reported. Our strategies include two directions[3,4]: one is to improve the interface stability by using high voltage electrolyte additives or surface coating, another is to stabilize the lattice structure by using suitable element doping.
For example, when extending the working voltage of LiCoO2 from 4.2V to 4.4V or even more, we must develop some new electrolyte recipes to stabilize corresponding electrode/electrolyte interface at high voltage. Our recent results show that a synergistic effects of suberonitrile-LiBOB binary additives in high-voltage cathode system, i.e. they could improve the cyclic performance of 4.5V LiCoO2 effectively. The corresponding working mechanism of the binary additives will be presented.
As to develop high energy density Na-ion battery, it is important to develop high-voltage cathode material. It is found that [6,7] the introduction of Zn2+ in the Na-Ni-Mn-O system can effectively overcome the drawback of voltage decay when charged to a higher cutoff voltage (>4.0 V), and significantly improve capacity retention compared to the unsubstituted material during cycling. In addition, a smoother charge/discharge profile can be observed between 3.0 and 4.0 V for Zn-substituted samples, demonstrating that Na+/vacancy ordering can be suppressed during sodium insertion/extraction. Na0.66Ni0.26Zn0.07Mn0.67O2 can deliver an initial capacity of 132 mAh g–1 at 12 mA g–1 with a high average voltage of 3.6 V and a capacity retention of 89% after 30 cycles. We have used a series of techniques such as in-situ XRD, in-situ XAS, ex-situ solid state NMR and HRTEM techniques to investigate the structural changes during cycling process and working mechanism of Zn2+ in the corresponding Na0.66Ni0.26Zn0.07Mn0.67O2 cathode materials.