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Mn-rich layered oxides are appealing cathodes for potassium ion batteries (PIBs) in view of their comprehensive virtues such as low cost, high energy density and mature craftsmanship. However, the insufficient covalency between transition metal (TM) and O usually induces irreversible structural evolution and cation migration during repeated insertion and extraction of K+, resulting in capacity loss, voltage fading and sluggish kinetics. Herein, an anion substitution strategy is proposed for a stable operation of layered oxide cathode by adjusting the valence electron layer structure between TM and O. The resultant strong TM−O skeleton can inhibit the occurrence of side effects derive from Ni4+during the deep potassium process, so as to achieve a gentle structural transition. Consequently, stable cycling performance of K0.39Mn0.77Ni0.23O1.9F0.1(KMNOF) cathode is achieved with 77% capacity retention over 350 cycles at 100 mA/g, yielding high discharge capacity 93.5 mAh/g at 20 mA/g and significantly improved rate capability of 50.1 mAh/g at 500 mA/g, whereas irreversible structural evolution and rapid capacity fade with KMNO cathode. Finally, in situ/ex situ characterizations and theoretical computations sheds light on the charge transfer and structure evolution mechanisms of KMNOF.

NASICON type solid electrolyte Li1+xAlxGe2−x(PO4)3(LAGP) is one of the most potential candidates in view of their high ionic conductivity, high oxidation resistance and excellent air stability. However, inevitable interface issues often cause severe performance degradation, seriously affecting its commercial application. Herein, a lithiophilic carbon buffer layer is constructed on the LAGP surface adjacent to the Li electrode side by a facile pyrolysis reaction, then the LiCxinterlayer is generated in situ between the carbon buffer layer and lithium metal, which can guide uniform ion transport while improving interface contact. Thus, the LiCx-LAGP showed excellent ionic conductivity, high flexibility and lithiophilic interphase. Specially, the Li|LiCx-LAGP|Li battery has achieved a 1000 h stable cycles at 0.1 mA/cm2, remarkably, the Li|LiCx-LAGP|LFP battery retains 85% of their initial capacity after 200 cycles under 1 C, even for the NCM811 cathode, the battery still has a good cycle performance.

Effective design of nanoheterostructure anode with high ion/electron migration kinetics can give electrode with superior electrochemical performance. However, the design and preparation of nanoheterostructure composites with high-capacity and long cycling life in half and pouch full cells remain a big challenge. Here, a novel micro-pore MnS/Mn2SnS4heterostructure nanowire were in situ encapsulated into the N and S elements co-doped amorphous carbon tubes (abbreviated as (MnS/Mn2SnS4)@N,S-ACTs) and showed superior energy storage properties in Na-/Li-ion half cells and pouch full cells. The Na-/Li-storage capabilities improvement are attribute to the strong synergistic effect between MnS/Mn2SnS4heterostructure and N,S-ACTs protective layer, the former induces an local built-in electric field between Mn2SnS4and MnS during charging/discharging, accelerating interfacial ion/electron diffusion dynamics, the latter effective maintains the morphology and volume evolution during Na+/Li+charging/discharging, achieving a long-term cycling stability (e.g., high discharge capacity of 79.2 mAh/g with the capacity retention of 79.3% can be gained after 2200 cycles at 3 C in (MnS/Mn2SnS4)@N,S-ACTs//LiFePO4pouch full cells; a high capacity of ∼34 mAh/g at 10 C can be got with a Coulombic efficiency of 100% after 1000 cycles in pouch (MnS/Mn2SnS4)@N,S-ACTs//Na3V2(PO4)2O2F full cells.

P2-type layered oxides are receiving significant interest due to their superior structure and intrinsic performances. There are strenuous attempts to balance the structure stability, phase transition as well as desirable electrochemical performances by inducing anion/cation ions, changing morphology, adjusting valence, etc. In this work, several same-period elements of Sc, Ti, V, Cr, Fe, Cu and Zn are doped into Na0.50Li0.08Mn0.60Co0.16Ni0.16O2cathodes, which are manipulated by ions radii and valence state, further studied by operando X-ray powder diffraction patterns (XRD). As a result, the Cu2+doped cathode performed higher rate capacities (as high as 86 mAh/g even at 10 C) and more stable structures (capacity retention of ∼89.4% for 100 cycles), which owing to the synergistic effect among the tightened TMO2layer, enlarged d-spacing, reduce O-O electrostatic repulsion, ameliorate lattice distortion as well as mitigate ordering of Na+/vacancy.