High‐energy Li‐rich layered cathode materials (≈900 Wh kg−1) suffer from severe capacity and voltage decay during cycling, which is associated with layered‐to‐spinel phase transition and oxygen redox reaction. Current efforts mainly focus on surface modification to suppress this unwanted structural transformation. However, the true challenge probably originates from the continuous oxygen release upon charging. Here, the usage of dielectric polarization in surface coating to suppress the oxygen evolution of Li‐rich material is reported, using Mg2TiO4 as a proof‐of‐concept material. The creation of a reverse electric field in surface layers effectively restrains the outward migration of bulk oxygen anions. Meanwhile, high oxygen‐affinity elements of Mg and Ti well stabilize the surface oxygen of Li‐rich material via enhancing the energy barrier for oxygen release reaction, verified by density functional theory simulation. Benefited from these, the modified Li‐rich electrode exhibits an impressive cyclability with a high capacity retention of ≈81% even after 700 cycles at 2 C (≈0.5 A g−1), far superior to ≈44% of the unmodified counterpart. In addition, Mg2TiO4 coating greatly mitigates the voltage decay of Li‐rich material with the degradation rate reduced by ≈65%. This work proposes new insights into manipulating surface chemistry of electrode materials to control oxygen activity for high‐energy‐density rechargeable batteries.

Citation denotes calendar and volume year of first online publication.

Molybdenum disulfide (MoS 2 ) is a promising high-capacity anode for lithium-ion batteries. However, the conversion reaction mechanism of MoS 2 (the delithiation pathway in particular) has been controversial, which limits the rational optimization of its electrochemical performance. The main challenge is how to precisely identify the amorphous nanomaterials generated during lithiation/delithiation. Here, the structural evolutions of MoS 2 during lithiation/delithiation are systematically investigated using synchrotron X-ray absorption spectroscopy at Mo K-edge and S K-edge and Raman spectroscopy. It is revealed that amorphous MoS 2 nanograins rather than sulfur as previously suggested, are formed after delithiation, and that the fully lithiated MoS 2 electrode contains additional Mo-S related phases besides the known Mo and Li 2 S. Density functional theory simulations suggest that the Mo nanoparticles formed during lithiation are very reactive with Li 2 S, thus enabling the regeneration of MoS 2 upon delithiation. These findings deepen the understanding of the lithiation/delithiation mechanism of MoS 2 , which will pave the way for the rational design of advanced MoS 2based electrodes.

Oxygen vacancies play crucial roles in defining physical and chemical properties of materials to enhance the performances in electronics, solar cells, catalysis, sensors, energy conversion and storage. Conventional approaches to incorporate oxygen defects mainly rely on reducing oxygen partial pressure for the removal of product to change equilibrium position. However, directly affecting reactants to shift the reaction towards generating oxygen vacancies is lacking and to fill this blank in synthetic methodology is very challenging. Here we Received: ((will be filled in by the editorial staff))Revised: ((will be filled in by the editorial staff))

MoS 2 holds great promise as high-rate electrode for lithium-ion batteries since its large interlayer can allowf ast lithium diffusion in 3.0-1.0 V. However,t he lowt heoretical capacity (167 mAh g À1 )l imits its wide application. Here,b y fine tuning the lithiation depth of MoS 2 ,wedemonstrate that its parent layered structure can be preserved with expanded interlayers while cycling in 3.0-0.6 V. The deeper lithiation and maintained crystalline structure endows commercially micrometer-sized MoS 2 with acapacity of 232 mAh g À1 at 0.05 Ag À1 and circa 92 %capacity retention after 1000 cycles at 1.0 Ag À1 . Moreover,t he enlarged interlayers enable MoS 2 to release ac apacity of 165 mAh g À1 at 5.0 Ag À1 ,w hichi sd ouble the capacity obtained under 3.0-1.0 Va tt he same rate.O ur strategy of controlling the lithiation depth of MoS 2 to avoid fracture ushers in new possibilities to enhance the lithium storage of layered transition-metal dichalcogenides.