Search

High-voltage lithium cobalt oxide (LiCoO 2 ) has the highest volumetric energy density among commercial cathode materials in lithium-ion batteries due to its high working voltage and compacted density. However, under high voltage (4.6 V), the capacity of LiCoO 2 fades rapidly due to parasitic reactions of high-valent cobalt with the electrolyte and the loss of lattice oxygen at the interface. In this study, we report a temperature-driven anisotropic doping phenomenon of Mg 2+ that results in surface-populated Mg 2+ doping to the side of the (003) plane of LiCoO 2 . Mg 2+ dopants enter the Li + sites, lower the valence state of Co ions with less hybridization between the O 2p and Co 3d orbitals, promote the formation of surface Li + /Co 2+ anti-sites, and suppress lattice oxygen loss on the surface. As a result, the modified LiCoO 2 demonstrates excellent cycling performance under 4.6 V, reaching an energy density of 911.2 Wh/kg at 0.1C and retaining 92.7% (184.3 mAh g -1 ) of its capacity after 100 cycles at 1C. Our results highlight a promising avenue for enhancing the electrochemical performance of LiCoO 2 by anisotropic surface doping with Mg 2+ .

Bottom-up synthesis based on site-selective atomic layer deposition is a powerful atomic-scale processing approach to fabricate materials with desired functionalities. Typical selective atomic layer deposition (ALD) can be achieved using selective activation of a growth area or selective deactivation of a protected area. In this work, we explored the site selectivity based on the difference of the inherent surface reactivity between different materials and within the same materials. By sequentially applying two site-selective atomic layer deposition, the ALD Pd catalyst is spatially confined on ALD SnO 2 modified h-BN substrate Pd/SnO 2 /h-BN shows improved catalytic activity and stability due to strong metal-support interactions and spatial confinement. The results reveal that sequential site-selective ALD is a feasible and effective synthesis strategy that provides an attractive path toward designing and developing highly stable catalysts.

Thin films with effective ion sieving ability are highly desired in energy storage and conversion devices, including batteries and fuel cells. However, it remains challenging to design and fabricate cost-effective and easy-to-process ultrathin films for this purpose. Here, we report a 300 nm-thick functional layer based on porous organic cages (POCs), a new class of porous molecular materials, for fast and selective ion transport. This solution processable material allows for the design of thin films with controllable thickness and tunable porosity by tailoring cage chemistry for selective ion separation. In the prototype, the functional layer assembled by CC3 can selectively sieve Li + ions and efficiently suppress undesired polysulfides with minimal sacrifice for the system's total energy density. Separators modified with POC thin films enable batteries with good cycle performance and rate capability and offer an attractive path toward the development of future high-energy-density energy storage devices.

Balancing interfacial stability and Li + transfer kinetics through surface engineering is a key challenge in developing high-performance battery materials. Although conformal coating enabled by atomic layer deposition (ALD) has shown great promise in controlling impedance increase upon cycling by minimizing side reactions at the electrode-electrolyte interface, the coating layer itself usually exhibits poor Li + conductivity and impedes surface charge transfer. In this work, we have shown that by carefully controlling postannealing temperature of an ultrathin ZrO 2 film prepared by ALD, Zr 4+ surface doping could be achieved for Ni-rich layered oxides to accelerate the charge transfer yet provide sufficient protection. Using single-crystal LiNi 0.6 Mn 0.2 Co 0.2 O 2 as a model material, we have shown that surface Zr 4+ doping combined with ZrO 2 coating can enhance both the cycle performance and rate capability during high-voltage operation. Surface doping via controllable postannealing of ALD surface coating layer reveals an attractive path toward developing stable and Li + -conductive interfaces for single-crystal battery materials.