Promotion of the Nucleation of Ultrafine Ni-Rich Layered Oxide Primary Particles by an Atomic Layer-Deposited Thin Film for Enhanced Mechanical Stability.

Understanding the atomistic mechanisms of non-equilibrium processes during solid-state synthesis, such as nucleation and grain structure formation of a layered oxide phase, is a critical challenge for developing promising cathode materials such as Ni-rich layered oxide for Li-ion batteries. In this study, we found that the aluminum oxide coating layer transforms into lithium aluminate as an intermediate, which has favorable low interfacial energies with the layered oxide to promote the nucleation of the latter. The fast and uniform nucleation and formation of the layered oxide phase at relatively low temperatures were evidenced using solid-state nuclear magnetic resonance and in situ synchrotron X-ray diffraction. The resulting Ni-rich layered oxide cathode has fine primary particles, as visualized by three-dimensional tomography constructed using a focused-ion beam and scanning electron microscopy. The densely packed fine primary particles enable the excellent mechanical strength of the secondary particles, as demonstrated by in situ compression tests. This strategy provides a new approach for developing next-generation, high-strength battery materials.

Monolithic Titanium Alkoxide Networks for Lithium-Ion Conductive All-Solid-State Electrolytes.

Reticular chemistry provides opportunities to design solid-state electrolytes (SSEs) with modular tunability. However, SSEs based on modularly designed crystalline metal-organic frameworks (MOFs) often require liquid electrolytes for interfacial contact. Monolithic glassy MOFs can have liquid processability and uniform lithium conduction, which is promising for the reticular design of SSE without liquid electrolytes. Here, we develop a generalizable strategy for the modular design of noncrystalline SSEs based on a bottom-up synthesis of glassy MOFs. We demonstrate such a strategy by linking polyethylene glycol (PEG) struts and nanosized titanium-oxo clusters into network structures termed titanium alkoxide networks (TANs). The modular design allows the incorporation of PEG linkers with different molecular weights, which give optimal chain flexibility for high ionic conductivity, and the reticular coordinative network provides a controlled degree of cross-linking that gives adequate mechanical strength. This research shows the power of reticular design in noncrystalline molecular framework materials for SSEs.

An Ultrathin Functional Layer Based on Porous Organic Cages for Selective Ion Sieving and Lithium-Sulfur Batteries.

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.

Simultaneous Enhancement of Interfacial Stability and Kinetics of Single-Crystal LiNi0.6Mn0.2Co0.2O2 through Optimized Surface Coating and Doping.

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 ZrO2 film prepared by ALD, Zr4+ surface doping could be achieved for Ni-rich layered oxides to accelerate the charge transfer yet provide sufficient protection. Using single-crystal LiNi0.6Mn0.2Co0.2O2 as a model material, we have shown that surface Zr4+ doping combined with ZrO2 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.