LiNi0.5Mn1.5O4 Cathode Microstructure for All-Solid-State Batteries

Multi-Electron Transfer Halide Cathode Materials Based on Intercalation-Conversion Reaction Towards All-Solid-State Lithium Batteries

All-solid-state lithium batteries (ASSLBs) with non-flammable solid-state electrolytes offer high energy density and enhanced safety. However, their energy densities are greatly limited by low-capacity and low-ionic-conductivity oxide cathode materials, typically relying on the intercalation-deintercalation mechanism with a catholyte content of 15-30 wt %. Here we introduce the LixFeXx+2 (X=Cl, Br) families as high-capacity and high-ionic-conductivity alternatives, operating via a 3 mol e- transfer intercalation-conversion coupling reaction. Notably, the catholyte-free ASSLBs using 95 wt % LiFeCl3 active material delivers a remarkable capacity of 446 mAh g-1 and a high energy density of 912 Wh kg-1, which surpasses most oxide cathode materials. Of particular interest is the formation of amorphous Fe during the conversion process. The amorphous Fe exhibits high activity, catalyzing the conversion of LiX back to LixFeXx+2, which proves instrumental in realizing reversible intercalation-conversion reactions. These halide cathode materials represent a significant advancement towards high-energy-density ASSLBs.

Advanced TiO2/Al2O3 Bilayer ALD Coatings for Improved Lithium-Rich Layered Oxide Electrodes

Surface modification is a highly effective strategy for addressing issues in lithium-rich layered oxide (LLO) cathodes, including phase transformation, particle cracking, oxygen gas release, and transition-metal ion dissolution. Existing single-/double-layer coating strategies face drawbacks such as poor component contact and complexity. Herein, we present the results of a low-temperature atomic layer deposition (ALD) process for creating a TiO2/Al2O3 bilayer on composite cathodes made of AS200 (Li1.08Ni0.34Co0.08Mn0.5O2). Electrochemical analysis demonstrates that TiO2/Al2O3-coated LLO electrodes exhibit improved discharge capacities and enhanced capacity retention compared with uncoated samples. The TAA-5/AS200 bilayer-coated electrode, in particular, demonstrates exceptional capacity retention (∼90.4%) and a specific discharge capacity of 146 mAh g-1 after 100 cycles at 1C within the voltage range of 2.2 to 4.6 V. The coated electrodes also show reduced voltage decay, lower surface film resistance, and improved interfacial charge transfer resistances, contributing to enhanced stability. The ALD-deposited TiO2/Al2O3 bilayer coatings exhibit promising potential for advancing the electrochemical performance of lithium-rich layered oxide cathodes in lithium-ion batteries.

Fluorination Effect on Lithium- and Manganese-Rich Layered Oxide Cathodes

Lithium- and manganese-rich (LMR) layered oxides are promising high-energy cathodes for next-generation lithium-ion batteries, yet their commercialization has been hindered by a number of performance issues. While fluorination has been explored as a mitigating approach, results from polycrystalline-particle-based studies are inconsistent and the mechanism for improvement in some reports remains unclear. In the present study, we develop an in situ fluorination method that leads to fluorinated LMR with no apparent impurities. Using well-defined single-crystal Li1.2Ni0.2Mn0.6O2 (LNMO) as a platform, we show that a high fluorination level leads to decreased oxygen activities, reduced side reactions at high voltages, and a broadly improved cathode performance. Detailed characterization reveals a particle-level Mn3+ concentration gradient from the surface to the bulk of fluorinated-LNMO crystals, ascribed to the formation of a Ni-rich LizNixMn2-xO4-yFy (x > 0.5) spinel phase on the surface and a "spinel-layered" coherent structure in the bulk where domains of a LiNi0.5Mn1.5O4 high-voltage spinel phase are integrated into the native layered framework. This work provides fundamental understanding of the fluorination effect on LMR and key insights for future development of high-energy Mn-based cathodes with an intergrown/composite crystal structure.

Interphase Stabilization of LiNi0.5 Mn1.5 O4 Cathode for 5 V-Class All-Solid-State Batteries

Employing high voltage cobalt-free spinel LiNi0.5 Mn1.5 O4 (LNMO) as a cathode is promising for high energy density and cost-effectiveness, but it has challenges in all-solid-state batteries (ASSBs). Here, it is revealed that the limitation of lithium argyrodite sulfide solid electrolyte (Li6 PS5 Cl) with the LNMO cathode is due to the intrinsic chemical incompatibility and poor oxidative stability. Through a careful analysis of the interphase of LNMO, it is elucidated that even the halide solid electrolyte (Li3 InCl6 ) with high oxidative stability can be decomposed to form resistive interphase layers with LNMO in ASSBs. Interestingly, with Fe-doping and a Li3 PO4 protective layer coating, LNMO with Li3 InCl6 displays stable cycle performance with a stabilized interphase at a high voltage (≈4.7 V) in ASSBs. The enhanced interfacial stability with the extended electrochemical stability window through doping and coating enables high electrochemical stability with LNMO in ASSBs. This work provides guidance for employing high-voltage cathodes in ASSBs and highlights the importance of stable interphases to enable stable cycling in ASSBs.