High-nickel layered oxide cathodes suffer seriously from the formation of residual lithium on the surface, which causes notorious issues, such as slurry gelation and gas evolution. Due to the use of water for the titration to determine the residual lithium content, certain practical issues remain unresolved. We present here, for the first time, a thorough study of residual lithium that reveals the following. (1) Li 2 CO 3 impurity in lithium raw materials contributes to an increase in residual lithium in high-Ni cathodes after synthesis. (2) LiOH formed due to a leaching of Li from high-Ni cathodes during analyte preparation in water exaggerates the LiOH content in residual lithium (employing a new titration method). (3) A dry cobalt hydroxide coating on high-Ni cathodes not only effectively reduces residual lithium content but also leads to the formation of a Co-rich concentration gradient layer on the surface that suppresses Li leaching when in contact with water.

total global passenger car and light duty vehicle sales in 2020, EV sales in 2030 are forecasted to contribute over 30% of the total sales. [1] The demand for automotive lithium-ion batteries is going to surpass 1.5 TWh per year in 2030, nearly a tenfold increase from the current demand of EV battery capacity globally. [2] With 89% of the overall battery demand projected to come from EVs alone in 2030, the future direction of lithium-ion battery research and development will undoubtedly be shaped by the performance demand of EVs.Rapid commercial adoption of EVs is primarily hindered by a relatively expensive vehicle price and low driving range per a single charge. The bottleneck lies within the high cost and inadequate energy density of EV battery packs. Current lithium-ion battery packs for EVs cost on average US$137 kWh -1 and delivers 160-170 Wh kg -1 of energy density at the pack-level. [3,4] For EVs to achieve a cost and range parity with internal combustion vehicles, next-generation battery packs should cost less than US$100 kWh -1 and deliver at least 235 Wh kg -1 according to the Office of Energy Efficiency and Renewable Energy. [5] Achieving these performance metrics largely depends on the energy density and cost of nickel-based layered oxide cathode materials. The prevailing trend within EV battery manufacturers is to increase the nickel content of LiNi 1−x−y Mn x Co y O 2 (NMC) for higher energy density, progressing incrementally from LiNi 0.33 Mn 0.33 Co 0.33 O 2 (NMC111) → LiNi 0.5 Mn 0.3 Co 0.2 O 2 (NMC532) → LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622) → LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811). However, high-Ni layered oxide cathode materials generally suffer from lattice and surface instabilities that diminish the longevity of the battery. [6,7] Dopants like Al have been proven effective in mitigating these detrimental effects, giving rise to LiNi 1−x−y Co x Al y O 2 (NCA) as another subset of layered oxide cathode materials that is employed in the Tesla Model 3. [8] Incorporating Co in cathode materials for EVs, on the other hand, is problematic from a cost and sustainability perspective. Cobalt is the most expensive element in the cathode composition and has experienced volatile price movements from US$30 kg -1 to over US$90 kg -1 . A rational compositional design of high-nickel, cobalt-free layered oxide materials for high-energy and low-cost lithium-ion batteries would be expected to further propel the widespread adoption of electric vehicles (EVs), yet a composition with satisfactory electrochemical properties has yet to emerge. The previous work has demonstrated a promising LiNi 0.883 Mn 0.056 Al 0.061 O 2 (NMA-89) composition that outperformed high-nickel, cobalt-containing analogs in cycling stability and maintained a comparable rate performance and thermal stability. Herein, the capacity fading mechanism of NMA-89 in a pouch full cell with a 4.2 V cutoff is compared to that of its cobalt-containing analogs. The results reveal that particle cracking in LiNi 0.89 Mn 0.055 Co 0.055 O 2 (NMC-89) and LiNi...

The implementation of high‐nickel layered oxide cathodes in lithium‐ion batteries is hampered by the inherent issues of formation of NiO‐like rock‐salt phase as well as residual lithium (e.g., LiOH, LiHCO3, and Li2CO3) on the surface. To overcome the challenges, here a rational strategy is presented of interdiffusion‐based surface reconstruction via dry coating and the design principles for identifying the optimum coating ions on a LiNi0.91Mn0.03Co0.06O2 (NMC91) cathode. Notably, the combined approach of theoretical screening, which involves the consideration of superexchange interactions among different oxidation states and density functional theory calculations, along with experimental analyses, which involve the characterization of the decrease in Ni content and residual lithium on the surface of NMC91, demonstrate the effective reduction in rock‐salt phase and residual lithium. Among the four ions investigated (Al, Co, Fe, and Ti), cobalt‐coated NMC91 is the most effective at reducing the rock‐salt phase and residual lithium by successfully reconstructing the surface of NMC91 and exhibits an excellent capacity retention of 85% in a full cell after 300 cycles at 30 °C.

Thick epitaxial BaTiO 3 films ranging from 120 nm to 1 μm were grown by off-axis RF magnetron sputtering on SrTiO 3 -templated silicon-on-insulator (SOI) substrates for use in electro-optic applications, where such large thicknesses are necessary. The films are of high quality, rivaling those grown by molecular beam epitaxy (MBE) in crystalline quality, but can be grown 10 times faster. Extraction of lattice parameters from geometric phase analysis of atomic-resolution scanning transmission electron microscopy images revealed how the in-plane and out-of-plane lattice spacings of sputtered BaTiO 3 changes as a function of layer position within a thick film. Our results indicate that compared to molecular beam epitaxy, sputtered films retain their out-of-plane polarization (c-axis) orientation for larger thicknesses. We also find an unusual re-transition from in-plane polarization (a-axis) to out-ofplane polarization (c-axis), along with an anomalous lattice expansion, near the surface. We also studied a method of achieving 100% a-axis-oriented films using a two-step process involving amorphous growth and recrystallization of a seed layer followed by normal high temperature growth. While this method is successful in achieving full a-axis orientation even at low thicknesses, the resulting film has a large number of voids and misoriented grains. Electro-optic measurement using a transmission setup of a sputtered BTO film grown using the optimized conditions yields an effective Pockels coefficient as high as 183 pm/V. A Mach− Zehnder modulator fabricated on such films exhibits phase shifting with an equivalent Pockels coefficient of 157 pm/V. These results demonstrate that sputtered BTO thick films can be used for integrated electro-optic modulators for Si photonics.