Lithium titanate epitaxial coating on spinel lithium manganese oxide surface for improving the performance of lithium storage capability

Review of the Scalable Core-Shell Synthesis Methods: The Improvements of Li-Ion Battery Electrochemistry and Cycling Stability

The demand for lithium-ion batteries has significantly increased due to the increasing adoption of electric vehicles (EVs). However, these batteries have a limited lifespan, which needs to be improved for the long-term use needs of EVs expected to be in service for 20 years or more. In addition, the capacity of lithium-ion batteries is often insufficient for long-range travel, posing challenges for EV drivers. One approach that has gained attention is using core-shell structured cathode and anode materials. That approach can provide several benefits, such as extending the battery lifespan and improving capacity performance. This paper reviews various challenges and solutions by the core-shell strategy adopted for both cathodes and anodes. The highlight is scalable synthesis techniques, including solid phase reactions like the mechanofusion process, ball-milling, and spray-drying process, which are essential for pilot plant production. Due to continuous operation with a high production rate, compatibility with inexpensive precursors, energy and cost savings, and an environmentally friendly approach that can be carried out at atmospheric pressure and ambient temperatures. Future developments in this field may focus on optimizing core-shell materials and synthesis techniques for improved Li-ion battery performance and stability.

High-Valence Surface-Modified LMO Cathode Materials for Lithium-Ion Batteries: Diffusion Kinetics and Operando Thermal Stability Investigation

Lithium manganese oxide (LiMn2O4) is a prevalent cathode material for lithium-ion batteries due to its low cost, abundant material sources, and ecofriendliness. However, its capacity fade, low energy density, and fast auto-discharge hinders its large-scale commercialization. Consequently, scientists are urged to achieve high-performance LMO cathodes through material doping and surface modification using a wide range of transition metals, polymers, and carbon precursors. Few studies have considered the potential of high-valence transition metal oxides in stabilizing the LMO's cycling process and enhancing the overall battery performance. In this work, we report the synthesis of surface-modified lithium manganese oxide using high-valence tungsten oxide (WVIO3). Different WO3 wt % were investigated before settling for 0.5%WO3-LMO as the synergic surface-modified LMO. Using galvanostatic charge-discharge, 0.50 WO3-LMO exhibited better rate capability by retaining 51% of its initial capacity at a 20C rate, compared to 34% for the pristine LMO. Furthermore, cyclic voltammetry at different scan rates showed that 0.50 WO3-LMO possesses better ion diffusion than pristine LMO, around 10-11 and 10-13 cm2·s-1 respectively. Finally, using in situ Raman spectroscopy, reaction mechanisms during cycling were investigated, and operando accelerating rate calorimetry (ARC) visualized the surface-modified LMO's cycling thermal stability and highlighted its potential use for safe high-voltage lithium-ion batteries in automotive applications.

Ti surface doping of LiNi0.5Mn1.5O4−δ positive electrodes for lithium ion batteries

The particle surface of LiNi_0.5Mn_1.5O_4−δ (LNMO), a Li-ion battery cathode material, has been modified by Ti cation doping through a hydrolysis–condensation reaction followed by annealing in oxygen. The effect of different annealing temperatures (500–850 °C) on the Ti distribution and electrochemical performance of the surface modified LNMO was investigated. Ti cations diffuse from the preformed amorphous ‘TiO_x’ layer into the LNMO surface during annealing at 500 °C. This results in a 2–4 nm thick Ti-rich spinel surface having lower Mn and Ni content compared to the core of the LNMO particles, which was observed with scanning transmission electron microscopy coupled with compositional EDX mapping. An increase in the annealing temperature promotes the formation of a Ti bulk doped LiNi_(0.5−w)Mn_(1.5+w)−tTi_tO₄ phase and Ti-rich LiNi_0.5Mn_1.5−yTi_yO₄ segregates above 750 °C. Fourier-transform infrared spectrometry indicates increasing Ni–Mn ordering with annealing temperature, for both bare and surface modified LNMO. Ti surface modified LNMO annealed at 500 °C shows a superior cyclic stability, coulombic efficiency and rate performance compared to bare LNMO annealed at 500 °C when cycled at 3.4–4.9 V vs. Li/Li⁺. The improvements are probably due to suppressed Ni and Mn dissolution with Ti surface doping.

LiNi_0.5Mn_1.5O_4−δ surface is doped with Ti ion maintaining the spinel structure at 500 °C, higher annealing temperatures cause Ti diffusion from surface towards the core.

Low-Temperature Carbon Coating of Nanosized Li1.015Al0.06Mn1.925O4 and High-Density Electrode for High-Power Li-Ion Batteries

Despite their good intrinsic rate capability, nanosized spinel cathode materials cannot fulfill the requirement of high electrode density and volumetric energy density. Standard carbon coating cannot be applied on spinel materials due to the formation of oxygen defects during the high-temperature annealing process. To overcome these problems, here we present a composite material consisting of agglomerated nanosized primary particles and well-dispersed acid-treated Super P carbon black powders, processed below 300 °C. In this structure, primary particles provide fast lithium ion diffusion in solid state due to nanosized diffusion distance. Furthermore, uniformly dispersed acid-treated Super P (ASP) in secondary particle facilitates lower charge transfer resistance and better percolation of electron. The ASPLMO material shows superior rate capability, delivering 101 mAh g^-1 at 300 C-rate at 24 °C, and 75 mAh g^-1 at 100 C-rate at -10 °C. Even after 5000 cycles, 86 mAh g^-1 can be achieved at 30 C-rate at 24 °C, demonstrating very competitive full-cell performance.

Hierarchical LiMn2O4 Hollow Cubes with Exposed {111} Planes as High-Power Cathodes for Lithium-Ion Batteries

Hierarchical LiMn2O4 hollow cubes with exposed {111} planes have been synthesized using cube-shaped MnCO3 precursors, which are fabricated through a facile co-precipitation reaction. Without surface modification, the as-prepared LiMn2O4 exhibits excellent cyclability and superior rate capability. Surprisingly, even over 70% of primal discharge capacity can be maintained for up to 1000 cycles at 50 C, and with only about 72 s of discharge time the as-prepared materials can deliver initial discharge capacity of 96.5 mA h g(-1). What is more, the materials have 98.4% and 90.7% capacity retentions for up to 100 cycles at 5 C under the temperatures of 25 and 60 °C, respectively. The superior electrochemical performance can be attributed to the unique hierarchical and interior hollow structure, exposed {111} planes, and high-quality crystallinity.

Flakelike LiCoO2 with Exposed {010} Facets As a Stable Cathode Material for Highly Reversible Lithium Storage

A thick and dense flakelike LiCoO2 with exposed {010} active facets is synthesized using Co(OH)2 nanoflake as a self-sacrificial template obtained from a simple coprecipitation method, and served as a cathode material for lithium ion batteries. When operated at a high cutoff voltage up to 4.5 V, the resultant LiCoO2 exhibits an outstanding rate capability, delivering a reversible discharge capacity as high as 179, 176, 168, 116, and 96 mA h g(-1) at 25 °C under the current rate of 0.1, 0.5, 1, 5, and 10 C, respectively. When charge/discharge cycling at 55 °C, a high specific capacity of 148 mA h g(-1) (∼88% retention) can be retained after 100 cycles under 1 C, demonstrating excellent cycling and thermal stability. Besides, the flakelike LiCoO2 also shows an impressive low-temperature electrochemical activity with specific capacities of 175 (0.1 C) and 154 mA h g(-1) (1 C) at -10 °C, being the highest ever reported for a subzero-temperature lithium storage capability, as well as 52% capacity retention even after 80 cycles under 1 C. Such superior high-voltage electrochemical performances of the flakelike LiCoO2 operated at a wide temperature range are mainly attributed to its unique hierarchical structure with specifically exposed facets. The exposed {010} active facets provide a preferential crystallographic orientation for Li-ion migration, while the micrometer-sized secondary particles agglomerated by submicron primary LiCoO2 flakes endow the electrode with better structural integrity, both of which ensure the LiCoO2 cathode to manifest remarkably enhanced reversible lithium storage properties.

High Cycling Stability and Extreme Rate Performance in Nanoscaled LiMn2O4 Thin Films

Ultrathin LiMn2O4 electrode layers with average crystal size of ∼15 nm were fabricated by means of radio frequency sputtering. Cycling behavior and rate performance was evaluated by galvanostatic charge and discharge measurements. The thinnest films show the highest volumetric capacity and best cycling stability, retaining the initial capacity over 70 (dis)charging cycles when manganese dissolution is prevented. The increased stability for film thicknesses below 50 nm allows cycling in both the 4 and 3 V potential regions, resulting in a high volumetric capacity of 1.2 Ah/cm3. It is shown that the thinnest films can be charged to 75% of their full capacity within 18 s (200 C), the best rate performance reported for LiMn2O4. This is explained by the short diffusion lengths inherent to thin films and the absence of phase transformation.