The Enhancement of Electrochemical Properties of Yttrium -Doped Single-Crystal Cathode Materials for High-Rate Charging and Discharging

Compared to conventional polycrystallines, single crystal layered cathode materials exhibit the excellent structural and thermal stability, storage and lifetime at high voltage and elevated temperature. However, these single crystal materials are less reported, especially for Ni ≥ 0.92 in nickel-rich cathode materials. In this paper, single crystal LiNi0.92Co0.06Mn0.01Al0.01O2 (NCMA) cathode materials are researched. The experiment demonstrates that co-doping fluxing agents in B-NCMA (NCMA with 1000ppm W and 1000 ppm Mo) sample facilitate to generate uniform and small crystal size, which delivers a high initial discharge capacity of 221.4 mAh g−1 at 0.1 C. Moreover, the superior capacity retention of 94.9% after 100th cycle at 45 °C is obtained. Furthermore, DSC analysis of cycled B-NCMA material displays high thermal release temperature and low gas emission, revealing decent thermal stability. XRD, dQ·dV−1 and EIS results suggest that co-doping fluxing agents beneficial to form less cationic mixing, more stable phase structure and less internal resistance, respectively, which are associated with excellent rate capacity, cycling and thermal stability of single crystal NCMA. In our opinion, this study will stimulate that more fluxing agents are found and applied on single crystal nickel-rich cathode materials, which will have a bright future in the high-energy lithium ion battery fields.

Toward high stability single crystal material by structural regulation with high and low temperature mixing sinter

Application of precursor with ultra-small particle size and uniform particle distribution for ultra-high nickel single-crystal cathode materials by coprecipitation method

To meet the increasing energy demands of portable devices and electric vehicles, high-nickel lithium-ion cathode materials with the general formula Li(NixMnyCoz)O2 (NMCXYZ) have been extensively researched. Currently, NMC811 is used commercially due to its high capacity and low cobalt content. However, capacity fade is still a prominent issue, with a variety of degradation mechanisms responsible. Of particular interest is secondary particle cracking, where the stress-strain effect of c-parameter expansion in the NMC crystal lattice leads to fractures. Boundaries between the primary particle grain that make up the secondary particle structure act as nucleation points for particle cracking. The exposed surface then reacts with the liquid electrolyte, leading to oxygen evolution and capacity loss. Single-crystal materials have shown promise as a method of improving cycle life, as the lack of agglomerated primary grains appear to make the monocrystalline particles more resilient to the mechanical strain of expansion during charging1.In parallel with the cycle life concerns, attention over battery safety continues to increase as instances of catastrophic battery failure are publicised across the world. While the specific steps that lead to battery thermal runaway have been extensively researched, the safety and thermal stability of degraded cells remains a scarcely investigated topic2. To that end, the goal of this work is to characterise the safety properties of different NMC morphologies, and study how charge-discharge cycling affects the thermal stability of these materials.In this work, we have combined accelerating rate calorimetry (ARC) with lab-based, post-mortem macro, micro and nano X-ray CT to observe the influence of cell structure on thermal runaway of NMC811 pouch cells with single-crystal and polycrystalline cathode materials in both the pristine and aged state. The results presented show that when pristine, the larger surface area of single-crystal materials provides more reaction sites and leads to a lower self-heating onset and thermal runaway initiation temperature compared to polycrystalline, suggesting a lower thermal stability. However, as polycrystalline particles break up during thermal runaway, the fragments create fresh surface to react with the electrolyte and continue the series of exothermic reactions, leading to a higher peak temperature. Macro-CT has revealed how the wound jellyroll structure of the cell focuses the force of the explosion through the flat sides of the cells, possibly increasing the likelihood of failure propagation. It has also been observed that the polycrystalline materials show a greater material ejection out from the centre of the cell, reinforcing the findings from the ARC investigations that although polycrystalline cells are more thermally stable initially, the peak temperatures produced during catastrophic failure are higher due to particle fracture. Micro and nano-CT are used to probe this idea further, revealing that polycrystalline particles show significant damage and fracturing during failure, whereas single-crystal materials remain largely intact.Both polycrystalline and single-crystal morphologies were cycled to 80% capacity retention, with EIS and diagnostic cycles used to identify prevalent degradation modes for both particle structures. As previously found, the single-crystal cells showed superior cycle life to the polycrystalline materials3. The same combination of ARC and X-ray CT was then applied to aged cells, where it was found that aged cells show lower thermal stability than their pristine counterparts.Overall, this work aims to build understanding of the interplay between material structure, safety and degradation of nickel-rich cathodes, with the goal of informing future material development to produce batteries that are safer throughout their lifetimes. G. Qian et al., Energy Storage Mater., 27, 140–149 (2020) https://doi.org/10.1016/j.ensm.2020.01.027.X. Feng et al., Energy Storage Mater., 10, 246–267 (2018) https://doi.org/10.1016/j.ensm.2017.05.013.D. Ren et al., eTransportation, 2, 100034 (2019) https://doi.org/10.1016/j.etran.2019.100034.

Single-Crystal Oxide Cathode Materials

Single crystal LiNi0.6Mn0.2Co0.2O2 cathode materials with excellent electrochemical properties were synthesized by adjusting the calcination, ball milling, and reheating procedures. The results showed that the particle size of single crystal material obtained by the optimization method was 1.2–4.4 μm. And the material exhibited a superior discharge capacity of 190.1 mAh g−1 with high capacity retention of 96.0% after 50 cycles at 1.0 C. And the material had a discharge capacity of 162.6 mAh g−1 at 5.0 C with the capacity retention of 83.0% compared with its capacity at 0.1 C. The diffusion coefficient of lithium ions in the single crystal material reached to 10−13 cm2 s−1 after 50 cycles. By proper reheating process, the particle morphology was optimized to form a smooth particle surface, and the lattice arrangement was more orderly, which was conductive to improving electrochemical performance of the material.

Enhancing structure and cycling stability of Ni-rich layered oxide cathodes at elevated temperatures via dual-function surface modification

While cathode material stability is essential for long-lasting, high-performing batteries, conventional polycrystalline cathodes produced via current industry standards are prone to structural damage, such as particle cracking during charge-discharge cycles, resulting in battery degradation. Polycrystalline cathode particles undergo pulverization during battery cycling because of the anisotropic volume change during lithium extraction/insertion. This intergranular fracture in polycrystalline particles directly drives impedance growth, disrupts electronic and ionic pathways, increases surface area, and exacerbates surface degradation mechanisms such as phase transformation, transition metal dissolution, oxygen release, and electrolyte decomposition. Consequently, robust single-crystal cathodes, resistant to cracking, are necessary to overcome these fundamental limitations of polycrystalline materials.The conventional synthesis of single-crystal cathode particles begins with the co-precipitation of a polycrystalline precursor, which then undergoes an energy-intensive and protracted heat treatment with a lithium source to induce lithiation and single-crystal growth. Achieving this growth demands high temperatures and long residence times during the heat treatment, often requiring twice calcination cycles and subsequent milling. This inherent complexity leads to significant energy waste and reduced productivity. Moreover, the harsh conditions of this lengthy heat treatment and lithiation can negatively impact the electrochemical performance of the final single-crystal cathode particles. Thus, developing simpler and faster manufacturing processes, which minimize the reliance on conventional energy-intensive and lengthy heat treatments, is crucial to unlock the full potential of robust single-crystal anode particles for favorable price and performance.A supercritical hydrothermal process has been developed and is being scaled up for the facile, rapid, and continuous one-step manufacturing of single-crystal cathode materials. This innovative process leverages the unique properties of supercritical water to enable the rapid production of fully lithiated, robust single-crystal cathode particles. By integrating single-crystal formation, lithiation, doping, and surface coating into a single-step reaction, this method inherently guarantees lower energy consumption and faster production. The details of this developed process, the resulting single-crystal cathode materials, their in-depth characterization, electrochemical performance evaluation, and the current status of process scale-up will be presented herein.

Single-crystal nickel-rich materials are promising alternatives to polycrystalline cathodes owing to their excellent structure stability and cycle performance while the cathode material usually appears high cation mixing, which may have a negative effect on its electrochemical performance. The study presents the structural evolution of single-crystal LiNi0.83 Co0.12 Mn0.05 O2 in the temperature-composition space using temperature-resolved in situ XRD and the cation mixing is tuned to improve electrochemical performances. The as-synthesized single-crystal sample shows high initial discharge specific capacity (195.5 mAh g-1 at 1 C), and excellent capacity retention (80.1 % after 400 cycles at 1 C), taking account of lower structure disorder (Ni2+ occupying Li sites is 1.56 %) and integrated grains with an average of 2-3 μm. In addition, the single-crystal material also displays a superior rate capability of 159.1 mAh g-1 at the rate of 5 C. This excellent performance is attributed to the rapid Li+ transportation within the crystal structure with fewer Ni2+ cations in Li layer as well as intactly single grains. In sum, the regulation of Li+ /Ni2+ mixing provides a feasible strategy for boosting single-crystal nickel-rich cathode material.

A high-nickel cathode with high reversibility Li[NixCoyMn1–x-y]O2 (x ≥ 0.6) is one of the most commonly used cathode materials in lithium-ion batteries. However, as the nickel content increases, the instability of the layered structure of the cathode increases, which adversely affects the life performance. In addition, such a high-nickel polycrystalline cathode material causes cracks in particles during pressing or charging and discharging, ultimately leading to the deterioration of cycle performance. To solve this problem, a single crystal cathode material synthesized at 900 Celsius degrees or higher has been proposed. However, research on specific temperature conditions of a high-nickel single crystal cathode is insufficient. In this study, a method of synthesizing LiNi0.8Co0.1Mn0.1O2 (NCM811) high-nickel single crystal cathode is presented, and the physical characterization and electrochemical performance of the cathode material are compared according to the pre-heating temperatures and the reheating temperatures.Keywords: Lithium-ion battery, Cathode material, single crystal cathode’s calcination temperature, LiNi0.8Co0.1Mn0.1O2 Figure 1

A synergistic modification strategy for enhancing the cycling stability and rate capacity of single-crystal nickel-rich cathode materials

Enhanced structure and electrochemical stability of single crystal nickel-rich cathode material by La2Li0.5Co0.5O4 surface coating

Flux-free synthesis of single-crystal LiNi0.8Co0.1Mn0.1O2 boosts its electrochemical performance in lithium batteries

Enhancing the electrochemical performance of single-crystal LiNi0.8Co0.1Mn0.1O2 cathode material by phosphorus doping

A universal etching method for synthesizing high-performance single crystal cathode materials