Ni-rich Layered Cathode Materials Research Articles

Understanding Ni-Rich Layered Cathode Materials for Fast-Charging Li-Ion Batteries

The market for electric vehicles (EVs) has experienced significant growth, and this trend is expected to continue in the coming years. While the lithium-ion battery (LIB) technologies for EVs have made significant progress so far, they still face several disadvantages compared to the internal combustion engines. A predominate challenge is reducing battery charging time. [1] Traditional LIBs typically use Li[Ni1-x-yCox(Mn and/or Al)y]O2 as cathode materials. To improve the driving range of EVs, energy density has been the focus of research and development in the past decade, which led to the wide adoption of Ni-rich (Ni content > 80%) layered oxide cathodes in LIBs.[2] With increasing Ni content, however, the structural changes that the cathode material undergoes during electrochemical reactions also become more severe, which negatively impact their fast-charging performances.[3-5] It is evident that addressing the fast charging limitations requires a deep understanding of the active materials. In this presentation, we show our recent effort in improving fast charging performances of Ni-rich layered cathodes. As the reactivity of Li[Ni1-x-yCox(Mn and/or Al)y]O2 cathodes vary with the states of dis/charges, their fast charging performances are directly linked to the charging/discharging protocol. In addition, we report how various physical properties of the cathode materials, such as microstructures and facets, can affect kinetics and charging rates. Our perspectives on future development strategies for fast charging Ni-rich layered cathode materials will also be discussed.[1] X. Wang, Y.-L. Ding, Y.-P. Deng, Z. Chen, Adv. Energy Mater. 2020, 10, 1903864.[2] S.-T. Myung; F. Maglia; K.-J. Park; C. S. Yoon; P. Lamp; S.-J. Kim; Y.-K. Sun, ACS Energy Lett. 2017, 2, 196.[3] F. Schipper; E. M. Erickson; C. Erk; J.-Y. Shin; F. F. Chesneau; D. Aurbach, J. Electrochem. Soc. 2017, 164, A6220.[4] H.-H. Ryu, K.-J. Park, C. S. Yoon, Y.-K. Sun, Chem. Mater. 2018, 30, 1155.[5] J. Park, H. Zhao, S. D. Kang, K. Lim, C.-C. Chen, Y.-S. Yu, R. D. Braatz, D. A. Shapiro, J. Hong, M. F. Toney, M. Z. Bazant, W. C. Chueh, Nat. Mater. 2021, 20, 991.

Unraveling the oxygen evolution in layered LiNiO2 with the role of Li/Ni disordering

Oxygen loss is widely recognized as a major factor in the structural degradation of Ni-rich layered cathode materials, while a study on the detailed oxygen evolution process and the role of inevitable Li/Ni disordering defects is still lacking. Using ab initio calculations with van der Waals correction, we performed an in-depth study on the oxygen evolution in layered LiNiO2 and considered the role of Li/Ni disordering. We find that excess Ni in Li slab act as a pillar role for the structural framework and increases bond strength of adjacent oxygen ions, both of which are beneficial to the thermal and kinetic stability of lattice oxygen in LiNiO2, thus inhibiting the oxygen evolution. For Li/Ni exchange and Excess Li defects, the Li ion in Ni slab preferred to return to the vacancy in Li slab with delithiation in both surface and bulk LiNiO2. This situation induces the weaken binding and fast migration of lattice oxygen, even Ni slab collapse and oxygen release in the surface. Furthermore, the ab-initio molecular dynamics simulations for LiNiO2 surface reveal three stages of oxygen loss in the pristine state: (i) the formation of pre-O-O dimer; (ii) the pre-O-O dimer oxidizing to O-O dimer; (iii) O2 release with oxygen oxidation and Ni migration. The Li/Ni exchange and Excess Li defects accelerate this process because of Li ion in Ni slab returning to Li slab, while the Excess Ni defects will inhibit this process. We hope this work will improve the understanding of oxygen evolution in layered LiNiO2 and provide theoretical guidance for the design of Ni-rich layered cathode materials with improved stability.

Single–crystalline LiNi0.8Co0.1Mn0.1O2 stabilized by F–doping–induced superlattice for 4.8 V lithium–ion batteries

Single–crystalline Ni–rich ternary layered oxides represent the cutting–edge cathode materials for lithium–ion batteries, offering enhanced cycling stability compared to the polycrystalline counterparts by eliminating grain boundaries. However, their structural stability encounters a significant challenge when operated under high voltages (cut–off charging potential ≥ 4.6 V). Excessive extraction of Li+ ions can lead to the localized collapse of transition metal (TM) slabs and accumulation of lattice dislocations, which hinders Li+ diffusion and eventually cause capacity decay. This study demonstrate that the introduction of F dopants triggers an ordered mixing of Li+ and Ni2+ ions to form a superlattice in single–crystalline LiNi0.8Co0.1Mn0.1O2. This unique F–doping–induced superlattice stabilizes the deintercalated structure through Ni2+ (Li layer)–O2––Ni2+ (TM layer) interlayer super–exchange strong interactions, thereby facilitating the reversible H2–H3 phase transformation during cycling. Consequently, when cycled between 2.8–4.8 V at 1C, the F doped single–crystalline LiNi0.8Co0.1Mn0.1O2 exhibits unprecedented cycling stability, retaining 90.3 % of its initial capacity after 200 cycles, while achieving a high discharge capacity of 186.8 mAh/g and an impressive energy density of 706.5 Wh/kg. This work sheds light on the microstructural engineering for Ni–rich layered cathode materials.

Strengthening the interfacial stability of single-crystal LiNi0.88Co0.09Mn0.03O2 cathode with multiple-function surface modification

The instability in the structural integrity caused by interfacial issues is commonly regarded as the primary drawback of Ni-rich layered cathode materials (LiNixCoyMn1-x-yO2, where x ≥ 0.8), which must be addressed before their commercial application. Herein, a novel multiple-function surface modification strategy is proposed based on the single crystal structure to in-situ achieve the construction of a coating layer and surface doping with Ce element to enhance the structural stability of the LiNi0.88Co0.09Mn0.03O2 (NCM). Notably, the introduction of Ce-O bonding adjusts the local oxygen coordination to achieve a more stabilized structure of the oxygen framework, which inhibits the evolution of lattice oxygen and enhances conductivity. Additionally, by benefiting from the in-situ synthesized coating layer of LixCeO2, the occurrence of side reactions on the surface is effectively alleviated, resulting in a reduction in electrode polarization. Combined with comprehensive electrochemical tests, it is confirmed that the improved electrochemical performance originates from the reduction of the detrimental H2-H3 phase transition and enhanced conductivity. As expected, the modified material with 1 wt% content of Ce (NCM@Ce) exhibits a high initial discharge capacity of 196.3 mAh g−1 with a capacity retention of 79.7 % after 200 cycles, and its energy density reaches 574.3 Wh kg−1 after 200 cycles.

Electron Beam-Induced Effects on a Ni-Rich Layered Cathode Material: A Comprehensive Investigation Using STEM and EELS

Electron Beam-Induced Effects on a Ni-Rich Layered Cathode Material: A Comprehensive Investigation Using STEM and EELS

Understanding improved cycling and thermal stability of compositionally graded Ni-rich layered LiNi0.6Mn0.2Co0.2O2 cathode materials

The concentration gradient is a strategic design, adjusting the distribution of Ni, typically with a higher Ni content in the core and a higher Mn content toward the surface. This design leverages the pivotal role of the Ni/Mn ratio, seeking to optimize cathode performance by balancing Ni's high capacity with Mn's stabilizing effects, particularly at the surface where degradation commonly occurs during cycling. Our study delves into the intricate structural and chemical transformations within concentration gradient cathode materials during electrochemical cycling. Utilizing advanced synchrotron X-ray techniques, including hard and soft X-ray absorption spectroscopy (hXAS, sXAS), and nanoscale X-ray imaging, we investigate buried changes in concentration gradient LiNi0.6Mn0.2Co0.2O2 (CG NMC622). Contrary to conventional assumptions, our findings challenge the notion that cycling stability relies solely on Mn stability. Unraveling the roles of Ni and Mn, we uncover how their individual and collective contributions impact the cathode's overall performance. This investigation transcends established paradigms, shedding light on the crucial mechanisms governing the enhanced cycling stability of Ni-rich layered cathode materials.

Microstructure and electrochemical properties of Mg/Nb/Zr co-doped LiNi0.94Mn0.04Al0.02O2 cathode materials

The increasing oil scarcity and environmental awareness have accelerated the rise of the new energy vehicle industry, but range and cost issues have hindered the rapid popularization of new energy vehicles. The Co-free Ni-rich layered cathode materials have received a wide attention due to their high energy density, low cost, and stable raw material supply. However, its structure and electrochemical stability still need to be further improved. In this study, the electrochemical properties of LiNi0·94Mn0·04Al0·02O2 (NMA), a Co-free Ni-rich layered cathode material, have been improved by co-doping of Mg, Nb, and Zr. Also, the effects of co-doping on the crystal structure, morphology and electrochemical properties of NMA cathode materials were investigated, too. The results show that the NMA material (NMA-333) with 0.9 mol% doping amount has the best electrochemical performance. The discharge-specific capacity in the first cycle at 1 C was 199.6 mAh g−1, and the capacity retention after 200 cycles reached 73.94 %, which is nearly 24 % higher than that of the original material (NMA-1.03). Meanwhile, the NMA-333 material has a relatively better rate performance, with a discharge-specific capacity of 125.2 mAh g−1 at 10 C. Moreover, the structure and morphology of the modified material were represented by SEM, TEM, XRD, and XPS. And the results showed that the co-doping modification could refine the primary particles of the NMA material, reduce the lithium-nickel mixing, and increase the lattice spacing. The XPS, SEM, and XRD of the post-cycle electrodes further showed that co-doping had stabilized the crystal structure, inhibited the generation and expansion of microcracks, and reduced the occurrence of harmful side reactions, thus improving the cycling performance of the NMA materials at high voltage. The method could be a feasible way to improve the electrochemical performance of layered high-nickel cobalt-free cathode materials.

Role of Salt Concentration in Stabilizing Charged Ni-Rich Cathode Interfaces in Li-Ion Batteries.

The cathode-electrolyte interphase (CEI) in Li-ion batteries plays a key role in suppressing undesired side reactions while facilitating Li-ion transport. Ni-rich layered cathode materials offer improved energy densities, but their high interfacial reactivities can negatively impact the cycle life and rate performance. Here we investigate the role of electrolyte salt concentration, specifically LiPF6 (0.5-5 m), in altering the interfacial reactivity of charged LiN0.8Mn0.1Co0.1O2 (NMC811) cathodes in standard carbonate-based electrolytes (EC/EMC vol %/vol % 3:7). Extended potential holds of NMC811/Li4Ti5O12 (LTO) cells reveal that the parasitic electrolyte oxidation currents observed are strongly dependent on the electrolyte salt concentration. X-ray photoelectron and absorption spectroscopy (XPS/XAS) reveal that a thicker LixPOyFz-/LiF-rich CEI is formed in the higher concentration electrolytes. This suppresses reactions with solvent molecules resulting in a thinner, or less-dense, reduced surface layer (RSL) with lower charge transfer resistance and lower oxidation currents at high potentials. The thicker CEI also limits access of acidic species to the RSL suppressing transition-metal dissolution into the electrolyte, as confirmed by nuclear magnetic resonance (NMR) spectroscopy and inductively coupled plasma optical emission spectroscopy (ICP-OES). This provides insight into the main degradation processes occurring at Ni-rich cathode interfaces in contact with carbonate-based electrolytes and how electrolyte formulation can help to mitigate these.

Highly stable nickel-rich cathode materials LiNi0.90Co0.05Mn0.05O2 with Mn concentration gradient for lithium-ion batteries

Ni-rich layered cathode materials (LiNixCoyMn1-x-yO2) have attracted much attention due to their high energy density and environmentally friendly advantages. However, the capacity fading and structural instability with the increase of Ni content are still the main problems restricting the commercialization of high nickel cathodes. In this paper, the method of co-precipitation and calcination is used to prepare LiNi0.90Co0.05Mn0.05O2 (CG-NCM5) with Mn concentration gradient, which the Ni content is decreasing from the core to the outer of CG-NCM5, while the Mn content is increasing. The CG-NCM5 has less Li/Ni mixing and a good layered structure. More importantly, the Mn-rich outer plays a key role in preventing the appearance of microcracks and enhancing the structure stability, because it can effectively suppress the volume change stemming from the phase transition during charge/discharge process. Meanwhile, the low Ni on the surface reduces the highly reactive Ni4+ that easily reacts with electrolyte, mitigates material surface degradation and accelerates lithium-ion transport. Therefore, it exhibits a superior reversible capacity of 191.4 mAh/gat 1C and a capacity retention of 83.7 % after 200 cycles in 2.7–4.3 V. These results indicate that Mn concentration gradient materials may provide a practical approach to highly stable nickel-rich cathode materials for lithium-ion batteries.

Improving electrochemical performance of Ni-rich layered cathode material with combining Co-enriched compositional gradient and radial microstructure

Ni-rich complex layered oxides LiNixMnyCozO2 (x > 0.85) with a combined Ni/Co concentration gradient and radially oriented elongated plate-like primary particles were synthesized with hydrothermal microwave-assisted treatment of an as-prepared mixed hydroxide precursor with aqueous solution of Co source and urea followed by a high temperature annealing with a Li source. The radial distribution of plate-like primary crystallites in microwave-treated materials was achieved through Co-enrichment at the surface, which likely triggered the surface-to-bulk growth of plate-like particles rather than isotropic octahedral crystallites. The Co-modified cathode materials demonstrate greatly improved cycling stability (capacity fade per cycle of 0.04 ± 0.01%) compared to unmodified Ni-rich NMCs (capacity fade per cycle of 0.13 ± 0.02%) with similar Ni concentration, as well as good rate capability (215, 210, 199, 189, 178 and 160 mAh/g at C/10, C/5, C/2, 1C, 2C, and 5C rates at 2.7–4.3V vs Li/Li+). Enhanced electrochemical performance is linked to the improved mechanical integrity, which was achieved through radial microstructure organization of the agglomerates triggered by Co concentration gradient, suppressing the intragranular crack formation.

Modification of the Ni-Rich Layered Cathode Material by Hf Addition: Synergistic Microstructural Engineering and Surface Stabilization.

The rapid decline of the reversible capacity originating from microcracks and surface structural degradation during cycling is still a serious obstacle to the practical utilization of Ni-rich LiNixCoyAl1-x-yO2 (x ≥ 0.8) cathode materials. In this research, a feasible Hf-doping method is proposed to improve the electrochemical performance of LiNi0.9Co0.08Al0.02O2 (NCA90) through microstructural optimization and structural enhancement. The addition of Hf refines the primary particles of NCA90 and develops them into a short rod shape, making them densely arranged along the radial direction, which increases the secondary particle toughness and reduces their internal porosity. Moreover, Hf-doping stabilizes the layered structure and suppresses the side reactions through the introduction of robust Hf-O bonding. Multiple advantages of Hf-doping allowed significant improvement of the cycling stability of LiNi0.895Co0.08Al0.02Hf0.005O2 (NCA90-Hf0.5), with a reversible capacity retention rate of 95.3% after 100 cycles at 1 C, as compared with only 82.0% for the pristine NCA90. The proposed synergetic strategy combining microstructural engineering and crystal structure enhancement can effectively resolve the inherent capacity fading of Ni-rich layered cathodes, promoting their practical application for next-generation lithium-ion batteries.

Doping-Induced Surface and Grain Boundary Effects in Ni-Rich Layered Cathode Materials.

In this work, the effects of dopant size and oxidation state on the structure and electrochemical performance of LiNi0.8Co0.1Mn0.1O2 (NCM811) are investigated. It is shown that doping with boron (B) which has a small ionic radius and an oxidation state of 3+, leads to the formation of a boron oxide-containing surface coating (probably Li3BO3), mainly on the outer surface of the secondary particles. Due to this effect, boron only slightly affects the size of the primary particle and the initial capacity, but significantly improves the capacity retention. On the other hand, the dopant ruthenium (Ru) with a larger ionic radius and a higher oxidation state of 5+ can be stabilized within the secondary particles and does not experience a segregation to the outer agglomerate surface. However, the Ru dopant preferentially occupies incoherent grain boundary sites, resulting in smaller primary particle size and initial capacity than for the B-doped and pristine NCM811. This work demonstrates that a small percentage of dopant (2mol%) cannot significantly affect bulk properties, but it can strongly influence the surface and/or grain boundary properties of microstructure and thus the overall performance of cathode materials.

Reduction of the Calcination Temperature for Improvement of Ni-Rich Single-Crystal Cathode

Synthesizing a high-performance single-crystal cathode with a Ni-rich composition for use in Li-ion batteries is a difficult task. This is because sintering of particles requires calcination at high temperatures, but performing calcination at very high temperatures can damage Ni-rich layered cathode materials. Therefore, finding ways to reduce the calcination temperature required for the synthesis of single-crystal cathodes can improve the cathode's performance. In this research, a Ce dopant was introduced to successfully synthesize a Ni-rich single-crystal cathode with the composition Li[Ni0.9Co0.05Mn0.05]O2 (NCM90) at a calcination temperature that was 50°C lower than its optimal temperature. Dopants affect the growth and sintering behavior of cathode materials during calcination depending on their properties. For example, W retards the growth and sintering of grains, preventing the formation of single-crystal particles, while Ce promotes the formation of single-crystal particles. Taking advantage of Ce's ability to promote single-crystal particle formation, a Ce-doped NCM90 cathode was synthesized at a calcination temperature of 800°C, while the undoped NCM90 cathode remained polycrystalline at this temperature. The Ce-doped NCM90 cathode showed an initial capacity of 199.7 mAh g−1 at 0.1 C, and after 100 cycles at 0.5 C, it retained 80.5% of its initial capacity, demonstrating better cycling stability than the undoped NCM90 cathode. The Ce dopant protracted the detrimental H2-H3 phase transition, which reduced capacity loss as revealed by differential capacity analysis. Additionally, the presence of Ce in the cathode improved its thermal stability.

Grain binding derived reinforced interfacial mechanical behavior of Ni-rich layered cathode materials

The fragmentation caused by cracks spreading along grain boundaries seriously deteriorates the cycling performance of high nickel (Ni ≥ 90%) layered cathode materials for lithium-ion batteries (LIBs). In this study, heterogeneous nucleation was utilized to epitaxially grow LiNbO3 layer onto LiNi0.90Co0.05Mn0.05O2 (NCM90). Importantly, the LiNbO3 layer was compatible with the highly reactive surface of NCM90. The formation process of LiNbO3 solid embryos was calculated and discussed based on crystal solidification theory, and the distribution of solid embryos revealed thin zone crystallization and aggregation zone grain pinning. More interestingly, the surface stiffness and surface Young's modulus of the NCM90 were significantly enhanced, and the grain movement (fragmentation) caused by the non-uniform contraction of the unit cell was bound correspondingly at high cut-off voltages. Originating from the binding effect of the coating layer, the value of surface hoop internal stress of NCM90 decreased by 22.88% to inhibit the cracking and reduce the loss of NCM90 during cycling. At the potential range of 3.0–4.3 V at 50 mA g−1, the specific discharge capacity of the optimized NCM90 increased from 109.3 mAh g−1 to 147.4 mAh g−1 after 200 cycles. It is believed that this study provides a simple, convenient but effective strategy to restrain the fragmentation of high nickel layered cathode materials for LIBs.

Bifunctional self-assembled molecular layer enables stable Ni-rich cathodes

Ni-rich layered oxides (LiNixCoyMnzO2, x ≥ 0.8, x + y + z = 1) are attractive cathode material candidates for building high-energy-density batteries owing to their higher specific capacity compared to their lower-Ni-content analogues. However, the high nickel content also brings challenges, such as storage instability in ambient conditions and poor cycle life. In this work, we propose a surface chemistry regulation strategy to simultaneously enhance the air storage stability and electrochemical stability of high-nickel cathode materials. A bifunctional ultrathin layer composed of trimethoxy(1H,1H,2H,2H-perfluorodecyl)silane (PFDTMS) was constructed on the surface of single-crystal LiNi0.83Co0.12Mn0.05O2 (NMC811) particles via molecular self-assembly. The passivating PFDTMS layer forms a superhydrophobic surface on the modified NMC811 particles, effectively mitigating deactivation reactions of NMC811 in air, and ensuring an uncompromised electrochemical performance of NMC811-based electrode after storing in air for two weeks. Furthermore, the self-assembled PFDTMS layer contributes to the formation of an electrochemical stable cathode–electrolyte interphase (CEI) on the NMC811 surface, improving the cycling stability of NMC811 at high cut-off voltages. The PFDTMS-based CEI also alleviates the chemical corrosion of NMC811 by the electrolyte, slows down the dissolution of transition metal ions during long term cycling. These findings present a straightforward, effective, eco-friendly, and cost-efficient approach to tackle the stability challenges inherent to Ni-rich layered cathode materials.

Fast charge induced phase evolution and element contribution of nickel-rich layered cathode for lithium-ion batteries

In nickel-rich layered cathode materials, three transition metals (TM = Ni, Co and Mn) play critical roles in Li storage performance. However, rate-dependent phase evolution and elemental contribution of nickel-rich cathode materials are not well understood, but very important for further design and development of these cathodes in high-power applications. Here, the rate-dependent phase evolution and elemental contribution of LiNi0.5Mn0.3Co0.2O2 (NMC532) cathode are investigated thoroughly by using time-resolved synchrotron-based in situ X-ray diffraction and absorption techniques. The increase of Ni content in NMC532 has been found to be the main cause of the complex structural changes, resulting in distortion of TM-O6 octahedron and strong static vibration between TM and O coordination. It is revealed that the fast charge (10 and 30C) of NMC532 leads to intermediate Li-poor phases, shrinking of H2 phase region, and prolonged O1 phase. During high-rate charging, Co is oxidized easily in low voltage region, while Ni mainly dominates charge compensation in high voltage region. It is found that delithiation-induced local structure distortion transfers from Ni to Co sites in fast kinetic process. These findings provide in-depth understanding for the fast charge behavior of Ni-rich layered cathode materials, and help to guide further development of advanced high power lithium-ion batteries.

O3-Type Ni-Rich NaNi2/3Mn1/6Fe1/6O2: A high-performance cathode material for sodium-ion batteries

Because of relative prominent capacity, layered oxide materials are regarded as promising candidate cathode materials for sodium-ion batteries (SIBs). Nevertheless, the permanent changes in structure accompanied by sodium extraction/insertion restrict their capacity and retention in cycles. The O3-type phase material has a stable structure and can obtain a steady high-capacity output combined with high nickel content. In this paper, a simple high-temperature solid-state approach is used to create Ni-rich NaNi2/3Mn1/6Fe1/6O2 materials aiming to achieve high capacity. Systematic researches are conducted through a combination of electrochemical measurements and structural characterization. The Ni-rich NaNi2/3Mn1/6Fe1/6O2 sample obtained at 850 °C exhibits a well-crystallized O3 phase, as well as comprises hexagonal plate-like particles. In the voltage range of 1.5–4.2 V, this sample demonstrates an impressive initial discharge capacity of 226 mAh/g at a rate of 0.2 C. Furthermore, even after 100 cycles, it still maintains a capacity retention of approximately 76 %, exhibiting outstanding cycling stability. This material demonstrating remarkable electrochemical performance highlights the potential of the Ni-rich layered cathode material candidate, and makes an important supplement to the research on commercialization electrode materials for SIBs.

High-Ni NMC Cathode Material with Concentration Gradients in Lithium-Ion Batteries

Due to the high capacity and the high discharge potential, Ni-rich layered cathode materials are considered as a class of promising cathode material and attracting considerable attention. Because of the Li+/Ni2+ cation mixing, Li residues, overcharging, crystal orientation of the secondary particles, poor cycling stability and rate capability are usually received in lithium ion batteries. In this presentation, we introduce a layered NMC811 with Ni-gradients by using metal-organic framework (MOF) as precursor ( Cell Reports Physical Science , 3 (2022), 100767). The self-healing phase by forming a cation mixing layer on the surface of particles effectively improved the structural stability by suppressing the phase transition and internal cracks upon cycling. In the half-cell battery, an initial capacity of 203.5 mAh/g at 0.1 C and a capacity retention of 88.5% after 300 cycles at 1/3 C were obtained. The battery still showed a CE of 99.47% at 1/3 C after 300 cycles at 55 ℃. In addition, the full-cell battery showed a capacity retention of >86.7% with a CE of >99.86% at 1/3 C after 300 cycles. Moreover, a pouch cell delivered an initial capacity of 297.62 mAh and a CE of 99.48%, which contributed to an energy density of 216.41 Wh/kg. The capacity retention was still as high as 84.1% after 500 cycles at 1.0 C. Keywords: Li-ion batteries; Ni-rich cathode materials; MOF; Concentration gradient

(Digital Presentation) Renewable Itaconic Acid As a Cathode Additive Stabilizing Ni-Rich Layered Cathode Materials for Lithium-Ion Batteries

Renewable materials applied in lithium-ion batteries industry has obvious advantages because of its wide range of sources and low cost. The residual lithium compounds on the surface of nickel-rich LiNi1-x-yCoxMnyO2 (Ni-rich NCM) cathodes hinder its large-scale industrial application in lithium-ion batteries. In the past, researchers proposed several approaches including coating (Al2O3, Li3PO4), water washing coupling heat treatment. These conventional approaches have been found beneficial for mitigating the residual lithium and improving electrochemical performance of high rich nickel cathode. However, most of these used conventional additions are non-renewable precious metal or salt accompanied by extra processing/handling costs. More seriously, layer Ni-rich NCM cathodes cost more than lithium iron phosphate, because transition nickel salt is expensive. Obviously, it is crucial for Ni-rich NCM cathodes to develop green and low-cost modification process.In this work, renewable itaconic acid (IA) as a cathode addition is used to convert the residual lithium on the Ni-rich NCM cathodes into sacrificial organic lithium salts containing polar carboxylic acid and unsaturated carbon-carbon double bond to build the Li conductive cathode-electrolyte interphase (CEI) rich in organic component containing polycarbonates/polymeric specie during the electrochemical process. As a result, the capacity of the 0.5wt% IA modified NCM cathode retains 94.1 % after 90 cycles. Itaconic anhydride, an important renewable resource, is widely used in food processing and other fields because of its wide range of sources and low price. As such, our work proposes a practical approach to mitigates residual lithium issue and control CEI formation, developing high energy and long spans lithium-ion batteries by utilizing cheap and renewable organic acid. Figure 1

Hybrid surface coating layers comprising boron and phosphorous compounds on LiNi0.90Co0.05Mn0.05O2 cathode materials to ensure the reliability of lithium-ion batteries

High-energy lithium-ion batteries (LIBs) have undergone significant technological advancements in response to the expanding market for electric vehicles (EVs). Ni-rich layered cathode materials (LiNixCo1-x-yMn1-x-yO2, x ≥ 0.8) are a viable option because of their high reversible capacity over 200 mAh/g. However, the inherent challenges of Ni-rich cathodes include the occurrence of residual lithium, side reactions, and structural instability. Herein, we propose a hybrid surface coating of boron and phosphorous on a LiNi0.9Co0.05Mn0.05O2 (NCM955) cathode material to minimise the side reactions and enhance the structural stability. The hybrid surface coating on NCM955 provides an excellent discharge capacity of 180 mAh/g at 5 C-rate compared to the bare NCM955 capacity of 159 mAh/g. After 300 cycles, the coated NCM955 retained 84% of its capacity, while the uncoated retained only 46%. The improvement can be attributed to the enhanced lithium-ion diffusion achieved through hybrid coating, as confirmed by impedance measurements and cyclic voltammetry analysis. TEM and XPS analyses were performed to validate the presence of the coating layer, confirming the presence of the desired material on the surface. This study provides practical guidance for designing highly reliable, high-capacity cathode materials for use in EV applications.