Performance Of Ni-rich Cathode Materials Research Articles

Dual Modification Strategy for Enhanced Cycling and Rate Performance of Ni-Rich Cathode Materials in Lithium-Ion Batteries.

A great challenge in the commercialization process of layered Ni-rich cathode material LiNixCoyMn1-x-yO2 (NCM, x ≥ 80%) for lithium-ion batteries is the surface instability, which is exacerbated by the increase in nickel content. The high surface alkalinity and unavoidable cathode/electrolyte interface side reactions result in significant decrease for the capacity of NCM material. Surface coating and doping are common and effective ways to improve the electrochemical performance of Ni-rich cathode material. In this study, an in situ reaction is induced on the surface of secondary particles of NCM material to construct a stable lithium sulfate coating, while achieving sulfur doping in the near surface region. The synergistic modification of lithium sulfate coating and lattice sulfur doping significantly reduced the content of harmful residual lithium compounds (RLCs) on the surface of NCM material, suppressed the side reactions between the cathode material surface and electrolyte and the degradation of surface structure of the NCM material, effectively improved the rate capability and cycling stability of the NCM material.

Unravelling the peculiar role of Co and Al in highly Ni-rich layered oxide cathode materials

Currently, the limited availability of cobalt resources has had a negative impact on the progress of commercial batteries, prompting the development of cobalt-free Ni-rich cathodes. However, the complete replacement of cobalt has faced challenges due to the lack of understanding the influence of dopants on cathode material performance. In this study, we aimed to address this knowledge gap by designing and preparing LiNi0.95Co0.05-xAlxO2 (x = 0.00, 0.01, 0.02, 0.03, 0.04, and 0.05) cathode materials. The impact of cobalt and aluminum doping on the morphology, crystallographic structure and electrothermal performance of Ni-rich cathode materials has been systematically investigated. Our findings confirmed the significant role of cobalt in increasing energy density and mitigating cationic disordering. However, it is found that cobalt doping contributes to the release of lattice oxygen during cycling, leading to rapid capacity fading. Conversely, aluminum doping could stabilize the crystal structure of the cathode material, resulting in slower capacity degradation. Furthermore, the substitution of aluminum effectively mitigates the crystal growth during the synthesis of highly Ni-rich cathode materials, leading to a reduced Li+ diffusion length and thereby excellent rate performance. Specifically, LiNi0.95Al0.05O2 could deliver a high discharge capacity of around 163 mAh g−1 at 10C. This study provides valuable insights for the design of cobalt-free Ni-rich cathodes and sheds light on the possibility of cobalt elimination.

Selenium treatment towards enhanced cyclic stability for single-crystal Ni-rich cathode at ultra-high voltage of 4.7 V

Developing high-voltage (≥4.3 V vs Li/Li+) single-crystal Ni-rich LiNixCoyMn1-x-yO2 offers an enticing strategy to achieve high energy density for lithium-ion batteries. However, at high-voltage operation, the cathode will be vulnerable to induce the intrinsic Oα- (α < 2) migration, triggering the serious structural degradation, notorious parasitic reaction and oxygen loss, which may ultimately result in the battery performance attenuation. Herein, an outside-in oriented nanostructure is well designed and constructed on the single-crystal LiNi0.6Co0.1Mn0.3O2 (SC-NCM) cathode materials, exhibiting an “anti-aging” effect of inhibiting the escape of oxygen from SC-NCM particles during the ultra-high voltage (4.7 V) cycling. Both theoretical calculation and experimental results confirm that the outside-in nanostructure would stabilize the oxygen lattice and suppress O2 release during long-term cycling. Meanwhile, the surface modification of thin Se layer will alleviate the parasitic reactions and improve the electronic conductivity. Under the synergistic strategy of surface modification and interface doping, the obtained SC-NCM exhibits boosted cyclic stability in coin half-cell and pouch full-cell simultaneously. Therefore, the reversible capacity of LiNi0.6Co0.1Mn0.3O2 at high voltage is competitive with comercial LiNixCoyMn1-x-yO2 (x ≥ 0.8), demonstrating more superior safety ability and cyclic property. It provides an effective approach for improving the long-term performance of Ni-rich cathode materials for practical application under ultra-high working voltage.

Constructing a stable interface on Ni-rich LiNi0.8Co0.1Mn0.1O2 cathode via lactic acid-assisted engineering strategy

Ni-rich layered oxides are potential cathode materials for next-generation high energy density Li-ion batteries due to their high capacity and low cost. However, the inherently unstable surface properties, including high levels of residual Li compounds, dissolution of transition metal cations, and parasitic side reactions, have not been effectively addressed, leading to significant degradation in their electrochemical performance. In this study, we propose a simple and effective lactic acid-assisted interface engineering strategy to regulate the surface chemistry and properties of Ni-rich LiNi0.8Co0.1Mn0.1O2 cathode. This novel surface treatment method successfully eliminates surface residual Li compounds, inhibits structural collapse, and mitigates cathode-electrolyte interface film growth. As a result, the lactic acid-treated LiNi0.8Co0.1Mn0.1O2 achieved a remarkable capacity retention of 91.7% after 100 cycles at 0.5 C (25 °C) and outstanding rate capability of 149.5 mA h g−1 at 10 C, significantly outperforming the pristine material. Furthermore, a pouch-type full cell incorporating the modified LiNi0.8Co0.1Mn0.1O2 cathode demonstrates impressive long-term cycle life, retaining 81.5% of its capacity after 500 cycles at 1 C. More importantly, the thermal stability of the modified cathode is also dramatically improved. This study offers a valuable surface modification strategy for enhancing the overall performance of Ni-rich cathode materials.

Silver Nanocoating of LiNi0.8Co0.1Mn0.1O2 Cathode Material for Lithium-Ion Batteries.

Surface coating has become an effective approach to improve the electrochemical performance of Ni-rich cathode materials. In this study, we investigated the nature of an Ag coating layer and its effect on electrochemical properties of the LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode material, which was synthesized using 3 mol.% of silver nanoparticles by a facile, cost-effective, scalable and convenient method. We conducted structural analyses using X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy, which revealed that the Ag nanoparticle coating did not affect the layered structure of NCM811. The Ag-coated sample had less cation mixing compared to the pristine NMC811, which could be attributed to the surface protection of Ag coating from air contamination. The Ag-coated NCM811 exhibited better kinetics than the pristine one, which is attributed to the higher electronic conductivity and better layered structure provided by the Ag nanoparticle coating. The Ag-coated NCM811 delivered a discharge capacity of 185 mAh·g-1 at the first cycle and 120 mAh·g-1 at the 100th cycle, respectively, which is better than the pristine NMC811.

Exploring the impact of metal oxide coating and metal atom doping on the electrochemical performance of Ni-rich cathode materials

In this research, we systematically examine the impact of atomic cation dopants and metal oxide coatings, including their respective oxidation states, on the electrochemical performance of Ni-rich NCA90 cathode materials.

Utilizing dual functions of LaPO4 to enhance the electrochemical performance of LiNi0.87Co0.09Al0.04O2 cathode material

In this paper, via a facile wet coating method, the LaPO4 coating layer has been introduced onto the LiNi0.87Co0.09Al0.04O2 (NCA) surface while a small part of La3+ has also been doped on the surface to realize the dual functions modification of coating and doping. The morphology and structure of the samples were investigated by XRD, SEM and TEM measurements. The chemical compositions of the samples were analyzed via EDS and XPS data. The results showed that the coating of LaPO4 and the doping of La3+ were successfully achieved on the surface of NCA. Electrochemical tests indicate that the sample modified with 2 wt% LaPO4 (L2-NCA) possesses the best electrochemical performance. After 100 cycles, compared with the capacity retention rate of pristine NCA of 87.1%/74.2% at 0.5 C at 25 °C/60 °C, L2-NCA showed better cycling stability, and the capacity retention rate increased to 96.0%/85.1%, respectively. Besides, the rate performance of the modified samples at 1 C, 2 C and 5 C were also significantly improved. These satisfactory results reveal that the surface modification of LaPO4 provides a feasible scheme to uprate the performance of Ni-rich cathode materials.

Directly revealing the structure-property correlation in Na+-doped cathode materials

The introduction of Na+ is considered as an effective way to improve the performance of Ni-rich cathode materials. However, the direct structure–property correlation for Na+ doped NCM-based cathode materials remain unclear, due to the difficulty of local and accurate structural characterization for light elements such as Li and Na. Moreover, there is the complexity of the modeling for the whole Li ion battery (LIB) system. To tackle the above-mentioned issues, we prepared Na+-doped LiNi0.6Co0.2Mn0.2O2 (Na-NCM622) material. The crystal structure change and the lattice distortion with picometers precision of the Na+-doped material is revealed by Cs-corrected scanning transmission electron microscopy (STEM). Density functional theory (DFT) and the recently proposed electrochemical model, i.e., modified Planck-Nernst-Poisson coupled Frumkin-Butler-Volmer (MPNP-FBV), has been applied to reveal correlations between the activation energy and the charge transfer resistance at multiscale. It is shown that Na+ doping can reduce the activation energy barrier from ΔG = 1.10 eV to 1.05 eV, resulting in a reduction of the interfacial resistance from 297 Ω to 134 Ω. Consequently, the Na-NCM622 cathode delivers a superior capacity retention of 90.8 % (159 mAh.g−1) after 100 cycles compared to the pristine NCM622 (67.5 %, 108 mAh. g−1). Our results demonstrate that the kinetics of Li+ diffusion and the electrochemical reaction can be enhanced by Na+ doping the cathode material.

Improvement in interfacial stability of high-rate Ni-rich oxide cathode by multifunctional LiTi0.5Zr1.5(PO4)3 conductive buffer layer

With the advent of the double carbon era, Ni-rich layered oxides with high energy density have become ideal cathode materials to support and secure the energy transition of basic power and transportation. However, with the increase in Ni content, Ni-rich layered oxides suffer from several problems, such as difficult precursor synthesis, structural instability, and high interfacial activity. In this study, a design scheme of uniformly coating LiTi0.5Zr1.5(PO4)3 (LTZP) conductive buffer layer on the outer surface of LiNi0.8Mn0.1Co0.1O2 (NCM811) grains was proposed to overcome the above problems. The results of first-principles calculations and various ex-situ characterizations showed that the NASICON-type LTZP material had excellent compatibility with the NCM811 material. The LTZP surface-modified NCM811cathode material presented outstanding electrochemical performance. The initial discharge specific capacity was 210.16 mAh g−1 at 0.2C, and a remarkably high discharge capacity of 147.68 mAh g−1 was recorded at 10C. The capacity retention rate reached 84.7% after 200 cycles of 1C (25 °C). This work presents a strategy for stabilizing the interface with a conductive buffer layer to enhance the electrochemical performance of Ni-rich cathode materials.

Comparison of structural and electrochemical properties of LiNi0.8Co0.15Al0.05O2 with Li site doping by different cations

Nickel-rich cathode materials are widely used for electronic devices because of their high capacity and rate performance. However, structural deterioration after long-term cycling leads to a significant decline in capacity and cycle life. In this work, the effects of three different cations doping on the structural stability and electrochemical performance of Ni-rich cathode materials were investigated. XRD characterization reveals that doped cation leads to broadening of the distance between Li layers and inhibiting Li+/Ni2+ mixing arrangement. Compared with Na+ and K+, the high valence Mg2+ provides a stronger Mg-O bond, which can effectively restrain the undesired phase transition and sustain the ordered structure. Electrochemical tests demonstrate that NCA with Mg doping has better cycle stability and rate performance than Na and K. The capacity retention rate of NCA with 1% Mg doping is 87.7% after 200 cycles at 1C, and it can still provide a specific capacity of 146.8 mAh g−1 at a high rate of 5C.

Knitting a sweater with UV-induced in situ polymerization of poly(pyrrole-co-citral nitrile) on Ni-rich layer oxide cathode materials for lithium ion batteries

Ni-rich layered oxide (LiNi0.8Co0.1Mn0.1O2) has become popular commercial cathode material for lithium ion batteries, due to its high working potential and high specific capacity. It is still a challenge, however, to maintain the structure and performance under extreme conditions, such as at high charging cutoff (≥4.5 V), high temperature (≥60 °C) and higher charge-discharge rate (≥3 C). Herein, Poly (pyrrole-co-citral nitrile) (PPC) optimized interfacial layer is designed and constructed on the surface of LiNi0.8Co0.1Mn0.1O2 by an in situ photopolymerization self-assembly technology. The sweater-like co-polymer coating provides an integral protection from side reaction, particle rupture and irreversible phase transition during cycling under the extreme conditions. Furthermore, the delocalized π bonds and cross-linked network structure of the co-polymer coating ensure the efficient and stable interface between electrolyte and electrode. This work offers a novel and useful strategy to enhance the electrochemical performance of Ni-rich cathode materials for high-energy lithium ion batteries at extreme conditions.

Improving the electrochemical performance of Ni-rich cathode materials using a fast ion conductor coating of Li2O–B2O3–LiBr

The high-Ni layered metal oxide, LiNi 0.8 Co 0.1 Mn 0.1 O 2 (LNCM811), has received widespread attention in the energy field because of its high specific capacity, but its large-scale applications are hindered due to severe capacity fading. Herein, a uniform and thin Li 2 O–B 2 O 3 –LiBr-glass (LBBrO-glass) coating was deposited on LNCM811 by a liquid-phase coating and thermal treatment method. The experimental results suggested that the LBBrO-glass coating acted as a protective layer that inhibited transition metal dissolution and side reactions, which helped improve the electrochemical properties of LNCM811. Remarkably, after 200 cycles, the 2 wt% coating (LBBrO@LNCM-2) delivered a superior capacity retention of 88.9%, while only 71.8% was obtained for the pristine material (LNCM811). The discharge capacity of LBBrO@LNCM-2 was 163.5 mAh g −1 at 5C, while it was only 139 mAh g −1 for the pristine material.

Enhanced Electrochemical Performance of Ni-Rich Cathode Materials with an In Situ-Formed LiBO2/B2O3 Hybrid Coating Layer

Surface Li residues on Ni-rich cathode materials lead to adverse interfacial side reactions, which in turn gives rise to rapid structural and capacity degradations during long-term cycling. Washing is a direct and effective method to remove the residual Li compounds but tends to change the surface structure of the Ni-rich cathode, increasing its air sensitivity. Herein, we report a facile single-step method to prepare an in situ-formed LiBO2/B2O3 hybrid coating layer on the surface of LiNi0.8Co0.1Mn0.1O2. The fast ion conductor, LiBO2, is generated via the consumption of surface Li impurities by H3BO3, forming a hybrid coating layer together with the cogenerated B2O3. Such an optimized hybrid coating layer combines the functions of removing surface Li residues, promoting Li+-ion transport, and isolating the cathode material and electrolyte, resulting in a modified Ni-rich cathode material that exhibits superior cycling stability and rate capability compared with the unmodified Ni-rich cathode material. The results demonstrate the feasibility of this hybrid coating strategy to remove the surface Li residues without adversely affecting the performance of Ni-rich cathode materials.

Protective and ion conductive: High-Rate Ni-Rich cathode with enhanced cyclic stability via One-Step bifunctional dual-layer coating

Ni-rich Li[NixCoyMn1-x-y]O2 (NCM, x > 0.6) is a promising cathode material for lithium-ion batteries while disadvantages like rapid capacity fading and poor rate performance hinder its practical application. In this work, a dual-layer coating is designed and utilized through a solid–gas reaction between the cathode particles and gaseous P2O5, where Li3PO4 acts as a protecting layer against acid attack and LiNiPO4 as a fast ion-conducting layer. The modified sample (LL-NCM94) exhibits a much higher capacity retention of 89.6% after 100 cycles at 1C between 2.8 and 4.3 V in comparison with the capacity retention of 65.9% for pristine sample (P-NCM94). Under the high C-rate of 5C and 10C, the discharge capacity of LL-NCM94 is 20% and 45% higher than P-NCM94, respectively. The better electrochemical performance of LL-NCM94 is attributed to the dual-layer coating in which each layer functions differently and simultaneous elimination of lithium residual compounds during the solid–gas reaction. This work provides an effective method and insights into surface coating design to enhance electrochemical performance of Ni-rich cathode materials.

Comprehensive study of tantalum doping on morphology, structure, and electrochemical performance of Ni-rich cathode materials

Due to their high specific capacity, nickel (Ni)-rich layered oxide cathode materials are considered to be promising for use as cathode materials in lithium (Li)-ion batteries. However, such materials exhibit poor cycling performance, which hinders their commercial applications. Herein, Ta bulk doping in Ni-rich layered oxide cathode materials is comprehensively analysed using experimental results and density functional theory calculations. It is observed that Ta5+ uniformly distributes in the bulk of the cathode materials. Further studies reveal that Ta prefers to enter both Li and TM sites, and when the doping amount increases Ta doped at TM site dominates. After Ta doping, the energy of the (001) facets is lowered, which thus affects the primary particle morphology, resulting in a preferential growth mode that produce elongated and radially oriented primary particles. A Ni-rich cathode material doped with 1 wt% of Ta shows the best cycling and rate performance, which indicates that a certain level of Ta doping is beneficial towards improving the structural stability and electrochemical performance of Ni-rich cathode materials.

Investigation of Li3PO4 Coating and Nb5+ Doping Effect on the Crystal Structure and Electrochemical Properties of Ni-Rich LiNi0.85Co0.05Mn0.10O2 Cathode

To overcome the poor rate capacity and weak cycling performance of Ni-rich cathode materials, the Li3PO4 coating and Nb5+ doping modified LiNi0.85Co0.05Mn0.10O2 series samples were prepared by using the co-precipitation and the sol-gel methods in this work. And the X-ray diffraction, transmission electron microscopy, field emission scanning electron microscopy, energy dispersive spectroscopy, X-ray photoelectron spectroscopy and electrochemical characterization were performed to comprehensively assess the effect of Li3PO4 coating and Nb5+ doping on the morphology, structure and electrochemical properties of LiNi0.85Co0.05Mn0.10O2. The results showed that the Li3PO4 nanoparticles were covered on the surface of cathode with success and the Nb5+ ions were inserted into the crystal structure with uniformity. In comparison with the bare LiNi0.85Co0.05Mn0.10O2, the cathodes after Li3PO4 coating and Nb5+ doping demonstrated the better electrochemical properties in terms of rate capability, cycling performance and thermal stability. The 2 wt% Li3PO4 coated Li(Ni0.85Co0.05Mn0.10)0.99Nb0.01O2 delivered the capacity retention of 92.0% at 25 °C and 90.8% at 45 °C after 300 cycles at 1C rate respectively, much larger than those (83.5% and 80.1%) of the bare one. These results indicated the Li3PO4 coating and Nb5+ doping co-modification could satisfy the performance requirement of maintaining the cycling stability for Ni-rich cathodes.

Surface coating with Li3BO3 protection layer to enhance the electrochemical performance and safety properties of Ni-rich LiNi0.85Co0.05Mn0.10O2 cathode material

To enhance the electrochemical properties and safety performance of Ni-rich cathode materials for Lithium-ion batteries, a typical wet chemical method followed by high temperature sintering was applied to make the Li+ conductive Li3BO3 with different mass fractions cover on the surface of Ni-rich LiNi0.85Co0.05Mn0.10O2. And the influence of the coating layer on the phase, crystal structure, particles morphology and electrochemical properties during cycling were systematically studied. The physicochemical characterization results suggested a coating layer with a thickness of 10–15 nm formed by Li3BO3 nanoparticles was equably adhered on the surface of cathode particles, without causing obvious variation of the crystal structure and morphology. The electrochemical measurement indicated the suitable amount of Li3BO3 coating layer could effectively enhance the rate capability, discharge ability at low temperature and cycling performance of LiNi0.85Co0.05Mn0.10O2 due to the increased Li+ diffusion rate and restrained side reaction from electrode with electrolyte. Particularly, the 2 wt% Li3BO3 coated LiNi0.85Co0.05Mn0.10O2 respectively delivered a capacity retention of 91.4% and 90.1% at 25 °C and 45 °C after 300 cycles, and the pristine one merely retained a capacity retention of 83.9% and 80.4% accordingly. Besides, the pouch full batteries with 2 wt% Li3BO3 coated LiNi0.85Co0.05Mn0.10O2 cathode demonstrated the obvious enhancement on the safety properties and storage performance when compared to the pristine one for the pouch batteries

Enhanced electrochemical properties of Ni-rich layered cathode materials via Mg2+ and Ti4+co-doping for lithium-ion batteries

To optimize the electrochemical performance of Ni-rich cathode materials, the 0.005 mol of Mg2+ and 0.005 mol of Ti4+co-doping LiNi0.83Co0.11Mn0.06O2 composite powders, labeled as NCM-11, are successfully prepared by being calcinated at 750 °C for 15 h following by an appropriate post-treatment, which are confirmed by XRD, EDS and XPS. The results suggest that NCM-11 presents a well-ordered layered structure with a low Li+/Ni2+ mixing degree of 1.46% and Mg2+ and Ti4+ ions are uniformly distributed across the lattice. The cell assembled with NCM-11 can deliver an initial discharge specific capacity of 194.2 mAh g−1 and retain a discharge specific capacity of 163.0 mAh g−1 after 100cycles at 2.0C at 25 °C. Furthermore, it still maintains a discharge specific capacity of 166.7 mAh g−1 after 100cycles at 2.0C at 60 °C. More importantly, it also exhibits a higher discharge specific capacity of about 150.7 mAh g−1 even at 5.0C. Those superior electrochemical performance can be mainly ascribed to the synergistic effect of Mg2+ and Ti4+co-doping, in which Mg2+ ions can occupy the Li+ layer to act as pillar ions and Ti4+ ions can occupy the transition metal ions layer to enlarge the interplane spacing. Thus, the heterovalent cations co-doping strategy can be considered as a simple and practical method to improve the electrochemical performance of Ni-rich layered cathode materials for lithium-ion batteries.

Effects of reheating temperature on the structure, morphology and electrochemical performance of Ni-rich cathode materials

The effects of reheating temperature on Ni-rich LiNi0.865Co0.095Al0.04O2 (NCA) are investigated since reheating process is required during surface modification and removal of adhered water molecules. It is shown that reheating temperature can exert observable influences on the structure, morphology, and electrochemical performance of the as-prepared Ni-rich cathode materials. In this work, commercial precursors were calcinated and reheated at 300, 450, 600, and 750 °C. After that, they were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and electrochemical tests. XRD results confirmed that the occupancy of Ni2+ in the Li layer first decreases and then increases with increasing reheating temperature, and variation of Li layer spacing follows the same trend. Increasing reheating temperature accelerates the aggregation of lithium-related compounds such as Li2CO3 and LiOH. Interestingly, as the reheating temperature increases to 750 °C, the sample reverted to a smooth-like morphology, with an increase in the amount of Ni3+ at the surface. A higher capacity with better cyclic performance can be attained for NCA when reheated at 750 °C. Hence, reheating Ni-rich cathodes at suitable temperature can result in promising electrodes with advanced electrochemical performance.

Constructing effective TiO2 nano-coating for high-voltage Ni-rich cathode materials for lithium ion batteries by precise kinetic control

In order to improve the performance of Ni-rich cathode materials for lithium-ion batteries at high cut-off voltage, a highly effective TiO2 nano-coating is constructed on the surface of LiNi0.8Co0.1Mn0.1O2 by precisely controlling the hydrolytic dynamics of Ti4+, and the effect of this coating layer is systematically studied, especially at high upper cut-off voltage. The continuous TiO2 nano-coating layer provides a complete protection for LiNi0.8Co0.1Mn0.1O2 particles and enhances the reversibility of the phase transition between hexagonal and hexagonal (H2→H3) during cycling, which guarantees an excellent cycling stability under high upper cut-off voltage up to 4.5 V. Electrochemical impedance spectroscopy results confirm a stable interface between electrolyte and electrode and the fast kinetics at the surface of the modified sample. High Resolution Transmission Electron Microscopy (HR-TEM) measurement for the cycled electrodes further verifies the slight structure decay of the coated sample comparing with the pristine one. Thus, the modified sample presents excellent cycling stability with capacity retention of 72.2% after 500 cycles and 63.4% after 1000 cycles with the upper cut-off voltage of 4.5 V and 4.3 V, respectively. This work provides a universal method to prepare conformal TiO2 nano-coating and also offer guidance to properly evaluate the function of a coating.